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European Journal of Inorganic Chemistry - Current Research Articles

Current research articles: Inorganic Chemistry

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European Journal of Inorganic Chemistry - published by Wiley-VCH

EurJIC is the fastest growing journal in inorganic chemistry. It publishes Full Papers, Short Communications, and Microreviews from the entire spectrum of inorganic, organometallic, bioinorganic, and solid-state chemistry.

Current articles of the journal:

Hydride Abstraction and Deprotonation – an Efficient Route to Low Coordinate Phosphorus and Arsenic Species

Treatment of Acenap(PiPr2)(EH2) (Acenap = acenaphthene-5,6-diyl; 1a, E = As; 1b, E = P) with Ph3C·BF4 resulted in hydride abstraction to give [Acenap(PiPr2)(EH)][BF4] (2a, E = As; 2b, E = P). These represent the first structurally characterised phosphino/arsino-phosphonium salts with secondary arsine/phosphine groups, as well as the first example of a Lewis base stabilised primary arsenium cation. Compounds 2a and 2b were deprotonated with NaH to afford low coordinate species Acenap(PiPr2)(E) (3a, E = As; 3b, E = P). This provides an alternative and practical synthetic pathway to the phosphanylidene-?4-phosphorane 3b and provides mechanistic insight into the formation of arsanylidene-?4-phosphorane 3a, indirectly supporting the hypothesis that the previously reported dehydrogenation of 1a occurs via an ionic mechanism. Hydride abstraction from a primary phosphine/arsine affords the first examples of secondary phosphino/arsino-phosphonium salts. Subsequent deprotonation provides a novel and high yielding route to phosphine-stabilised phosphinidene/arsinidene. These investigations indirectly support an ionic mechanism for the spontaneous dehydrogenation of the primary arsine.

Posted on 6 October 2015 | 1:40 pm

Ferrocene-Based N-Heterocyclic Carbenes with Functionalised Benzyl Substituents

We describe herein N-heterocyclic carbenes (NHCs) with a 1,1?-ferrocenylene backbone that contain substituents at the nitrogen atoms relevant for applications in the area of metallopharmaceuticals, namely benzyl units functionalised with dimethylamino and methoxy groups at the para position. These carbenes are too unstable for isolation. They were generated from the corresponding formamidinium tetrafluoroborates by deprotonation and efficiently trapped in situ. Trapping with elemental selenium afforded the corresponding selenourea derivatives, the 77Se NMR chemical shifts of which are in accord with the comparatively high electrophilicity typical of expanded-ring NHCs. Coordinative trapping with [{Rh(?-Cl)(cod)}2] (cod = cycloocta-1,5-diene) furnished air-stable complexes of the type [RhCl(cod)(NHC)], the benzyl CH2 groups of which are engaged in pronounced anagostic C–H···Rh interactions, both in solution and in the solid state. N-Heterocyclic carbenes with a 1,1?-ferrocenylene backbone have been equipped with functionalised benzyl substituents to make them amenable as ligands for applications in the field of metallopharmaceuticals. The 77Se NMR chemical shifts of the selenourea derivatives of these NHCs demonstrate the comparatively high electrophilicity of these carbenes.

Posted on 6 October 2015 | 1:40 pm

Synthesis of the Single-Crystalline Form and First-Principles Calculations of Photomagnetic Copper(II) Octacyanidomolybdate(IV)

A gel crystallization technique was successfully applied in the pioneering preparation of a single-crystalline form of the three-dimensional copper(II) octacyanidomolybdate(IV) network, which is a photomagnetic material. This assembly crystallizes with the formula {[CuII(H2O)]2[MoIV(CN)8]}·2H2O in the tetragonal crystal system and reveals a three-dimensional cyanido-bridged framework constructed of five-coordinate square-pyramidal [CuII(H2O)(NC)4]2– complexes and [MoIV(CN)8]4– ions of square-antiprismatic geometry. First-principles calculations by the GGA + U method indicate that the visible-light absorption band, crucial for the observation of a photomagnetic effect, is interpreted in terms of MoIV to CuII charge transfer, which is enabled owing to the accompanying pz??spx transition of the nitrogen atoms of the bridging cyanido ligands. The optical transitions in the visible range are anisotropic, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges. A single-crystalline form of three-dimensional copper(II) octacyanidomolybdate(IV) photomagnetic material is prepared. First-principles calculations indicate that an optical transition in the visible range is a charge transfer from MoIV to CuII, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges.

Posted on 6 October 2015 | 1:30 pm

Synthesis, Characterization, and Hydrolytic Behavior of Diorganotin(IV) Coordination Polymers with Layered Structural Motifs

The synthesis and structural characterization of the layered diorganotin coordination polymers nBu2Sn(HL)(OSO2Me) (1) and nBu2Sn(HL1)(OSO2Me) (2) derived from the silaalkylphosphonic acids RR12Si(CH2)3P(O)(OH)2 [R = Ph, R1 = Me (H2L); R = R1 = Et (H2L1)] are presented. The structure of H2L exhibits O–H···O hydrogen bonding and ?–? interactions to form a unique three-dimensional supramolecular assembly in the solid state. The asymmetric units of 1 and 2 are composed of centrosymmetric eight-membered [–Sn–O–P–O–]2 cyclic rings with appended sulfonate groups, which provide layered connectivity to the structures. For 1, the presence of C–H···? interactions between the dangling phenyl rings of the silaalkyl chains favors a lamellar arrangement with an interlayer spacing of 16.9 Å. Upon exposure to humid conditions, these polymers undergo slow transformation to nBu2Sn[O3P(CH2)3SiRR12] with the elimination of methanesulfonic acid. The mixed-ligand diorganotin(IV) coordination polymers nBu2Sn[OP(O)(OH)R]OSO2Me [R = PhMe2Si(CH2)3 (1), Et3Si(CH2)3 (2)] featuring lamellar and layered structural motifs, respectively, are synthesized and structurally characterized.

Posted on 5 October 2015 | 12:50 pm

Comparative Study of Lactide Polymerization with Lithium, Sodium, Potassium, Magnesium, Calcium, and Zinc Azo­naphthoxide Complexes

A series of lithium, sodium, potassium, magnesium, calcium and zinc azonaphthoxide complexes [M(?m-{2-O(C10H6)N=N(C6H4R)})]n (R = H, m = 2; M = Li 1, Na 2, K 3; R = OMe, m = 3; M = Li 4, Na 5, K 6) and [M(?m-{2-O(C10H6)N=N(C6H4R)})2]n (R = H, m = 2; M = Mg 7, Zn 8, Ca 9; R = OMe, m = 3; M = Mg 10, Zn 11, Ca 12) have been synthesized and fully characterized. The solid-state molecular structures of the zinc complexes 8 and 11 and the magnesium derivative 10 have been determined by X-ray diffraction studies. The alkali-metal compounds 1–6 are extremely active catalysts for the ring-opening polymerization (ROP) of L-lactide. A catalytic-activity study has been performed by varying the metal complex and the coordination sphere of the metal in the presence and absence of a coinitiator. Stoichiometric reactions involving the catalysts, BnOH and lactide have been performed to elucidate mechanistic aspects related to the polymerization of L-lactide. Lithium, sodium, potassium, magnesium, calcium and zinc complexes stabilized by monoanionic bidentate and tridentate azonaphthoxide ligands are synthetized. Although the extremely active alkali-metal complexes follow an activated-monomer mechanism, the alkaline-earth and zinc complexes follow a coordination–insertion mechanism assisted by the ligand.

Posted on 5 October 2015 | 12:50 pm

Mechanism Involving Hydrogen Sulfite Ions, Chlorite Ions, and Hypochlorous Acid as Key Intermediates of the Autocatalytic Chlorine Dioxide–Thiourea Dioxide Reaction

The kinetics of the chlorine dioxide–thiourea dioxide reaction was investigated by monitoring absorbance–time profiles at ? = 360 nm. Under acidic conditions, the primary carbon-containing product is cyanamide, not urea as considered previously for many oxidation reactions of thiourea dioxide. Increase of the rate of the reaction by an increase of pH can be readily explained by the slow pH-dependent formation of a more reactive form of thiourea dioxide (TDO) that is produced steadily and unavoidably as the stock TDO solution ages. We have also found that the absorbance–time profiles of the chlorine dioxide–TDO reaction are sigmoidal with excess TDO. The addition of methionine as a hypochlorous acid scavenging agent inhibits the reaction significantly, whereas the addition of chlorite ions and trace amounts of hydrogen sulfite ions accelerates the decay of chlorine dioxide. On the basis of these experiments, a sixteen-step kinetic model involving hypochlorous acid, chlorite ions, and hydrogen sulfite ions as key intermediates that provide an autocatalytic cycle is proposed to account for the overall kinetic behavior observed, including the slow rearrangement of TDO. The sigmoidal decay of ClO2 in the thiourea–ClO2 reaction is explained by a chain mechanism including HSO3– ions, HOCl, and ClO2– ions as key short-lived intermediates. The mechanism incorporates the recently discovered slow rearrangement of thiourea dioxide, which is necessarily involved in each reaction in aqueous solutions.

Posted on 5 October 2015 | 12:50 pm

Supramolecular Assembly of Metal-Organic Tubes Constructed from the Ditopic Heteroscorpionate Ligand (4-NH2C6H4)­CHpz2 (pz = Pyrazol-1-yl) and Silver(I)

The possibility of constructing tubular metal-organic structures with aid of weak hydrogen-bonding interactions between suitably designed metallacycles was explored. For this purpose, the new heteroditopic ligand (4-NH2C6H4)CHpz2 (L1) was prepared in good (75?%) yield by a one-pot procedure starting from commercial 4-acetamidobenzaldehyde. The equimolar reactions between L1 and various silver(I) salts gave the intended 1:1 complexes in which the metallacycles were assembled into tubes. However, the exact nature of the assemblies (including their solvate compositions) varied depending on anion, solvent, and concentration of the original crystallization solution. For the trifluoromethanesulfonate anion, a hexameric structure was observed, whereas cyclic dimers were obtained for other anions. In the case of PF6–, an unusual, opened-cycle structure with the composition [(L1)Ag(?-L1)Ag(CH3CN)2]2+ was also identified crystallographically. The capacity for desolvated tubular structures to be used for gas adsorption was also investigated. Silver(I) complexes of a new heteroditopic heteroscorpionate have a proclivity for forming tubular assemblies with the aid of weak charge-assisted hydrogen-bonding interactions.

Posted on 2 October 2015 | 11:40 am

Influence of Synthesis Conditions on the Mesopore Distribution and Morphology Control of Hierarchical ZSM-5 Zeolites Synthesized by Double-Acyloxy Organosilane Surfactants

A novel type of double-acyloxy amphiphilic organosilanes with different alkyl chain lengths were synthesized as mesoporous templating agents to prepare mesoporous ZSM-5 zeolites. The zeolites obtained had sponge-like surfaces and variable morphology; mesopores of 4, 13, and 33 nm were constructed in the crystals without damaging their crystallinity. The H2O/Si ratio, Si/Algel ratio, and organosilane template content all had an influence on zeolite crystallinity and surface properties as indicated by X-ray diffraction (XRD), nitrogen physisorption analysis, and scanning electron microscopy (SEM). In addition, variation of the alkyl chain length of the organosilanes resulted in different zeolite crystal size, morphology, and pore-size distribution. Hierarchical ZSM-5 zeolites were synthesized by using a novel type of double-acyloxy organosilane surfactant and the influence of the synthesis conditions and alkyl chain length on the mesopore distribution and morphology control were studied.

Posted on 2 October 2015 | 11:40 am

Organometallic Reactivity of [Silver(I)­(Pyridine-Containing Ligand)] Complexes Relevant to Catalysis

Silver(I) complexes of pyiridine-containing macrocyclic ligands (Pc-L) have already been demonstrated as active catalysts for some domino and multicomponent reactions. Here, we report new chiral [AgI(Pc-L*)] cationic complexes that have been synthesized and fully characterized, including structural determination by single-crystal X-ray diffraction. The complexes show a rich coordination chemistry, demonstrating both the ?-philic (alcohol and nitrile coordination) and the ?-philic (alkyne coordination) nature of silver. The ?2 coordination mode of the naphthyl pendant arm of the ligands on silver has been observed in solution by NMR spectroscopic experiments. 2D NMR spectroscopy revealed the presence of positive cross peaks resulting from rotational processes and the rate of rotation was measured by using 2D exchange spectroscopy (EXSY). Chiral pyridine-containing macrocyclic ligands were employed to form stable silver(I) cationic complexes, [AgI(Pc-L*)], which were fully characterized, along with a study of their organometallic reactivity and structure elucidation, both in the solid state and in solution, by different NMR spectroscopic techniques, including 2D exchange spectroscopy (EXSY).

Posted on 1 October 2015 | 2:40 pm

Synthesis and Characterization of Chloro- and Alkyliron Complexes with N-Donor Ligands and Their Reactivity towards CO2

New iron(II) compounds with N-donor ligands [2,2?-bipyridine (bpy) and 2-(2-pyridyl)ethylamine (pyea)] were synthesized, and their reactivity with carbon dioxide was investigated. The reactions of Fe(bpy)(pyea)Cl2 (1) with CO2 (0.9 MPa) afforded the carbamato derivative Fe(bpy)(pyea-CO2)Cl2 (2), which reacted with CH3Li to afford the monomethyl carbamato complex Fe(bpy)(pyea-CO2)ClCH3 (3), an example of a carbamato species that is stable over a carboxylato moiety. Fe[(bpy)(pyea)](CH3)2 (4), obtained by reaction of 1 with CH3Li, was treated with CO2 (0.3–0.5 MPa) to afford the dicarboxylato species Fe[(bpy)(pyea)](O2CCH3)2 (5), which provides evidence of normal double insertion of CO2 into the Fe–C bond. The reaction of 5 with HCl afforded 1 and CH3–CO2H, which confirmed the mode of bonding of the –O2CCH3 moiety to the Fe center. To verify the preference of insertion of CO2 into the Fe–C or the Fe–N bond, 1 was treated with MeLi (1 equiv.), and Fe(bpy)(pyea)Cl(CH3) (6) was isolated as a low-melting solid. The latter was treated with CO2 (0.5 MPa), and the product of insertion into the Fe–CH3 bond was observed as the only carboxylate (7). The faster insertion into the Fe–CH3 bond is explained by the fact that the N donor is quaternarized upon interaction with the metal center and has no free electrons available to interact with the C acceptor of the cumulene molecule; thus, more-forcing conditions (0.9 MPa) are required for the insertion to occur. Iron(II) compounds bearing N-donor ligands are synthesized, and their reactivity towards carbon dioxide is studied. This leads to the isolation and characterization of a carbamato derivative (3) and a dicarboxylato species (5).

Posted on 1 October 2015 | 2:40 pm

FeII Carbonyl Complexes Featuring Small to Bulky PNP Pincer Ligands – Facile Substitution of ?2P,N-Bound PNP Ligands by Carbon Monoxide

Complexes trans- and cis-[Fe(?3P,N,P-PNP)(CO)Cl2] bearing sterically demanding to small PNP ligands based on the 2,6-diaminopyridine scaffold are synthesized. The aromatic pyridine ring and the phosphine PR2 moieties are connected through NH, N-alkyl, or N-aryl linkers. For bulky PNP ligands, with the exception of the ligands with PtBu2 units, these complexes are obtained upon the treatment of [Fe(?3P,N,P-PNP)Cl2] with CO. With small PNP ligands, such complexes are not accessible directly owing to the formation of [Fe(?3P,N,P-PNP)(?2P,N-PNP)Cl]Cl. These complexes liberate the ?2-P,N-bound PNP ligand in the presence of CO to yield [Fe(?3P,N,P-PNP)(CO)Cl2] in yields of less than 50?%. High yields are achieved by reacting FeCl2 with PNP ligands under a CO atmosphere. For structural and reactivity comparisons, [Fe(?3P,N,P-PNP-Ph)(?2P,N-PN-Ph)Cl]+ was prepared, and this complex does not react with CO. In contrast to the reactions in solution, in the solid state, complexes [Fe(?3P,N,P-PNP)Cl2] with NH linkers are also converted quantitatively into trans- or cis-[Fe(?3P,N,P-PNP)(CO)(Cl)2] upon treatment with CO, as indicated by a color change and by IR spectroscopy monitoring. Those with N-alkyl and N-aryl linkers did not react with CO. To rationalize why most [Fe(?3P,N,P-PNP)Cl2] complexes react readily with CO but those with tBu substituents do not, the additions of CO to [Fe(?3P,N,P-PNP-iPr)Cl2] and [Fe(?3P,N,P-PNP-tBu)Cl2] were investigated by DFT calculations. Complexes trans- and cis-[Fe(?3P,N,P-PNP)(CO)Cl2] bearing PNP ligands in which a pyridine ring and PR2 moieties are connected through NH, N-alkyl, or N-aryl linkers are prepared. For small PNP ligands, the treatment of [Fe(?3P,N,P-PNP)(?2P,N-PNP)Cl]+ with CO liberates the ?2-P,N-bound PNP ligand and affords the desired [Fe(?3P,N,P-PNP)(CO)Cl2] complexes.

Posted on 30 September 2015 | 1:30 pm

Crystal and Magnetic Structure of Sr2BIrO6 (B = Sc, Ti, Fe, Co, In) in the Framework of Multivalent Iridium Double Perovskites

The preparation, crystal structure and magnetic properties of Sr2BIrO6 (B = In, Sc, Fe, Co or Ti) oxides are reported. For B = Sc, Fe, Co or In materials, X-ray and neutron powder diffraction (NPD) studies confirm the presence of 1:1 B-ordered perovskite-like structures crystallizing in the monoclinic I2/m and P21/n space groups, with unit-cell parameters a ? ?2a0, b ? ?2a0, c ? 2a0 and ? ? 90°. Sr2TiIrO6 is described as a disordered perovskite with orthorhombic symmetry in the Pbnm space group. For B = Fe and Co, low-temperature NPD data and magnetic measurements indicate the existence of an antiferromagnetic structure resulting from the Fe3+/Co3+ magnetic moment interaction. X-ray absorption spectroscopy corroborates that the oxidation states of B and Ir are 3+ and 5+, respectively. The bond lengths and other structural features are discussed in the framework of other recently reported iridium double perovskites where iridium adopts tetravalent, pentavalent and hexavalent oxidation states, and in the wider context of Sr double perovskites. Selected members of the Sr2BIrO6 family, containing cations of different nature and Ir with oxidation states 4+, 5+ and 6+, have been obtained under synthesis conditions carefully chosen to select the required iridium valence. Additionally, the influence of the Mn+ radius on the internal parameters, obtained from an X-ray neutron powder diffraction (NPD) analysis, is discussed.

Posted on 30 September 2015 | 11:30 am

Synthesis and Assessment of CO-Release Capacity of Manganese Carbonyl Complexes Derived from Rigid ?-Diimine ­Ligands of Varied Complexity

Four manganese carbonyl complexes of the type [MnBr(CO)3(NN)] (NN = ?-diimine ligands): namely [MnBr(CO)3(bpy)] (1), [MnBr(CO)3(phen)] (2), [MnBr(CO)3(dafo)] (3), and [MnBr(CO)3(pyzphen)] (4) (where bpy = bipyridine, phen = 1,10-phenanthroline, dafo = 4,5-diazafluoren-9-one, and pyzphen = pyrazino[2,3-f][1,10]-phenanthroline) have been synthesized and structurally characterized. These four complexes, each containing the fac-[Mn(CO)3] motif, release CO upon illumination with low-power visible and UV light. The CO release rates and the absorption maxima of the complexes are, however, very similar, despite the systematic increase in structural complexity in the rigid ?-diimine ligand frameworks. This contrasts strongly with manganese carbonyl complexes derived from ?-diimine ligands in which at least one of the imine functions is not part of a rigid ring system. The results of this study should provide help in the future design of ligand frameworks suitable for the syntheses of photoCORMs to deliver CO to biological targets under the control of light. The rates of CO photorelease from MnI carbonyl complexes based on rigid ?-diimine ligands are quite similar to one another despite significant variations in the ligand frameworks.

Posted on 30 September 2015 | 11:30 am

Iridium(I) Complexes Bearing a Noninnocent PNP-Pincer-Type Phosphaalkene ­Ligand: Catalytic Application in the Base-Free N-Alkylation of Amines with Alcohols

A series of IrI complexes [Ir(L)(PPEP*)] [L = Cl– (3), CO (4), tBuNC (5), PMe3 (6), PPh3 (7)], coordinated with a PNP-pincer-type phosphaalkene ligand bearing a dearomatized pyridine ring (PPEP*), have been prepared and their catalytic properties for the dehydration/condensation of amines with alcohols has been examined. The catalytic reactions successfully proceed under base-free conditions to give N-alkylated amines and their dehydrogenation derivatives (imines). The product selectivity is dependent on L coordinated with Ir(PPEP*). Complexes 4 and 5 that contain ?-accepting ligands (CO, tBuNC) form N-alkylated amines as the major products in a closed system using a nitrogen-gas-filled Schlenk tube. In contrast, complex 7 that contain PPh3 as L produces imines as the major products under a nitrogen-gas flow. The reason for the selectivity change depending on L is discussed based on stoichiometric reactions using model compounds of presumed catalytic intermediates. PNP-pincer-type phosphaalkene complexes of IrI bearing a dearomatized pyridine ring have been found to catalyze the dehydration/condensation of amines with alcohols under base-free conditions to afford N-alkylated amines and imines in high yields. The product selectivity can be controlled by the choice of auxiliary ligands (L) as well as the reaction conditions.

Posted on 29 September 2015 | 4:10 pm

Design and Synthesis of an Au@MIL-53(NH2) Catalyst for a One-Pot Aerobic Oxidation/Knoevenagel Condensation Reaction

Highly dispersed gold nanoparticles were deposited on an amino-functionalized Al-based MIL-53 metal–organic framework by a facile adsorption/reduction strategy. The aromatic amino groups were utilized for adsorption and stabilization of AuCl4– and as basic catalytic sites in the Knoevenagel reaction. The bifunctional Au@MIL-53(NH2) catalyst was utilized to develop an efficient one-pot aerobic oxidation of alcohols/Knoevenagel condensation reaction that takes advantage of Au0 and NH2 incorporation at the same time. The roles of Au and NH2 groups were systematically investigated to elucidate their functionality during the one-pot reaction. In addition, the Au@MIL-53(NH2) catalyst can be easily recycled up to five times without leaching of the active centres or significant loss of catalytic activity. Highly dispersed Au nanoparticles (NPs) were deposited on an amino-functionalized Al-based MIL-53 metal–organic framework by a facile adsorption/reduction strategy. A one-pot aerobic alcohol oxidation/Knoevenagel condensation reaction cascade was developed by taking advantage of the Au0 NPs and NH2 groups of the resulting bifunctional Au@MIL-53(NH2) catalyst.

Posted on 29 September 2015 | 3:10 pm

Nanobioinorganic Chemistry: Converging Inorganic Chemistry and Biology at the Nanoscale

It has become clear in recent years that the interaction of inorganic nanomaterials with biological systems is of paramount importance for further advancements in important fields, including nanomedicine, nanotoxicology, tissue engineering, biotechnology, environmental science, and bioimaging, among many others. This development reflects not merely new applications of nanoparticles to biological systems but also the emergence of new biotechnologies involving inorganic nanomaterials. It has become clear in recent years that the interaction of inorganic nanomaterials with biological systems is of paramount importance for further advancements in important fields, including nanomedicine, nanotoxicology, tissue engineering, biotechnology, environmental science, and bioimaging, among many others. This development reflects not merely new applications of nanoparticles to biological systems but also the emergence of new biotechnologies involving inorganic nanomaterials.

Posted on 25 September 2015 | 2:25 pm

Graphical Abstract: Eur. J. Inorg. Chem. 27/2015

Posted on 25 September 2015 | 2:25 pm

Miniaturization in Bioinorganic Chemistry

The cluster issue “Nanobioinorganic Chemistry: Converging Inorganic Chemistry and Biology at the Nanoscale” presents a selection of applications at the border between materials chemistry and biology tailored to an inorganic chemistry perspective. The cluster issue “Nanobioinorganic Chemistry: Converging Inorganic Chemistry and Biology at the Nanoscale” presents a selection of applications at the border between materials chemistry and biology tailored to an inorganic chemistry perspective.

Posted on 25 September 2015 | 2:25 pm

Back Cover: Synthesis of CaTiO3 Nanofibers with Controllable Drug-Release Kinetics (Eur. J. Inorg. Chem. 27/2015)

The back cover picture shows calcium titanate nanofibers with controlled microstructures that were successfully fabricated by an electrospinning method. The nanofibers synthesized without the F127 surfactant are of markedly increased surface area and pore volume, and thus present the highest drug loading capacity and the most sustained release kinetics. The nanofibers may serve as a promising drug delivery system for a variety of pharmaceutical and tumor therapy applications that require a sustained release to reduce the significant side effects of the drugs. Details are discussed in the article by Xiang Li, Gaorong Han, Chuanbin Mao et al. on p. 4532 ff.

Posted on 25 September 2015 | 2:25 pm

Masthead: Eur. J. Inorg. Chem. 27/2015

Posted on 25 September 2015 | 2:24 pm

Long-Term Stability and Reproducibility of Magnetic Colloids Are Key Issues for Steady Values of Specific Power Absorption over Time

Invited for the cover of this issue are the groups of Beatriz Sanz and Gerardo F. Goya at the University of Zaragoza, Spain. The cover image shows the relationship between the key parameters for reproducibility and stability in time with the heat amounts delivered to target cells. These parameters are important for the standardization of magnetic hyperthermia. Because the need of a solid standardization of the protocols of magnetic hyperthermia is now evident,...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 4524 ff.

Posted on 25 September 2015 | 2:24 pm

Cover Picture: Long-Term Stability and Reproducibility of Magnetic Colloids Are Key Issues for Steady Values of Specific Power Absorption over Time (Eur. J. Inorg. Chem. 27/2015)

The front cover picture shows the relations between the key parameters for reproducibility and stability in time with the heat amounts delivered to target cells. The steadiness of these parameters is at the foundation of the standardization of the thermal dosage in magnetic hyperthermia. Details are discussed in the article by B. Sanz, G. F. Goya et al. on p. 4524 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 25 September 2015 | 2:24 pm

A Comparative Study of the Redox-­Induced Linkage Isomerization of Ruthenium and Osmium Complexes

A dispersion-corrected DFT study on the redox-induced linkage isomerization of a family of [M(bpy)2AL]2+ complexes {M = Ru, Os; bpy = 2,2-bipyridine; AL = 2-[(isopropylsulfinyl)methyl]pyridine (pySO), 2-[2-(isopropylsulfinyl)ethyl]pyridine (pyESO), 2-[3-(isopropylsulfinyl)propyl]pyridine (pyPSO)} was undertaken. The calculated results indicated that modification of the metal center or ancillary ligand could produce distinct electronic and photophysical properties of the complexes. In good agreement with experimental absorption spectrum results, a redshift in the absorption maximum was observed if the metal center of the complex was changed from ruthenium to osmium. More importantly, the relative thermodynamic stabilities of the two linkage isomers in these complexes could also be tuned by modifications to the metal center or ancillary ligand. It was found that the relative energies between the S- and O-linked ruthenium sulfoxide complexes were smaller than those between the osmium sulfoxide isomers. Intrinsic reaction pathway results demonstrated that intramolecular SO and OS isomerization was easier in the ruthenium complexes than in the osmium complexes with the same coordinated ligands. Moreover, intramolecular isomerization was more favorable if the number of methylene units between the sulfoxide group and the pyridine ring in the ancillary ligand was increased. Intramolecular SO isomerization is more favorable in ruthenium complexes than in osmium complexes with the same coordinated ligands. Moreover, it is observed that SO isomerization is preferred if the number of methylene units between the sulfoxide group and the pyridine ring in the ancillary ligand is increased. bpy = 2,2-bipyridine; pySO = 2-[(isopropylsulfinyl)methyl]pyridine; pyESO = 2-[2-(isopropylsulfinyl)ethyl]pyridine; pyPSO = 2-[3-(isopropylsulfinyl)propyl]pyridine.

Posted on 25 September 2015 | 12:20 pm

From a Germylene to an “Inorganic Adamantane”: [{Ge4(?-O)2(?-OH)4}{W(CO)5}4]·4THF

Germanium(II) (2-methoxyphenyl)methoxide (1) and [W(CO)5(thf)] gave rise reproducibly (79?% yield) to a new, uncharged transition-metal complex of a germanium(II) hydroxido oxido cluster – [{Ge4(?-O)2(?-OH)4}{W(CO)5}4]·4THF (2·4THF) – as a product of hydrolysis. The germylene 1 is monomeric in solution at ambient temperature but forms dimers in solution at low temperatures and in the solid state. Dimerization of compound 1 was studied by 1H NMR spectroscopy and with the aid of DFT-D calculations. The tetranuclear cluster 2 shows an adamantane-like core structure with coordination of tungsten pentacarbonyl to germanium(II) in the solid state as well as in solution. Characterization of both compounds, including by single-crystal X-ray diffraction analysis, by 1H NMR, 13C{1H} NMR, FTIR spectroscopy, and through thermal analyses, is presented. Germylene 1 and [W(CO)5(thf)] gave rise to 2, a transition-metal complex of a germanium(II) hydroxido oxido cluster, after hydrolysis. Germylene 1 is monomeric in solution at ambient temperature but forms dimers at low temperatures in solution and in the solid state. Cluster 2 has an adamantane-like structure based on a Ge4O2(OH)4 core, thus complementing the series of “inorganic adamantanes”.

Posted on 23 September 2015 | 2:40 pm

Stabilization of CuII–I Bonds Using 2-Benzoylpyridine Thiosemicarbazones – Synthesis, Structure, Spectroscopy, Fluo­rescence, and Cyclic Voltammetry

The reactions of copper(I) iodide with N1-substituted 2-benzoylpyridine thiosemicarbazones [(C6H5)(C5H4N)C2=N3–N2H–C(=S)–N1HR (R = Me, HLMe; Et, HLEt; Ph, HLPh)] in acetonitrile/dichloromethane mixtures have formed the complexes [Cu2III2(?4-N,N,S-LMe)2] (1), [CuIII(?3-N,N,S-LEt)] (4), and [CuIII(?3-N,N,S-LPh)] (7) through proton-coupled electron transfer (PCET), and these complexes have rare CuII–I bonds. The above thio ligands with copper(I) bromide and copper(I) chloride also formed similar CuII–Br and CuII–Cl bonds in complexes of stoichiometry [CuIIX(?3-N,N,S-L)] (L = LMe, LEt, LPh, X = Br 2, 5, 8; X = Cl 3, 6, 9) by PCET. All of the complexes have been characterized by elemental analysis, infrared spectroscopy, electronic absorption spectroscopy, ESR spectroscopy, magnetic susceptibility measurements, molecular fluorescence, cyclic voltammetry, and single-crystal X-ray crystallography. The thio ligands coordinate as monoanionic N,N,S donors in 1–9. The ESR data support the divalent oxidation state of the metal centers in the complexes, and the ESR parameters follow the trend g??>?g??>?2 with G values in the range 2–4, which suggests a d?x?2–y?2 ground state for the copper(II) complexes with variable exchange interaction in the solid complexes. The geometry around each copper(II) center is distorted square planar (mononuclear, 2–9) or square pyramidal (dinuclear, 1). The stabilization of copper(II)–iodide bonds as well as the formation of CuII–Br and CuII–Cl bonds from thio ligands and copper(I) halides by a PCET process represents basic research of topical interest. The direct reactions of N1-substituted 2-benzoylpyridine thiosemicarbazones [(C6H5)(C5H4N)C2=N3–N2H–C(=S)–N1HR] with copper(I) halides form square-planar or square-pyramidal paramagnetic complexes with CuII–I, CuII–Br, and CuII–Cl bonds through proton-coupled electron transfer. For R = Et, complexes 4–6 are obtained.

Posted on 23 September 2015 | 2:40 pm

Third-Generation Scorpionates [RBpz3]– – How Influential Is the Nondonor Substituent R?

Five pairs of perfluorophenyl- and phenyl-substituted tris(pyrazol-1-yl)borate complexes have been prepared and thoroughly investigated, namely, [(C6R?5Bpz3)2Fe], [(C6R?5Bpz3)2Cu], [(C6R?5Bpz3)Mn(CO)3], K[(C6R?5Bpz3)Mo(CO)3], and [(C6R?5Bpz3)Mo(CO)2(2-methallyl)] (R? = F, H; pz = pyrazol-1-yl). X-ray crystal structure analyses and IR spectroscopical measurements reveal only a minor influence of the spectator substituents on the corresponding parameters. In contrast, significant differences between the redox potentials of the fluorinated and non-fluorinated species are evident in their cyclic voltammograms. Large differences have been found between the crystal packings of the complexes with perfluorinated and non-fluorinated phenyl rings. Cyclic voltammetry, IR spectroscopy, and X-ray crystallography are employed with selected complexes of (C6F5Bpz3)– and (C6H5Bpz3)– (pz = pyrazol-1-yl) to reveal differences in the electronic structures and crystal packings of fluorinated and non-fluorinated species.

Posted on 23 September 2015 | 2:40 pm

Highly Reactive NiII-Bound Nitrile–Oxime Coupling Intermediates Stabilized by Substituting Conventional Nitriles with a Dialkylcyanamide

Nickel(II)-mediated coupling between the cyanamide Me2NCN and the ketoximes Me(R)C=NOH (R = Me, Ph) gives chelates of the general formula [NiClx(H2O)y{HN=C(NMe2)(ON=C(R)Me)}2]n+ ([1]+: R = Me; x = 1, y = 0; salts with both Cl– and [NiCl4]2– were isolated; [2]2+: R = Me; x = 0, y = 2; salt with Cl– was isolated; [3]+: R = Ph; x = 1, y = 1; salt with Cl– was isolated) and the iminium salts [H2N=C(NMe2)ON=C(R)Me]+ ([4]+: R = Me; salt with [NiCl4]2– was isolated; [5]+: R = Ph; salt with Cl– was isolated). This reaction demonstrates the difference in the reactivity between conventional nitriles and dialkylcyanamides: whereas nitriles RCN (R = Alk, Ar) react with NiII/ketoxime systems to afford (1,3,5-triazapentadiene)NiII species, formed by postulated nitrile–oxime coupling intermediates, cyanamides under the same conditions give either stable cyanamide–oxime coupling products or the Busch-type complex [Ni{HN=C(Me)CH2C(Me2)NH2}2]Cl2 ([6]Cl2). The reason for the different stability of the coupling products was interpreted theoretically on the basis of quantum chemical calculations (M06-L/6-31G* level of theory). The NMe2 moiety in the chelate ligands leads to an increase in electron-density delocalization and also stabilizes the systems in terms of electrostatic factors. Conventional nitriles and dialkylcyanamides display different reactivity in NiII/oxime-mediated reactions. Whereas nitriles RCN react with NiII/ketoxime systems to afford (1,3,5-triazapentadiene)NiII species, formed by postulated nitrile–oxime coupling intermediates, cyanamides under the same conditions give either stable cyanamide–oxime coupling products or a Busch-type complex.

Posted on 23 September 2015 | 2:40 pm

A Methyl-Substituted Thiophene–Tetra­thiafulvalene Donor and Its Salts

?-Methyldithiophene–tetrathiafulvalene (?-mDT-TTF), the first alkyl-substituted thiophene–tetrathiafulvalene electronic donor, and some of its charge-transfer salts were explored. The crystal structure of ?-mDT-TTF is composed of molecular stacks aligned parallel to each other. Its cyclic voltammetry shows higher electron-donor ability than the unsubstituted analogue. This material was employed as a semiconductor in an organic field-effect transistor and showed a mobility of 4?×?10–4 cm2?V–1?s–1. Two charge-transfer salts of this donor with [M(mnt)2]– anions (mnt = maleonitriledithiolate), M = Co and Au, were obtained by electrocrystallization; they present unusual stoichiometries: (?-mDT-TTF)[Co(mnt)2] and (?-mDT-TTF)3[Au(mnt)2]2. In the cobalt compound, the donor molecules are fully oxidized and the Co complex is dimerized; it presents semiconducting behavior (7?×?10–3 S?cm–1). The gold compound is composed of alternating stacks of donor trimers and pairs of anions. ?-Methyldithiophene–tetrathiafulvalene has lower oxidation potentials than the unsubstituted analogue and shows a mobility of 4?×?10–4 cm2?V–1?s–1 if used as a semiconductor in an organic field-effect transistor. Two charge-transfer salts are obtained by electrocrystallization; they present unusual stoichiometries and interesting crystal structures that are modulated by the donor's methyl group.

Posted on 22 September 2015 | 10:20 am

Host-Sensitized Photoluminescence and Coordination Environment Evolution in Ba6(Bi1–xTbx)9B79O138 (0 ? x ? 1)

Borates are well-known candidates for optical materials and, here, we are particularly interested in Ba6Bi9B79O138 (BBBO), which has an interesting layered-type structure and Bi3+-containing characteristics that has prompt us to explore its host-sensitized photoluminescence (PL). Solid solutions of BBBO:xTb3+ (0 ? x ? 1) were prepared and its host-sensitized photoluminescence was confirmed, which is a result of the efficient Bi3+-to-Tb3+ energy transfer. Furthermore, an evolution of the coordination environments of the Bi3+/Tb3+ sites was observed when increasing x. This evolution was found to correlate to the variation of the PL spectra. In particular, the value of the ratio of cyan/green [defined as I(5D47F6)/I(5D47F5) of Tb3+] was about 0.28 when x < 0.4, and it increased to 0.71 at x = 0.9 and thereafter remained almost constant. Ba6(RE0.3–yBiyTb0.7)9B79O138 (RE = La or Y, 0 ? y ? 0.3) were also prepared for better understanding of the host-sensitization effect and in both series, Ba6(RE0.1Bi0.2Tb0.7)9B79O138 show the highest emission. Host-sensitized photoluminescence was confirmed in Ba6(Bi1–xTbx)9B79O138 (0 ? x ? 1), which originates from the highly efficient Bi3+-to-Tb3+ energy transfer. An evolution of the coordination environments of the Bi3+/Tb3+ sites was observed to be correlated with the variation of the ratio of cyan/green [defined as I(5D47F6)/I(5D47F5) of Tb3+].

Posted on 21 September 2015 | 12:20 pm

Fluorescent Boron Complexes of 25-Oxa­smaragdyrins Containing Axial Silyloxy Groups

A series of fluorescent BIII complexes of meso-triaryl-substituted 25-oxasmaragdyrins containing axial silyloxy groups were prepared in 80–85?% yields by treating B(OH)2 complexes of meso-triaryl 25-oxasmaragdyrins with different alkyl/aryl chlorosilanes in toluene in the presence of base at reflux temperature followed by simple column chromatographic purification. The eight axially silyloxy-substituted BIII complexes of smaragdyrins were freely soluble in common organic solvents and were characterized by HRMS, 1D and 2D NMR, absorption, fluorescence and electrochemical studies, as well as by X-ray crystallography in the case of one of the complexes. The crystal structure revealed that the smaragdyrin macrocycle is almost planar and that the –OSiMe3 groups on BIII are oriented in the up and down directions relative to the macrocycle. The absorption studies indicated that the axially silyloxy-substituted BIII smaragdyrins are strongly absorbing in the 710–440 nm region with absorption coefficients higher than those of B(OH)2-smaragdyrin complexes. The silylation of –OH groups at the BIII centrein the BIII smaragdyrin complex results in five- to sixfold enhancements in the fluorescence quantum yields and in longer singlet state lifetimes. Thus, the axial silyloxy BIII complexes are strongly fluorescent with quantum yields in the 0.65–0.78 range and singlet state lifetimes in the 4.3–4.9 ns range. The complexes are highly stable under redox conditions and each exhibit two reversible oxidations and one reversible reduction. The synthesis, structures and properties of highly fluorescent BIII complexes of 25-oxasmaragdyrins containing axial silyloxy groups are described. The presence of silyloxy groups as axial ligands on boron in BIII-smaragdyrin complexes results in hypsochromic shifts in absorption and emission bands, in enhancement in the fluorescent yields and in the macrocycles become electron-rich.

Posted on 18 September 2015 | 12:30 pm

Comparative Study of the Catalytic Amination of Benzylic C–H Bonds Promoted by Ru(TPP)(py)2 and Ru(TPP)(CO)

A combined experimental and DFT-based theoretical analysis elucidated the influence of the axial ligand L on the catalytic activity of Ru(porphyrin)L complexes in promoting the amination of benzylic C–H bonds by organic azides (RN3). Experimental data indicated that the catalytic activity of Ru(TPP)(CO) (1) (TPP = dianion of tetraphenylporphyrin) is comparable to that of Ru(TPP)(py)2 (2) (py = pyridine). DFT modelling disclosed that 2 can be regarded as a precatalyst that becomes active after the endergonic loss of one pyridine ligand to give the unsaturated species [Ru](py) (11) {[Ru] = Ru(porphine)}. This complex would react with RN3 to give the mono-imido singlet complex [Ru](py)(NR)S (6S), which can be easily transformed into the triplet isomer 6T having diradical character at the imido N atom. The subsequent formation of the benzylic amine PhCH2NHR occurs through a radical homolytic activation of one C–H bond of the toluene substrate (PhCH3). Conversely, by staying on the singlet potential-energy surface, 6S can undergo dissociation of the pyridine ligand to form [Ru](NR). This complex can activate another RN3 molecule to form the bis-imido compound [Ru](NR)2, which is also catalytically active. At this point, the mechanism becomes independent of the nature of the original ligand L coordinated to [Ru]. The catalytic activity of Ru(TPP)(py)2 (2) (TPP = dianion of tetraphenylporphyrin, py = pyridine) in the amination of C–H bonds by organic azides (RN3) was experimentally compared to that of Ru(TPP)(CO) (1). A computational analysis corroborates similar radical mechanisms with a triplet imido intermediate, in spite of the electronic differences of the apical ligands.

Posted on 18 September 2015 | 12:30 pm

Electrospun TiO2 Nanofibers Surface-Loaded with Ag Nanoparticles as a Sensitizer and Their Enhanced Effect in Photocatalytic Applications

In this work, Ag–TiO2 nanofibers were prepared by a simple electrospinning and photoreduction method. A mechanism for the synthesis of the Ag–TiO2 nanofibers was proposed on the basis of XRD, X-ray photoelectron spectroscopy (XPS), SEM, and energy-dispersive X-ray spectroscopy (EDX) results. The photocatalytic activities of the nanofibers were characterized for the degradation of aqueous solutions of methyl orange (MO) and hydrogen evolution from water with methyl alcohol as a sacrificial reagent under the simulated sunlight irradiation. The results indicate that the Ag-modified TiO2 nanofibers are efficient and stable photocatalysts for dye degradation and hydrogen evolution. Compared with pure TiO2 nanofibers, the Ag–TiO2 composite nanofibers have higher photocatalytic activities, and the best load of Ag was 5 mol-%. The Ag nanoparticles serve as charge-transfer sites and broaden the spectral absorption band of the catalyst. TiO2 is a high-performance catalyst for photocatalytic degradation and hydrogen evolution. However, its wide band gap and the fast recombination of the photogenerated electron–hole pairs limit its applications. Ag nanoparticles are loaded onto TiO2 nanofibers by photoreduction to enhance the photocatalytic efficiency of the catalyst. The optimum Ag loading is 5?%.

Posted on 18 September 2015 | 12:30 pm

1,1-Carboboration Through Activation of Silicon–Carbon and Tin–Carbon Bonds

In the course of 1,1-carboborations, the activation of polar Si–C and Sn–C bonds by electrophilic triorganoboranes (BR3, R = alkyl, aryl, C6F5) is used to build new C–C bonds. As would be expected, organotin compounds were found to be much more reactive than the corresponding silanes, and Sn–C(sp) bonds were more reactive than other tin–carbon bonds. Monoalkynyl derivatives lead to organometallic-substituted alkenes, quantitatively and stereoselectively in most cases. Dialkynylsilanes R22Si(C?C–R1)2 (R1 = alkyl, aryl, silyl; R2 = H, alkyl, allyl, vinyl, aryl, Cl) react with BR3 by twofold 1,1-carboboration through selective formation of siloles. In the case of dialkynylstannanes R22Sn(C?C–R1)2, (R1 = alkyl, aryl, silyl; R2 = alkyl, benzyl, aryl, amino) the analogous reactions lead mainly to stannoles or alternatively to 1-stanna-4-bora-cyclohexa-2,5-diene derivatives, in a way that depends in a complex manner on the substituents R at boron and R1 at the C?C bond. Vinyltin compounds and triorganoboranes also react by 1,1-carboboration. The high reactivity of the Sn–C(sp) bonds allows the reactions to be conducted under mild conditions, enabling the isolation and structural characterisation of intermediates. These are of a zwitterionic structure, in which typically an almost trigonal-planar surrounded tin atom is coordinated "side-on" to the C?C bond of an alknylborate unit. On extending these reaction principles to tetraalkynylsilanes Si(C?C–R1)4, one obtains 1,1?-spirobisiloles through fourfold 1,1-carboboration. Similarly, 1,1?-spirobistannoles can be prepared by starting from tetraalkynylstannanes Sn(C?C–R1)4 (R1 = iPr, tBu, SiMe3). Combination of 1,2-hydroboration and 1,1-carboboration opens the way to numerous silicon heterocycles, not readily available by any other method. Triorganoboranes activate Sn–C(sp) or Si–C(sp) bonds, leading to inter- and intramolecular 1,1-carboboration reactions. The zwitterionic intermediates were characterized in the solid state and in solution. Many new silicon heterocycles are accessible by combining 1,2-hydroboration and 1,1-carboboration.

Posted on 17 September 2015 | 11:51 am

Influence of the Crystal Structure on the Luminescence Properties of Mixed Eu,La–(1,10-Phenanthroline) Complexes

A series of europium Eu- and La-doped complexes with two different crystal structures, namely, EuxLa1–x(phen)2(NO3)3 [phen = 1,10-phenanthroline, x = 1.0 (1), 0.88 (2), 0.73 (3), and 0.52 (4)] and {[EuxLa1–x(phen)2(H2O)2(NO3)2](NO3)·2(phen)(H2O)} [x = 0.28 (5) and 0.0 (6)], were synthesized in aqueous solution by using different Eu/La ratios.The complexes were characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetry, and scanning electron microscopy. Compounds 1–4 and 5, 6 were obtained for Eu/La molar ratios higher than 5:5 and smaller than 3:7, respectively. The photoluminescence properties of these compounds depend on the crystal structure, which is determined by the Eu/La reactant ratio. Complexes 1–4 exhibit a quantum efficiency (? = 55?%) and quantum yield (q = 31?%) higher than 5 (? = 23?% and q = 6?%). The photophysical properties assessed by using the LUMPAC software are in good accord with the experimental values, particularly, the calculated (26?%) and measured emission quantum yields (31?%; excitation at the ligands at 255 nm). A series of europium Eu- and La-doped complexes with two different crystal structures were synthesized in aqueous solution by using different Eu/La ratios. Eu/La ? 5:5 afforded a Eu(phen)2(NO3)3 structure (phen = 1,10-phenanthroline), while Eu/La ? 3:7 resulted in the formation of a {[La(phen)2(H2O)2(NO3)2](NO3)·2(phen)(H2O)} structure.

Posted on 17 September 2015 | 11:51 am

3-(Pyridin-2-yl)imidazo[1,5-a]pyridine (Pyridylindolizine) as Ligand in Complexes of Transition and Main-Group Metals

The coordination of the easily prepared 3-(pyridin-2-yl)imidazo[1,5-a]pyridine (pyridylindolizine, Py-indz) ligand to several metal moieties was studied, and its electronic properties, similar to those of the classical ligands 2,2?-bipyridine (bipy) and 1,10-phenanthroline (phen), are reported. The new complexes were prepared and fully characterized by X-ray crystallography and other typical spectroscopic methods if possible. Paramagnetic complexes [Ni(S2X)2(Py-indz)] X = P(OEt)2 (1), COEt (2); [Ni(acac)2(Py-indz)] (3, acac = acetylacetonate); [Ni(Py-indz)3](PF6)2 (4); [Mn2Cl4(Py-indz)2] (6); and [MnCl2(Py-indz)2] (7) have the magnetic moment expected for a metallic cation with two or five unpaired electrons. Diamagnetic complexes show NMR spectra with similar patterns with small differences depending on the complex. [M{S2P(OEt)2}2 (Py-indz)] M = Zn (8), Cd (9) have pentacoordinate and hexacoordinate structures, respectively. Octahedral tin complexes [SnL4(Py-indz)] L4 = I4 (10), Cl3Ph (11), and Cl2nBu2 (12) have different behaviors in solution; whereas complex 10 is practically insoluble, complex 11 displays the expected pattern in its NMR spectrum, and complex 12 shows dynamic behavior. The Py-indz ligand is also able to stabilize copper(I) and forms [Cu(PPh3)2(Py-indz)]BF4 (13). The synthesis of the carbonyl complexes [MBr(CO)3(Py-indz)] M = Mn (14), Re (15) and [Mo(CO)4(Py-indz)] (16) was followed by IR spectroscopy in solution. [RuCl·p-cym(Py-indz)]PF6 (17, p-cym = p-cymene) has the familiar half-sandwich “three-legged piano-stool” geometry. Thorough screening confirms the potential of the now easily available 3-(pyridin-2-yl)imidazo[1,5-a]pyridine (Py-indz) ligand in the preparation of complexes with transition and main-group metallic centers in very different environments.

Posted on 17 September 2015 | 11:51 am

5-Nitriminotetrazole 1-Oxide: An Exciting Oxygen- and Nitrogen-Rich Heterocycle

5-Nitriminotetrazole 1-oxide (CH2N6O3) and selected salts (e.g., dipotassium, diammonium, dihydroxylammonium) were prepared and characterized for the first time. The neutral molecule can be obtained by nitration of an O-protected 5-aminotetrazole 1-oxide. The new compounds were characterized by using low-temperature X-ray diffraction as well as IR, Raman, and multinuclear NMR spectroscopy and elemental analysis. Differential scanning calorimetry measurements showed a large range for the decomposition temperatures. The highest value of 320 °C was observed for the dipotassium salt. The energetic performances (detonation velocities up to 9842 m?s–1) were calculated with the EXPLO5 code by using calculated (CBS-4M) heats of formation and experimentally obtained X-ray densities. Calculated performance data support the highly energetic character of these new compounds. The sensitivities toward impact, friction, and electrostatic discharge were also determined. N + O = 90.4?%: The exploration and characterization of 5-nitrimino-tetrazole 1-oxide is a logical consequence in the trend of synthesizing not only nitrogen-rich but also oxygen-rich energetic materials with superior performance. Twofold deprotonation by using KOH results in a dramatic increase (ca. 200 °C) in the decomposition temperature.

Posted on 17 September 2015 | 11:51 am

Metal–Halogen Secondary Bonding in a 2,5-Dichlorohydroquinonate Cobalt(II) Complex: Insight into Substrate Coordination in the Chlorohydroquinone Dioxygenase PcpA

Despite the unprecedented selectivity of the hydroquinone ring-cleaving dioxygenase PcpA for ortho-chlorohydroquinones, there are no examples of an ortho-chlorohydroquinone bound to a transition-metal complex. Herein, the synthesis and characterization of (TpPh2Co)2(?-2,5-dichlorohydroquinonate), for which TpPh2 is tris(3,5-diphenylpyrazolyl)borate, were explored. The dianionic 2,5-dichlorohydroquinonate bridges two (TpPh2Co) moieties and coordinates each cobalt(II) center through the oxygen and chlorine atoms of the chlorohydroquinone. The Co–Cl distance of 2.778 Å shows the characteristics of a metal–halogen secondary bond, as we previously showed in ortho-halophenolate complexes. This compound represents the first example of metal–halogen secondary bonding with a halohydroquinone and, thus, provides a potential structural model for selective substrate binding to the metal center in PcpA. We report the synthesis of (TpPh2Co)2(?-2,5-dichlorohydroquinonate) [TpPh2 = tris(3,5-diphenylpyrazolyl)borate], in which a bridging 2,5-dichlorohydroquinonate coordinates each CoII through an unusual metal–halogen secondary bond (Co–Cl 2.778 Å). This first example of M–X secondary bonding with a halohydroquinone provides a potential structural model for substrate binding in the ortho-chlorohydroquinone dioxygenase PcpA.

Posted on 17 September 2015 | 11:51 am

Cooperative Effects in Copper Polyamido­amine Dendrimer Complexes Catalyzing the Reduction of Molecular Oxygen

Generation-dependent cooperation was observed in the reduction of molecular oxygen by a series of Cu2+ complexes of pyridine-modified polyamidoamine (PAMAM) dendrimers. The cooperative behavior of the metal ions was examined by preparing (G2–G6)-dendri-PAMAM-(Py)n and testing the dendrimers for their ability to reduce oxygen catalytically in the presence of several Cu2+ ion concentrations. Spectrophotometric measurements during the reactive metallic ion titrations revealed that the maximum numbers of reactive Cu2+ ions available for O2 reduction were 4.8, 7.6, 22.2, 57.3, and 81.7 in each of the second- to sixth-generation (G2–G6) dendrimer complexes, respectively. An analysis revealed that each Cu2+ ion worked independently as an active center in the G2 to G4 dendrimer complexes. By contrast, pairs of Cu2+ ion active species were present in the G5 and G6 dendrimer complexes. A kojic acid titration indicated that the copper ions were proximal and formed a bicopper active center in the G5 and G6 dendrimer complexes. Catalytic reactions with catechol as a reducing agent further demonstrated the activity of the dinuclear copper center in the G5 and G6 dendrimer complexes. The present findings suggest that generations of dendrimer–metal complexes can alter their catalytic behavior. Generation-dependent cooperation is observed in O2 reduction by Cu2+ complexes of pyridine-modified polyamidoamine (PAMAM) dendrimers. Spectrophotometric titrations suggest the existence of bicopper active centers in the fifth- and sixth-generation (G5 and G6) analogs, which was further confirmed by the same reaction with catechol as a reductant and kojic acid titration experiments.

Posted on 14 September 2015 | 11:30 am

Towards Ruthenium-Based Building Blocks for CuAAC Click Reactions: Challenges in Generating Ruthenium(II) Poly­pyridine Alkynes

Ag+-free complexation of alkyne-bipyridines at ruthenium(II) polypyridine centers proceeds with surprisingly low yields. The alkyne-bipyridine-substituted ruthenium(II) polypyridine complexes in this work were characterized by NMR spectroscopy, ESI spectrometry, and single-crystal X-ray structural analysis. A detailed analysis of the side products revealed an unexpected carbon–carbon alkyne bond splitting promoted by the ruthenium(II) center, leading to the formation of a CO–RuII species, methyl-bipyridine, and a methyl-bipyridine-substituted ruthenium(II) complex accompanying the target product. The side products were characterized using complimentary methods including X-ray crystallography. A possible mechanism is suggested based on these side products and exemplary reaction studies. For the coordination reaction of alkyne-bipyridines with Ru(bpy)2Cl2 unexpected side reactions take place, forming a RuII–CO species and methyl-bipyridine. Here we give a detailed mechanism of the side reactions and an adequate workup procedure to obtain a pure alkyne-substituted ruthenium(II) polypyridine complex, which is the intended product.

Posted on 14 September 2015 | 11:30 am

The Reaction between Diazadienes and Element Tribromides EBr3 (E = P, B) Revisited: Metal-Free Synthesis of Halogenated N-Heterocyclic Phosphanes and Boranes

Reactions of selected diazadienes with PBr3 and BBr3 in the presence of a tertiary amine yielding N-heterocyclic phosphanes (NHPs) and N-heterocyclic boranes (NHBs) were studied. It is demonstrated that heterocycle formation occurs even without an amine or another auxiliary reagent, and the amine acts mainly as scavenger of Br2 formed as by-product, but also that the additive speeds up reactions and has an influence on the product selectivity. In extension of the results of earlier studies it is shown that the reactions can follow two different pathways to give either 2-bromo- or 2,4-dibromo-substituted heterocycles. Computational studies enabled to propose a reaction mechanism, which relates the observed behaviour to the availability of two competing reaction channels and provides also a rational explanation for the different behaviour of ECl3, EBr3, and EI3 (E = B, P) in cycloaddition reactions with diazadienes, which is empirically well established. In the borane series, a tribromo-NHB is formed in a follow-up reaction between the initial products and Br2, which seems to be the first example of an electrophilic backbone functionalization in an NHB. The 2-bromo derivative is formed exclusively when PPh3 is used as auxiliary reagent. Selected products are isolated and fully characterised, proving the synthetic utility of the reactions studied. The reaction of diazadienes with EBr3 may follow two different pathways to yield either 2-bromo- or 2,4-dibromo-substituted N-heterocyclic products. DFT studies were used to provide a mechanistic explanation for the diverse behaviour, which also allows to understand the differing reactivity of ECl3 and EBr3 towards diazadienes. The usability of the “metal-free” syntheses is demonstrated in selected examples.

Posted on 14 September 2015 | 8:20 am

Powerful Antibacterial Activity of Phenyl-Thiolatobismuth(III) Complexes Derived from Oxadiazolethiones

Seven novel 5-substituted phenylthiazole oxadiazolethiones: [Me-PTOT(H)], [MeO-PTOT(H)], [MeS-PTOT(H)], [F-PTOT(H)], [Cl-PTOT(H)], [Br-PTOT(H)], and [CF3-PTOT(H)], {where X-PTOT(H) = 5-[2-(4-X)thiazol-4-yl]-1,3,4-oxadiazole-2(3H)-thione, 4-X = C6H4}, were synthesised from their corresponding thioamides. From these seven heteroleptic thiolatobismuth complexes: BiPh(Me-PTOT)2 6, BiPh(MeO-PTOT)2 7, BiPh(MeS-PTOT)2 8, BiPh(F-PTOT)2 9, BiPh(Cl-PTOT)2 10, BiPh(Br-PTOT)2 11 and BiPh(CF3-PTOT)2 12 were synthesised and characterised. Complexes [10(DMSO)2] and [11(DMSO)2] were structurally characterised using X-ray diffraction. Evaluation of the antibacterial properties of the thiones and their BiIII complexes against Mycobacterium smegmatis, Staphylococcus aureus (S. aureus), Methicillin-resistant Staphylococcus aureus (MRSA), Vancomycin-resistant Enterococcus (VRE), Enterococcus faecalis (E. faecalis) and Escherichia coli (E. coli) showed that all bismuth(III) complexes were highly effective against all the bacteria, as demonstrated by very low MIC values (1.1–2.1 ?M). Complexes BiPh(Me-PTOT)2 6, BiPh(Cl-PTOT)2 10 and BiPh(Br-PTOT)2 11, showed best activity against the multi-drug resistant bacteria VRE and MRSA with an MIC value of 1.0 ?M. All these complexes and their corresponding thiones failed to show any prominent activity against M. smegmatis and E. coli, even at high concentrations. These complexes showed little or no toxicity towards mammalian COS-7 cells at 20 ?g/mL. Seven heteroleptic thiolatobismuth(III) complexes [BiPh(X-PTOT)2] derived from a series of 5-substituted phenylthiazole oxadiazolethiones [X-PTOT(H)] provide powerful antibacterial action against the multi-resistant bacteria MRSA and VRE.

Posted on 11 September 2015 | 9:20 am

Photocrystallographic, Spectroscopic, and Calorimetric Analysis of Light-Induced Linkage NO Isomers in [RuNO(NO2)2­(pyridine)2OH]

Through photocrystallography at T = 80 K, light-induced linkage isonitrosyl NO isomers (?O-bound) are detected and refined in the complex fac-[RuNO(NO2)2Py2OH]·H2O (Py = pyridine) after irradiation with light in the blue spectral range. The infrared and Raman spectra reveal the downshift of the ?(NO), ?(Ru–NO), and ?(Ru–N–O) vibrations by 120–150 cm–1 upon photoexcitation. Furthermore, the infrared spectrum show a significant downshift of the ?as(NO2) and ?s(NO2) bands by ca. 10 cm–1 but without any isomerization of the NO2 ligands. Furthermore, the downshifts of the ?(Ru–O–H) and ?(Ru–O–H) vibrational modes show the trans influence of the NO isomer on the OH ligand. The populations of the isonitrosyl isomer determined (66–75?% at ? = 443–445 nm) by all three techniques (X-ray crystallography, IR and Raman spectroscopy) agree well. Such a high population of the isonitrosyl structure is visible in the photodifference map. The activation parameters Ea = 63.9?±?1 kJ/mol and k0 = (1.8?±?0.1)?×?1013 s–1 of the reverse transition were determined by differential scanning calorimetry (DSC). The second metastable state (side-on ?2NO mode) was generated by a two-step irradiation with blue light followed by irradiation with light in the near-infrared spectral range (980 nm) and identified through its characteristic NO stretching vibration at $\tilde {\nu}$ = 1592 and 1600 cm–1. Through photocrystallography, IR spectroscopy, and Raman spectroscopy, a light-induced isonitrosyl linkage isomer (MS1) is detected and refined in fac-[RuNO(NO2)2Py2OH]; after irradiation at ? = 445 nm, the population of MS1 is ca. 66–75?%. The infrared and Raman spectra reveal the downshift of the ?(NO), ?(Ru–NO), and ?(Ru–N–O) vibrations by 120–150 cm–1.

Posted on 11 September 2015 | 9:10 am

Effects of Buffers and pH on the Reaction of a trans-Platinum Complex with 5?-Guanosine Monophosphate

The aquation of platinum anticancer drugs is a crucial step for their activation and the consequent binding to the target DNA. These processes can be influenced by small molecules, such as carbonate and phosphate, which are present in high concentration in physiological conditions. In this work, the effects of buffer and pH on the reaction of trans-EE {trans-[PtCl2{E-HN=C(OCH3)CH3}2]} with 5?-guanosine monophosphate (5?-GMP) have been studied in detail. The reactions were monitored by HPLC at different pH in the presence of carbonate, phosphate, and HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid] buffers. trans-EE showed a very low affinity for the nitrogen atoms of HEPES, but formed monofunctional adducts with carbonate and phosphate ions. The platination of GMP by trans-EE was significantly affected by the choice of buffer and pH. Carbonate buffer decreased the reaction rate, mostly due to its competition with GMP. Although phosphate buffer formed a similar monofunctional adduct with trans-EE, it had a negligible effect on the platination rate of GMP. This may be due to the formation of ternary adducts with trans-EE and GMP. In all cases, the platination reaction was slower at higher pH, probably due to the deprotonation of an aqua ligand on the mono-aqua complex of trans-EE. The results in this paper indicate that the solution conditions have a different effect on the reaction of trans-platinum complexes compared with cisplatin. The reaction of an anti-tumor trans-platinum agent with GMP is influenced by buffer at physiological concentrations. Carbonate buffer reacts with trans-EE and significantly reduces the platination of GMP, whereas the reaction of phosphate buffer has much less of an effect.

Posted on 11 September 2015 | 9:10 am

Isomer Dependence of Efficiency and Charge Recombination in Dye-Sensitized Solar Cells Using Ru Complex Dyes Bearing Halogen Substituents

We have synthesised Ru(H2-dcbpy)(N,N?-Y2-bpy)(NCS)2 dyes (where N = 4, 5; Y = F, Cl, Br; N is the position on the bipyridyl ring where the halogen substituent is located) for dye-sensitised solar cells. We show that careful consideration of the position of the substituent, in conjunction with the nature of the substituents, on a bpy ring is important to optimize the solar cells performance. Changing the position (from 4,4? to 5,5?) along with the nature of the halogen (F, Cl, or Br) substituents were observed to cause changes in the electronic and spectroscopic properties of the dyes as well as influence the recombination rates at the TiO2–dyes–I–/I3– interface affecting the performance of the dyes in DSSCs. Changing the position (from 4,4? to 5,5?) along with the nature of the halogen (F, Cl, or Br) substituents affects the electronic and spectroscopic properties of the Ru(H2-dcbpy)(N,N?-Y2-bpy)(NCS)2 dyes as well as the recombination rates at the TiO2-dyes-I–/I3– interface hence affecting the performance of the dyes in DSSCs.

Posted on 11 September 2015 | 9:10 am

Highly Selective and Sensitive Detection of Picric Acid Explosive by a Bisporphyrin Cleft: Synergistic Effects of Encapsulation, Efficient Electron Transfer, and Hydrogen Bonding

A flexible diethylpyrrole-bridged bisporphyrin (H4DEP) is employed to encapsulate highly explosive picric acid (PA) in its cleft, and information about the chemical environment in the interior of the host–guest assembly is obtained. The synthesis, X-ray structure, and photophysical properties of the encapsulated host–guest complex (H4DEP·PA) are reported here. The host–guest assembly is also retained in solution with a binding constant (K) of (2.63?±?0.2)?×?105 M–1. Such an efficient complexation is due to the perfect match of the host–guest size, H bonding, and strong ?–? interactions between the host and guest, which collectively make the binding of PA rapid and highly selective with a detection limit of 2.4 ppm. The host H4DEP can also discriminate the highly explosive PA from other nitroaromatic compounds. The extremely low HOMO–LUMO gap (HOMO = highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital) in the host–guest complex leads to an efficient and highly facile electron transfer from the host to the guest, which results in substantial quenching of the emission intensity of H4DEP. Such an efficient electron transfer is only possible if the donor and acceptor moieties are close to each other, as this lowers the reorganization energy. All of the experimental evidence is further substantiated by DFT calculations. An efficient host–guest complexation leads to rapid, highly selective, and efficient detection of picric acid (PA) in the presence of other nitroaromatics in solution as well as in the solid phase.

Posted on 11 September 2015 | 9:10 am

Pyrazole-Stabilized Dinuclear Palladium(II) Chalcogenolates Formed by Oxidative Addition of Bis[2-(4-bromopyrazol-1-yl)ethyl] Dichalcogenides to Palladium(II) – Tailoring of Pd–S/Se Nanoparticles

Bis[2-(4-bromopyrazol-1-yl)ethyl] disulfide and diselenide L1 and L2 were synthesized by the reactions of 4-bromo-1-(2-chloroethyl)-1H-pyrazole with the in situ generated Na2S2 and Na2Se2. The reactions of L1 and L2 with 2 equiv. of [PdCl2(CH3CN)2] in CH3CN at 70 °C proceed through an oxidative addition/reductive elimination sequence to the PdII center to form the chalcogenolato-bridged dinuclear palladium(II) complexes [Pd2Cl2(?-EN)2] [1 (E = S) and 2 (E = Se); EN = 2-(4-bromopyrazol-1-yl)ethanechalcogenolate]. The reactions of 1 and 2 with CH3CN and AgBF4 resulted in the formation of [Pd2(CH3CN)2(?-EN)2]·2BF4 (3 and 4). Compounds L1, L2, and their complexes 1–4 have been characterized through 1H, 13C{1H}, and 77Se{1H} nuclear magnetic resonance (NMR) spectroscopy; infrared (IR) spectroscopy; and high-resolution mass spectrometry (HRMS). The single-crystal X-ray structures of 2–4 have revealed distorted square-planar geometries around the Pd center in each case. The Pd–S and Pd–Se bond lengths are in the ranges 2.277(2)–2.296(2) and 2.372(9)–2.3971(17) Å, respectively. Single-source precursor routes for the synthesis of palladium chalcogenide nanoparticles (NPs) have been developed by the thermolyses of 1–4 in 1:1 mixtures of oleic acid (OA) and 1-octadecene (ODE). Pd17Se15 NPs were formed from both PdII selenolates 2 and 4, whereas Pd4S NPs and a mixture of Pd16S7 (ca. 68?%) and PdS (ca. 32?%) NPs were obtained from PdII thiolates 1 and 3, respectively. Transmission electron microscopy (TEM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), and powder X-ray diffraction (PXRD) have been used to authenticate the NPs. X-ray photoelectron spectroscopy (XPS) studies on the NPs have revealed that there is a charge transfer from Pd to S/Se. The compositions of the NPs determined from XPS are consistent with the PXRD results. The thermolyses of chalcogenolato-bridged dinuclear PdII complexes of pyrazole-based thiolates and selenolates in 1:1 mixtures of oleic acid (OA) and 1-octadecene (ODE) afford Pd17Se15, Pd4S, and Pd16S7 + PdS nanoparticles (NPs).

Posted on 9 September 2015 | 10:10 am

Bioinspired Nanoparticle-Assembly Route to a Hybrid Scaffold: Designing a Robust Heterogeneous Catalyst for Asymmetric Dihydroxylation of Olefins

A hierarchical polyamine-silica structure is shown to encase osmate ions resulting in robust and reusable catalysts for asymmetric dihydroxylation of olefins with a high TON (>700). Whilst the polypeptide and related polyamines resembling a proteinaceous matrix in biosilica nanostructures preserve the osmate as the active centre, the surrounding assembly of silica nanoparticles imparts stability and textural properties to the catalyst. This confinement of osmate in the microsphere leads to higher catalytic activity and enantioselectivity for a variety of olefins as the substrate. The hybrid nature of the catalyst not only allows for the usage of various solvent systems, but also provides a means to be integrated with multi-components/functions for tuning the activity, catalysis separation and reusability. Interestingly, the presence of polyamine makes the catalyst retain its activity even in the presence of chelating acids like citrate that are known to diminish enantioselectivity. A bioinspired hybrid design based on the biosilica nanostructure allows chemical transformations with entrapped osmium species enabling superior catalytic activity, stability and reusability in the asymmetric dihydroxylation of olefins.

Posted on 9 September 2015 | 10:10 am

A Family of IrIII Complexes with High Nonlinear Optical Response and Their Potential Use in Light-Emitting Devices

We synthesized a new family of IrIII complexes [Ir(R1-ppy)2(R2-ppl)](PF6), where R1-ppy = 2-phenylpyridine (ppy) or 2,4-difluorophenylpyridine (F2-ppy) and R2-ppl = pyrazino[2,3-f][1,10]phenanthroline (ppl) or 2,3-diethoxycarbonylpyrazino [2,3-f][1,10]phenanthroline (deeppl). The complexes were experimentally and theoretically characterized, noting the importance of the R1 substituent on the modulation of HOMO level and its impact on the electronic properties. These compounds exhibit high second-order nonlinear optics (NLO) activity, especially, those with F2-ppy ligands; this substituent modulates the charge transfer, optimizing the NLO response. The compounds also show blueshifted emissions, both in solution and as a solid film, which is desirable for use in light-emitting devices. This is the first use of the synthesized complexes for application in the two tasks. The synthesis and photophysical analysis of a series of IrIII complexes was performed. The complexes show nonlinear optics activity, and appear to have potential as efficient emitters for light electrochemical cells.

Posted on 9 September 2015 | 9:50 am

Polyhalide Ions (Br82– and I2Br62–) and Chains (···Br3–···Br2··· and ···IBr4–···) Stabilised by Using Cu(dafone)32+ as Counter Ion (dafone = 4,5-Diazafluoren-9-one)

Two new iodobromides [I2Br62– (analogue of I82– and Br82–) and IBr4– (analogue of Br5– and I2Br3–)] and new chains formed from Br3–, Br2 and IBr4– have been obtained in three compounds all containing the same CuII tris-chelate cation Cu(dafone)32+ {[Cu(dafone)3](Br3)(Br5) (1), [Cu(dafone)3](Br5)(Br8)0.5·CH3CN (2) and [Cu(dafone)3](IBr4)(I2Br6)0.5·CH3CN (3)} by a procedure employing bromine, iodine, CuII bromide and dafone in acetonitrile. The formation of chains and isolated polyhalide ions is facilitated by templating with the tris-chelate cation. The Raman spectra of the polyhalides and EPR and other spectral characteristics of the fluxional CuII complex cation are presented. Templating by a fluxional CuII tris-chelate cation facilitates the crystallisation of new polybromide chains and iodobromides: the V-shaped ions Br5– and IBr4–, both organised as one-dimensional chains, as well as isolated Br3–, Br82– and I2Br62– ions. Both octahalides have acute-angled Z-shapes in the crystals, whereas the “gas-phase” ions are computed to be more stretched out.

Posted on 8 September 2015 | 9:51 am

[NaCu(2,4-HPdc)(2,4-Pdc)] Mixed Metal–Organic Framework as a Heterogeneous Catalyst

The synthesis of a new mixed metal–organic framework (M?MOF) has been accomplished by the metalloligand approach. [NaCu(2,4-HPdc)(2,4-Pdc)] (2,4-H2Pdc = pyridine-2,4-dicarboxylic acid) has been obtained from the hydrothermal reaction of the metalloligand [Cu(2,4-HPdc)2(H2O)2] NaOH, and a transition metal salt. [NaCu(2,4-HPdc)(2,4-Pdc)] is isostructural to [CuMn(2,4-Pdc)2] and crystallizes in the triclinic space group P$\bar {1}$. The 3D structure is built up from [Cu(2,4-HPdc)2(H2O)2] metalloligands and [NaO6] octahedra in a pcu ?-Po-like uninodal six-connected net. The compound is stable to 290 °C, and its crystal structure undergoes a 3?% volume expansion between room temperature and thermal decomposition. The unsaturated CuII centers at the surface act as a heterogeneous Lewis acid catalyst for the cyanosilylation of aldehydes and Knoevenagel C–C bond-forming reactions. The catalytic activity has been compared with those of other copper(II) porous metal–organic frameworks such as HKUST-1 and MOF-74. A new mixed metal–organic framework, [NaCu(2,4-HPdc)(2,4-Pdc)] (2,4-H2Pdc = pyridine-2,4-dicarboxylic acid), with heterogeneous catalytic properties is synthesized by the metalloligand approach.

Posted on 8 September 2015 | 9:51 am

Optimal Synthesis of Faujasite-Type Zeolites with a Hierarchical Porosity from Natural Clay

Raw clay, which is an interstratified illite-kaolinite, has been used as a raw material to prepare Faujasite-type zeolites. The synthesis was based on the alkaline fusion method followed by hydrothermal treatment without the addition of any extra silica or alumina sources. The effects of various factors on the synthesis process, such as NaOH/clay ratio, crystallization time and temperature, were investigated. The results obtained underlined that these parameters determined whether or not Faujasite-type zeolites were formed. The optimum synthesis conditions for the synthesis of a single Faujasite zeolite phase were a weight ratio of NaOH/clay of 1.2 fused at 500 °C for 2 h and crystallized at 60 °C for 24 h after homogenization for 12 h. The compounds obtained were characterized by X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy. Their textural properties were investigated by N2 adsorption/desorption measurements. The BET surface area of the product synthesized with the optimum conditions was 360 m2/g with a relatively high total pore volume of 0.33 m3/g. Toluene adsorption on the synthesized trimodal Faujasite zeolite was four times higher than on commercial zeolite. This synthesis is therefore a good way to obtain a cheap and efficient adsorbent for environmental applications. Faujasite-type zeolites have been successfully synthesized from natural illitic kaolinite clay by alkaline fusion prior to hydrothermal treatment. The synthesis was optimized and the products characterized. The Faujasite-type zeolite obtained under the optimum conditions showed a large number of zeolitic crystals with well-defined hexagonal morphology as well as a hierarchical porosity.

Posted on 8 September 2015 | 9:51 am

Combined Oxidation, Deprotonation, and Metal Coordination of a Redox-Active Guanidine Ligand

Guanidino-functionalized aromatic compounds (GFAs) are strong organic electron donors and redox-active ligands. The diversity of GFA chemistry results from reaction sequences that are triggered by their oxidation. This work reports on reactions of a new GFA compound, namely, 1,2,4,5-tetrakis(N,N?-dicyclohexylguanidino)benzene, with transition metals, and analyzes the interplay between GFA oxidation, coordination, and hydrogen-bond formation up to deprotonation. The reaction of the new GFA with [{PdCl(C3H5)}2] led to coordination and a coupled proton- and electron-transfer reaction. The synthesis and reactivity of the guanidino-functionalized aromatic compound 1,2,4,5-tetrakis(N,N?-dicyclohexylguanidino)benzene are reported. Its reaction with [{PdCl(C3H5)}2] resulted in a coupled oxidation, deprotonation, and coordination process that led directly to a hexanuclear palladium complex.

Posted on 8 September 2015 | 9:50 am

Mechanism of CO2 Fixation by IrI–X Bonds (X = OH, OR, N, C)

Density functional theory calculations have been used to investigate the CO2 fixation mechanism proposed by Nolan et al. for the IrI complex [Ir(cod)(IiPr)(OH)] (1; cod = 1,5-cyclooctadiene; IiPr = 1,3-diisopropylimidazol-2-ylidene) and its derivatives. For 1, our results suggest that CO2 insertion is the rate-limiting step rather than the dimerization step. Additionally, in agreement with the experimental results, our results show that CO2 insertion into the Ir–OR1 (R1 = H, methyl, and phenyl) and Ir–N bonds is kinetically facile, and the calculated activation energies span a range of only 12.0–23.0 kcal/mol. Substantially higher values (35.0–50.0 kcal/mol) are reported for analogous Ir–C bonds. We report the DFT-based investigation of the mechanism of CO2 insertion into IrI–C and IrI–heteroatom bonds (such as Ir–N and Ir–O). The calculated barriers show that CO2 insertion is the rate-limiting step, in accordance with experimental results.

Posted on 8 September 2015 | 9:50 am

Seven-Coordinate Luminophores: Brilliant Luminescence of Lanthanide Complexes with C3v Geometrical Structures

Enhanced luminescence properties of mononuclear lanthanide complexes with asymmetric seven-coordination structures are reported for the first time. The lanthanide complexes are composed of a lanthanide ion (EuIII or TbIII), three tetramethyl heptanedionato ligands, and one triphenylphosphine oxide ligand. The coordination geometries of the lanthanide complexes have been evaluated by using single-crystal X-ray analyses and shape-measurement calculations. The complexes are categorized to be seven-coordinate monocapped octahedral structures (point group C3v). The seven-coordinate lanthanide complexes show high intrinsic emission quantum yields, extra-large radiative rate constants, and unexpected small nonradiative rate constants. The brilliant luminescence properties have been elucidated in terms of the asymmetric coordination geometry and small vibrational quanta related to thermal relaxation. This work reports on lanthanide complexes with seven-coordination structures that show brilliant luminescence properties owing to their asymmetric geometrical structure. The complexes exhibit extra-large radiative rate constants and unexpected small nonradiative rate constants.

Posted on 7 September 2015 | 9:50 am

PEGylated DOTA-AHA-Based GdIII Chelates: A Relaxometric Study

Three PEGylated derivatives of 6-amino-2-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetrazacyclododec-1-yl]hexanoic acid (DOTA-AHA) with different molecular weights were prepared and characterized. Their GdIII chelates were studied in aqueous solution through variable-temperature 1H nuclear magnetic relaxation dispersion (NMRD) and 17O NMR spectroscopy to determine their relaxivities and the parameters that govern them. The relaxivity varied from 5.1 to 6.5 mM–1?s–1 (37 °C and 60 MHz) as the molecular weight of the polyethylene glycol (PEG) chain increased and was slightly higher than that of the parent chelate Gd(DOTA-AHA), owing to a small contribution of a slow global rotation of the complexes. A variable-temperature 1H NMR spectroscopy study of several LnIII chelates of DOTA-A(PEG750)HA allowed the determination of the isomeric M/m ratio (M = square-antiprismatic isomer and m = twisted square-antiprismatic isomer; the latter presents a much faster water exchange), which was estimated to be ca. 1:0.2 for the GdIII chelate, very close to that of [Gd(DOTA)]–. This explains why the PEGylated GdIII chelate has a water rate exchange similar to that of [Gd(DOTA)]–. The predominance of the M isomer is a consequence of the bulky PEG moiety, which does not favor the stabilization of the m isomer in sterically crowded systems at the substituent site, in contrast to what happens with less packed asymmetrical DOTA-type chelates with substitution at one of the four acetate C(?) atoms. Three PEGylated derivatives of DOTA-AHA with different molecular weights are prepared, and their GdIII chelates are studied by variable-temperature 1H nuclear magnetic relaxation dispersion (NMRD) and 17O NMR spectroscopy. The isomeric M/m ratio is determined by a 1H NMR study of several LnIII chelates of DOTA-A(PEG750)HA to shed light on the relaxometric behavior of the GdIII chelates.

Posted on 4 September 2015 | 12:20 pm

Probing the Limits of Tetraazamacrocycle-Glyoxal Condensates as Bidentate Ligands for Cu2+

Tetracyclic bisaminals formed by condensation of tetraazamacrocycles and glyoxal have rarely been utilized as ligands for transition metal ions. Five novel Cu2+ complexes are presented to expand this set. Glyoxal derivatives of pyruvic aldehyde and butanedione were expected to further rigidify the bisaminal skeleton because of the steric requirements of the methyl groups, while the previously unutilized homocyclam was expected to increase flexibility due to the presence of a seven-membered ring. Additionally, a nitrato complex was prepared to examine the effect of more bulky monodentate ligands on the bisaminal framework. The new complexes showed similar four-coordination of Cu2+, but with significant changes in coordination geometry caused by substitution of the glyoxal bridge by one or two methyl groups. The homocyclam derivative produced a completely different coordination mode due to the flexibility of the larger macrocycle ring. Both structural and electronic properties were affected by the use of nitrato in place of the typical chlorido monodentate ligands. Overall, the electronic properties (magnetic moment, electronic spectra, and cyclic voltammetry) were only subtly affected. However, larger changes were observed when the larger homocyclam macrocycle was used or the nitrato anion was used in place of the chlorido ligand to complete the coordination. Additionally, the recently published geometric index ?? was evaluated by using this series of closely related Cu2+ complexes. A series of tetraazamacrocycle-glyoxal derivative condensate bisaminal ligands and their Cu2+ complexes have been prepared and structurally and electronically characterized. Butanedione and pyruvic aldehyde glyoxal derivatives and the homocyclam tetraazamacrocycle give additional members to this family of rigid, bidentate chelate complexes, which offer surprising control over coordination geometry.

Posted on 4 September 2015 | 12:20 pm

Photoredox Properties of Homoleptic d6 Metal Complexes with the Electron-Rich 4,4?,5,5?-Tetramethoxy-2,2?-bipyridine Ligand

A synthetic procedure leading to 4,4?,5,5?-tetramethoxy-2,2?-bipyridine [(MeO)4bpy] was developed, and the first three metal complexes with this ligand were synthesized. A few ligand precursor compounds, the final ligand, and its homoleptic iron(II) complex were characterized structurally by X-ray diffraction. The combination of cyclic voltammetry, optical absorption, luminescence, and transient absorption spectroscopy provided detailed insight into the electronic structure of the entire series of homoleptic FeII, RuII, and OsII complexes. The ruthenium(II) complex is a more potent photoreductant than the [Ru(bpy)3]2+ parent compound by approximately 0.4 V as confirmed by 3MLCT excited-state quenching experiments with a relatively mild oxidant, 1-chloro-4-nitrobenzene. In the presence of methanesulfonic acid in CH3CN, the photoexcited [Ru{(MeO)4bpy}3]2+ complex is able to undergo proton-coupled electron transfer (PCET) with acetophenone to yield a ketyl radical. Chemically robust and potent photoreductants are of interest for the phototriggering of electron-transfer reactions, for example, in photoredox catalysis, in dye-sensitized solar cells, in fundamental studies of (proton-coupled) electron transfer, or for the generation of solvated electrons. A fourfold methoxy-substituted 2,2?-bipyridine molecule was used as a ligand for homoleptic complexes with FeII, RuII, and OsII. The last two are strong electron donors in their long-lived 3MLCT excited states. Their ability to act as photoredox reagents in acidic media has been demonstrated with the example of acetophenone reduction by proton-coupled electron transfer (PCET).

Posted on 4 September 2015 | 12:20 pm

Self-Assembly Growth and Photocatalytic Performance of Nanostructured Copper Compounds

Flowerlike CuO structures were synthesized by a simple chemical method. These 3D structures are formed by self-assembly growth of smaller nanosheets as basic building units. Their crystalline phase, morphology, and optical properties were characterized by XRD, field-emission SEM, and UV/Vis absorption spectroscopy. The effect of annealing on the morphology and properties of nanostructured Cu(OH)2/CuO was also investigated. The obtained CuO nanosheets with highly energetic (111) facets have excellent capacity for absorbing visible light, and their band-gap energies, which were evaluated from the UV/Vis spectrum, range from 1.33 to 1.70 eV. Hence, their photocatalytic performance in the degradation of methyl blue (MB) was evaluated, and the highest photocatalytic degree of degradation of MB was 93.3?%. Further, the growth mechanism of the transformation from Cu(OH)2 nanowires (or nanoscrolls) to 3D CuO structures is discussed. Flowerlike CuO structures with nanosheets as building units were prepared from Cu foil by a simple chemical method. The band gaps of the films range from 1.33 to 1.70 eV, and they show excellent performance in the photocatalytic degradation of methyl blue, with highest degrees of degradation of 93.3 and 92.5?% for Cu(OH)2/CuO and pure CuO films, respectively.

Posted on 3 September 2015 | 1:50 pm

Crystal Structure, Magnetic and Electrical Properties of Compounds in the RCrMnO5 Family (R = Sm, Eu, Gd, Tb, Ho and Er) Synthesized Under High Oxygen Pressure

RCrMnO5 (R = Sm, Eu, Gd, Tb, Ho, and Er) were synthesized at high O2 pressures and 900–950 °C. Crystal structures were refined by using powder X-ray diffraction (PXRD) and powder neutron diffraction (PND) for Tb, Ho, and Er compounds and PXRD for Sm, Eu and Gd compounds. All compounds were isostructural with RMn2O5. By using the bond-valence model we found that (Cr/Mn)4+ mainly occupy the octahedral sites and (Cr/Mn)3+ occupy the pyramidal sites. Antisite disorder between octahedral and pyramidal sites was found in the three samples analyzed by PND. From the values obtained for the occupancies of Cr and Mn in the pyramidal and octahedral sites and from the approximate average oxidation states for each crystallographic site obtained by the bond-valence calculations, an estimated ionic distribution model was proposed. The ?eff value for RCrMnO5 could be explained by considering the contribution of all the paramagnetic species and by using the ionic distribution model. No magnetic long-range order was observed by PND in R = Er, Ho, and Tb compounds. All the Curie–Weiss temperatures obtained from the magnetic susceptibility were negative (? < 0), indicating antiferromagnetic correlations. For the compounds with Eu and Sm, ? close to –200 K were obtained for the Cr–Mn sublattice. The semiconducting properties could be described by a variable range hopping mechanism associated with antisite disorder of Cr/Mn. No dielectric transitions were observed in the electric permittivity in the measured temperature range. RCrxMnyO5 (R = Sm, Eu, Gd, Tb, Ho, and Er) with “ideal” composition x = y = 1 where synthesized at moderate high O2 pressures. Refinement of powder neutron diffraction (PND) data allow us to obtain the “real” RCrxMnyO5 compositions with x and y values slightly deviated from 1. The real composition allowed us to calculate the effective magnetic moments, which were in very good agreement with experimental values.

Posted on 2 September 2015 | 4:10 pm

Synthesis of Carbon-Encapsulated Cu–Ag Dimetallic Nanoparticles and Their Recyclable Superior Catalytic Activity towards 4-Nitrophenol Reduction

A facile one-pot route has been developed for the synthesis of carbon-encapsulated Cu–Ag dimetallic nanoparticles (C–CuAg NPs). The synthesis was conducted using AgNO3 and Cu(NO3)2 as metal precursors and ascorbic acid as the reduction agent and carbon source. The catalytic activities of the C–CuAg NPs for the reduction of 4-nitrophenol (4-NP) with NaBH4 were tracked by UV/Vis spectroscopy, which demonstrates that the as-prepared C–CuAg NPs exhibit significantly enhanced catalytic activity compared with carbon-encapsulated Cu nanoparticles (C–CuNPs) and carbon-encapsulated Ag nanoparticles (C–Ag NPs). Notably, the catalysts are stable, and there is a high conversion efficiency for at least ten successive cycles. Considering the green facile preparation procedure and high catalytic activity, the prepared C–CuAg NPs hold great promise as highly efficient, cost-effective, and environmentally friendly catalysts for industrial applications. Carbon-encapsulated Cu–Ag dimetallic nanoparticles (C–CuAg NPs) were prepared using a facile one-pot route. The formation of C–CuAg NPs involved two steps: (1) the formation of the Cu–Ag alloy and (2) the in situ formation of the carbon layer at a low temperature (120 °C). The as-prepared C–CuAg NPs exhibited high catalytic activity and perfect reusability towards the reduction of 4-nitrophenol.

Posted on 2 September 2015 | 3:40 pm

Intercalation of Lamellar Mineral Kaolinite with 2-Picolinic Acid: Facile Preparation, Crystal Structure Optimization, and Proton Conductivity

Kaolinite intercalated with 2-picolinic acid was prepared and characterized by scanning electron microscopy, powder X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The proton conductivity (?) of the material is 1.85?×?10–10 S?cm–1 at 353 K and gradually increases to 1.7?×?10–7 S?cm–1 at 393 K under N2 (anhydrous environment) with an activation energy of Ea = 1.93 eV, whereas ? = 1.56?×?10–7 S?cm–1 under 80?% relative humidity at 353 K with Ea = 0.91 eV. The crystal structure optimized with the Cambridge Sequential Total Energy Package discloses the absence of a dense H-bond network in the layer space of kaolinite, which explains the low proton conductivity and high proton transfer activation energy of the intercalated proton conductor. An anhydrous proton conductor is achieved by inserting 2-picolinic acid into the layer space of kaolinite, and the proton transport in this intercalated hybrid material is mainly through the vehicle mechanism owing to the absence of a dense H-bond network.

Posted on 1 September 2015 | 1:10 pm

Nickel-Molybdenum and Nickel-Tungsten Dithiolates: Hybrid Models for Hydrogenases and Hydrodesulfurization

The heterobimetallic complexes [(dppe)Ni(pdt)Mo(CO)4], [(dcpe)Ni(pdt)Mo(CO)4], [(dppe)Ni(pdt)W(CO)4] and [(dcpe)Ni(pdt)W(CO)4] {dppe = Ph2P(CH2)2PPh2; dcpe = Cy2P(CH2)2PCy2; pdt2– = –S(CH2)3S–} have been prepared and structurally characterized. The internuclear separation in these NiIIM0 species is highly sensitive to diphosphine basicity and is smallest in the dppe complexes wherein the planar Ni centres are electron-poor and require interaction with the group 6 metal. The NiIIW0 species [(dppe)Ni(pdt)W(CO)4] was converted into its stable conjugate acid [(dppe)Ni(pdt)HW(CO)4]+, a rare example of a nickel–tungsten hydride. This NiIIHWII complex is an electrocatalyst for H+ reduction and is relevant to both biological and synthetic H2-processing catalysts. A family of [(diphosphine)NiII(1,3-propanedithiolato)M0(CO)4] (M = Mo, W) complexes is described. Structural studies provide insight into the electronic demands of NiII in these species. Such complexes blend themes from hydrodesulfurization catalysts as well as the nickel–iron hydrogenase enzymes, allowing access to heptacoordinate motifs in a bimetallic scaffold catalytically active for proton reduction.

Posted on 1 September 2015 | 1:10 pm

Aryl–F Bond Cleavage vs. C–E Reductive Elimination: Competitive Pathways of Metal–Ligand-Cooperation-Based E–H Bond Activation (E = N, S)

An 8-fluoroquinoline-based dearomatized PNF-pincer (Ar)PdII complex 1 reacts with N-methylaniline to give an aromatized PNNH-pincer complex, the product of the aromatic nucleophilic substitution of the PNF ligand fluorine atom. In contrast, the reaction between 1 and thiophenol leads exclusively to the Ar–S coupling product. Experimental and theoretical (DFT) studies suggest that both reactions proceed via substrate coordination and substrate-to-PNF hydrogen atom transfer through a metal–ligand cooperation mechanism to produce a PdII amide or sulfide intermediate. In the case of the amide, intramolecular nucleophilic substitution of the fluorine by the amide has a lower activation barrier than Ar–N coupling, whereas in the case of the phenylsulfide intermediate, Ar–S elimination is favored kinetically. Interestingly, for EtSH, both reaction pathways have similar activation energies, consistent with the experimentally observed formation of mixtures of products of both reactions. Overall, the DFT calculations support the feasibility of the Ar–E (E = N, S) coupling reactions via a metal–ligand cooperation mechanism. While it looks like a simple substitution, the Pd-assisted nucleophilic aromatic substitution involves metal cooperation with the non-innocent quinoline ligand, which undergoes reversible aromatization–dearomatization. Computational studies reveal a fine line between aryl–F activation and aryl–E reductive elimination via a metal–ligand cooperation mechanism.

Posted on 1 September 2015 | 1:10 pm

A Complex Self-Catenated Coordination Framework with a Rare (3,12)-Connected Underlying Net Showing Selective Adsorption of CO2

Herein, we report a unique self-catenated metal-organic framework (MOF) with an underlying (3,12)-connected topology based on Co4 clusters. Moreover, the special dumbbell-like pore configuration, the exact match between the pore aperture and the kinetic diameter of CO2, as well as the coexistence of acylamide and NH2 groups in the MOF enhances the selectivity of adsorption of CO2 over other gases such as CO, CH4, O2, and N2. We report a complex self-catenated MOF showing a highly rare (3,12)-connecting underlying net built on a 12-connecting Co4 node and a 3-connecting ligand node. This MOF is the first that features a (3,12)-connecting net and self-catenation.

Posted on 31 August 2015 | 12:10 pm

On the Role of Chalcogen Donor Atoms in Diimine-Dichalcogenolate PtII SONLO Chromophores: Is It Worth Replacing Sulfur with Selenium?

Two new diimine-diselenolate PtII chromophores [Pt(bipy)(Me-dset)] (1) and [Pt(phen)(Me-dset)] (2) (Me-dset2– = N-methyl-2-thioxothiazoline-4,5-diselenolate) were synthesized and characterized. The effect of replacing sulfur with selenium was investigated by comparing the UV/Vis spectroscopic and electrochemical properties of 1 and 2 with those of the corresponding sulfur analogues, [Pt(bipy)(Me-dmet)] (3) and [Pt(phen)(Me-dmet)] (4), with a particular focus on their linear and nonlinear optical properties. The effect of replacing sulfur with selenium as the donor atoms in the class of SONLO chromophores [Pt(NN)(EE)] (EE = N-methyl-2-thioxothiazoline-4,5-dichalcogenolate; NN = bipy, phen) was investigated by comparatively investigating their UV/Vis spectroscopic, electrochemical, and SONLO properties.

Posted on 31 August 2015 | 12:10 pm

From Cyclen to 12-Crown-4 Copper(II) Complexes: Exchange of Donor Atoms Improves DNA Cleavage Activity

Macrocyclic CuII complexes with [NXOY] donor sets of different N/O ratios were synthesised resulting in a series ranging from cyclen (X = 4, Y = 0: 1) to 12-crown-4 (X = 0, Y = 4: 6) complexes. In order to elucidate the structure of the complexes UV/Vis spectroscopy and X-ray crystallography were applied, focusing especially on the literature-unknown compounds with regioisomeric [N2O2] and [NONO] donor sets (3, 4). The complexes were subjected to DNA cleavage experiments under reducing conditions and were also tested in the absence of a reducing agent. Although 3 and 6 were the most active DNA cleavers in the presence of reducing ascorbate, both of them and 4 also cleaved DNA (not hydrolytically) in its absence. This brings up questions regarding the cleavage mechanism. The present study is an expansion of our previously reported finding that heterosubstitution in macrocyclic ligands leads to changes in oxidative DNA cleavage activity of CuII complexes. For the use as artificial nucleases macrocyclic CuII complexes with [NXOY] donor sets were synthesised and characterised. The NNOO and O4 derivatives showed the highest activity in DNA cleavage reactions in the presence and absence of a reducing agent. In the latter case, interestingly, a hydrolytic mechanism could be excluded. This is in contrast to what was expected from comparison with literature-known examples.

Posted on 31 August 2015 | 12:10 pm

Monitoring the Hemolytic Effect of Mesoporous Silica Nanoparticles after Human Blood Protein Corona Formation

The interaction of promising nanoparticles with red blood cells (RBCs) is a critical point to be addressed in nanomedicine and nanotoxicology, and the hemolytic assay is a classical and common test used to evaluate such interactions and the consequent nanoparticle toxicity. In addition, the protein corona is an emergent concept in bionanoscience associated with the manifestation of energetically driven protein–nanoparticle interactions, with a great impact on the nanomaterial toxicity assessment. In the convergence of these two concepts, we evaluated the influence of the formation of the protein corona during the hemolysis induced by spherical mesoporous silica nanoparticles with silanol groups on the external surface (MSN-SiOH), which present a confirmed toxicity on RBCs when they are dispersed as a colloid in phosphate buffer saline solution (PBS). It was observed that human blood proteins such as human serum albumin (HSA), human plasma (HP), hemoglobin (Hb), and RBC lysate, termed hemolysate (HL), can suppress the hemolytic effect induced by MSN-SiOH in a dose-dependent manner. The EC50 values of hemolysis suppression were 24, 8.0, 19, and 28 ?g?mL–1 for HSA, HP, Hb, and HL, respectively. This work thus shows that the results of the hemolytic assay that defines the toxicity and bioreactivity of silica nanoparticles (and others) must be interpreted as a function of the formation of the protein corona. The potential toxicity of protein-corona-coated nanoparticles is mitigated as a result of the steric and electrosteric barriers generated by adsorbed proteins, which largely prevents new interactions between the bare surface of the nanoparticles and red blood cell (RBC) membranes.

Posted on 26 August 2015 | 11:50 am

Covalent Attachment of Thiophene Groups to Polyoxomolybdates or Poly­oxotungstates for the Formation of Hybrid Films

A novel bisphosphonate ligand bearing a thiophene group (AleThio) was synthesized and its covalent grafting to polyoxometalates (POMs) investigated. The hybrid polyoxomolybdate [(Mo3O8)4(O3PC(O)(C3H6NH2CH2C4H3S)PO3)4]8– [Mo12(AleThio)4] was synthesized in water by the reaction of Na2MoO4 with AleThio. It is built of four {MoVI3O8} units connected by phosphonate groups around a central Na+ ion. The reaction of the trivacant [PW9O34]9– units with CoII or NiII ions in the presence of AleThio led to the sandwich-type anions [(PW9O34)2(OH)2(H2O)4M7(O3PC(O)(C3H6NH2CH2C4H3S)PO3)2]14– [M = Ni, Co; M7(AleThio)2]. Salts soluble in organic solvent were prepared by cation-exchange with bis(triphenylphosphine)iminium ions. 31P NMR spectroscopy showed that Mo12(AleThio)4 is stable in acidic medium (pH ? 4) while the M7(AleThio)2 POMs are stable in alkaline medium (6 ? pH ? 13). Their cyclovoltammograms were recorded in solution. Attempts to surface immobilize the POMs through homo-polymerization were unsuccessful but co-polymerization employing 3-methylthiophene led to polymeric films with covalently attached POMs. A bisphosphonate ligand functionalized by a thiophene group has been covalently grafted to a polyoxomolybdate and Co- and Ni-containing polyoxotungstates. The hybrid polyoxometalates have been copolymerized with 3-methylthiophene.

Posted on 26 August 2015 | 11:50 am

Toxicity and Protective Effects of Cerium Oxide Nanoparticles (Nanoceria) Depending on Their Preparation Method, Particle Size, Cell Type, and Exposure Route

Nanoceria (cerium oxide nanoparticles) toxicity is currently a concern because of its use in motor vehicles in order to reduce carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons in exhaust gases. In addition, many questions arise with respect to its biomedical applications exploiting its potential to protect cells against irradiation and oxidative stress. Indeed, toxicology studies on nanoceria report results that seem contradictory, demonstrating toxic effects in some studies, protective effects in others, and sometimes little or no effect at all. The variability in the experimental setups and particle characterization makes these studies difficult to compare and the toxicity of newly developed nanoceria materials challenging to predict. This microreview aims to compare the toxicity of nanoceria in terms of preparation method, particle size, concentration, host organism, and exposure method. Nanoceria has attracted a lot of attention for biomedical applications thanks to its radiation-protecting, UV-protecting, and antioxidative properties. However, many studies report toxic effects for nanoceria. This microreview aims to compare the toxicity of nanoceria in terms of preparation method, particle size, concentration, host organism, and exposure method.

Posted on 20 August 2015 | 2:10 pm

Iron Oxide Based Nanoparticles for Magnetic Hyperthermia Strategies in Biological Applications

The use of multifunctional nanoparticles (NPs), usually in the range of 3–100 nm, with their newly discovered properties – such as superparamagnetic (SPM) behaviour, enhancement of activity and selectivity in catalytic processes and localised surface plasmon resonance (LSPR) – offers new technical possibilities for biomedical applications such as magnetic hyperthermia (MH), plasmonic photothermal therapy (PPTT) and enhanced magnetic resonance imaging (MRI). In addition, the small size of NPs presents a unique opportunity to interfere, in a highly localised and specific way, with natural processes involving viruses, bacteria or cells and allows interference in the development of complex diseases like many types of cancer and neuropathies (Alzheimer's, Parkinson's, Kreutzer–Jacobs'). The design of biological applications based on MH is a chemical challenge and core@shell structures are most often used to endow NPs with multifunctional abilities. The success of such MH-based biological applications depends on the magnetic functionality of the core as well as the properties of the surface shell in direct interaction with the biological medium. In this review we will describe the most important methodologies developed to synthesise magnetic core@shell nanostructures and their MH applications. Hierarchical core–shell architectures based on magnetic cores decorated with several agents (polymers, drugs, proteins, etc.) allow for multipurpose applications including magnetic hyperthermia, magnetic resonance imaging (MRI) or tissue engineering within a single design. The designed criteria emerge from the interaction of the nano–bio interface, and the planned therapeutic applications.

Posted on 20 August 2015 | 2:10 pm

Synthesis of CaTiO3 Nanofibers with Controllable Drug-Release Kinetics

Calcium titanate (CaTiO3) nanofibers with controlled microstructure were fabricated by a combination of sol–gel and electrospinning approaches. The fiber morphology has been found to rely significantly on the precursor composition. Altering the volume ratio of ethanol to acetic acid from 3.5 to 1.25 enables the morphology of the CaTiO3 nanofibers to be transformed from fibers with a circular cross section to curved ribbon-like structures. Ibuprofen (IBU) was used as a model drug to investigate the drug-loading capacity and drug-release profile of the nanofibers. It was found that the BET surface area and the pore volume decrease markedly with the utilization of F127 surfactant. The nanofibers synthesized without F127 surfactant present the highest drug-loading capacity and the most sustained release kinetics. This study suggests that calcium titanate nanofibers can offer a promising platform for localized drug delivery. Calcium titanate (CaTiO3) nanofibers with controlled microstructure were fabricated by electrospinning. The nanofibers synthesized without F127 surfactant, which are of markedly increased surface area and pore volume, present the highest drug-loading capacity and the most sustained release kinetics.

Posted on 18 August 2015 | 7:20 pm

Multifunctional Hybrid Silica Nanoparticles with a Fluorescent Core and Active Targeting Shell for Fluorescence Imaging Biodiagnostic Applications

We prepared hybrid nanoparticles with a brightly fluorescent silica core and a biocompatible thermoresponsive polymer shell containing tumor-targeting folic acid (FA) groups. The silica core has a perylenediimide fluorescent dye anchored covalently to the structure for traceability and bioimaging applications. The polymeric shell was synthesized by reversible addition–fragmentation chain-transfer (RAFT) polymerization to guarantee the homogeneous size of the particle shell. The shell is composed of copolymer chains with one block of oligo(ethylene glycol)methacrylate and 2-(2?-methoxyethoxy)ethylmethacrylate with another block of the reactive monomer N-acryloxysuccinimide (NAS). The NAS groups were used to covalently attach a large amount of amino-functionalized FA to the particle shells to provide active targeting properties towards cancer cells and tissues. The targeting capability of the folate-containing nanoparticles was evaluated against NCI-H460 tumor cells, which overexpress folate receptors. The nanoparticles with FA show a higher uptake efficiency compared to that of the equivalent nanoparticles without FA. This result validates the imaging capabilities and active targeting efficiency of our nanoparticles, an important step towards the goal of developing vehicles for precision drug delivery systems that combine therapeutic and diagnostic (theranostic) functionalities with large drug payloads, active targeting, and stimuli-activated drug release. We prepare hybrid nanoparticles with a brightly fluorescent silica core and a biocompatible thermoresponsive polymer shell containing a large amount of folic acid (FA) groups. The active cancer-targeting properties of the FA are evaluated against NCI-H460 tumor cells. The FA-loaded nanoparticles internalize faster and in larger amounts than control counterparts without FA.

Posted on 14 August 2015 | 11:20 am

Carrageenan–Silica Hybrid Nanoparticles Prepared by a Non-Emulsion Method

Spherical and monodispersed sub-micrometer sized particles of organic–inorganic hybrids were prepared by means of a sol–gel non-emulsion method using the biopolymer ?-carrageenan and the alkoxysilane 3-isocyanatopropyltriethoxysilane (ICPTES). The structural characterization of the carrageenan–silica hybrid particles was performed by using FTIR spectroscopy and solid-state 29Si and 13C NMR spectroscopy and confirmed that ?-carrageenan was covalently linked to the siliceous network via urethane bonds. Zeta-potential measurements indicate the hybrids were functionalized on the surface with sulfonate groups from the polysaccharide. These hybrids display thermal sensitivity, which is of great relevance for biomedical applications such as drug encapsulation and thermally controlled drug-delivery systems. Nanoparticles of ?-carrageenan–silica hybrids with narrow size distribution were prepared by using a sol–gel non-emulsion method. Unlike silica particles, these hybrids display thermal sensitivity, which is of great relevance for biomedical applications such as drug encapsulation and thermally controlled drug-delivery systems.

Posted on 3 August 2015 | 11:50 am

Orthogonal Functionalization of Ferritin via Supramolecular Re-Assembly

To investigate if the degree of functionalization of ferritin could be controlled using a supramolecular self-assembly process, two photophysical separable batches of ferritin were created by functionalizing ferritin capsids with either Cy3- or Cy5-dye (loading rate of about 50?%). After dis-assembly, Cy3-, Cy5- as well as non-functionalized ferritin subunits were mixed in variable ratios. Photophysical measurements revealed that the ratio in which the subunits were mixed was indeed indicative for the ratios in which the functionalized subunits were observed in the re-assembled capsids. During re-assembly, however, a slight preference for the inclusion of non-functionalized subunits was observed, indicating the reactivity decreased following functionalization. The iron biomineralization properties of ferritin were retained by the multi-functionalized capsids as FeII diffused rapidly inside making it visible by transmission electron microscopy (TEM). These combined data indicate that it is possible to functionalize ferritin in an orthogonal manner using the supramolecular interaction between ferritin subunits. To investigate the control on ferritin functionalization by supramolecular re-assembly, ferritin with modular functionality and still capable of iron mineralization was created. The ratio in which Cy3-, Cy5-, and non-functionalized subunits were mixed, was indicative for the ratio in which the variable subunits were observed in the re-assembled capsids.

Posted on 24 July 2015 | 3:20 pm

Cytocompatible Fluorescent Quantum Dot/PEG-Chitosan Bioconjugates for Nanomedicine Applications

In this study, novel nanobioconjugates based on quantum dots and a PEGylated chitosan derivative (PEG-CHI) have been designed and synthesised by a single-step aqueous route at room temperature. Chitosan was chemically modified by PEGylation aiming to significantly improve its water solubility and used as the capping ligand in the preparation of CdS quantum dot (QD) colloidal systems. UV/Vis and photoluminescence spectroscopy, transmission electron microscopy, dynamic light scattering, and the zeta potential were used to characterise the biopolymer-capped semi-conductor nanocrystals and their relative stability. The results clearly demonstrated that the PEG-CHI derivative is remarkably effective in nucleating and stabilising ultra-small colloidal CdS QDs in aqueous suspensions under acidic, neutral and alkaline media with an average size of approximately 2.0–3.0 nm and simultaneously showing luminescent activity in the visible range. In addition, the results of cell viability analysis in vitro using two cell cultures based on MTT bioassays demonstrated no cytotoxicity of the CdS QD/PEG-chitosan bioconjugates. Thus, based on these findings, it can be envisioned that these bioconjugates have potential use as biocompatible fluorescent biomarkers for nanomedicine applications. Novel nanobioconjugates based on Cd-based quantum dots and a PEGylated chitosan derivative as capping ligand have been designed and synthesised by a single-step aqueous route at room temperature. These nanohybrids are luminescent and cytocompatible towards two cell lines tested in vitro, therefore showing potential as biomarkers in nanomedicine applications.

Posted on 23 July 2015 | 2:20 pm

Understanding and Tuning Bioinorganic Interfaces for the Design of Bionanocomposites

Interactions between biological molecules and inorganic species are of tremendous importance in nature. Attempts to create bionanocomposites associating nanoscale inorganic objects with biomolecules face major challenges with regard to controlling their mutual reactivity and preserving their intrinsic properties. This review describes the interactions arising between polyoxometallates or silica particles and biomolecules – including proteins, polysaccharides, lipids and nucleic acids – that depend on physicochemical conditions. It shows that chemical modification of the inorganic and/or bio-organic partner allows fine-tuning of their interface. The specific properties of these bionanocomposites are illustrated, with emphasis on their potential in biotechnology and biomedicine. This field contributes to a better understanding of the “biochemistry of solids” and offers an almost unlimited playground for the elaboration of new materials that combine molecular biodiversity with chemistry in its many facets. Understanding and controlling interfacial interactions between biological molecules – from lipids to proteins – and inorganic nano-objects, polyoxometallates and colloids allows the synthesis of bionanocomposites with applications in biotechnology and biomedicine.

Posted on 14 July 2015 | 5:52 pm

The Effects of Morphology and Linker Length on the Properties of Peptide–Lanthanide Upconversion Nanomaterials as G2 Phase Cell Cycle Inhibitors

In this work, the shape effect of our same-sized hybrid nanomaterials conjugated with two different Plk1-specific peptides had been investigated in terms of their photophysical properties, cellular uptake efficiencies, and selective inhibitory effects towards cancer and normal cells. The results clearly indicate that our spherical NaGdF4@SiO2-P1 nanoparticles achieve the best performance for in vitro imaging, G2 phase cell arrest, and, hence, cell cycle inhibition. Plk1-specific peptides are bioconjugated onto spherical and cubic NaGdF4@SiO2 nanoparticles, and the inhibitory effects of the hybrid materials towards normal cells and cancer cells are investigated.

Posted on 8 July 2015 | 10:50 am

Platinum Nanoparticles Stabilized by Glycerodendrimers: Synthesis and Application to the Hydrogenation of ?,?-Unsaturated Ketones under Mild Conditions

Air-stable platinum nanoparticles stabilized by glycerodendrimers were prepared in water and analyzed by TEM. These platinum nanoparticles showed good catalytic activity for the reduction of ?,?-unsaturated ketones to saturated ketones at room temperature in water or in water/THF (1:1) under H2 (101.3 kPa). The catalytic species was recovered and recycled several times. Pt nanoparticles are stabilized by glycerodendrimers (GD) and used (and recycled) for the reduction of ?,?-unsaturated ketones to saturated ketones at room temperature in water under H2 (101.3 kPa).

Posted on 24 June 2015 | 12:20 pm

Magnetofluorescent Nanoaggregates Incorporating Terbium(III) Complexes as Potential Bimodal Agents for Magnetic Resonance and Optical Imaging

Terbium(III) ions were coordinated to two diethylenetriaminepentaacetic acid (DTPA) amphiphilic bisamide ligands, and the complexes were assembled into micellar nanoaggregates. The magnetic and optical properties of the resulting nanoaggregates were examined in detail. Upon excitation into the ligand levels at 265 nm, the complexes show characteristic TbIII emission at 546 nm with quantum yields of up to 7.6?%. Nuclear magnetic relaxation dispersion (NMRD) measurements have shown that the transverse relaxivity r2 at 500 MHz and 310 K reaches a maximum value of 9.4 s–1?mM–1. The efficient T2 relaxivity at high magnetic field strengths is sustained by the increased rotational correlation time of the nanoaggregates and high magnetic moment of the terbium ion. Magnetofluorescent nanoaggregates incorporating amphiphilic terbium(III) complexes are created and their potential as bimodal agents for magnetic resonance and optical imaging are examined.

Posted on 23 June 2015 | 10:40 am

Uniform Poly(acrylic acid)-Functionalized Lanthanide-Doped LaVO4 Nanophosphors with High Colloidal Stability and Biocompatibility

Ln-doped (Ln = Eu or Nd) LaVO4 nanoparticles functionalized with poly(acrylic acid) (PAA) were prepared from lanthanide and vanadate precursors in the presence of PAA by a simple one-pot method that consists of a homogeneous precipitation reaction in ethylene glycol/water at a moderate temperature (120 °C). The size of the nanoparticles could be modified in the 40–70 nm range by adjusting the amount of PAA added. The effects of the Eu and Nd contents of these nanomaterials on theirs optical properties (emission intensity and lifetime) were also analyzed to find the optimum nanophosphors. Finally, the nanoparticles showed negligible cytotoxicity for Vero cells at concentrations up to 0.05 mg?mL–1 and a high colloidal stability in physiological buffer solutions; therefore, they satisfy the most important requirements for in vitro biotechnological applications. Uniform lanthanide-doped LaVO4 nanospheres functionalized with poly(acrylic acid) are synthesized with a controllable size by a one-pot procedure. As these nanoparticles present strong red (Eu) or near-infrared (Nd) luminescence, are nontoxic for cells, and show high colloidal stability in physiological buffer, they are good candidates as optical biomarkers for in vitro applications.

Posted on 22 June 2015 | 12:10 pm

Patent Blue Derivatized Dendronized Iron Oxide Nanoparticles for Multimodal Imaging

Dendronized nanoparticles were designed for the bimodal (optical and magnetic) detection of lymph nodes with a hand-held probe during surgery. Patent Blue VF dye and iron oxide nanoparticles with 20 nm diameter, displaying high magnetization and located at the superparamagnetic/blocked monodomain boundary, were associated through a dendritic PEGylated coating to obtain stable water suspensions. Conjugation procedures (the sulfonamide link formed between the PEGylated dendron and the dye, together with the phosphonate anchoring on the iron oxide surface) were shown to be strong enough to survive in vivo conditions when the prepared nanohybrids were tested in an inflammatory node model. Moreover, magnetization of 20 nm nanoparticles increased when dendrons were grafted onto the surface, showing that they are good candidates for magnetic particle imaging, which requires high magnetization values. Preliminary lymphatic node uptake experiments performed in an inflammatory animal model showed higher uptake of the 10 nm nanoparticles relative to that of 20 nm nanoparticles. The highest probe concentration was reached 2 d after injection. Iron oxide particles of 10 and 20 nm diameter, dendronized and derivatized with Patent Blue VF dye, survived subcutaneous injection for bimodal lymph node detection with a hand-held probe during surgery.

Posted on 2 June 2015 | 10:10 am

Long-Term Stability and Reproducibility of Magnetic Colloids Are Key Issues for Steady Values of Specific Power Absorption over Time

Virtually all clinical applications of magnetic nanoparticles (MNPs) require the formulation of biocompatible, water-based magnetic colloids. For magnetic hyperthermia, the requirements also include a high colloidal stability against precipitation and agglomeration of the constituent MNPs to maintain the heating efficiency of the ferrofluid in the long term. Agglomeration can change the heating efficiency by forming MNP clusters that modify the magnetic dipolar interactions between particles. Additionally, precipitation of the MNPs (i.e., the heating sources within the liquid) can change the measured heating rates of a colloid by altering the heat flow dynamics as the particles plunge to the precipitate. The specific power absorption (SPA) of single-domain MNPs depends critically on the average particle size and size distribution width and therefore first-rate reproducibility of different batches with respect to these parameters is also needed. We have studied the evolution of the SPA of highly reproducible and stable water-based colloids composed of polymer-coated Fe3O4 magnetic nanoparticles. By measuring the specific power absorption (SPA) values for 1 year as a function of field amplitude and frequency (H ? 24 kA/m; 260 ? f ? 830 kHz), we have demonstrated that the SPA values of these samples can be reproduced in successive synthetic batches and stable for several months due to the in situ polymer coating that provides colloidal stability and keeps dipolar interactions negligible. The poly(ethyleneimine)-coated magnetic nanoparticles (PEI-MNPs) prepared in this work by oxidative hydrolysis show good reproducibility of size and size distribution. In addition, these PEI-MNPs show only a moderate decrease in the specific power absorption when they aggregate over time. These results render these particles suitable for applications in magnetic hyperthermia.

Posted on 2 June 2015 | 10:10 am

Bio-Inspired Formation of Silica Thin Films: From Solid Substrates to Cellular Interfaces

Silica formation in biological systems (biosilicification) has been intensively studied for synthesizing inorganic materials such as silica and titania under biocompatible conditions. Inspired by biosilicification, biocompatible strategies have been developed to fabricate silica thin films on the surfaces of solid substrates such as flat wafers and micro/nanoparticles. In the search for biological applications, these strategies have been applied to cellular surfaces to coat living cells with silica or titania thin films while maintaining cell viability, and it was found that the inorganic coat is beneficial for the protection of living cells and to control cell division. This Microreview focuses on bio-inspired approaches to the formation of silica thin films on solid substrates and cellular surfaces, and includes the bio-inspired formation of other inorganic thin films that have been formed by bio-inspired silicification. The current status and future prospects of this field are also discussed. The bio-inspired formation of silica thin films on the surfaces of flat solids, microparticles, nanoparticles, and living cells is reviewed.

Posted on 19 May 2015 | 4:40 pm

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