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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:



Synthesis and Characterization of the Nitrophenol Energetic Ionic Salts of 5,6,7,8-Tetrahydrotetrazolo[1,5-b][1,2,4]triazine

Nitrophenol energetic ionic salts based on the 5,6,7,8-tetrahydrotetrazolo[1,5-b][1,2,4]triazine (TZTN, 1) cation and nitrophenol anions have been synthesized in high yields by neutralization reactions. All the salts were characterized by X-ray single-crystal diffraction technology, IR spectroscopy, elemental analysis, and DSC measurements. The heats of formation of 2–4 were calculated by using isodesmic reactions. The calculated detonation pressures of these salts range from 29.7 to 32.6 GPa and their detonation velocities fall between 8337 and 8613 m?s–1; these properties make them competitive energetic materials. In addition, the sensitivities towards impact, friction, and flame were tested, and the results indicated that salts 2 and 3 have acceptable sensitivities, whereas salt 4 shows relatively high sensitivity towards impact and flame. Three nitrogen-rich energetic salts of 5,6,7,8-tetrahydrotetrazolo[1,5-b][1,2,4]triazine (TZTN) have been prepared and characterized by single-crystal X-ray diffraction analysis. The salts exhibit excellent detonation performance and combine good thermal stabilities with acceptable sensitivities.

Posted on 1 September 2014 | 2:10 pm


Main-Chain Oligomers from NiII- and CuII-Centered Unsymmetrical N2O2 Schiff-Base Complexes: Synthesis and Spectral, Structural, and Second-Order Nonlinear Optical Properties

Oligomeric main-chain Schiff-base compounds 4 and 5 have been synthesized by the trans-esterification of their respective doubly functionalized monomeric precursors [M{(?5-C5H5)Fe(?5-C5H4)C(=O)CH=C(4-C6H4OH)NCH2CH2N=CH-(2-O,4-CO2H–C6H3)}] [M = Ni (2), Cu (3)] in dmf. The new compounds were characterized by elemental analysis, FTIR and multidimensional NMR spectroscopy, mass spectrometry, and cyclic voltammetry. Compounds 2, 3, and 6, the corresponding amide of 2, were characterized by X-ray structural investigation. Gel permeation chromatography established that oligomers 4 and 5 are formed of approximately six monomeric units, and differential scanning calorimetry and thermal gravimetric analysis indicated that they are thermally stable with decomposition temperatures exceeding 230 °C. Harmonic light scattering measurements showed that compounds 2–5 exhibit rather high second-order nonlinear responses, between 224?×?10–30 and 399?×?10–30 esu, with hyperpolarizability ?1.91 values that increase significantly on passing from the monomeric to the oligomeric species. The esterification of binuclear phenol and carboxylic acid functionalized ferrocenyl-containing metal-centered Schiff-base complexes (M = Ni, Cu) in the presence of N,N?-dicyclohexylcarbodiimide and dmap afforded their corresponding main-chain oligomers. They are formed of approximately six monomeric units, are redox active, and exhibit good thermal stability and high second-order NLO responses.

Posted on 29 August 2014 | 12:20 pm


Triangular [Ag3]3+ Complexes Supported by Picolyl-Substituted N-Heterocyclic Carbene Ligands

A series of 12 picolyl-containing NHC ligand precursors and their AgI salts are reported. The complexes [Ag3{Sim(CH2pyCl)2}3]X3 [2(PF6)3], [Ag3{Sim(CH2pyBr)2}3]X3 [3(PF6)3], [Ag3{Sim(CH2isoquin)2}3]X3 [4(PF6)3], [Ag3{5,6-Cl2-benzim(CH2py)2}3]X3 [6(BF4)3], [Ag3{5,6-Me2-benzim(CH2py)2}3]X3 [7(PF6)3], [Ag3(benzim{CH2py-3,4-(OMe)2}2)3]X3 [8(PF6)3], [Ag3{benzim(CH2py-3,5-Me2-4-OMe)2}3]X3 [9(PF6)3], [Ag3(5,6-Me2-benzim{CH2py-3,4-(OMe)2}2)3]X3 [10(PF6)3], [Ag3{5,6-Me2-benzim(CH2py-3,5-Me2-4-OMe)2}3]X3 [11(PF6)3], and [Ag3{5-OMe-benzim(CH2py)2}3]X3 [12(PF6)3] (X = PF6– or BF4–) each contain a central [Ag3]3+ core spanned by three NHC ligands. The optically pure [Ag3{(R,R)-cyclohexylim(CH2py)2}3](PF6)3 [(R,R)-5(PF6)3] adopts a different coordination mode. All complexes were characterized by NMR spectroscopy and HRMS. In addition, complexes 3(PF6), (R,R)-5(PF6), 6(BF4), 7(PF6), and 8(PF6) were characterized by single-crystal X-ray diffraction and found to exhibit Ag–Ag distances of approximately 2.7 Å. A series of 12 picolyl-substituted benzimidazolylidene- and imidazolinylidene-based N-heterocyclic carbene ligands have been prepared. Eleven underwent complexation with AgI to form trimetallic complexes with short AgI–AgI metal–metal separations. In solution, all but one of these complexes are dynamic and dissociate and exchange ligands.

Posted on 29 August 2014 | 12:20 pm


Mechanistic Insights into the PdII-Catalyzed Chemoselective N-Demethylation vs. Cyclometalation Reactivity Pathways in 1-Aryl-N,N-dimethylethanamines

Two structurally isomeric substituted N,N-dimethylethanamines have been prepared. Treatment of the 2,4-di-tert-butylphenyl isomer with PdII ions generated the ortho-metalated complexes. On the other hand, treatment of the 2,5-di-tert-butylphenyl-substituted amine resulted in the unexpected chemoselective cleavage of one of the three N–C bonds, thus generating the corresponding secondary amine. The N-demethylation process could be catalyzed at room temperature by palladium(II) catalysts such as PdCl2 or Pd(OAc)2. Furthermore, treatment with a stoichiometric amount of PdII ions gave a metal complex in which both secondary amines were bound to Pd in an N-monodentate fashion. When triethylamine was introduced, one of the N-ethyl groups in NEt3 was cleaved, and an unexpected heteroamine complex was produced. The products generated were isolated and characterized by X-ray crystallography. Mechanistic insights into the cyclometalation and C–N cleavage observed are discussed. Two structurally isomeric substituted N,N-dimethylethanamines have been prepared. Treatment of one isomer with PdII ions generated the ortho-metalated complex, whilst the other isomer resulted in the unexpected chemoselective C–N bond cleavage to afford the corresponding secondary amine.

Posted on 29 August 2014 | 12:20 pm


Synthesis, Structures and Coordination Chemistry of Singly Bridged Phosphane-Boranes with Coordinately Unsaturated Platinum Group Metals

A range of singly bridged phosphane-boranes (PBs) have been investigated as potential ligands for basic transition metals. The PBs Ph2PC(Ph)=C(R)BR2 (R = Bu 1, Ph 2, Et 3), based on a rigid cis-ethylene bridges, have been prepared, improving upon limited literature precedent. All three compounds have been comprehensively characterised for the first time, including by X-ray diffraction studies. Significant intramolecular PB association is apparent in each case, which serves to preclude their engagement as ligands. In contrast, the more flexible PBs R2P(CH2)2BBN (R = Fu 5, Ph 6) readily coordinate to the platinum group metals Pt, Pd and Rh. These complexes have been fully characterised, including an X-ray diffraction study of [Rh(CO){Fu2P(CH2)2BBN}2Cl] (13). The synthesis and characterisation of a range of singly bridged phosphane-boranes is described. Their coordination complexes with co-ordinately unsaturated platinum group metals demonstrate a propensity for adopting structures with pendant borane moieties occupying distal positions.

Posted on 29 August 2014 | 12:20 pm


Unusual Solvent Dependence of a Molecule-Based FeII Macrocyclic Spin-Crossover Complex

This work illustrates in detail the reversible hydration–dehydration process of a molecule-based material, which involves a drastic change of the switchable magnetic properties of the sample. Concretely, the complex [FeL222N3O2(CN)2]·H2O exhibits a spin crossover (SCO) accompanied by a change of the coordination number. The dehydration and rehydration of this SCO complex was carried out and monitored by different methods, which include X-ray diffraction analysis. The corresponding samples display a thermal spin transition as well as a thermal quenching of the metastable high-spin state at low temperature. In particular it was observed that the rehydrated material exhibits a particularly high temperature of relaxation, T(TIESST), of the metastable high-spin state. On the other hand, it was shown that this compound exhibits a uncommon correlation between T(TIESST) and the thermal SCO, as compared with other spin-crossover compounds that do not exhibit a change in coordination number. The solvent dependence of spin-crossover behavior and metastability of the FeII complex [FeL222N3O2(CN)2]·H2O were investigated. Compared with the pristine and the dehydrated complex, the rehydrated complex shows enhanced metastability and an increased spin-transition temperature. This solvent dependence indicates new possibilities to improve metastability toward further applications.

Posted on 29 August 2014 | 12:20 pm


Evolution of the Coordination-Sphere Symmetry in Copper(II), Nickel(II), and Zinc(II) Complexes with N,N?-Double-Armed Diaza-Crown Ethers: Experimental and Theoretical Approaches

N,N?-Bis(triazolyl)diaza[18]crown-6 and corresponding diaza[15]crown-5 ethers were synthesized by means of click chemistry. The interaction of these ligands with NiII, CuII, and ZnII cations were studied by UV/Vis and 1H and 13C NMR spectroscopy. The solid-state structure of NiII and ZnII complexes formed by the diaza[18]crown-6 ligand were determined by means of X-ray crystallography. The NiII complex is centrosymmetric; the geometry around the metal ion is slightly distorted octahedral whereby the equatorial sites were occupied by four N atoms, and the axial positions by two O atoms that come from the crown moiety. For the ZnII–diaza[18]crown-6 complex, an irregular octahedral coordination was observed whereby the metal ion is asymmetrically placed in the macrocyclic cavity. The equatorial plane is occupied by two N and two O atoms of the crown moiety, and two N atoms of the triazolyl motifs on the pendant arms occupy the axial positions. The diamagnetic character of the ZnII ion allows its structural study in solution by NMR spectroscopy. A dynamic behavior was observed at room temperature, which corresponds to the displacement of the ZnII ion between the bond end and the nonbond end of the macrocycle. This movement results in an S4-symmetrical structure in solution. Quantum chemical calculations at the DFT level have allowed us to interpret the experimental results observed in the solid state for the symmetry of the complexes in terms of covalent and noncovalent interactions, which favor the centrosymmetric and irregular octahedral coordination modes, respectively. Only the structure of the CuII complex with N,N?-bis(triazolyl)diaza[15]crown-5 ligand has been investigated in the solid state, for which a pentagonal bipyramidal coordination sphere was observed. This coordination geometry was confirmed in solution in MeCN by UV/Vis spectroscopy, and also for the ZnII complex by NMR spectroscopy. In the case of the NiII complex, a structural modification was suggested in solution in MeCN based on the UV/Vis spectrum. The rearrangement of heptadentate coordination to hexadentate is proposed. Symmetric versus asymmetric octahedral coordination geometry changes were observed for Cu2+, Ni2+, and Zn2+ complexes of a N,N?-triazolyl-biarmed diaza[18]crown-6 macrocycle. Quantum chemical calculations at the DFT level confirmed these observations and allowed us to interpret them in terms of covalent or noncovalent metal–ligand interactions.

Posted on 29 August 2014 | 12:10 pm


New Lithium-Containing Pnictides with 1-D Infinite Chains of Supertetrahedral Clusters: Synthesis, Crystal and Electronic Structure of Ba4Li2Cd3Pn6 (Pn = P, As and Sb)

The novel complex pnictides Ba4Li2Cd3Pn6 (Pn = P, As and Sb) have been synthesized by direct combination of the respective elements at high temperature, and structurally characterized by single-crystal X-ray diffraction. The three isostructural compounds crystallize with their own structure type in the centrosymmetric orthorhombic space group Cmcm (Pearson code oC60). The crystal structure is based on one-dimensional infinite chains of supertetrahedral clusters, [Cd4Pn10], running parallel the a-axis. These chains are connected through Pn2-type dumbbells. Tight-binding electronic structure calculations show that the electronic stability of these compounds requires strong covalent Pn–Pn and Cd–Pn bonds. The interactions within the polyanionic sub-structure are complimented by weaker Ba–Pn and Li–Pn bonds, which also show a substantial degree of covalency, and the strength of all interactions correlates very well with the corresponding interatomic distances. The precise satisfaction of the valence rules and the Zintl–Klemm concept is not essential though as structural vacancies on Cd and Li sites bring about an interplay between ionicity and covalency among the electronegative components. Electronic structure calculations show that Ba4Li2Cd3P6 is expected to be a semiconductor with a band gap of ca. 0.5 eV, while the gap decreases and vanishes altogether for the As- and Sb-analogs, respectively. Solid solutions between arsenides and antimonides appear possible, which could be an effective way to fine-tune transport properties. Since the latter two compounds can be considered as moderately-to-heavily doped intrinsic semiconductors, these materials might be suitable candidates for thermoelectric applications. Three new Zintl phases have been synthesized for the first time, and their crystal structures have been established by single-crystal X-ray diffraction. They crystallize with their own-structure type in the orthorhombic space group Cmcm (Pearson code oC60) and their crystal structure is based on one-dimensional infinite chains of supertetrahedral clusters, [Cd4Pn10].

Posted on 29 August 2014 | 12:10 pm


Two-Dimensional {Co3+–Co2+} and {Fe3+–Co2+} Networks and Their Heterogeneous Catalytic Activities

We report the synthesis and characterization of two-dimensional homodimetallic {Co3+–Co2+} and heterodimetallic {Fe3+–Co2+} coordination networks with Co3+- and Fe3+-based metalloligands. The crystal structures reveal 2D networks in which the metalloligands are connected through secondary Co2+ ions. The kinetic lability of the secondary Co2+ ions, their Lewis acidity, and the presence of dissociable coordinated water molecules have been utilized in Knoevenagel condensation and cyanation reactions of assorted aldehydes. These reusable networks catalyze these reactions heterogeneously and efficiently. Reusable two-dimensional {Co3+–Co2+} and {Fe3+–Co2+} networks heterogeneously catalyze Knoevenagel condensation and cyanation reactions of assorted aldehydes owing to the kinetic lability and Lewis acidity of the secondary Co2+ ions.

Posted on 29 August 2014 | 12:10 pm


Phosphate Diester Cleavage, DNA Interaction and Cytotoxic Activity of a Bimetallic Bis(1,4,7-triazacyclononane) Zinc Complex

Invited for the cover of this issue are researchers from the National University of Ireland, Galway, and the University of Padua, Italy. The cover image shows the X-ray structure of the dinuclear bis(1,4,7-triazacyclononane) zinc complex synthesized in this work. The complex converts supercoiled plasmid DNA into the nicked form at low micromolar concentration and shows promising in vitro antitumor activity against pancreatic and lung cancer cell lines. We are particularly intrigued and inspired by zinc enzymes that hydrolyze highly stable phosphate esters and are among the most efficient catalysts invented by Nature with regard to rate acceleration over the uncatalyzed reaction...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 4084 ff.

Posted on 29 August 2014 | 9:42 am


Phosphate Diester Cleavage, DNA Interaction and Cytotoxic Activity of a Bimetallic Bis(1,4,7-triazacyclononane) Zinc Complex (Eur. J. Inorg. Chem. 25/2014)

The cover picture shows the X-ray structure of the dinuclear zinc complex [Zn2{bcmp(-H)}(?-Cl)](ClO4)2·H2O, where bcmp is the phenolate scaffold ligand 2,6-bis(1,4,7-triazacyclonon-1-ylmethyl)-4-methylphenolate. The complex converts supercoiled plasmid DNA into the nicked form at low micromolar concentration under physiological conditions and shows promising in vitro antitumor activity against pancreatic and lung cancer cell lines. Details are discussed in the article by D. Montagner, A. Erxleben et al. on p. 4084 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 29 August 2014 | 9:42 am


Masthead: Eur. J. Inorg. Chem. 25/2014

Posted on 29 August 2014 | 9:42 am


Graphical Abstract: Eur. J. Inorg. Chem. 25/2014

Posted on 29 August 2014 | 9:42 am


Masthead: Eur. J. Inorg. Chem. 25/2014

Posted on 29 August 2014 | 9:42 am


An Ionic Dysprosium Complex Made of a Hexanuclear Dy6 Cationic Cluster and a Mononuclear Dy Anionic Unit

A genuine 2-hydroxy-N?-{[3-(hydroxyimino)butan-2-ylidene]}benzohydrazide ligand, characterized by 1H, 13C, and 15N NMR spectroscopy and chemical analysis, has been used to synthesize a novel ionic dysprosium species. The structural determination confirms the existence of a hexanuclear Dy cationic entity along with a mononuclear Dy anionic unit. The topological analysis of the hexanuclear cluster indicates that it corresponds to a 2,4M6–1 graph, observed for the first time for Dy complexes. The electrostatic model for the determination of the magnetic anisotropy in Dy complexes implemented in the Magellan program confirms that it is difficult to control the orientation of the different anisotropy axes of the six Dy ions in order to obtain large anisotropy in polynuclear Dy entities, which is in agreement with the ac susceptibility measurements that show frequency-dependent signals and absence of maxima for the out-of-phase susceptibility signals above 2 K, even under a dc bias field of 0.1 T or 0.2 T. A novel hydrazide ligand allows the preparation of an ionic species made of a cationic hexanuclear Dy6 cluster and an anionic mononuclear Dy unit, which corresponds to the 2,4M6–1 + 1(0) motif observed for the first time with Ln ions.

Posted on 27 August 2014 | 12:10 pm


Efficient Ruthenium Sensitizer with a Terpyridine Ligand Having a Hexylthiophene Unit for Dye-Sensitized Solar Cells: Effects of the Substituent Position on the Solar Cell Performance

A novel ruthenium sensitizer with a terpyridine ligand having a hexylthiophene unit at the 4-position (TUS-38) has been synthesized to investigate the effects of the substituent position on the photo- and electrochemical properties and on solar cell performance. The dye-sensitized solar cell (DSC) with TUS-38 showed a 10.6?% conversion efficiency under AM 1.5 (100 mW/cm2) irradiation, which is much higher than that of the DSC with a previously reported ruthenium sensitizer with a terpyridine ligand having two hexylthiophene units at the 5- and 5?-positions. A novel ruthenium sensitizer with a terpyridine ligand having a hexylthiophene unit at the 4-position (TUS-38) has been synthesized, and the dye-sensitized solar cell with TUS-38 showed a 10.6?% conversion efficiency under AM 1.5 (100 mW/cm2) irradiation.

Posted on 27 August 2014 | 12:10 pm


Chromophores, Fluorophores and Robust Ancillary Ligands for Molecular Catalysts: 1,3-Bis(2-pyridylimino)isoindolines

Since the first report in the early 1950s, 1,3-bis(2-pyridylimino)isoindolines (BPIs) have found widespread applications in organic, inorganic and materials chemistry. This microreview focuses on recent progress towards chiral BPI derivatives as ligands for enantioselective catalysis as well as developments in the use of BPI complexes in materials science, focusing on luminescent and birefringent materials. This microreview focuses on the development of 1,3-bis(2-pyridylimino)isoindolines (BPI) from their synthesis over half a century ago through to their current diverse applications in organic, inorganic and materials chemistry.

Posted on 27 August 2014 | 12:10 pm


Unprecedented Borylene Insertion into a C–N Bond

Carbenes are well established reactive intermediates and play an important role in organic synthesis, whereas the scope of borylenes is rather limited. Selective borylene insertion into a C–N bond to yield boryl-functionalized N-heterocyclic olefins (NHOs), [{N(Dipp)N(DippBH)CHCH}CCH2]2 (6) and [{N(Dipp)N(DippBPh)CHCH}CCH2][{N(Dipp)N(2-iPr-6-CHMeCH2BC6H3)CHCH}CCH2] (8) (Dipp = 2,6-iPr2C6H3) is reported for the first time. KC8 reduction of (IPrCH2)BRX2 adducts (IPrCH2 = {N(Dipp)CH}2CCH2; R = X = I (2); R = Ph, X = Cl (4)) affords compounds 6 and 8. Surprisingly, treatment of (IPrCH2)BHCl2 (3) with KC8 yields completely unexpected diborane compound (IPr)BH2BH2(IPr) (7). Compound 2 is unstable in THF and induces ring opening reaction to form the borenium ion [(IPrCH2)B{O(CH2)4I}2]I (5). Formation of a boryl-functionalized NHO 6 as a dimer suggests the involvement of a borylene insertion into a C–N bond. The parent borylene (R = H) follows a completely different route in which hydrogen abstraction and intermolecular B–B coupling events seem operative to afford a diborane (7) stabilized by an NHC.

Posted on 26 August 2014 | 10:20 am


Chiral MnIII–salalen and –salan Complexes Derived from (S)-Pyrrolidin-2-yl­methanamine and Their Catalytic Activity in the Asymmetric Strecker Reaction

The salalen and salan ligands have been synthesized by the reactions of (S)-pyrrolidin-2-ylmethanamine and salicylaldehyde derivatives. These ligands were treated with Mn(CH3COO)2·4H2O followed by air oxidation to give (S,R)-MnIII–salalen and –salan complexes in yields of 84–88?%. The absolute configuration of (S,R)-MnIII–salalen was determined by single-crystal X-ray diffraction and CD analysis of the ligands and complexes showed similiar Cotton effects. The MnIII–salalen and –salan complexes were screened for their catalytic activity in the asymmetric Strecker reaction. (S,R)-2,4-Di-tert-butyl-6-({[1-(3,5-di-tert-butyl-2-hydroxybenzyl)pyrrolidin-2-yl]methylimino}methyl)phenolatomanganese(III) chloride (5 mol-%) was found to be a suitable catalyst for the asymmetric Strecker reaction of N-(4-methoxybenzylidene)diphenylmethanamine with ethyl cyanoformate, which gave 89?% yield and 55?% ee of 2-(benzhydrylamino)-2-(4-methoxyphenyl)acetonitrile at –15 °C after 24 h. Chiral MnIII–salalen and –salan complexes have been synthesized and used as a catalyst for the asymmetric Strecker reaction. These complexes were characterized by elemental analysis, FTIR and UV/Vis spectroscopy, exact mass determination and single-crystal XRD. The catalyst 9a catalysed the Strecker reactions of a range of substrates with moderate enantioselectivity of the corresponding products.

Posted on 26 August 2014 | 10:20 am


The Nature of the Active Site in Ziegler–Natta Olefin Polymerization Catalysis Systems – A Computational Investigation

Full quantum chemical calculations with density functional theory (DFT) show that a principal role of donors in Ziegler–Natta (ZN) olefin polymerization catalysts is to coordinate to the metal center at the active sites on the MgCl2 surface. Thereby, the behavior of the catalyst is modulated to favor insertion over termination and, thus, polymerization occurs. This is shown to be true for a range of different donors. The calculations indicate that active sites that feature anionic chloride ligands at the titanium center (the conventional model for the active site) would lead to lower-molecular-weight polymers. If an –OC2H5 group were present instead of a chloride ligand, the active site would much more effectively produce long chain polymers. Therefore, the current work provides important new insights into the nature of the ZN polymerization process. The nature of the active site in Ziegler–Natta heterogeneous catalysis systems has been explored with density functional theory (DFT). New insights include the understanding that donor coordination to the metal center can lead to an increase in the molecular weight of the polymer. The role of AlEt3 as a possible donor has also been investigated.

Posted on 26 August 2014 | 10:20 am


Electrochemical Implication of a Hydrogen-Bonded Imidazole on a Redox-Active-Bound Phenolate Group

We report the synthesis of a pentadentate N4O ligand with an imidazole group in the ortho position of the phenol group. The syntheses and crystallographic structures are reported for zinc(II) complexes by using the previously reported tert-butyl-substituted ligand and the imidazole-substituted ligand in two different protonation states. We describe the influence of the ortho substituent (tert-butyl, imidazole, and imidazolium) on the electrochemical behavior of the zinc(II) complexes. The substitution of the tert-butyl group in the ortho position by an imidazole group shifts the oxidation potential of the phenolate by more than 300 mV. The o-tert-butyl-substituted ligand allows the formation of a stable radical phenoxylzinc(II) complex upon electrochemical oxidation, but it is unstable in the case of the imidazole-substituted complex. The imidazole-substituted ligand can be reversibly protonated without altering the electrochemical properties of the phenolate group. We report the synthesis and crystallographic structures of zinc complexes with a pentadentate N4O ligand with an imidazole group placed in the ortho position of the phenol group. Furthermore, we describe the influence of the outer-sphere imidazole fragment on the electrochemical behavior of the redox-active-bound phenolate ligand.

Posted on 25 August 2014 | 12:10 pm


Mono- and Hetero-Dinuclear Complexes of Janus-Head NHC Ligands Possessing Backbone Phosphinoyl Groups: the Case of Soft and Hard Metal Centers

The synthesis and structures of RhI and IrI complexes bearing 4-phosphinoyl- and 4,5-bis(phosphinoyl)imidazol-2-ylidene ligands (NHCP) is reported. Deprotonation of the corresponding imidazolium hydrogen sulfate salts by KOtBu in the presence of [M(cod)Cl]2 afforded complexes of the formula [M(cod)Cl(NHCP)] [5a/5b: NHCP = 4-Ph2P(O)-IiPrMe, 5a: M = Rh, 5b: M = Ir and 7a/7b: NHCP = 4,5-{Ph2P(O)}2-InBuMe]. The RhI complexes 5a and 7a were then converted into [Rh(CO)2Cl(NHCP)] 8a and 9a via reaction with carbon monoxide; the average CO stretching frequencies [8a: $\tilde {\nu}$(CO)av = 2036 cm–1 and 9a: $\tilde {\nu}$(CO)av = 2038.4 cm–1] led to the conclusion that mono- and bis-functionalized NHCPs act as relatively weaker donors than backbone unsubstituted NHC. A first examination of Janus-head ligand properties of complex 7a revealed that reaction with TiCl4 afforded hetero-dinuclear 10a,a? as a mixture of isomeric monodentate phosphinoyl titanium(IV) adducts. All products were characterized by elemental analyses, spectroscopic and spectrometric methods and, in addition, complexes 7a and 7b by single-crystal X-ray structure analysis. A family of hybrid ligands composed of hard phosphine oxides and soft N-heterocyclic carbene donor sites have been employed to synthesize [M(cod)Cl(NHCP)] complexes I, which were further converted into the corresponding dicarbonyl complexes in order to study their donor properties. The advantage of backbone phosphinoyl groups was exploited to generate hetero-dinuclear TiIV, RhI complexes 10a,a?.

Posted on 25 August 2014 | 12:10 pm


Synthesis of Metforminium(2+) Decavanadates – Crystal Structures and Solid-State Characterization

Three new compounds were formed between decavanadate and diprotonated metformin (H2Metf) at different pH values and in the presence or absence of ammonium cations, namely, [H2Metf]3[V10O28]·8H2O (1), [H2Metf]2[NH4]2[V10O28]·10H2O (2), and [H2Metf]2[NH4]2[V10O28]·4H2O (3). We present their spectroscopic, thermal, and single-crystal X-ray diffraction characterization. The solid-state structure of 1 shows that the three H2Metf2+ dications that counterbalance the charge of the decavanadate anion are in the close vicinity of the latter, as a result of the strong Coulombic forces that arise from the ionic charges. The replacement of one metforminium(2+) cation by two ammonium cations results in two hydrates 2 and 3, which differ only in their water content. Although 2 and 3 crystallize in the same centrosymmetric space group as 1, a remarkable difference for 2 and 3 is that the [V10O28]6– anion is placed on an inversion center, which is not the case for 1. The synthesis, solid-state characterization, and X-ray analyses of three new metforminium(2+) decavanadates are presented. The compositions and stabilities of the three hydrates are strongly modified by the stoichiometry of the reaction and the presence or absence of ammonium cations.

Posted on 25 August 2014 | 12:10 pm


A Nickel-Containing Model System of Acireductone Dioxygenases that Utilizes a C(1)-H Acireductone Substrate

A mononuclear NiII complex bearing the monoanion of 1-acetoxy-3-phenylpropane-2,3-dione (4) as a ligand has been prepared {[(6-Ph2TPA)Ni{PhC(O)C(O)CHOC(O)CH3)]ClO4, 5; 6-Ph2TPA = N,N-bis[(6-phenyl-2-pyridyl)methyl]-N-(2-pyridylmethyl)amine}. This complex was characterized by 1H NMR, UV/Vis and IR spectroscopy, mass spectrometry, and elemental analysis. Exposure of solutions of 5 to O2 did not result in any reaction over the course of hours. Deprotection of 5 by the addition of NaOCH3 in methanol generated a NiII species (6) that contains a coordinated dianionic C(1)-H acireductone. Exposure of 6 to O2 led to regioselective oxidative cleavage reactivity akin to that found for the NiII-containing acireductone dioxygenase enzyme. The strategy outlined herein is the first synthetic approach that enables examination of the oxidative reactivity of a synthetic NiII species containing a dianionic C(1)-H acireductone ligand. A NiII complex of a protected C(1)-H acireductone ligand can be deprotected by using NaOCH3 in the presence of O2 to give oxidative aliphatic C–C bond-cleavage products akin to those produced by the NiII-containing acireductone dioxygenase enzyme.

Posted on 25 August 2014 | 12:10 pm


Properties of an Indium Tin Oxide Electrode Modified by a Laser Nanostructured Thin Au Film for Biosensing

Structural, optical, and electrochemical characteristics of the indium tin oxide (ITO) electrode modified by Au nanoparticle (NPs) produced by pulsed UV laser irradiation of thin films are investigated in this work. Properties of the NP arrays depend on the film thickness and parameters of the laser interaction. Semi-regular structures characterized by broad size distributions of mean values ca. 62–92 nm are observed in the SEM images. In absorbance spectra the plasmon resonance peaks located around 544 nm reveal an IR shift and an increase of damping of the plasmonic enhancement with increasing NP size. Despite the broad size distribution and negative effect of damping that results in plasmon decay times of below 3.2 fs, the ITO electrode modified by Au NP arrays shows marked improvement of the electrochemical activity towards the Fe2+/Fe3+ redox couple and also glucose. Results obtained for non-enzymatic glucose detection indicate the potential for cost-effective solutions in the area of biosensing. Thin Au films on ITO that were stepwise patterned by means of nanosecond UV laser pulses transformed into semi-regular nanoparticle arrays. The modified electrode showed enhanced activity towards ferricyanide redox systems as well as glucose, and can be considered for the production of a non-enzymatic biosensor.

Posted on 21 August 2014 | 12:13 pm


Tetranuclear Nickel and Cobalt Complexes with an Incomplete Double-Cubane Structure – Homo- and Heterometallic Complexes and Their 1D Coordination Polymers

The reactions of M(OAc)2·4H2O (M = Ni, Co) with three unsymmetrical amine-diol ligands RN(CH2CH2OH)(CH2CH2CH2OH) (H2Ln: n = 1, R = benzyl; n = 2, R = 4-methylbenzyl; n = 3, R = 2-naphthalenylmethyl) in the presence of NEt3 or pyridine in MeOH or BnOH gave the tetranuclear complexes [M4(HLn)2(OAc)6(MeOH)2] {M = Ni, n = 1 (1a), 2 (1b), 3 (1c); M = Co, n = 1 (4a), 2 (4b), 3 (4c)} and [M4(HLn)2(OAc)6(BnOH)2] {M = Ni, n = 1 (2a), 2 (2b), 3 (2c); M = Co, n = 1 (5a), 2 (5b), 3 (5c)}. When p-xylene-?,??-diol was used instead of monoalcohols, the tetranuclear {M4O6} units were linked by p-xylene-?,??-diol to form the 1D coordination polymers [M4(HLn)2(OAc)6(p-HOCH2C6H4CH2OH)]m {M = Ni, n = 1 (3a), 2 (3b); M = Co, n = 1 (6a), 2 (6b)}. The structures of 1–6 were determined by X-ray crystallography and consist of centrosymmetrical tetranuclear {M4O6} face-shared defective double-cubane cores supported by two monodeprotonated (HLn)– ligands. The mixed-metal tetranuclear complexes [Ni2.2Co1.8(HL1)2(OAc)6(MeOH)2] (7) and [Mn1.7Ni2.3(HL1)2(OAc)5(OMe)2] (8) were also synthesized by using equimolar amounts of Ni2+ and M2+ (M = Co, Mn) ions. X-ray crystallographic and fluorescent analyses revealed that 7 is isomorphous with 1a and 4a and contains nonstoichiometric amounts of disordered Ni2+ and Co2+ ions in an average ratio of 2.2:1.8 with different occupancies for the two crystallographically independent metal centers. In contrast, 8 consists of a C2-symmetrical face-shared defective double-cubane {MII3MnIIIO6} core with a Ni/Mn ratio of 2.3:1.7; the amounts of Ni2+ and Mn2+ ions vary depending on the metal sites, and one of the C2 axial positions is exclusively occupied by Mn3+ ions. Detailed magnetostructural analyses on the nickel (1a, 2a, 3a) and cobalt (4a) complexes with appropriate spin-Hamiltonian models showed that both ferro- and antiferromagnetic spin exchange interactions were involved within the tetranuclear units, and their extent depends on the combination of the metal ions and the ligand systems in a delicate fashion. Unsymmetrical amine-diol ligands are suitable for the assembly of homo- and heterometallic tetranuclear {M4O6} complexes. 1D coordination polymers are formed by linking the tetranuclear nickel and cobalt complexes with a diol linker ??((<=Author: the size of the graphic for the table of contents had to be reduced for technical reasons))??.

Posted on 21 August 2014 | 12:13 pm


Development of a SO3H-Functionalized UiO-66 Metal–Organic Framework by Postsynthetic Modification and Studies of Its Catalytic Activities

A novel metal–organic framework UiO-66-NH2-derived Brønsted acid catalyst was synthesized on a gram scale by employing a postsynthetic modification strategy under mild conditions. The nanomorphology of the catalyst was designed and developed to enhance its catalytic performance. Acetalization and benzimidazole formation were evaluated to demonstrate the high reactivity and selectivity of the nanoscaled UiO-66-NH-RSO3H catalyst, which were found to be comparable to the reactivity and selectivity of the strong homogeneous Brønsted acid catalyst. Furthermore, the UiO-66-NH-RSO3H catalyst was recycled several times without compromising the yield and selectivity. A novel metal–organic framework UiO-66-NH2-derived Brønsted acid catalyst is synthesized by employing a postsynthetic modification strategy under mild conditions. Acetalization and benzimidazole formation are evaluated to demonstrate the high reactivity and selectivity of the nanoscaled UiO-66-NH-RSO3H catalyst.

Posted on 21 August 2014 | 12:13 pm


Insight into Structure: Function Relationships in a Molecular Spin-Crossover Crystal, from a Related Weakly Cooperative Compound

The ClO4– salt of [FeL2]2+ {L = 2,6-bis(3-methylpyrazol-1-yl)pyridine} undergoes very gradual thermal spin-crossover centered just below room temperature. In contrast, the BF4– salt of the same complex exhibits an abrupt and structured spin-transition at lower temperature, with a complicated structural chemistry. The difference can be attributed to a much larger change in molecular structure between the spin states of the complex in the more cooperative BF4– salt, leading to an increased kinetic barrier for their interconversion. Consistent with that suggestion, the high-spin and low-spin structures of weakly cooperative [FeL2][ClO4]2 are almost superimposable. The ClO4– salt of [FeL2]2+ {L = 2,6-bis(3-methylpyrazol-1-yl)pyridine} undergoes very gradual thermal spin-crossover. In contrast, the BF4– salt of the same complex exhibits an abrupt and structured spin-transition, with a complicated structural chemistry. The difference can be attributed to a much larger change in molecular structure between the spin states of the complex in the more cooperative BF4– salt (the weakly cooperative ClO4– salt is pictured).

Posted on 21 August 2014 | 12:13 pm


Mid- and Far-Infrared Marker Bands of the Metal Coordination Sites of the Histidine Side Chains in the Protein Cu,Zn-Superoxide Dismutase

Vibrational spectroscopy gives important information on the properties of ligand and metal–ligand bonds in metalloenzymes. Infrared spectroscopy is appealing for the study of metal active sites that are not amenable to Raman spectroscopy. We present a combined experimental and theoretical approach to analyze the mid- and far-IR spectra of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) as a probe of the histidine ligands. This metalloenzyme provides a unique model to identify specific IR signatures of metal–histidine coordination and to study their alterations as a function of the metal (copper/zinc), the copper valence state (+I/+II), the histidine coordination mode (N? and N?) and the histidine protonation state. DFT calculations combined with normal mode descriptions from potential energy distribution calculations were performed on two slightly different cluster models. Differences in the constraints at the side chain of one histidine Cu ligand sensibly modify the geometric parameters and vibrational properties. Electrochemically induced FTIR difference spectroscopy provided mid- and far-IR fingerprint spectra of the Cu protein in aqueous media that are sensitive to the redox state of the Cu centre at the active site. Comparisons of the DFT predictions with the experimental IR modes of the histidine ligands at the Cu,Zn-SOD active site showed that useful mid-IR markers of histidine N? and N? coordination were predicted with good accuracy. The DFT analysis further demonstrated a link between the ?(C4–C5) mode frequency of His46 and the specific properties of the His46–Cu bond in Cu,Zn-SOD. A combined theoretical and experimental approach on samples in H2O and 2H2O or 15N-labelled samples identified the contributions from the histidine side chain modes in the 669–629 cm–1 region. The metal–histidine vibrations of the Cu,Zn-superoxide dismutase enzyme are analyzed by mid- and far-infrared difference spectroscopy. The histidine metal–ligand markers are analyzed and assigned from a combination of experimental and computational data. The contributions of the histidine modes are identified through additional data collected and calculated for labelled samples.

Posted on 21 August 2014 | 12:12 pm


Combining Cobalt-Assisted Alkyne Cyclotrimerization and Ring Formation through C–H Bond Activation: A “One-Pot” Approach to Complex Multimetallic Structures

Multiferrocenyl-substituted benzenes could be obtained in a “one-pot” reaction of 1,4-diferrocenylbutadiyne with substoichiometric amounts of [CoCp(CO)2] (Cp = cyclopentadienyl) by combining cobalt-assisted formal [2+2+2] cycloaddition with C–H bond activation at a single catalyst. A mechanism for the reaction is discussed. The newly synthesized hexaferrocenyl species belongs to the rather scarcely examined family of multimetallic aromatic compounds. It is one of the few examples in which the ferrocenyl units are either single bonded or 1,2-substituted to give rise to planar chirality at three of the ferrocenyl units. Electrochemical studies showed that up to six consecutive ferrocenyl-based redox events are observed. Within in situ spectro-electrochemical measurements of both compounds it is shown that two intervalence charge-transfer pathways are possible. At different excitation energies either a charge transfer through the peripheric ethylene bridging unit or through the central benzene unit occurs. A straightforward one-pot synthetic method including cyclotrimerization, C–H activation, and ring formation to novel hexaferrocenylbenzene is discussed. The electrochemical and spectro-electrochemical behavior as well as a mechanism for the formation of the title compound is reported.

Posted on 20 August 2014 | 12:10 pm


Protonated Digermane, Distannane, and Diplumbane: Can They Be Made in the Laboratory?

The geometries, proton affinities, and relative energies of protonated digermane (Ge2H7+), distannane (Sn2H7+), and diplumbane (Pb2H7+) have been investigated by density functional theory using the correlation-consistent cc-pVnZ-PP basis sets (n = D, T, Q). The results of the caluclations are consistent with the very limited experimental and theoretical results that are available. The lowest-lying structure of Ge2H7+ is predicted to have C2 symmetry with a bent 3-center-2-electron Ge–H–Ge bridge, analogous to Si2H7+. For Sn2H7+ and Pb2H7+, the lowest-lying structures are predicted to be different, with a D3d structure for Sn2H7+ and a C1 structure for Pb2H7+. The predicted proton affinities decrease in the order Pb2H6 (9.84 eV)?>?Sn2H6 (8.48 eV)?>?Ge2H6 (8.11 eV)?>?Si2H6 (7.72 eV)?>?C2H6 (6.18 eV). Similarly to C2H7+ and Si2H7+, the Ge2H7+, Sn2H7+, and Pb2H7+ cations are predicted to be energetically favorable to varying degrees, and they appear to have different low-lying structures.

Posted on 20 August 2014 | 11:10 am


Vapochromic Platinum(II) Complexes: Crystal Engineering toward Intelligent Sensing Devices

Vapochromic materials that show reversible color change driven by vapor adsorption/desorption have drawn significant attention because of their potential applications in chemical sensors and chemical-switching modules. Among the vapochromic coordination complexes reported so far, a series of square-planar PtII complexes has been studied and represents one of the most promising systems for practical chemical sensors. For such systems, the color of the complexes strongly depends not only on the ligand-field splitting, but also on the intermolecular distance between the PtII ions. This microreview presents recent results of vapochromic complexes centered on one-dimensionally stacked PtII systems from the viewpoint of the origin of their vapochromic behavior. The design of vapochromic materials has been facilitated because several useful chromophores, including metallophilic interaction between PtII ions, have been developed. However, it is still challenging to realize a specifically sensitive and selective response to targeted vapors. This review focuses on strategies to achieve assembled PtII complexes with selective vapochromic responses. Square-planar platinum(II) complexes that exhibit intense changes in luminescence and color based on metallophilic interactions are promising vapochromic materials. In an effort to generate highly sensitive and selective vapor responses, various PtII complexes have been developed by utilizing different intra- and intermolecular interactions.

Posted on 20 August 2014 | 11:10 am


Synthesis, Characterisation and Antiproliferative Studies of Allyl(dicarbonyl)(cyclopentadienyl)molybdenum Complexes and Cyclodextrin Inclusion Compounds

The complexes [(?5-C5H4–CO–R)Mo(CO)2(?3-C3H5)] [R = OH (1), Phe–OMe (2)] have been examined as guests for the cyclodextrin (CD) hosts ?-CD and heptakis(2,3,6-tri-O-methyl)-?-CD (TRIMEB), and the resultant inclusion compounds have been characterised in the solid state by elemental and thermogravimetric analyses, powder X-ray diffraction, 13C{1H} cross-polarisation (CP) magic angle spinning (MAS) NMR spectroscopy and FTIR spectroscopy. Single-crystal X-ray analysis of 1 shows that the unit cell contains centrosymmetric supramolecular dimers comprising two dicarbonyl complexes linked through hydrogen-bonding interactions involving the carboxylic acid groups. In screening tests for antiproliferative effects, the CD adducts containing 1 displayed enhanced antitumour activity against mouse melanoma (when compared with nonincluded 1), while showing minimal activity towards human adenocarcinoma and nontumour rat myoblast cell lines. TRIMEB encapsulation resulted in a predominant toxic effect on tumour cells versus the non-neoplastic myoblast cells. The crystal structure of [(?5-C5H4–COOH)Mo(CO)2(?3-C3H5)] (1) is presented. Both 1 and its phenylalanine derivative were included into ?-cyclodextrin (CD) and per-O-methylated ?-CD (TRIMEB). Overall, the inclusion contributed to a higher and more specific action on tumour cells, thereby lowering deleterious effects on a healthy myoblast line.

Posted on 19 August 2014 | 11:20 am


Tetranuclear Copper(II) Complexes with Macrocyclic and Open-Chain Disiloxane Ligands as Catalyst Precursors for Hydrocarboxylation and Oxidation of Alkanes and 1-Phenylethanol

Two new tetranuclear copper(II) complexes [Cu4(?4-O)(L1)Cl4] (1) and [Cu4(?4-O)(L2)2Cl4] (2), where H2L1 is a macrocyclic ligand resulting from [2+2] condensation of 2,6-diformyl-4-methylphenol (DFF) and 1,3-bis(aminopropyl)tetramethyldisiloxane, and HL2 is a 1:2 condensation product of DFF with trimethylsilyl p-aminobenzoate, have been prepared. The structures of the products were established by X-ray diffraction. The complexes have been characterised by FTIR, UV/Vis spectroscopy, ESI mass-spectrometry and magnetic susceptibility measurements. The latter revealed that the tetranuclear complexes can be described as two ferromagnetically coupled dinuclear units, in which the two copper(II) ions interact antiferromagnetically. The compounds act as homogeneous catalyst precursors for a number of single-pot reactions, including (i) hydrocarboxylation, with CO, H2O and K2S2O8, of a variety of linear and cyclic(n = 5–8) alkanes into the corresponding Cn+1 carboxylic acids, (ii) peroxidative oxidation of cyclohexane, and (iii) solvent-free microwave-assisted oxidation of 1-phenylethanol. Two new tetranuclear copper(II) complexes act as homogeneous catalyst precursors for the single-pot hydrocarboxylation of a variety of linear and cyclic Cn (n = 5–8) alkanes into the corresponding Cn+1 carboxylic acids, peroxidative oxidation of cyclohexane, and solvent-free microwave-assisted oxidation of 1-phenylethanol.

Posted on 18 August 2014 | 11:10 am


Smart Decoration of Mesoporous TiO2 Nanospheres with Noble Metal Alloy Nano­particles into Core–Shell, Yolk–Core–Shell, and Surface-Dispersion Morphologies

Noble metal alloy-decorated spherical mesoporous TiO2 nanoparticles were synthesized by the one-pot, single-step reaction of Ti(OiPr)4, Au3+, Pt4+, and Pd2+ or by the one-pot reaction of hollow mesoporous TiO2 nanospheres with Au3+, Pt4+, and Pd2+ by means of a solvothermal method in methanol. Au–Pt–Pd@TiO2, Au–Pt@TiO2, and Au@TiO2 mesoporous nanoparticles with core–shell, yolk–core–shell, and surface-dispersion morphologies were easily constructed. The noble metal alloy cores of the Au–Pt–Pd@TiO2 and Au–Pt@TiO2 yolk–core–shell nanoparticles have Au@Pt–Pd and Au@Pt embedded sub-core–shell structures, respectively. Au–Pt–Pd@TiO2, Au–Pt@TiO2, and Au@TiO2 mesoporous nanoparticles with core–shell, yolk–core–shell, and surface-dispersion morphologies are synthesized by a solvothermal method in methanol. The alloy cores of the Au–Pt–Pd@TiO2 and Au–Pt@TiO2 yolk–core–shell nanoparticles have Au@Pt–Pd and Au@Pt embedded sub-core–shell structures, respectively.

Posted on 15 August 2014 | 11:30 am


Redox and Photochemistry of Bis(terpyridine)ruthenium(II) Amino Acids and Their Amide Conjugates – from Understanding to Applications

The push-pull-substituted bis(terpyridine)ruthenium(II) amino acid [Ru(4?-tpy-COOH)(4?-tpy-NH2)]2+ ([5]2+; tpy = 2,2?;6?,2?-terpyridine) with carboxylic acid and amino substituents features exceptional chemical and photophysical properties. Its interaction with photons, electrons, and/or protons results in room-temperature phosphorescence, reversible oxidative and reductive redox chemistry, reversible acid/base chemistry, proton-coupled electron transfer, photoinduced reductive and oxidative electron transfer, excited-state proton transfer and energy transfer reactions. These properties can be fine-tuned by variations of the bis(terpyridine) amino acid motif, namely extension of the ? system and expansion of the chelate ring. Furthermore, the chemically orthogonal functional groups enable the incorporation of this metallo amino acid into peptide architectures in a highly selective manner, even by solid-phase peptide synthesis protocols. Amide-linked conjugates with other metal complexes [(terpyridine)ruthenium(II), ferrocene, (bipyridine)rhenium(I), (bipyridine)platinum(II)], organic chromophores, or ZnO nanoparticles underscore the versatile synthetic, redox, and photochemistry of this building block. First real-world applications of [5]2+ and its derivatives include light-emitting electrochemical cells (LECs) and dye-sensitized solar cells (DSSCs). Ruthenium(II) amino acid [Ru(4?-tpy-COOH)(4?-tpy-NH2)]2+ interacts with photons, electrons, and/or protons, to lead to phosphorescence, oxidative and reductive chemistry, acid/base chemistry, proton-coupled electron transfer, photoinduced reductive and oxidative electron transfer, excited-state proton transfer, and energy transfer. Applications include light-emitting electrochemical and dye-sensitized solar cells.

Posted on 15 August 2014 | 11:30 am


Defining the Structural Parameters of Tri­azole Ligands in the Templated Synthesis of Silver Nanoparticles

This manuscript describes a one-pot method for the synthesis of size- and shape-selected silver nanoparticles (AgNPs) using Tollens' reagent [Ag(NH3)2OH] as the silver source. Sugar triazole ligands facilitate the formation of monodisperse AgNPs in which the size and shape can be controlled according to the reaction conditions. Increasing the size of the ligand reduces size tunability but enhances colloidal stability in high-salt buffers. A key conclusion from this study is that the AgI-binding affinity of these triazole ligands determines their capacity to tune the size of the resultant AgNPs formed. Weaker AgI-binding ligands can be used to form monodisperse, angular AgNPs over a wider range of sizes [(12?±?3) to (33?±?7) nm], whereas triazole ligands that exhibit a higher AgI-binding affinity produce monodisperse, spherical AgNPs of a single size [(18?±?5) nm]. Control of both the size and shape of silver nanoparticles (AgNPs) can be achieved using triazole sugar ligands and the Tollens' reagent [Ag(NH3)2OH] as the silver source. Higher affinity for AgI results in smaller AgNPs, whereas ligands with lower affinity for AgI form larger AgNPs in which the size can be tuned according to the reaction conditions.

Posted on 15 August 2014 | 11:23 am


Mixed-Metal Oxo Clusters Structurally Derived from Ti6O4(OR)8(OOCR?)8

The mixed-metal oxo clusters FeTi5O4(OiPr)4(OMc)10 (OMc = methacrylate), Zn2Ti4O4(OiPr)2(OMc)10, Cd4Ti2O2(OAc)2(OMc)10(HOiPr)2, [Ca2Ti4O4(OAc)2(OMc)10]n, and [Sr2Ti4O4(OMc)12(HOMc)2]n were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures are derived from Ti clusters with the composition Ti6O4(OR)8(OOCR?)8. The Ca and Sr derivatives consist of chains of condensed clusters. Fe/Ti, Zn/Ti, Cd/Ti, Ca/Ti, and Sr/Ti mixed-metal oxo clusters were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures can be traced back to that of Ti6O4(OR)8(OOCR?)8 clusters and the structural variations to the different ionic radii and coordination numbers.

Posted on 15 August 2014 | 11:23 am


Contributions to the Chemistry of N-Methylnitramine: Crystal Structure, Synthesis of Nitrogen-Rich Salts, and Reactions towards 2-Nitro-2-azapropyl Derivatives

This work compares the hitherto unknown crystal structure of N-methylnitramine with its gas-phase diffraction structure. A series of alkaline, alkaline earth and some transition-metal salts were investigated. Furthermore, a series of new nitrogen-rich salts was synthesized and characterized for the first time. The Mannich reaction of N-methylnitramine with formaldehyde yields 2-nitro-2-azapropanol, which was treated with 2-nitro-2-azapropyl isocyanate to furnish new bis-N,O-(2-nitro-2-azapropyl)carbamate. The analogue bis-N,N?-(2-nitro-2-azapropyl)urea derivative is formed when 2-nitro-2-azapropyl isocyanate is treated with water. Owing to the energetic nature of all compounds, their energetic properties were determined. The sensitivities towards impact, friction and electrostatic discharge were determined using the BAM drophammer and friction tester as well as a small-scale electrical discharge device. Standard enthalpies of formation were calculated at the CBS-4M level of theory. With these values and the experimental densities, several detonation parameters such as detonation pressure and velocity of the compounds were computed using the EXPLO5 (V6.01) computer code and compared to currently used explosives. The hitherto unknown crystal structure of N-methylnitramine has been determined. Its Mannich product with formaldehyde was treated with 2-nitro-2-azapropyl isocyanate or water to provide products that were characterized as energetic materials and compared to currently used explosives.

Posted on 15 August 2014 | 11:20 am


Optical and Electrooptical Properties of Porous-Silicon/Conjugated-Polymer Composite Structures

We report on the fabrication and characterization of porous-silicon/conjugated-polymer hybrids, created by combining a host columnar matrix of mesoporous silicon and a network of organic nanowires made from poly(N-vinylcarbazole) (PVK). A uniform and homogeneous filling of the pores by the polymers was accomplished by electrochemical polymerization of organic monomers inside the pores by using cyclic voltammetry. Spectroscopic measurements showed that polymerization inside the confined environment of the nanometric pores results in a tighter and denser packing of the polymer due to a change of the polymerization process from the vinyl groups to the conjugated carbazole groups, giving rise to a redshift of the absorption spectra and better electrical conductivity. Current-voltage characterization of the hybrids under dark conditions and under illumination were investigated. We demonstrate a simple method to control the band alignment between the organic polymer and the porous silicon, altering it from a type-I to a type-II interface by changing the doping polarity of the silicon substrate (from p-type to n-type, respectively). An efficient photoinduced charge separation was observed for the type-II interface (n-type porous-silicon–polymer interface), while no such effect was observed for the type-I organic–inorganic interface. An organic–inorganic hybrid structure consisting of porous silicon and nanowires of poly(N-vinylcarbazole) (PVK) exhibits optical behavior of the PVK nanowires, which is unique when compared with the bulk material. Furthermore, a simple method to control the band alignment between type-I and type-II is demonstrated. Our results enable a variety of applications and electrooptical characteristics.

Posted on 15 August 2014 | 11:20 am


Spin-State Energetics of FeII Complexes – The Continuing Voyage Through the Density Functional Minefield

Computing absolute spin-state energies continues to challenge quantum chemistry. Correlated wavefunction methods offer high accuracy but are expensive, whereas density functional theory (DFT) is faster, but its accuracy is variable. No “universal” functional has emerged, but predicting trends in spin-state energies is easier. Here, a simple DFT protocol is applied to the subtle variations in magnetic moments for FeII–R,R?Pytacn complexes (Inorg. Chem. 2013, 52, 9229). Both BP86 and OPBE give satisfactory correlation coefficients (R2 = 0.87 and 0.75, respectively), whereas the range-separated functional CAM-B3LYP performs worse (R2 = 0.37). However, even for BP86 and OPBE, the p-CO2Et substituent is predicted to be too electron-donating. The relatively poor performance of CAM-B3LYP may be due to the more exacting test of DFT provided by mixed-ligand systems, where the competition between donors is an additional factor. Calculating the absolute spin-state energies of metal complexes is a challenge for quantum chemistry. Computing trends is easier, but caution is required. Not all functionals perform equally, and even for the good ones, there are generally outliers. Despite significant progress, the “universal functional” remains elusive.

Posted on 15 August 2014 | 11:20 am


o-Oxazolinyl- and o-Thiazolinylphenol as Antennae in Luminescent EuIII and TbIII Complexes

Europium(III) and terbium(III) complexes have been prepared using the ligands 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol (HL1) and 2-(4,5-dihydro-1,3-thiazol-2-yl)phenol (HL2) in yields ranging between 74 and 100?%. Metal-to-ligand ratios of 1:3 and 1:4 can be achieved, giving rise to compounds with the formulae [Ln2(L)6] and NR4[Ln(L)4], Ln = Eu, Tb. Recrystallisation of the complexes from DMSO resulted in the formation of octanuclear complexes [Na2(Ln(L1)3)2(CO3)(DMSO)2]2 held tightly together by carbonate ions that have been formed from CO2 from the atmosphere. Five structures have been determined, showing a bidentate binding mode of the ligand through the phenolate oxygen and the nitrogen atom of the five-membered ring. Most terbium compounds show bright luminescence upon excitation with near-UV radiation, with quantum yields of 16?% to 79?%. Strong emission is observed for NBu4[Eu(L1)4] and NEt4[Eu(L2)4] with quantum yields of 43?% and 20?%, respectively. Complexes of europium(III) and terbium(III) using the ligands 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol and 2-(4,5-dihydro-1,3-thiazol-2-yl)phenol have been prepared with M/L ratios of 1:3 and 1:4; five of these compounds show bright luminescence upon excitation by near-UV radiation. Crystallisation from DMSO resulted in the formation of CO3-containing octanuclear complexes.

Posted on 14 August 2014 | 12:10 pm


Towards Deep-Blue Phosphorescence: Molecular Design, Synthesis and Theoretical Study of Iridium Complexes with Cyclometalating 2-Phenyl-2H-[1,2,3]tri­azole Ligands

We report on the synthesis and characterization of two bis-cyclometalated iridium(III) complexes with 2-phenyl-2H-[1,2,3]triazole as a new type of cyclometalating ligand. The photophysical and electrochemical properties of the two complexes were investigated experimentally as well as theoretically by using density functional theory. The properties of the two new complexes were compared with classical blue-emitting iridium complex FIrpic. The two complexes both exhibited deep-blue emission at 77 K, indicating that the introduction of cyclometalating 2-phenyl-2H-[1,2,3]triazole ligands can, in general, cause a spectral blueshift. Two blue-emitting iridium complexes with cyclometalating 2-phenyl-2H-[1,2,3]triazole ligands were synthesized and characterized. The two complexes both show strong deep-blue emission at 77 K, but no emission at room temperature. Calculations suggest that this lack of emmission might be caused by distorted excited state structures of the complexes.

Posted on 14 August 2014 | 12:10 pm


Synthesis and Characterization of Cationic Synphos-Rhodium Complexes

Different types of cationic Rh complexes bearing the Synphos ligand were characterized by NMR and X-ray analysis for the first time. This set of compounds includes diolefin rhodium precursors [Rh(Synphos)(cod)]BF4 and [Rh(Synphos)(nbd)]BF4, solvate complexes [Rh(Synphos)(MeOH)2]BF4, [Rh(Synphos)(acetone)2]BF4 as well as the toluene complex [Rh(Synphos)(toluene)]BF4, trinuclear complexes [Rh3(Synphos)3(?3-OH)2]BF4 and [Rh3(Synphos)3(?3-Cl)2]BF4 and arene-bridged dimer [Rh2(Synphos)2](BF4)2. Several types of cationic Rh complexes generated under reaction conditions starting from the precursor [Rh(Synphos)(diolefin)]BF4 were identified by NMR spectroscopy. Furthermore, six of these species were characterized by X-ray analysis for the first time; this includes the active species [Rh(Synphos)(acetone)2]BF4 as well as deactivating arene complex [Rh(Synphos)(methyl-?6-benzene)]BF4.

Posted on 14 August 2014 | 12:10 pm


A Differential Scanning Calorimetry and Theoretical Study on the Isomerization of trans-[Co(cyclam)(ONO)2]X (X = PF6–, ClO4–)

The solid-state interconversion of trans-[Co(cyclam)(ONO)2]X (X = PF6–, ClO4–; cyclam = 1,4,8,11-tetraazacyclotetradecane, [14]aneN4; dinitrito isomer) and trans-[Co(cyclam)(NO2)2]X (dinitro isomer) was investigated by differential scanning calorimetry (DSC). The conversion of the dinitrito isomer to the dinitro isomer was accompanied by the appearance of exothermic peaks. However, no isomerization DSC peak was observed for the dinitro isomers. The observed DSC peak for the dinitrito isomer was resolved into two peaks that correspond to two isomerization stages. The low-temperature peak was ascribed to the conversion of the metastable dinitrito isomer to an unstable nitro–nitrito one, whereas the high-temperature peak was attributed to the subsequent conversion of the nitro–nitrito isomer to the dinitro isomer. The kinetic parameters of the isomerization were determined by the Kissinger method. The electronic structures and thermodynamic stabilities of the linkage isomers, as well as the nature of the transition states, were investigated by DFT. The thermal linkage isomerization of the title compounds in the solid state was studied by differential scanning calorimetry (DSC). The observed exothermic DSC peak of the dinitrito isomer was resolved into two peaks that correspond to two isomerization stages. A comparative experimental and DFT study was performed on the thermodynamics and kinetics of the dinitrito to dinitro isomerization.

Posted on 14 August 2014 | 12:10 pm


Reactions of 1,3,2-Diselenaphospholanes with Lewis Acids: Borane and (Pentamethylcyclopentadienyl)rhodium and -iridium Dichloride

2-R-1,3,2-Diselenaphospholanes (R = iPr, Ph) with an annelated 1,2-dicarba-closo-dodecaborane(12) unit were treated with Lewis acids such as borane reagents (BH3 in THF, and BH3–SMe2) as well as Cp*-rhodium and -iridium dichloride (Cp* = pentamethylcyclopentadienyl). In all cases, the adduct formation in the beginning was followed by ring expansion through insertion of the borane or Cp*MCl2 into one of the P–Se bonds accompanied by transfer of a hydrido or chlorido ligand to phosphorus. Finally, the P–R unit was displaced from the ring to give the exchange products, in which the boron or the metal had become part of the five-membered rings. The reactions were monitored by NMR spectroscopy (1H, 11B, 13C, 31P, and 77Se). The proposed reaction sequences were found to be in agreement with calculated [B3LYP/6-311+G(d,p), LANL2DZ (Rh, Ir) level of theory] relative energies of optimized gas-phase structures of the various products. The novel molecular structure of the preferred insertion product with M = Ir, R = iPr was determined by X-ray analysis. Borane reagents as well as Cp*MCl2 (Cp* = pentamethylcyclopentadienyl; M = Rh, Ir) react with 1,3,2-diselenaphospholanes by the formation of adducts, followed by ring insertion, and finally by exchange.

Posted on 12 August 2014 | 12:10 pm


A Macrocyclic 2,2?-Bibenzimidazole Ruthenium(II) Chromophore as a Versatile Building Block for Supramolecular Devices

We present the synthesis of a macrocyclic ruthenium(II) complex that combines the versatile photophysics and supramolecular chemistry of biimidazole ruthenium(II) chromophores with a macrocyclic geometry that allows for its introduction into mechanically interlocked frameworks. Structural information on the core framework was gained from a solid-state structure. The new supramolecular building block shows that the principal photophysics of the ruthenium chromophore, that is, the cation-driven light-switch effect, are retained during the formation of the macrocycle. A new pH- and cation-switchable ruthenium(II) chromophore is presented. Owing to the versatility of the macrocyclic 2,2?-bibenzimidazole ligand, the complex presents itself as an attractive new building block for supramolecular arrays.

Posted on 11 August 2014 | 1:10 pm


Uranyl Ion Complexes with trans-3-(3-Pyridyl)acrylic Acid Including a Uranyl–Copper(II) Heterometallic Framework

As a heterofunctional pro-ligand with both hard and soft coordination sites, trans-3-(3-pyridyl)acrylic acid (LH) is of potential interest for the design of heterometallic complexes of f- and d-block cations, as previously shown in the case of lanthanides. The reaction of LH with uranyl nitrate in water/acetonitrile at 180 °C yields the complex [(UO2)3(L)(HL)(O)(OH)3]·2.5H2O·CH3CN (2), which is different from the previously reported complex [UO2(L)(OH)] (1). Complex 2 crystallizes as a ribbon-like 1D coordination polymer with a skeleton bridged by oxido and hydroxido ligands, in which the uranyl cation is bound to the bridging bidentate carboxylato groups, and the pyridyl groups (one of them protonated) are directed sideways. In the presence of copper nitrate, the reaction affords the heterometallic complex [(UO2)2Cu(L)3(O)(H2O)](NO3) (3), in which the harder uranium atom is bound to two ?3-oxido anions and to chelating and bridging carboxylato groups to generate a tetranuclear secondary building unit, whereas the softer copper cations are bound to three pyridyl groups and only one carboxylato donor. The copper atoms are further involved in cation–cation interactions with uranyl oxido groups, and the Cu–O(oxido) bond lengths of 2.162(13) and 2.248(16) Å are among the shortest measured to date. 3 crystallizes as a 3D assembly, which displays narrow channels, and it illustrates the ability of copper cations, in combination with a ditopic ligand, to assemble discrete uranyl-containing units into a framework structure. The emission spectra of complexes 1 and 2 in the solid state display the usual vibronic progression of the uranyl ion in the range 450–650 nm, and the width of the bands indicates that they may be the superposition of slightly different series, due to the inequivalent uranyl centres in the lattices. The heterofunctional pro-ligand trans-3-(3-pyridyl)acrylic acid was used to build a uranyl–copper(II) heterometallic complex, in which the preferential bonding of the two cations reflects hard and soft affinities and which crystallizes as a 3D framework. The crystal structure of a new 1D homometallic uranyl complex with the same ligand is also described.

Posted on 11 August 2014 | 1:10 pm


Rationalizing and Disrupting Fluxional Processes in Agostically Stabilized 14-Electron Alkyliridium Hydride Complexes

We have investigated the fundamental patterns of reactivity for the cationic IrIII complexes [(6-Mes)(6-Mes?)Ir(H)]+ and [(7-Mes)(7-Mes?)Ir(H)]+ [6-Mes, 7-Mes = ring-expanded N-heterocyclic carbene (NHC) ligands, ? indicates that NHC is tethered through an iridium-bound CH2 group], each of which undergoes degenerate fluxional exchange between an iridium-bound agostic C–H bond and the discrete alkyl/hydride ligands resulting from C–H activation. A comparison between the activation parameters ?H‡ and ?S‡ determined by variable-temperature NMR (VT-NMR) spectroscopy line-shape analysis and those obtained from DFT calculations on model systems offers a basis to discriminate between different possible exchange mechanisms, and an oxidative addition pathway gives the lowest barrier and also the best agreement between experiment and theory. The addition of neutral Lewis base donors to [(6-Mes)(6-Mes?)Ir(H)]+ resulted in the displacement of the weak agostic C–H···Ir interaction and the generation of static (alkyl)iridium(III) hydride complexes such as [(6-Mes)(6-Mes?)Ir(H)(CNtBu)2]+. The analogous carbonyl complex is more labile, with the enhanced ?-acceptor properties of the ancillary ligands leading to C–H reductive elimination and to the formation of the IrI complex [(6-Mes)2Ir(CO)2]+, which incorporates unactivated NHC donors and has the ability to reversibly take up H2. By NMR spectroscopy and DFT methods, the mechanism of fluxional exchange in cationic bis(NHC) IrIII systems with an agostic C–H bond and cis-alkyl/hydride ligands is shown to feature an oxidative pathway. Related nonfluxional systems can be “trapped” by the addition of two-electron donors (L), and their stability to C–H reductive elimination can be tuned through the ?-acceptor properties of L.

Posted on 11 August 2014 | 1:10 pm


Triphenylamine-Substituted Metalloporphyrins for Solution-Processed Bulk Heterojunction Solar Cells: The Effect of the Central Metal Ion on Device Performance

A series of metal(II)-substituted 5,10,15,20-tetrakis[4-(diphenylamino)phenyl]porphyrins (P) were designed and synthesized. Incorporation of the flexible and strong electron-donating triphenylamine substituent endowed the porphyrins with enhanced solubility and intermolecular interactions. The distinct properties arising from different central metal ions were investigated by studying the absorption spectra, electrochemistry behavior, charge transport properties, thermal stability, and morphology characterization of the porphyrins. The PdII 5,10,15,20-tetra(4-diphenylaminophenyl)porphyrins (PPd) were found to have more matching energy levels with methyl [6,6]-phenyl-C-61-butyrate (PC61BM), higher hole mobility and longer triplet exciton lifetime. Bulk heterojunction solar cells based on porphyrins and PC61BM have been fabricated, with PPd-based solar cells exhibiting greatly enhanced photovoltaic performance originating from a combination of elements. These results will help guide the future molecular design of porphyrins for application in organic small molecule bulk heterojunction solar cells. Porphyrins with enhanced solubility and intermolecular interactions have been developed by incorporating the flexible and strong electron-donating triphenylamine substituent. Furthermore, different metal(II) ions have been introduced to the porphyrin and applied in organic photovoltaics to study the effects of the central metal ions on device performance.

Posted on 11 August 2014 | 12:40 pm


Mechanochemical Synthesis of SiO44–-Substituted Hydroxyapatite, Part II – Reaction Mechanism, Structure, and Substitution Limit

For the first time, silicate-substituted hydroxyapatites have been prepared from mixtures containing different amounts of silicon (0.2–2 mol per mol of apatite unit cell) by dry mechanochemical synthesis at room temperature in a planetary ball mill. The XRD, FTIR, TEM, and NMR spectroscopic data show that the product of the mechanochemical synthesis is a single-phase nanocrystalline apatite containing different amounts of carbonate and silicate ions and adsorbed water. In the annealed samples, three silicon concentration subranges can be distinguished, each of which is characterized by specific evolution of the lattice parameters. The formation mechanism of the silicate-substituted hydroxyapatite obtainable by this method is discussed. The studies indicate that the silicon substitution limit in the silicate-substituted lattice achievable by the dry mechanochemical synthesis followed by heat treatment is 1.2 mol per mol of apatite unit cell. Silicate-substituted hydroxyapatite powders containing different amounts of silicon have been synthesized by the mechanochemical method. Several apatite crystal structures that differ by the position of the hydroxy groups have been identified.

Posted on 11 August 2014 | 12:40 pm


Synthesis of Urchin-Like FeF2 Nanoarchitectures and Their Conversion into Three-Dimensional Urchin-Like Mesoporous ?-Fe2O3 Nanoarchitectures for Methane Activation

Novel urchin-like FeF2 nanoarchitectures have been fabricated by an unconventional nonhomogeneous ionic liquid/diphenyl ether solvothermal method. Subsequent solid-state thermal annealing was utilized to convert the FeF2 nanoarchitectures into 3D urchin-like mesoporous ?-Fe2O3 nanoarchitectures. The reaction system and temperature played important roles in the morphology of FeF2 and the growth of the 3D urchin-like ?-Fe2O3. A study of methane activation over the 3D urchin-like mesoporous ?-Fe2O3 nanoarchitectures revealed that methane was activated and converted into carbon dioxide at a low temperature (230 °C). Compounds containing C–C bonds were produced at 600 °C. This 3D urchin-like mesoporous ?-Fe2O3 shows excellent potential as a catalyst for methane conversion in the chemical industry. Novel urchin-like FeF2 nanoarchitectures have been fabricated by an unconventional nonhomogeneous ionic liquid/diphenyl ether solvothermal method and converted into 3D urchin-like mesoporous ?-Fe2O3 nanoarchitectures by solid-state thermal annealing. The ?-Fe2O3 nanoarchitectures exhibit good catalytic properties in methane activation reactions.

Posted on 11 August 2014 | 12:40 pm


Mechanochemical Synthesis of SiO44–-Substituted Hydroxyapatite, Part I – Kinetics of Interaction between the Components

The kinetics of the room-temperature dry mechanochemical synthesis of hydroxyapatite modified by SiO44– ions has been studied for the first time. The changes in the composition of the reaction mixture as a function of the time of mechanical activation in a planetary ball mill as well as the composition of the final product have been investigated by X-ray phase analysis and IR spectroscopy. Certain stages of the interaction of the reactants have been analyzed with the help of high-resolution electron microscopy. The mechanochemical synthesis conducted in air is accompanied by the incorporation of carbonate ions into the apatite lattice, which results in the formation of B-type carbonated hydroxyapatite. The apatite structure starts to form after 5 min of mechanochemical activation of the reaction mixture, and the final single-phase nanocrystalline powder of silicate-substituted carbonated hydroxyapatite is formed after 30 min of activation. The kinetics of the dry mechanochemical synthesis of hydroxyapatite modified by SiO44– ions is studied. From the first seconds of mechanical activation, the initial Ca(H2PO4)2·H2O partially reacts with CaO to form CaHPO4 (interior of the nanoparticles); the nanoparticle shell is Ca(H2PO4)2·H2O, and the material located near the nanoparticles is a mechanical mixture of the initial components.

Posted on 6 August 2014 | 2:40 pm


[Ge(H)(2-C6H4PPh2)3] as Ligand Precursor at Ruthenium: Formation and Reactivity of [Ru(Cl){Ge(2-C6H4PPh2)3}]

The germane [Ge(H)(2-C6H4PPh2)3] (2) was synthesized by reaction of Li[Ge(2-C6H4PPh2)3] (1) with water. The presence of nBuBr led to the formation of [Ge(nBu)(2-C6H4PPh2)3] (3). The complex [Ru(Cl){Ge(2-C6H4PPh2)3}] (4) was obtained by reaction of 2 with [Ru(Cl)2(PPh3)3] and NEt3. The ruthenium-bound Ge(2-C6H4PPh2)3 moiety in 4 can be converted into a Ge(Cl)(2-C6H4PPh2)2 fragment on treatment of 4 with a solution of HCl in diethyl ether to yield [Ru(Cl){Ge(Cl)(2-C6H4PPh2)2}(PPh3)] (5). The reaction of complex 4 with potassium hydride in an atmosphere of dihydrogen led to [Ru{Ge(2-C6H4PPh2)3}(H)(H2)] (6). Complex 6 reacted with hydrazine to give [Ru{Ge(2-C6H4PPh2)3}(H)(N2H4)] (7). With an excess of hydrazine, complex 6 catalyzed the disproportionation of hydrazine to produce ammonia and the ruthenium complex [Ru{Ge(2-C6H4PPh2)3}(H)(NH3)] (8). The ruthenium complex [Ru(Cl){Ge(2-C6H4PPh2)3}] can be converted into the dihydrogen complex [Ru{Ge(2-C6H4PPh2)3}(H)(H2)] on treatment with KH in a dihydrogen atmosphere. A reaction of [Ru{Ge(2-C6H4PPh2)3}(H)(H2)] with hydrazine led to its catalytic disproportionation to give ammonia and the ammonia complex [Ru{Ge(2-C6H4PPh2)3}(H)(NH3)].

Posted on 6 August 2014 | 2:40 pm


Copper(II)-Coordinated ?-Azophenols: Effect of the Metal-Ion Geometry on Phenoxyl/Phenolate Oxidation Potential and Reactivity

Two copper(II) complexes were synthesized from tridentate ligands involving a (Nquinoline,Nazo,Ophenol) donor set. The copper(II) ion is tetracoordinate with a chloride ion occupying the fourth position of the coordination sphere. Both X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy reveal that the copper(II) ion geometry is square planar in 1. In contrast, significant tetrahedral distortions are observed in 2, as a result of the steric clash between the hydrogen atoms of the methyl substituent of the quinoline group and the chloride ion. Cyclic voltammetry curves of 1 and 2 in CH2Cl2 display a reversible oxidation wave at E1/2 = 0.59 V and 0.56 V versus ferrocenium/ferrocene, respectively, which was assigned to the phenoxyl/phenolate redox couple. Compounds 1+ and 2+ were generated and characterized by UV/Vis and EPR spectroscopy. Their reactivity with benzyl alcohol was investigated by kinetic measurements. Tetrahedral distortion at the metal ion in a copper(II) complex containing tridentate ligands with a (Nquinoline,Nazo,Ophenol) donor set is tuned by the ?-quinoline substituent. The CuII–phenoxyl radical species oxidizes benzyl alcohol at rate constants that are essentially independent of the distortion at the metal center.

Posted on 6 August 2014 | 2:40 pm


Sila-?-galbanone and Analogues: Synthesis and Olfactory Characterization of Silicon-Containing Derivatives of the Galbanum Odorant ?-Galbanone

Silicon compounds 1b–3b are sila-analogues of the galbanum odorants ?-galbanone (1a), ?-spirogalbanone (2a), and nor-?-galbanone (3a), respectively. Sila-?-galbanone (1b), sila-?-spirogalbanone (2b), and sila-nor-?-galbanone (3b) were synthesized in multistep syntheses in isomerically pure form, starting from Me2SiCl2, (CH2=CH)2SiCl2, and Me2(CH2=CH)SiCl, respectively. Hydroformylation of vinylsilanes, followed by either ring-closing aldol condensation or ring-closing alkene metathesis, were the key steps in these syntheses. The C/Si pairs 1a/1b, 2a/2b, and 3a/3b were studied for their olfactory properties. All compounds possess green-fruity galbanum-type odors with pineapple aspects and thus are olfactorily related. However, sila-analogues 1b–3b were found to be weaker than the corresponding parent carbon compounds 1a–3a. This effect is most pronounced for the C/Si pair 2a/2b as indicated by the odor thresholds of 0.023 ng?L–1 air (2a) and 3.8 ng?L–1 air (2b). However, due to their higher molecular mass, the silicon compounds are less volatile and thus more substantive in functional applications. In contrast to the stable 5-silacyclohex-1-enes 1b and 2b, the 4-silacyclopent-1-ene 3b shows a limited chemical stability. For compound 3a an extremely low odor threshold of 0.0087 ng?L–1 air was measured, and the silicon analogue 3b with an odor threshold of 0.085 ng?L–1 air is the sila-odorant with the lowest odor threshold measured so far. Sila-?-galbanone, sila-?-spirogalbanone, and sila-nor-?-galbanone (sila-analogues of ?-galbanone, ?-spirogalbanone, and nor-?-galbanone) were synthesized starting from Me2SiCl2, (CH2=CH)2SiCl2, and Me2(CH2=CH)SiCl, respectively. These sila-analogues proved to be less volatile and thus more tenacious than the parent carbon compounds while also providing insight into structure–odor correlations.

Posted on 5 August 2014 | 2:30 pm


Microwave-Assisted C–C and C–S Couplings Catalysed by Organometallic Pd-SCS or Coordination Ni-SNS Pincer Complexes

A family of SCS and SNS pincer compounds of the type [PdCl{C6H3-2,6-(CH2SR)2}] {R = tBu (3a), sBu (3b), iBu (3c)} and [NiCl2{C5H3N-2,6-(CH2SR)2}] {R = tBu (4a), sBu (4b)} have been prepared. Among these, complexes 3b, 3c, 4a–4c are reported for the first time. Dimeric compounds such as [NiCl{C5H3N-2,6-(CH2SiBu)2}?-Cl]2 (4c) were found in the solid state for the nickel complexes with lower steric hindrance exhibiting octahedral metal centers, whereas other nickel structures such as [NiCl2{C5H3N-2,6-(CH2StBu)2}(iPrOH)] (4d) could also expand their coordination number by coordinating to solvents. The single crystal X-ray diffraction results for 4a, 4c and 4d are presented. The catalytic activity of the six compounds was studied in C–C and C–S cross-coupling reactions under conventional heating and under microwave irradiation conditions. The palladium catalysts enabled good to excellent conversions in Suzuki–Miyaura couplings of p-substituted halobenzenes with phenylboronic acid. Comparable yields resulted from application of the nickel complexes in the thioetherification of iodobenzene with different disulfides. The fast increase in reaction temperature associated with microwave irradiation, in combination with the robust pincer catalysts, allowed for quantitative conversions in only minutes. A series of SCS-PdII and SNS-NiII pincer compounds of the type [PdCl{C6H3-2,6-(CH2SR)2}] and [NiCl2{C5H3N-2,6-(CH2SR)2}] {R = tBu, sBu, iBu} were synthesized and used as efficient catalysts in C–C Suzuki–Miyaura and C–S thiolation cross-coupling reactions.

Posted on 5 August 2014 | 2:23 pm


Syntheses and Solid-State Structures of Et2SbTeEt and Et2BiTeEt

Diethylstibanyl- and diethylbismuthanyl telluranes Et2MTeEt (M = Sb 1, Bi 2) as well as tBu3Sb (3) were structurally characterized by single-crystal X-ray diffraction. Single crystals of 1–3 were grown by using an IR-laser-assisted technique. Compounds 1 and 2 form short intermolecular E···Te interactions in the solid state, which were further investigated with dispersion-corrected density functional theory. Single crystals of Et2M–TeEt (M = Sb 1, Bi 2) as well as tBu3Sb (3) were grown by using an IR-laser-assisted technique. Compounds 1 and 2 form short intermolecular E···Te interactions in the solid state, which were further investigated with dispersion-corrected density functional theory.

Posted on 5 August 2014 | 2:20 pm


NaB3O5·0.5H2O and NH4NaB6O10: Two Cluster Open Frameworks with Chiral Quartz and Achiral Primitive Cubic Nets Constructed from Oxo Boron Cluster Building Units

Two new cluster open framework borates, NaB3O5·0.5H2O (1) and NH4NaB6O10 (2) have been made under solvothermal conditions and characterized by IR, emission, and diffuse reflectance spectroscopy, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. The common structural features contain the oxoboron cluster building units, B3O7 and B6O13 cluster units for 1 and 2, in which the B3O7 and B6O13 clusters act as 4- and 6-connected nodes to further link each other, resulting in chiral qtz and achiral pcu nets, respectively. By incorporating oxo boron cluster units, two inorganically templated cluster open frameworks with intersecting channels are made under solvothermal conditions that exhibit chiral quartz and achiral primitive cubic nets, as well as blue luminescence.

Posted on 5 August 2014 | 10:10 am


The YBaCo4O7+?-Based Functional Oxide Material Family: A Review

The complex cobalt oxide YBaCo4O7+? is an exciting material from both a fundamental scientific and an applied technological point of view. It has a unique ability to reversibly absorb and desorb large amounts of oxygen in an exceptionally low-temperature range, which makes it a promising candidate for applications in which efficient oxide ion conductivity or large oxygen storage capacity is required. It has also been considered as a model system for geometrically frustrated magnetism, which originates from the nature of the layered crystal structure of YBaCo4O7+?, with alternating triangular and Kagome-type cobalt oxide layers. The structure is also extremely flexible in a chemical sense, with all three cation constituents accepting a number of different substitutions, thereby allowing its properties to be tuned. In this review, our aim is to provide a compact but comprehensive overview of the work published so far on this interesting family of functional oxides. The YBaCo4O7+? family of layered cobalt oxide materials has unique and interesting properties with regard to both magnetism and oxygen storage. The crystal lattice structure allows a large oxygen nonstoichiometry and chemical substitution at each cation site, allowing the properties of these oxides to be tuned.

Posted on 5 August 2014 | 10:10 am


(Arene)ruthenium Complexes with Imidazolin-2-imine and Imidazolidin-2-imine Ligands

Imidazolin-2-imine and imidazolidin-2-imine ligands are versatile N donors in transition metal chemistry. Here, we describe the synthesis and characterization of (arene)Ru complexes with these ligands. Simple adducts of the type [(p-cymene)Ru(L)Cl2] (L = 1,3-diarylimidazolin-2-imine or 1,3-dimesitylimidalzolidin-2-imine) can be converted into complexes in which the imines act as ? ligands with tethered imine groups. Furthermore, the high basicity of the N donor group can promote self-activation of the (arene)Ru complexes. (Arene)Ru complexes with imidazolin-2-imine and imidazolidin-2-imine ligands of the general formula [(cymene)RuCl2L] are described. Photochemical activation allows the preparation of complexes in which the imines act as ? ligands with tethered imine groups.

Posted on 5 August 2014 | 10:10 am


BOX Ligands in Biomimetic Copper-Mediated Dioxygen Activation: A Hemocyanin Model

The ?-?2:?2-peroxodicopper(II) core found in the oxy forms of the active sites of type III dicopper proteins have been a key target for bioinorganic model studies. Here, it is shown that simple bis(oxazoline)s (BOXs), which are classified among the so-called “privileged ligands”, provide a suitable scaffold for supporting such biomimetic copper/dioxygen chemistry. Three derivatives R,HBOX-Me2 (R = H, Me, tBu) with different backbone substituents have been used. Their bis(oxazoline)-copper(I) complexes bind dioxygen to yield biomimetic ?-?2:?2-peroxodicopper(II) species. O2 can be reversibly released upon an increase in temperature. Their formation kinetics have been studied under cryo-stopped-flow conditions for the tBu derivative, giving activation parameters ?H‡on = (2.27?±?0.18) kcal?mol–1, ?S‡on = (–46.3?±?0.8) cal?K–1 mol–1 for the binding event and ?H‡off = (11.7?±?1.9) kcal?mol–1, ?S‡off = (–16.1?±?8.2) cal?K–1 mol–1 for the release of O2, as well as thermodynamic parameters ?H° = (–10.0?±?1.7) kcal?mol–1 and ?S° = (–32.7?±?7.4) cal?K–1 mol–1 for this equilibrium. The ?-?2:?2-peroxodicopper(II) complexes have been isolated as surprisingly stable solids and investigated in depth by a variety of methods, both in solution and in the solid state. Resonance Raman spectroscopy revealed a characteristic isotope-sensitive stretch $\tilde {\nu}$O–O = 731–742 cm–1 (?[18O2] ? –39 cm–1) and an intense feature around 280 cm–1 diagnostic for the fundamental symmetric Cu2O2 core vibration. A slight butterfly-shape of the Cu2O2 core has been derived from EXAFS data and DFT calculations. SQUID magnetic data evidenced strong antiferromagnetic coupled CuII2 (–2J ? 1000 cm–1). Thermal degradation in solution yields bis(hydroxo)-bridged [(tBu,HBOX-Me2)(L)Cu(OH)]2(PF6)2 (L = H2O, MeCN or THF); whereas in the case of H,HBOX-Me2, ligand oxygenation has been detected. Preliminary reactivity studies with the substrate 2,4-di-tert-butylphenol indicate the formation of the C–C coupling product 3,3?,5,5?-tetra-tert-butyl-2,2?-biphenol, whereas ortho-hydroxylation was not observed. The copper(I) complex [(tBu,HBOX-Me2)Cu(MeCN)]PF6 as well as two dicopper(II) complexes [(L)(tBu,HBOX-Me2)Cu(OH)]2(PF6)2 have been characterised by single-crystal X-ray diffraction. Considering the vast number of known BOX derivatives, a rich and versatile Cu/O2 chemistry based on this platform is anticipated. A series of bis(oxazoline)-copper(I) complexes reversibly bind dioxygen to yield biomimetic ?-?2:?2-peroxo-dicopper(II) species, which represent new functional hemocyanin models. Their kinetics of formation have been studied under cryo conditions, and the complexes have been isolated as surprisingly stable solids. All were investigated by a variety of methods, both in solution and in the solid state.

Posted on 1 August 2014 | 12:40 pm


Thiacrown Ethers with Oxygen and Sulfur for Coordination: Formation of the Pd and Pt Complexes and Pseudorotaxane with Dialkylammonium

Mono-, di- tri-, and tetrathiadibenzo[24]crown-8-ethers with eight oxygen or sulfur atoms within the 24-menbered ring have been synthesized by using 1,2-benzenedithiol and 2-hydroxythiophenol as the starting materials. The thia[24]crown ethers form [2]pseudorotaxanes with dibenzylammonium salts, the association constants of which vary depending on the numbers and positions of the sulfur and oxygen atoms. The [2]pseudorotaxane of 1,4-dithiadibenzo[24]crown-8-ether (1,4-DTC) was converted into its Pd complex [PdCl2(1,4-DTC)] by the addition of [PdCl2(cod)] (cod = 1,5-cyclooctadiene), accompanied by the liberation of dibenzylammonium. Subsequent addition of PPh3 to the mixture led to regeneration of the [2]pseudorotaxane. A [2]pseudorotaxane composed of 1,4-DTC and dialkylammonium with two vinyl groups at both ends of the axis component underwent a cross-metathesis reaction with an acrylate ester to form the corresponding [2]rotaxane with an interlocked structure. Mono-, di-, tri-, and tetrathiacrown ethers form pseudorotaxanes with dialkylammonium salts and transition-metal complexes with palladium(II) and platinum(II). The pseudorotaxanes of di- and tetrathiacrown ethers undergo decomplexation/complexation cycles by competitive metal coordination with PdCl2.

Posted on 1 August 2014 | 12:40 pm


Divalent Transition Metal Silylamide Ate Complexes

Dimetallic ate complexes were synthesized from the divalent transition metal silylamide complexes {Fe[N(SiMe3)2]2}2, Cr[N(SiMe3)2]2(thf), Co[N(SiMe3)2]2(thf)2, and {Mn[N(SiHMe2)2]2}2 (thf = tetrahydrofuran) by the addition of the corresponding lithium or sodium silylamide salt. Accordingly, donor-free LiFe[N(SiMe3)2]3 and NaMn[N(SiHMe2)2]3 as well as thf-coordinated (thf)NaCr[N(SiMe3)2]3 and (thf)NaCo[N(SiMe3)2]3 were obtained. The thf-containing mixed iron(II)/lithium bis(trimethylsilyl)amide complex (thf)LiFe[N(SiMe3)2]3 was synthesized by the simple addition of thf to the donor-free complex LiFe[N(SiMe3)2]3. All of the complexes were characterized by IR spectroscopy and elemental analysis, and the effective magnetic moments in solution were determined by the Evans method. The solid-state structures of these bis(trimethylsilyl)amido-derived complexes were additionally determined by X-ray crystallography. Donor-free and tetrahydrofuran-coordinated (thf-coordinated) ate complexes of the type (thf)x(AM)M(NR2)3 (x = 0, 1; AM = Li, Na; M = Fe, Cr, Co, Mn) have been synthesized and characterized. The implications of ion size and donor-solvent coordination on the solid-state structures are discussed.

Posted on 1 August 2014 | 12:40 pm


?- or ?-Coordination? Complexes of Univalent Gallium Salts with Aromatic Nitrogen Bases

To answer the question as to whether gallium in its oxidation state +1 favors a ?- or a ?-coordination of aromatic nitrogen bases, we reacted [Ga(C6H5F)2]+[Al(ORF)4]– {RF = C(CF3)} with pyrazine and 2,6-di-tert-butyl-4-methylpyridine (DTBMP). In doing so, we obtained the first tricoordinate, nonchelated, homoleptic N-donor complex of gallium(I): [Ga(pyrazine)3]+[Al(ORF)4]–, in which each gallium(I) cation is coordinated in a trigonal-pyramidal fashion by three ?1-donating pyrazine ligands. Hence, the gallium(I) cations favor ?- over ?-coordination. Depending on the reaction conditions, and due to the bifunctionality of pyrazine, 1D coordination polymers of {[Ga(?-pyrazine)2(?1-pyrazine)]+[Al(ORF)4]–}? were also obtained. With the sterically demanding DTBMP, which is conventionally used as a proton scavenger, the mixed complex [Ga(C6H5F)2(DTBMP)]+[Al(ORF)4]– was isolated, thus proving incorrect the perception of DTBMP being “non-nucleophilic”. The structural findings were confirmed by multinuclear NMR investigations and density functional performed at the RI-BP86/SV(P) level. Upon interaction of [Ga(C6H5F)2]+[Al(ORF)4]– with pyrazine or 2,6-di-tert-butyl-4-methylpyridine, ?-coordination prevails. Thus, these two aromatic nitrogen bases function as Lewis bases, yielding homoleptic and mixed N-donor complexes or coordination polymers of gallium(I).

Posted on 1 August 2014 | 12:30 pm


Trigonal Bipyramidal or Square Pyramidal Coordination Geometry? Investigating the Most Potent Geometry for Vanadium Phosphatase Inhibitors

The five-coordinate geometry is an important factor in phosphoryl group transfer, particularly for phosphate ester hydrolysis. In the following review we analyze the five-coordinate geometries for a range of VO4X coordination spheres with regard to their structure from the point of view of square pyramidal or trigonal bipyramidal geometries. The actual differences for the coordination environment of the reported small molecule structures are compared to the coordination environment of vanadate complexed to a protein tyrosine phosphatase (PTP) with four coordinating O atoms and one S atom. These considerations demonstrate that actual differences between the coordination environments are very small and presumably less critical than generally anticipated. This analysis suggests that it is a combination of structural and electronic properties leading to the perfect combination of reactivity and stability for the potent protein phosphatase inhibitor complex, thus confirming the fact that some other geometries have been reported. In this microreview, we analyze the five-coordinate geometries (an important factor in phosphoryl group transfer) for a range of VO4X coordination spheres with regard to their structure, considered as square pyramidal or trigonal bipyramidal geometries. We demonstrate that actual differences between the coordination environments are very small and presumably less critical than generally anticipated.

Posted on 1 August 2014 | 12:20 pm


Synthesis and Characterisation of Bridged Titanocene Oxido Complexes and Their Reactions with Water

The synthesis of two pyridine-stabilised ansa-titanocene oxido complexes is described. Oxidation of the titanocene sources Cpb2Ti(?2-Me3SiC2SiMe3) (Cpb2 = bridged ?5-cyclopentadienyl, 1a and 1b) with nitrous oxide yields corresponding oxido compounds 2a and 2b, respectively, in high yields. These can be hydrolysed to give dihydroxido complexes 3a and 3b, respectively, without the formation of by-products. The hydrolysis reaction was monitored by means of in situ IR spectroscopy. Hitherto unknown complexes 2a and 2b were fully characterised, and their molecular structures are reported in this paper. Oxidation of titanocene alkyne complexes with nitrous oxide in the presence of pyridine gives the corresponding ligand-stabilised oxido complexes, which can be hydrolysed to yield dihydroxido compounds quantitatively in very short reaction times, as evidenced by stopped-flow IR spectroscopy.

Posted on 30 July 2014 | 11:20 am


One-Pot Multiple Metal–Organic Framework Formation: Concomitant Generation of Structural Isomers or of Drastically Distinct Materials

The solvothermal reaction of 2,5-dihydroxyterephthalic acid (H2dhtp) and magnesium(II) nitrate in N,N-dimethylformamide (DMF) led to the simultaneous formation of two structural isomers, namely, the lvt network Mg(dhtp)(dmf)2 (1) and the compound Mg3(dhtp)3(dmf)6·0.75H2O (2) with the pcu ?-Po primitive cubic topology. The same reaction conditions with manganese(II) nitrate and terephthalic acid (H2tp) resulted in the concomitant generation of two drastically different metal–organic frameworks (MOFs), namely, Mn2(tp)2(dmf)2 (3) and [Mn(HCOO)3][NC2H8] (4), in which the formato ligands and N,N-dimethylammonium cations arise from DMF degradation. The (solvothermal) reactions to produce MOFs may lead to the simultaneous generation of multiple solid materials, for instance, structural isomers or even radically different compounds.

Posted on 30 July 2014 | 11:20 am


Inclusion of an Iodine Molecule in a Tiara-Like Octanuclear Palladium Thiolate Complex

An iodine molecule was successfully inserted into the inner cavity of a tiara-like octanuclear palladium thiolate complex, [Pd(?-SCH2CO2Me)2]8. The included iodine molecule coordinated weakly to six palladium atoms in both linear and bent modes, as confirmed by X-ray crystallography and DFT calculations. The inclusion complex reacted with an excess amount of I2 to produce a disulfide, which was accompanied by decomposition of the tiara ring. An iodine molecule is successfully inserted into the inner cavity of a tiara-like octanuclear palladium thiolate complex, [Pd(?-SCH2CO2Me)2]8. The included iodine molecule coordinates weakly to six palladium atoms in both linear and bent modes. The inclusion complex reacts with an excess amount of I2 to produce a disulfide, which is accompanied by decomposition of the tiara ring.

Posted on 23 July 2014 | 8:20 am


Photoluminescence of Zinc Complexes: Easily Tunable Optical Properties by Variation of the Bridge Between the Imido Groups of Schiff Base Ligands

A series of organic–metal chelate complexes of symmetric tetradentate Schiff base ligands derived from salicylaldehyde and 2-hydroxy-1-naphthaldehyde were designed and investigated. The combination of five nonconjugated flexible spacers and five conjugated rigid spacers with four salicylaldehyde derivatives provided a series of forty complexes. The series of blue to red photoluminescent complexes was investigated by UV/Vis absorption and luminescence spectroscopy in solution and in the solid state as well as cyclic voltammetry. The nature of the bridge in the ligand scaffold was determined to be the main parameter that influences the absorption and the emission color of the investigated zinc(II) complexes. Forty Schiff base zinc(II) complexes have been designed and studied for their photoluminescence properties. Interestingly, the nature of the diamine spacer in the ligand is the unique factor that influences the optical properties of the complexes.

Posted on 23 July 2014 | 8:20 am


X-ray Crystallographic Analysis of a Tailor-Made Bis(phthalocyaninato)-TbIII Single-Molecule Magnet as a Fundamental Unit for Supramolecular Spintronic Devices

The single-crystal X-ray diffraction analysis of the title compound, the pyrene-substituted unsymmetrical bis(phthalocyaninato)terbium(III) Single-Molecule Magnet (SMM) [Pc–Tb–Pc*]0 (1) (Pc = dianion of phthalocyanine, P* = dianion of phthalocyanine decorated with six flexible hexyl chains and one 4-pyren-1yl-butoxy group), was carried out. Both phthalocyaninato ligands in 1 are distorted from planarity and, therefore, adopt a biconcave shape. Effective ?–? interactions between the molecules lead to the formation of head-to-tail ? dimers. These dimers are stacked in the crystal, forming adjacent, parallel columns, the axes of which are tilted by 30° with respect to the C4 axes of the macrocycles. Herein, we also report the synthesis and characterization of the new isostructural Dy (compound 2) and Ho (compound 3) analogues of 1. The structure of a [Pc–Tb–Pc*] SMM was determined. A single-crystal X-ray diffraction analysis revealed an effective intermolecular ?–? interaction leading to the formation of ? dimers, which are stacked with neighboring dimers in parallel columns with an axis tilted by 30° with respect to the C4 axis of individual molecules. Isostructural Dy and Ho analogues were synthesized and characterized.

Posted on 23 July 2014 | 8:20 am


Compositionally Controlled Self-Assembly of Hierarchical Pd–Ni Bimetallic Chains

Magnetic Pd–Ni bimetals with various compositions were synthesized by a one-pot reaction, in which chain-like Pd–Ni bimetals formed through the self-assembly of Pd–Ni nanoparticles. The self-assembly behaviour of the Pd–Ni bimetals gradually changes with the changes in composition. The Pd–Ni nanoparticles form simple chains at lower Pd content, while the Pd–Ni bimetals take on a beads-on-string structure composed of sphere-shaped Pd–Ni-nanoparticle assemblies at higher Pd content. Magnetic hysteresis loops show that Ni-rich assemblies have a higher saturation magnetization than Pd-rich assemblies. The formation mechanism for these Pd–Ni assemblies is proposed, in which the self-assembly behaviours are controlled by the competition of the surfactant interaction and the magnetic dipole interaction. The catalytic activity and selectivity of the hydrogenation of acetophenone over these Pd–Ni bimetals depend on their compositions. The self-assembly of Pd–Ni bimetals with various compositions was performed by a one-pot reaction. The formation mechanism for these assemblies is proposed, in which the self-assembly behaviours were controlled by the competition between the surfactant interaction and the magnetic dipole interaction. The catalytic performance of these Pd–Ni assemblies is strongly dependent on their compositions.

Posted on 23 July 2014 | 8:10 am


Synthesis and Molecular Structures of Monosubstituted Pentamethylcobaltocenium Cations

(Amino-?5-cyclopentadienyl)(pentamethyl-?5-cyclopentadienyl)cobalt(III) hexafluorophosphate (6PF6) was prepared by a route that started with the synthesis of the zwitterion (oxycarbonyl-?5-cyclopentadienyl)(pentamethyl-?5-cyclopentadienyl)cobalt(III) (1). The acidification of 1 created the carboxylic acid 2PF6, which was converted into the acyl chloride 3PF6. The reaction with NaN3 afforded the azide 4PF6, which was transformed to the carbamate 5PF6. The hydrolysis of 5PF6 afforded the desired aminocobaltocenium compound 6PF6. The oxidation of 6PF6 yielded the (nitro-?5-cyclopentadienyl)(pentamethyl-?5-cyclopentadienyl)cobalt(III) cation 7+. For 1, 2+, 4PF6, 6PF6, and 7PF6, X-ray structure analyses were performed. The electronic structure of 6+ calculated by DFT methods revealed a short C–N bond, which is in agreement with the molecular structure obtained from X-ray structure analysis. The pKa value of 6PF6 was estimated from aqueous solution. Cyclic voltammetry studies show a reversible one-electron reduction and an irreversible one-electron oxidation. From the zwitterion 1, the aminocobaltocenium cation 6+ can be synthesized in five steps. The target compound 6+ demonstrates an electronic structure between that of an amine and that of an iminium cation. It reacts as a weak acid in aqueous solution and can be oxidized to the corresponding nitrocobaltocenium cation 7+ like primary amines.

Posted on 22 July 2014 | 12:10 pm


Kinetics and Mechanism of the Reaction of Hydrogen Sulfide with Diaquacobinamide in Aqueous Solution

We conducted a detailed kinetic study of the reaction of the vitamin B12 analog diaquacobinamide [(H2O)2Cbi(III)] with hydrogen sulfide in water from pH 3 to 11. The reaction proceeds in three steps: (1) the formation of three different complexes between cobinamide and hydrogen sulfide, viz., (HO–)(HS–)Cbi(III), (H2O)(HS–)Cbi(III), and (HS–)2Cbi(III); (2) inner-sphere electron transfer (ISET) in the two complexes with one coordinated HS– ligand to form the reduced cobinamide complex [(H)S]Cbi(II); and (3) the addition of a second molecule of hydrogen sulfide to the reduced cobinamide. ISET does not proceed in the (HS–)2Cbi(III) complex. The final products of the reaction between cobinamide and hydrogen sulfide were found to be independent of pH, and the main product is a complex of cobinamide(II) with the anion radical SSH2–. The reduction of diaquacobinamide [(H2O)2Cbi(III)] by hydrogen sulfide proceeds through inner-sphere electron transfer (ISET) in the two complexes with one coordinated HS– ligand, viz., (HO–)(HS–)Cbi(III) and (H2O)(HS–)Cbi(III), to form the reduced cobinamide complex [(H)S]Cbi(II). ISET does not proceed in the (HS–)2Cbi(III) complex.

Posted on 21 July 2014 | 1:10 pm


Aerial CO2 Trapped as CO32– Ions in a Dimeric Capsule That Efficiently Extracts Chromate, Sulfate, and Thiosulfate from Water by Anion-Exchange Metathesis

The tris(2-aminoethyl)amine-based (tren-based) 3-cyanophenyl-substituted tripodal urea L1, one of the familiar urea-based anion receptors, has shown encapsulation of CO32– ions as the carbonate capsule [(L1)2·(CO3)·(TBA)2] (1, TBA = tetrabutylammonium) by the fixation of aerial carbon dioxide from basic dimethyl sulfoxide (DMSO) solution. Single-crystal X-ray structural analysis confirmed the encapsulation of CO32– ions in the cavity of a dimeric capsular assembly of L1 (9.62 Å) through the formation of twelve strong N–H···O hydrogen-bonding interactions. The excellent CHCl3 and CH2Cl2 solubility of 1 has been exploited for the liquid–liquid (L–L) extraction of CrO42–, SO42–, and S2O32– ions from water by anion-exchange metathesis. The extraction of these anions from water was unambiguously confirmed by 1H NMR spectroscopy, IR spectroscopy, powder XRD (PXRD), and single-crystal X-ray diffraction analysis. The 1H NMR spectroscopic analysis of the bulk extracts supports the formation of 2:1 (host–guest) complexes. For the CrO42– ion, the 53Cr NMR spectrum of the bulk extract shows a characteristic peak at ? = –99.98 ppm. The complexes of CrO42–, S2O32–, and SO42– ions with L1 (i.e., 2–4, respectively) were obtained from crystallization of the bulk extracts and show anion-assisted dimeric capsular assemblies of L1 through multiple N–H···X (X = O, S) interactions. The dimensions of the anion-encapsulated capsular assemblies are quite similar to that of the carbonate capsule and are 9.70 Å for [(L1)2·(CrO4)·(TBA)2] (2), 9.61 Å for [(L1)2·(S2O3)·(TBA)2] (3), and 9.71 Å for [(L1)2·(SO4)·(TBA)2] (4). Quantification by weighing the bulk extract shows that 1 can separately extract ca. 90?% of the above three anions from water by anion-exchange metathesis. The quantitative estimations of the extractions of SO42– and CrO42– ions were further verified by gravimetric analysis by BaSO4 and BaCrO4 precipitation techniques, respectively. The extraction of SO42– ions from water was also demonstrated under alkaline conditions (pH 12.5) and in the presence of an excess of nitrate ions. Further, the quantification of CrO42– extraction was established by solution-state UV/Vis studies. In the solid state, a tripodal urea receptor encapsulates CO32– ions in its dimeric capsular assembly, which is further exploited for the liquid–liquid (L–L) extraction of CrO42–, S2O32–, and SO42– ions from water. Different spectroscopic techniques and X-ray diffraction studies confirm the efficient extraction of these environmentally relevant anions.

Posted on 21 July 2014 | 1:10 pm


Tetranuclear [2×2] Square-Grid Lanthanide(III) Complexes: Syntheses, Structures, and Magnetic Properties

The reactions of lanthanide(III) nitrate salts (DyIII, TbIII, GdIII, and ErIII) with the aroylhydrazone-based multidentate ligand 6-(hydroxymethyl)-N?-[1-(pyridin-2-yl)ethylidene]picolinohydrazide (LH2) in the presence of Et3N in a molar ratio of 1:1:4 afforded a series of homometallic tetranuclear lanthanide(III) complexes, [Ln4(LH)4(?2-OH)3(?2-OMe)]4NO3·xMeOH·yH2O (1, Ln = Dy, x = 2, y = 4; 2, Ln = Tb, x = 2, y = 4; 3, Ln = Gd, x = 2, y = 5; and 4, Ln = Er, x = 3, y = 3). X-ray diffraction studies revealed that all of the complexes contain a tetracationic [2×2] square-grid-like [Ln4(?2-OH)3(?2-OMe)(?2-O)4]4+ core, which is assembled by the concerted coordination action of four monoanionic [LH]– ligands along with three ?2-OH ligands and a ?2-OMe ligand. All of the lanthanide centers are eight-coordinate and adopt distorted triangular-dodecahedral coordination geometries with two different types of coordination environments (6O,2N and 4O,4N). The magnetic susceptibility measurements of the complexes reveal both the presence of all-antiferromagnetic coupling interactions as well as both isotropic (3) and anisotropic (1, 2, 4) single-ion contributions, which do not result in slow relaxation characteristics typical of single-molecule magnets. The reactions of a multicompartmental ligand with rare-earth(III) nitrate salts afford a series of homometallic Ln4 complexes [Ln = Dy, Tb, Gd, and Er] with [2×2] square-grid topology. Magnetic studies reveal the presence of all-antiferromagnetic exchange interactions and ligand-field-induced effects for the Dy, Tb, and Er complexes, whereas an isotropic model suffices for the Gd complex.

Posted on 21 July 2014 | 1:10 pm


Hydrophilic Pd0 Complexes Based on Sugars for Efficient Suzuki–Miyaura Coupling in Aqueous Systems

Two classes of hydrophilic Pd0 complexes containing P,N and N,N sugar-based ligands were prepared and tested in the Suzuki–Miyaura cross-coupling reaction under environmentally friendly aqueous conditions. The best catalyst was tolerant towards different substrates, and its activity is comparable with the highest values reported so far for reactions in aqueous media [loading 0.0010?%, turnover frequency (TOF) 3.5?×?104 h–1]. Sugar-derived hydrophilic Pd0 complexes are prepared and tested in aqueous Suzuki–Miyaura cross-coupling reactions. These conditions allow the green and sustainable synthesis of biaryls. The best catalysts achieve very good performances [turnover frequencies (TOFs) up to 3.5?×?104 h–1; catalyst loadings down to 0.0010 mol-%], among the best reported for this reaction in aqueous conditions.

Posted on 21 July 2014 | 1:10 pm


High-Yielding Synthesis of a Hetero-Pacman Compound and the Characterization of Intermediates and Side-Products

Through an optimized synthetic procedure, metalloligand 5, which features a hetero-Pacman scaffold comprising a porphyrin and a terpyridine moiety, has been assembled by a double Suzuki reaction. In a subsequent step, a ruthenium-bipyridine fragment was introduced at the terpyridine coordination site of metalloligand 5 to form complex 6, which was fully characterized and its potential application in water oxidation catalysis tested. A number of side-products were isolated and characterized during the two-step synthesis procedure, including a hydroxylated version of the boronic acid substituted precursor molecule derived by a base-assisted rearrangement. The compounds described herein extend the Pacman concept to the assembly of different metal combinations with different coordination spheres and their interactions in the activation of small molecules. A new high-yielding synthesis towards xanthene-porphyrin precursors is presented. These building blocks can be used for the formation of a multitude of different heterodinuclear complexes with the Pacman architecture. A hetero-Pacman scaffold featuring a porphyrin and a ruthenium polypyridine complex fragment that shows intriguing structural and spectroscopic properties was produced herein by a double Suzuki reaction.

Posted on 21 July 2014 | 1:10 pm


Salicylate-Functionalized Bismuth Oxido Clusters: Hydrolysis Processes and Microbiological Activity

Hydrolysis of either Bi(HSal4Me)3 (A) or [Bi22O26(HSal4Me)14](B) in dmso gave the 4-methylsalicylate-substituted bismuth oxido cluster [Bi38O45(HSal4Me)24(dmso)14(H2O)2]·4H2O (1·4H2O), which crystallizes in the triclinic space group P$\bar {1}$ with cell parameters of a = 20.7214(5), b = 20.9654(6), c = 22.2128(6) Å, ? = 100.867(2), ? = 114.108(2), ? = 107.895(2)° and V = 7815.1(4) Å3. The hydrolysis of A was studied by using 1H DOSY NMR spectroscopy and electrospray ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometry, both of which showed the formation of several larger species under ambient conditions in the presence of moisture. Furthermore, ESI-FTICR MS analysis of cluster B showed the formation of mainly {Bi23O26} species, which indicates the partial dissociation of cluster B in solution. In addition, the three different bismuth species containing 1 (A), 22 (B) or 38 (1·4H2O) bismuth atoms per molecular formula were tested for their microbiological activity against three strains of Helicobacter pylori (251, 26695 and B128). A minimum inhibitory concentration (MIC) of 6.25 ?g?mL–1 for the mononuclear bismuth complex A was obtained, whereas the bismuth oxido cluster B showed a lower activity with MIC values in the range 25–50.0 ?g?mL–1. The activity of 1·4H2O is comparable to commercial remedies based on antimicrobial bismuth subsalicylate (BSS; 12.5 ?g?mL–1). Hydrolysis of either Bi(HSal4Me)3 or [Bi22O26(HSal4Me)14] in dmso gave the 4-methylsalicylate-substituted bismuth oxido cluster [Bi38O45(HSal4Me)24(dmso)14(H2O)2]·4H2O. 1H DOSY NMR and ESI-FTICR MS revealed an on-going growth process to finally give the large cluster. Microbiological activity tests against three strains of H. pylori showed higher activity for smaller bismuth species.

Posted on 18 July 2014 | 9:40 am


Diiron Azamonothiolates by the Scission of Dithiadiazacyclooctanes by Iron Carbonyls

The reactions of [Fe3(CO)12] with the dithiadiazacyclooctanes [SCH2N(R)CH2]2 (R = Me, Bn) afford the diiron complexes [Fe2{SCH2N(R)CH2}(CO)6] (1Me, 1Bu). The methyl derivative 1Me was characterized crystallographically [Fe–Fe = 2.5702(5) Å]. Its low symmetry was verified by variable-temperature 13C NMR spectroscopy, which revealed that the turnstile rotation of the {S(CH2)Fe(CO)3} and {S(NMe)Fe(CO)3} centers are subject to very different energy barriers. Although 1Me resists protonation, it readily undergoes substitution by tertiary phosphines, first at the {S(CH2)Fe(CO)3} center, as verified crystallographically for [Fe2{SCH2N(Me)CH2}(CO)5(PPh3)]. Substitution by the chelating diphosphine Ph2PCH2CH2PPh2 (dppe) gave [Fe2{SCH2N(Me)CH2}(CO)4(dppe)] by substitution at both the {S(CH2)Fe(CO)3} and {S(NMe)Fe(CO)3} sites. It has long been known that Fe0 reagents activate many organosulfur compounds by scission of C–S bonds. Here, we report that S2N2 heterocycles undergo smooth activation by [Fe3(CO)12] to give azamonothiolates, not the well precedented azadithiolates. In these azathiolate complexes, all six CO ligands are diastereotopic.

Posted on 18 July 2014 | 9:40 am


Phosphorescent PtII Systems Featuring Both 2,2?-Dipyridylamine and 1,3,5-Triazapentadiene Ligands

The treatment of cis-[Pt(dpa)(RCN)2][SO3CF3]2 {dpa = 2,2?-dipyridylamine, R = Me, Et, CH2Ph, Ph; [2a–d](OTf)2} (OTf = SO3CF3) with 2 equiv. of N,N?-diphenylguanidine [NH=C(NHPh)2] in CH2Cl2 solutions at room temp. for 16 h gives [Pt(dpa){NH=C(R)NC(NHPh)=NPh}][SO3CF3] {[3a,b,d](OTf)} as the addition products and [Pt(dpa){NH=C(R)NHC(R)=NH}][SO3CF3]2 {[4a,b](OTf)2} as the tailoring products. The formulation of complexes [3a,b,d](OTf) and [4a,b](OTf)2 was supported by satisfactory C, H, and N elemental analyses and agreeable high-resolution ESI-MS, IR, and 1H (including 1H–1H COSY experiments) and 13C{1H} NMR data. The structures of all of the platinum species were determined by single-crystal X-ray diffraction. The resultant complexes are nonemissive in solution, mainly because of the interaction between the empty d?z?2 orbital in a square-planar configuration and solvent molecules. However, in the solid state, complexes [3a,b,d](OTf) exhibit strong phosphorescence with quantum yields (peak wavelength) of 0.23 (490 nm), 0.27 (483 nm), and 0.20 (532 nm), respectively. The interplay between N,N?-diphenylguanidine and cis-(dpa)(RCN)2PtII species (dpa = 2,2?-dipyridylamine) gives both the so-called tailoring products and the addition products. The latter exhibit intense luminescence in the solid state.

Posted on 18 July 2014 | 9:40 am


Homoleptic Molybdenum Cluster Sulfides Functionalized with Noninnocent Diimine Ligands: Synthesis, Structure, and Redox Behavior

Thiourea (tu) has been coordinated to the Mo3S44+ cluster unit to afford the new cluster compound [Mo3S4(tu)8(H2O)]Cl4·4H2O (1). The high substitutional lability of the thiourea ligands can be exploited to achieve smooth ligand substitution in the Mo3S4 cluster. The reactions of 1 with 1,10-phenanthroline (phen) and 2,2?-bipyridine (bpy) have resulted in new trisubstituted diimino complexes [Mo3S4Cl3L3]+ [L = phen (2), bpy (3)]. The crystal structure of [Mo3S4Cl3(phen)3]Cl·4H2O was determined by X-ray analysis. A solid-state cyclic voltammetry study of 2 shows a ligand-centered reversible two-electron reduction. DFT calculations for [Mo3S4Cl3(phen)3]+ and the 2e-reduced species [Mo3S4Cl3(phen)3]– support our interpretation of the reduction process. Compound 3 undergoes a reversible two-electron reduction, which is more metal-centered on the basis of DFT calculations. An Mo3S4 cluster coordinated by thiourea ligands is a new precursor in the chemistry of Mo3S4 clusters. Its potential as a convenient starting material has been demonstrated by reactions with 2,2-bipyridine and 1,10-phenanthroline to afford new diimino cluster complexes. The Mo3S4 cluster bearing 1,10-phenanthroline undergoes a reversible two-electron reduction that is phen-centered with strong delocalization on the metal.

Posted on 18 July 2014 | 9:30 am


Neutral and Cationic Alkyl and Amido Group 3 Metal Complexes of Amidine-Amidopyridinate Ligands: Synthesis, Structure, and Polymerization Catalytic Activity

Alkane and amine elimination reactions between the amidine-aminopyridine proligands (NR1NNR1CMeNR2)H [R1 = R2 = Me (1a), R1 = H, R2 = Me (1b), R1 = Me, R2 = iPr (1c)] and the precursors [Ln(CH2SiMe3)3(thf)2] (Ln = Sc and Y) and [Ln{N(SiHMe2)2}3(thf)x] (Ln = Sc, Y, and La) have been investigated. Bulky 1c and [Ln(CH2SiMe3)3(thf)2] (Ln = Sc and Y) selectively afforded dialkyl complexes 2c-Sc and 2c-Y. Yttrium and lanthanum diamido complexes 3a-Y, 3b-Y, 3c-Y, and 3c-La were synthesized and isolated in high yields; however, similar aminolysis reactions to prepare the scandium analogues were unsuccessful. Detailed 29Si NMR spectroscopic studies combined with X-ray crystallography revealed the presence of ?-Si–H···Ln agostic interactions in the diamido complexes. Cationic monoamido complex 4a-Y was obtained from the reaction of 3a-Y with [Et3NH]+[BPh4]–. Both the dialkyl and diamido complexes, activated with [Ph3C]+[B(C6F5)4]–/AliBu3 or [PhNMe2H]+[B(C6F5)4]–/AliBu3, were found to be moderately active at 60 °C in the trans-1,4-selective polymerization of isoprene, and the diamido complexes promoted the ring-opening polymerization of rac-lactide with moderate activities. New dialkyl, diamido, and cationic amido group 3 metal complexes of amidine-amidopyridine ligands, some featuring ?-Si–H···Ln agostic interactions, evidenced in the solid state and by 29Si NMR spectroscopy, have been prepared and used in the polymerization of isoprene and ring-opening polymerization of racemic lactide.

Posted on 17 July 2014 | 12:20 pm


The Chemistry of Ni–Sb Carbonyl Clusters – Synthesis and Characterization of the [Ni19Sb4(CO)26]4– Tetraanion and the Viologen Salts of [Ni13Sb2(CO)24]n– Carbonyl Clusters

Within the reinvestigation of Ni–Sb carbonyl cluster chemistry, we report here the synthesis and characterization of the new [Ni19Sb4(CO)26]4– cluster and the synthesis, structure, magnetic characterization and electrical resistivity of the viologen salts of the previously known [Ni13Sb2(CO)24]n– (n = 2, 3) anionic species. The crystal structures of [NEt4]4[Ni19Sb4(CO)26], [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 and [EtV]3[Ni13Sb2(CO)24]·1.5THF (EtV = 1,1?-diethyl-4,4?-bipyridilium cation, DMF = N,N-dimethylformamide, THF = tetrahydrofuran) are described. Notably, the unit cell of [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 involves a mixture of two [Ni13Sb2(CO)24]3– trianions and one [Ni13Sb2(CO)24]2– dianion, as it also contains eight [EtV]+· radical monocations, which are assembled in infinite stacks. In contrast, the unit cell of the [EtV]3[Ni13Sb2(CO)24]·1.5THF salt contains four [Ni13Sb2(CO)24]3– trianions along with twelve [EtV]+· radical monocations, four of which are arranged into two pairs of isolated dimers, whereas the other two sets of four form two infinite stacks that extend over the whole crystal. The charges of the miscellaneous ions have been assigned on the basis of electroneutrality and spectroscopic evidence. More specifically, the infrared spectra of [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14, both in the solid state and in solution, clearly indicate the presence of a 2:1 mixture of [Ni13Sb2(CO)24]3– and [Ni13Sb2(CO)24]2– anions. Resistivity measurements performed on pellets of powdered samples indicate that the [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 salt substantially behaves as an insulator. A study of the magnetic behaviour of [EtV]8[Ni13Sb2(CO)24]3·4DMF·2C6H14 evidences pairing among the electrons of the EtV+· molecules, in agreement with DFT calculations, and the odd-electron clusters behave as paramagnetic centres of spin S = 1. The synthesis and characterization of the new [Ni19Sb4(CO)26]4– cluster, as well as the synthesis, structure, magnetic characterization and electrical resistivity of the viologen salts of the previously known [Ni13Sb2(CO)24]n– (n = 2, 3) anionic species are reported.

Posted on 17 July 2014 | 12:10 pm


Phosphate Diester Cleavage, DNA Interaction and Cytotoxic Activity of a Bimetallic Bis(1,4,7-triazacyclononane) Zinc Complex

The dinuclear zinc complex [Zn2{bcmp(-H)}(?-Cl)](ClO4)2·H2O {bcmp = 2,6-bis(1,4,7-triazacyclonon-1-ylmethyl)-4-methylphenol} has been synthesized and structurally characterized. The DNA binding affinity was assessed by ethidium bromide fluorescence quenching experiments. The complex relaxes supercoiled pUC19 DNA into the nicked form at low micromolar concentration. Mechanistic studies were carried out using the DNA and RNA models bis(2,4-dinitrophenyl) phosphate (BDNPP) and 2-hydroxypropyl p-nitrophenyl phosphate (HPNP). A detailed kinetic analysis suggested that the bridging OH group of the solution species [Zn2{bcmp(-H)}(?-OH)]2+ acts as the nucleophile in the hydrolysis of BDNPP, while in the case of HPNP, the bridging OH group acts as a general base and seems to shift to a terminal position upon substrate coordination. Finally, the cytotoxicity profile of the dinuclear zinc(II) complex was assessed. The complex showed promising in vitro antitumour activity against pancreatic and lung cancers cell lines. A new bimetallic Zn complex with a phenolate scaffold ligand with two aza-crown binding sites has been synthesized and characterized. DNA binding, cleavage and cytotoxicity results are reported.

Posted on 24 June 2014 | 5:11 pm





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