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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 ortho-Thio-Functionalized Triarylmethyl Palladium Complexes

A series of triarylmethyl palladium complexes with ortho coordination sites were synthesized. Thereby, the palladium atom exhibits various inter- and intramolecular binding modes towards the organic ligand. Further, the first crystallographically proven, exclusively ?-coordinated triarylmethyl palladium complexes, stabilized by ortho-thio-substituents, were discovered. The NMR spectra of the palladium complexes indicate temperature-dependent dynamic behavior. Various inter- and intramolecular binding modes between palladium salts and ortho-thio-substituted triarylmethyl ligands are detected in the solid state. The corresponding dynamic behavior in solution is studied by temperature-dependent NMR spectroscopy.

Posted on 21 November 2014 | 3:20 pm

Structural and Morphological Transformations of In–MIL-68-Based Hexagonal Lumps to QMOF-2-Based Pointed Hexagonal Rods by Means of Destruction and Reconstruction Processes

Simple thermal treatment of three-dimensional Kagomé-like [In(OH)(BDC)]n (In–MIL-68) hexagonal lumps in the presence of an extra amount of 1,4-benzenedicarboxylic acid (H2BDC) induces structural and morphological transformations of the hexagonal lumps into three-dimensional quartz-structured [InH(BDC)2]n (QMOF-2) pointed hexagonal rods. Transformation processes have been monitored by scanning electron microscopy to verify the destruction of the In–MIL-68-based hexagonal lumps and the simultaneous reconstruction of QMOF-2-based pointed hexagonal rods. We have also discovered the production of In–MIL-68-based hexagonal wires as early-stage kinetic products and the generation of QMOF-2-based pointed hexagonal rods as final-stage thermodynamic products from one-step solvothermal reaction of In(NO3)3 with an excess amount of H2BDC. Simple thermal treatment of In–MIL-68-based three-dimensional Kagomé-like structured hexagonal lumps in the presence of an excess amount of 1,4-benzenedicarboxylic acid (H2BDC) induces structural and morphological transformations into quartz-structured QMOF-2-based pointed hexagonal rods.

Posted on 21 November 2014 | 3:20 pm

Synthesis of Multifunctional Fe3O4@mSiO2@Au Core–Shell Nanocomposites for pH-Responsive Drug Delivery

A multifunctional nanocomposite has been successfully prepared for pH-responsive and magnetic-targeting drug delivery. First, Fe3O4@mesoporous silic (mSiO2) core–shell nanoparticles were synthesized as the nanocapsules. Doxorubicin hydrochloride was adopted as the model drug; after drug loading, gold nanoparticles (5 nm) were connected to block the mesopore through the hydrazone linkage. The hydrazone bond, a typical acid-sensitive bond, could undergo hydrolysis in an acidic environment to induce the release of the capping agent, so that the multifunctional nanocomposite revealed acid-enhanced release performance. What's more, before reaching acid conditions, little premature release was found to take place. Cell experiments were also carried out to reveal the good biocompatibility, fast uptake, and improved toxicity toward HeLa cells. Thus, in association with the magnetic target, the multifunctional nanocomposite shows the potential application for some low-pH tissue-targeted therapy, such as for inflammation and tumors. A pH-responsive and magnetic-targeted drug-delivery system was prepared with a Fe3O4@mesoporous silica core–shell nanostructure as host. Au nanoparticles were used as the capping agent. These were connected to the surface of the mesopore through the hydrazone linkage to restrict the drug release. The system has potential applications in low-pH tissue-targeted therapy.

Posted on 21 November 2014 | 3:20 pm

Two-Photon Absorption Properties of Eu3+-DPA-Triazolyl Complexes and the Derived Silica Nanoparticles Embedding These Complexes

Several complexes and silica-based nanohybrids of rare-earth ions (Eu3+, Gd3+) have been synthesized from dimethyl 4-azidopyridine-2,6-dicarboxylate (4) following the Click chemistry approach. A complete spectroscopic study indicates that such compounds exhibit strong sensitization by the antenna effect from both UV and NIR excitations. The Gd3+-based materials show phosphorescence under ambient conditions, which originates from the lowest-energy intra-ligand triplets. Fine analysis of the NIR excitation spectra using time resolved photoluminescence spectroscopy (TRS) indicates that the spectral repartition of the triplet T1 state differs notably between the complexes and the NPs embedding the complexes. Moreover the dependence of Eu3+ luminescence vs. incident beam power in the NIR region diverges from pure quadratic dependence expected in the framework of the two-photon absorption process. The results are discussed considering the occurrence of a direct singlet-to-triplet optical absorption transition (S0T1) upon NIR excitation. The TRS technique is used at 300 K to analyze the phosphorescence and the NIR excitation spectra of Gd3+-, Eu3+-DPA-triazolyl complexes and derived NPs embedding them. The TPA excitation spectra of the NPs are located on the low-energy side of the phosphorescence spectrum and consist of narrow bands attributed to the S0(0)T1(0–2) pure electronic transition.

Posted on 21 November 2014 | 3:20 pm

Quenching of Fluorescence in Bodipy-Derived Trifluoromethyl Enaminone Ligands upon Coordination to Copper(II)

The synthesis of two trifluoromethyl-derived enaminone ligands, L1H (bidentate) and L2H2, (tridentate), which bear a fluorescent 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (Bodipy) moiety, leads to the preparation and characterization of two CuII complexes {[Cu(L1)2]·2(CH2Cl2) (A) and [Cu4(L2)4]·4(C4H8O2) (B)} that exhibit different architectures. The magnetic properties of the cubane-like complex B evidence a dominant ferromagnetic behavior characterized by exchange coupling constants J1 = +20.56(3) cm–1 and J2 = –10.29(2) cm–1. Indeed, whereas the luminescence properties of the Bodipy-derived trifluoromethyl enaminones L1H and L2H2 are typical of the Bodipy skeleton, the emission is totally quenched in both mononuclear (A) and cubane (B) CuII complexes. To elucidate this quenching phenomenon, the Rehm–Weller equation has been used based on experimental cyclic voltammetry redox potential measurements. The result remains ambiguous for complexes A and B, and the origin of the quenching phenomenon, photoinduced electron transfer (PET) versus energy transfer (Förster or Dexter), cannot be deduced. Syntheses of two derived enaminone ligands bearing a fluorescent 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (Bodipy) moiety lead to two mono- and tetranuclear CuII complexes with redox and magnetic properties, respectively. Whereas the luminescence properties of the ligands are typical of the Bodipy skeleton, the emission is quenched in the complexes.

Posted on 21 November 2014 | 3:20 pm

Graphical Abstract: Eur. J. Inorg. Chem. 33/2014

Posted on 20 November 2014 | 1:19 pm

Investigating the Formation Mechanism of Arene Ruthenium Metallacycles by NMR Spectroscopy

Invited for the cover of this issue is Bruno Therrien from the University of Neuchatel, Switzerland. The cover image uses the analogy of growing a plant in a pot to show the simple mixing of different building blocks in an appropriate solvent, followed by a germination period, before harvesting the resulting metalla-assembly. Studying this “germination period” by NMR spectroscopy has thrown light on the formation mechanism, providing insight for the design of new arene ruthenium metalla-assemblies. These intelligent metalla-cages will allow perfect control over the spatial and temporal release of the guest molecule...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 5651 ff.

Posted on 20 November 2014 | 1:19 pm

Investigating the Formation Mechanism of Arene Ruthenium Metallacycles by NMR Spectroscopy (Eur. J. Inorg. Chem. 33/2014)

The cover picture shows how straightforward the synthesis of arene ruthenium metalla-assemblies is: It consists of mixing different building blocks in an appropriate solvent with a precise stoichiometry, followed by a germination period, before harvesting the resulting metalla-assembly. The germination period, involving assembly-disassembly, self-repairing, and rearrangement of the building blocks, has been studied by NMR spectroscopy. The elucidation of the formation mechanism has given valuable answers for the future design of arene ruthenium metalla-assemblies. Details are discussed in the article by B. Therrien et al. on p. 5651 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 20 November 2014 | 1:19 pm

Masthead: Eur. J. Inorg. Chem. 33/2014

Posted on 20 November 2014 | 1:19 pm

Glycine–Nitrate Process for the Elaboration of Eu3+-Doped Gd2O3 Bimodal Nanoparticles for Biomedical Applications

Monoclinic and cubic europium-doped Gd2O3 structures were selectively synthesized by the glycine–nitrate process by fine control of the synthesis temperature through the crucial fuel/oxidant ratio. The cubic phase is obtained under fuel-rich conditions, whereas stoichiometric conditions induce the simultaneous formation of cubic and monoclinic polymorphs. The samples were subjected to appropriate sintering to obtain highly crystalline and carbon-free materials. The average nanoparticle (NP) size determined by TEM for these nanopowders (23 nm) agrees with the average crystallite sizes obtained from XRD Rietveld analysis; therefore, the particles are monocrystalline. Both electron energy loss spectroscopy (EELS) and photoluminescence studies showed that the europium-doped NPs are highly luminescent, and the Eu3+ ions are homogeneously distributed over the whole material as well as over the two gadolinium crystallographic sites of the cubic phase. These fluorescent NPs exhibit relaxivities that define them as potential T1 contrast agents for further biomedical applications. By fine control of the flame temperature in the glycine–nitrate process, highly crystalline Eu3+-doped and undoped Gd2O3 nanoparticles are obtained. In the doped samples, the Eu3+ ions are homogeneously distributed over the whole material. The Eu:Gd2O3 NPs are highly luminescent and exhibit relaxivities that define them as potential T1 contrast agents for biomedical applications.

Posted on 18 November 2014 | 10:23 am

Lanthanide(III) Nitride Bismuthides M2NBi (M = La–Nd) and Their Potential as Topological Insulators

Four lanthanide(III) nitride bismuthides of the new class M2NBi (M = La–Nd) have been synthesized by the reaction of the respective lanthanide metal (M) with caesium azide (CsN3), elemental bismuth (Bi), the corresponding lanthanide trichloride (MCl3), and caesium chloride (CsCl) as flux in evacuated silica tubes for 7 days at 900 °C. The M2NBi compounds crystallize tetragonally in the space group P4/nmm with Z = 2 with the lattice parameters a = 480.61(4) pm, c = 948.34(9) pm (M = La), a = 475.48(4) pm, c = 938.76(9) pm (M = Ce), a = 471.80(4) pm, c = 929.51(9) pm (M = Pr), and a = 468.13(4), c = 921.08(9) pm (M = Nd). As the main structural feature of the crystal structures, ?2{[NM2]3+} layers of condensed nitride-centered square pyramids of M3+ cations dominate. These pyramids, in which the base is built of (M1)3+ and the top of terminal (M2)3+ cations (t), are connected by all four basal edges (e) to form a two-dimensional network according to ?2{[N(M1)e4/4(M2)t1/1]3+} that is separated by square double layers of Bi3– anions. Both crystallographically independent M3+ cations bear two types of anions (N3– and Bi3–) as ligands. (M1)3+ is coordinated in the shape of a square antiprism by four N3– and four Bi3– anions, and (M2)3+ is surrounded by a distorted octahedron consisting of one N3– and five Bi3– anions. The Bi3– anions reside in capped square antiprisms of nine M3+ cations. The partial density of states (PDOS) and the band structure of La2NBi show that this compound has to be considered as a zero-band-gap semiconductor with a nontrivial topology and a high potential as a topological insulator. Four lanthanide(III) nitride bismuthides of the class M2NBi (M = La–Nd) were synthesized and characterized by X-ray diffraction. All four compounds crystallize tetragonally in the space group P4/nmm and anti-isotypically with KCoO2 or BaNiS2. The partial density of states and the band structure of La2NBi show that this compound has to be considered a zero-band-gap semiconductor.

Posted on 17 November 2014 | 11:10 am

Syntheses, Crystal Structures and Solid-State Properties of the Lanthanoid-Containing Nanoclusters [(Ln2PW10O38)4(W3O8)(OH)4(H2O)2]26–

A series of lanthanoid-substituted polyoxometalates have been synthesized by a self-assembly process in potassium chloride solution by the reaction of dilacunary [P2W19O69(H2O)]14– with mid- and late-lanthanoid Ln(NO3)3·nH2O salts leading to the formation of the tetrameric tungstophosphates [(Ln2PW10O38)4(W3O8)(OH)4(H2O)2]26– [Ln = Y3+ (1), Sm3+ (2), Eu3+ (3), Gd3+ (4), Tb3+ (5), Dy3+ (6), Ho3+ (7), Er3+ (8), Tm3+ (9), Yb3+ (10)]. The polyanions were isolated as potassium or mixed-alkali salts. Most of the compounds were characterized by single-crystal X-ray diffraction and various analytical techniques, such as FTIR, UV/Vis, 31P NMR and photoluminescence spectroscopy, magnetism, as well as thermogravimetric analysis. The FTIR spectra suggest that all the compounds are isomorphous. The crystal structures of these complexes consist of four A-[?-PW10O36]7– units, each incorporating two LnIII ions to create four Keggin-like anions that further assemble with three additional tungstate units to form a tetramer species with C2 symmetry. The photoluminescent properties of 3a and 6a were investigated following photoexcitation at room temperature. The magnetic properties of 3a, 4a, 5a and 6a were investigated at room temperature, the complexes exhibiting paramagnetic behaviour. Ten tetrameric lanthanoid-containing polytungstate nanoclusters [(Ln2PW10O38)4(W3O8)(OH)4(H2O)2]26– (Ln = Y3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+) have been synthesized in a one-pot reaction in aqueous KCl and structurally characterized in the solid state. Their photoluminescence and magnetic properties were studied at room temperature.

Posted on 14 November 2014 | 1:23 pm

ZrIV Coordination Polymers Based on a Naturally Occurring Phenolic Derivative

The reactivity under solvothermal conditions of the ZrIV ion with the naturally occurring gallic acid ligand has been evaluated in depth. The study led to the isolation of four microcrystalline hydroxycarboxylate-based coordination polymers (MIL-151 to -154). Through the use of a combination of solid-state NMR and high-resolution X-ray powder diffraction analyses, the structures of two of these phases (MIL-153, MIL-154) were solved. In both cases, the gallol motifs favour the formation of rod-like inorganic units built up from ZrO8 polyhedra. Although one compound (MIL-151) was found to be microporous (SBET ? 470 m2?g–1), its poor crystallinity prevented comprehensive structural analysis. Nevertheless, a comparison of its physicochemical features with those of the fully characterized solids allows a plausible structural model to be proposed. An investigation into the reactivity of carboxyphenolic gallic acid with the ZrIV ion led to the isolation of four microcrystalline solids, amongst which one was found to be microporous. Such ligand/cation pairing strongly favours the formation of chain-like inorganic motifs.

Posted on 14 November 2014 | 1:23 pm

Highly Stable Complexes of Divalent Metal Ions (Mg2+, Ca2+, Cu2+, Zn2+, Cd2+, and Pb2+) with a Dota-Like Ligand Containing a Picolinate Pendant

The stability constants of complexes of the macrocyclic ligand do3a-pic4– (H4do3a-pic = 2,2?,2?-{10-[(6-carboxypyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triyl}triacetic acid) with several divalent metal ions (Pb2+, Cd2+, Zn2+, Cu2+, Ca2+, and Mg2+) have been determined by using pH-potentiometric titrations (I = 0.1 M KCl, 25 °C). The stability of these complexes follows the trend Cu2+?> Cd2+???Pb2+???Zn2+?>>?Ca2+?>>?Mg2+. A particularly high stability constant has been determined for the Cu2+ complex [log?KCuL = 23.20(4)]. Analysis of the titration curves indicate the presence of protonated forms of the complexes in solution, with protonation constants of log?KM(HxL) = 6.9–2.0 (x = 1, 2, or 3). The structure of the complexes in solution has been investigated by using 1H and 13C NMR spectroscopy and DFT calculations performed in aqueous solution at the TPSSh/6-31G(d) level. In the case of the Pb2+ and Cd2+ complexes, relativistic effects were considered with the use of relativistic effective core potentials. Calculations show that the complexes with the largest metal ions (Pb2+ and Ca2+) are nine-coordinate, with their coordination polyhedra being best described as capped twisted square antiprisms. The Cd2+ and Mg2+ complexes are seven-coordinate, with the metal ions being bound to the four nitrogen atoms of the cyclen unit and the three acetate pendant arms. Finally, in the Cu2+ and Zn2+ complexes, the metal ions are six-coordinated, with the metal ions being asymmetrically placed inside the macrocyclic cavity of the ligand, and the coordination polyhedra can be described as an octahedron and a trigonal prism, respectively. A detailed study of the thermodynamic stability of complexes formed by divalent metal ions with a macrocyclic ligand containing a picolinate arm is reported. The complexes of Cu2+, Zn2+, Cd2+, and Pb2+ present high stability constants [log?KML?> 20]. DFT calculations and NMR spectroscopy point to variable coordination numbers and geometries for this series of metal complexes.

Posted on 13 November 2014 | 2:10 pm

Tuning the Morphology of GeS2 Hybrid Materials Using Ionic Liquids as Structuring Agents

Control of the surface chemistry and morphology of chalcogenide materials, which are highly polarizable, is a very interesting challenge as it might lead to breakthroughs in various fields such as electrochemistry, catalysis, and gas-phase separation. With this in mind, a new approach to synthesize structured Ge-based chalcogenide products has been investigated. It involves the use of tetraethoxygermanium (TEOG) and thioacetamide with an ionic liquid (IL) as structuring agent. This innovative synthesis process has two main advantages: it is performed under soft conditions, and it also enables the morphological control of the obtained hybrid organic–GeS2 particles. In the absence of the IL, the synthesis leads to an agglomeration of nanospheres, whereas the introduction of the ionic liquid leads either to microspheres or to gypsum rosette-like particles. It has been clearly highlighted that the morphology of the hybrid organic–GeS2 particles strongly depended on the nature of the cationic part of the IL. Hybrid organic–GeS2 particles, the morphology of which depended upon the cationic part of an ionic liquid that was added as structuring agent, were prepared by means of an innovative nonhydrolytic soft-chemistry route at room temperature at atmospheric pressure.

Posted on 13 November 2014 | 1:30 pm

Molecular Mechanisms of [Bi6O4(OH)4](NO3)6 Precursor Activation, Agglomeration, and Ripening towards Bismuth Oxide Nuclei

Molecular dynamics simulations have been employed to characterize the role of [Bi6O4(OH)4](NO3)6 cage structures in DMSO solution as precursors to larger bismuth oxide aggregates. We find that the nitrate ions play a twofold role: (i) the association of [Bi6O4(OH)4](NO3)6 clusters – which are fully coordinated by six nitrate ligands – is electrostatically disfavored giving rise to stable [Bi6O4(OH)4](NO3)6 solutions; (ii) in contrast, the dissociation of a single nitrate ligand results in attractive cluster–cluster interactions. This results in the formation of oligomers, which are initially bridged by one to three nitrate ions, but then form Bi–O contacts by sharing common edges and faces and eventually ripen into nuclei of bismuth oxide. Strikingly, this process may be induced by a single activated species, the [Bi6O4(OH)4](NO3)5+ cluster, which may bind several [Bi6O4(OH)4](NO3)6 clusters. Molecular dynamics simulations unravel the early steps of bismuth oxide precursor association and ripening into larger aggregates. Nitrate ions play a twofold role in the process by preventing the association of Bi6O4(OH)4(NO3)6 clusters but at the same time inducing the formation of oligomers comprising under-coordinated Bi ions.

Posted on 13 November 2014 | 1:30 pm

Possible Roles of the Spatial Distribution of Organic Guest Species in Mesoporous Silicas to Control the Properties of the Hybrids

Mesoporous silicas are promising materials for the construction of host–guest hybrids by the accommodation of functional unit/guest species into the mesopore, and moreover, by hierarchical assembly with controlled location, density, and orientation. Precisely designed structures open up the versatile functions of mesoporous silicas and their host–guest systems. In this microreview, the spatial distribution (location, density, and orientation) of the organic functional units/guest species in mesoporous silicas (mainly one-dimensional cylindrical) is discussed to highlight the present status of the host–guest chemistry of mesoporous silicas. The spatial distribution (location, density, and orientation) of the functional units (guest species) attached/included on/in mesoporous silicas are discussed to highlight the status of the host–guest chemistry of mesoporous silicas.

Posted on 12 November 2014 | 12:40 pm

Oxidation of Alkylbenzenes with Cerium Complexes Containing a Tripodal Oxygen Ligand

The treatment of [Ce(LOEt)2(NO3)2] (LOEt– = [Co(?5-C5H5){P(O)(OEt)2}3]–) with KMnO4 in water afforded a diamagnetic purple solid 1, which is tentatively formulated as a CeIV permanganate complex, “[Ce(LOEt)2(MnO4)2]”. The ZrIV analogue, [Zr(LOEt)2(MnO4)2] (2), has been prepared similarly from [Zr(LOEt)2(NO3)2] and KMnO4. The recrystallization of 1 from CH2Cl2/hexanes at –18 °C led to the isolation of dinuclear [(CeLOEt)2(?-LOEt?)2][MnO4]2 (3), which contains the dianionic tripodal ligand [LOEt?]2– ([(?5-C5H5)Co{P(O)(OEt)2}2{P(O)2(OEt)}]2–). The reactions of 1 with K[ReO4] and [NH4][OsO3N] afforded the heterodimetallic complexes [Ce(LOEt)2(ReO4)2] (4) and [Ce(LOEt)2(NOsO3)2] (5), respectively. The crystal structures of 3 and 5 have been determined. Freshly prepared 1 can oxidize alkylbenzenes such as toluene, ethylbenzene, and cumene at room temperature to give the corresponding ketone and/or alcohol products. Ce–LOEt complexes are efficient promoters of the aerobic oxidation of alkylbenzenes by a radical mechanism. For example, cumene in the presence of [Ce(LOEt)2(H2O)2]Cl (1 mM) in air at 100 °C for 10 h afforded a ca. 6:1 mixture of 2-phenyl-2-propanol and acetophenone with a total turnover number of 6810. The treatment of [Ce(LOEt)2(NO3)2] (LOEt– = [Co(?5-C5H5){P(O)(OEt)2}3]–) with KMnO4 affords a diamagnetic purple solid tentatively formulated as “[Ce(LOEt)2(MnO4)2]” that can oxidize alkylbenzenes at room temperature. The Os analogue [Ce(LOEt)2(NOsO3)2] has been synthesized and structurally characterized. Ce–LOEt complexes promote the aerobic oxidation of alkylbenzenes by a free radical mechanism.

Posted on 12 November 2014 | 12:40 pm

Controlled Linker Dependence of Solution- and Solid-State Emission of Vaulted trans-Bis(salicylaldiminato)platinum(II) Complexes with Amino Functionalities

The synthesis, structures, and emission properties of vaulted trans-bis(salicylaldiminato)platinum(II) complexes 1 with diethylamino functionalities are described and compared with the non-substituted analogues. The amino substitution provides an improvement of the linker dependence both for the color change of the trans-bis(salicylaldiminato)platinum(II) platform in the glass state and for the acid-induced emission enhancement in the solution state. The linker dependence of the crystalline-state emission intensity changes with the amino functionality, which leads to intense emission of the vaulted crystals with low structural dependence. Single-crystal X-ray diffraction studies and DFT calculations revealed that the unique photophysical properties arising from the amino functionality are attributable to enhanced planarity and self-constraint of the coordination platform, which is due to their strong contribution to d–? conjugation and intermolecular hydrogen bonding. Amino substitution provides an improvement of the linker dependence of both the color change of the trans-bis(salicylaldiminato) PtII platform in the glass state and the acid-induced emission enhancement in the solution state. The linker dependence of the solid-state emission intensity changes with the amino functionality and leads to intense emission of the vaulted crystals.

Posted on 12 November 2014 | 12:40 pm

A Copper Complex of a Noninnocent Iminophenol-Amidopyridine Hybrid Ligand: Synthesis, Characterization, and Aerobic Alcohol Oxidation

Reaction of the noninnocent iminophenol-iminopyridine hybrid ligand HLIPIP, where LIPIP denotes [2-((E)-{(E)-2-[(E)-pyridin-2-ylmethyleneamino]benzylidene}amino)-4,6-di-tert-butylphenolate], with copper acetate afforded a copper complex, LAPIPCuII, in which one of the imine functional groups is oxidized to an amide during metal complexation. The new CuII complex is capable of catalyzing efficient aerobic alcohol oxidation under mild conditions. The crystal structure of LAPIPCuII exhibits a square-planar geometry with the CuII center coordinated by three nitrogen atoms and one oxygen atom. Electrochemical studies were conducted to evaluate the redox-active behavior of the complex, and the results showed a quasireversible reduction and a ligand-based oxidation process. The neutral species of LAPIPCuII is EPR active, which is consistent with a paramagnetic electronic ground state (d9, S = 1/2), whereas the one-electron oxidized complex was X-band EPR silent. One-electron chemical oxidation of LAPIPCuII gave a new species that can be attributed to a CuII-phenoxyl radical complex. Based on EPR measurements in conjunction with density functional theory calculations, [LAPIPCuII]+ is proposed to have a triplet electronic ground state, exhibiting a weak ferromagnetic interaction between the CuII center and the coordinated phenoxyl radical. A new copper complex of a noninnocent iminophenol-pyridine hybrid ligand that is capable of efficient aerobic alcohol oxidation was studied.

Posted on 12 November 2014 | 12:40 pm

Synthesis of Advanced Nanoreinforced Polyurethane with Thiolene Photografted Organo-Modified Layered Double Hydroxide

New bionanocomposites with strongly intertwined structures based on polyurethane and layered double hydroxides (LDH) were obtained by using two different intermolecular thiolene coupling strategies in which the modification of LDH with oleic acid was either performed first and then followed by the thiolene photografting using 2-mercaptoethanol, or the initial thiolene photografted oleic acid/2-mercaptoethanol product was subsequently used to modify the LDH platelets. The resultant photografted oleate/LDH was condensed with diisocyanate and the addition of poly(ethyleneglycol) yielded a final hybrid polymer. The interleaved LDH materials were characterized by X-ray diffraction and thermogravimetric analysis, underlining the possible commutative steps between photografting and organo-modification processes. The resultant polyurethanes were characterized by FTIR spectroscopy, nuclear magnetic resonance, differential scanning calorimetry and rheology. Furthermore, the durability of the resultant polymers was assessed by photo-FTIR. The results showed that strongly intermingled polyurethanes were processed by both strategies. Enhanced mechanical properties as well as more prolonged durability were found after anchoring LDH sheets and this was even more amplified when using the photografted acid direct intercalation into the LDH during the first synthesis step. Successive processes to yield layered double hydroxide filled polyurethane nanocomposite including (1) organo-modification of LDH platelets, (2) functionalization using UV thiolene coupling and (3) monomer addition.

Posted on 12 November 2014 | 12:40 pm

Super-Reduced Mechanism of Nitric Oxide Reduction in Flavo-Diiron NO Reductases

Flavo-diiron nitric oxide reductases (FNORs) are non-haem diiron proteins that protect anaerobic organisms against toxic nitric oxide by reducing it to nitrous oxide. The exact mechanism by which these enzymes operate is still unclear. Recent experimental evidence favors the diiron-dinitrosyl mechanism involving [{FeNO}7]2 as a reactive intermediate in contrast to the previously suggested diiron-mononitrosyl pathway. In this work a computational study of the diiron-dinitrosyl, or the super-reduced, mechanism has been undertaken and the key reactive intermediates have been identified. The two-electron reduction of [{FeNO}7]2 to form [{FeNO}8]2 is confirmed as a key step for initiating the mechanism and leads to the instant formation of a hyponitrite adduct. The energy requirements for the formation of the intermediates competes well with the mono-nitrosyl mechanism. This study provides an insight and a step forward towards gaining a better understanding of the mechanism of NO reduction by FNORs. We have investigated the super-reduced mechanism of nitric oxide reduction by flavo-diiron nitric oxide reductases, a favorable alternative to the previously proposed mono-nitrosyl mechanism. The two-electron reduction of [{FeNO}7]2 to [{FeNO}8]2 is proposed to initiate the reaction whereas N–O cleavage of the hyponitrite formed to yield nitrous oxide is suggested to be the rate-limiting step.

Posted on 12 November 2014 | 12:30 pm

Hybrid Polymer Electrolytes Based on a Poly(vinyl alcohol)/Poly(acrylic acid) Blend and a Pyrrolidinium-Based Ionic Liquid for Lithium-Ion Batteries

Polymer blends of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were prepared with different molar ratios by a solvent-casting technique. The XRD patterns of the blends show that the degree of crystallinity of the PVA membranes decreases with the addition of PAA owing to the formation of interpenetrating polymer chains. The vibrational spectra of the blend membranes reveal the formation of strong hydrogen bonding between PVA and PAA. Dynamic mechanical analysis (DMA) reveals that the storage modulus of a 25 mol-% PAA sample is comparable to that of pure PVA and, therefore, confirms the mechanical stability of the blend membranes. Significant changes in the peak areas and chemical shifts of the PVA hydroxyl signal (? = 4–5 ppm) in the 1H NMR spectra of the blend membranes confirm the strong hydrogen bonding between the OH groups of PVA and PAA. The ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) with 0.2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to the polymer blend to prepare flexible, nonvolatile hybrid polymer electrolytes for lithium-ion batteries. A maximum ionic conductivity of 1 mS?cm–1 is observed at 90 °C for the membrane with 70 mol-% IL. Mechanically stable polymer membranes for lithium-ion batteries consist of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI) doped with 0.2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

Posted on 11 November 2014 | 2:10 pm

Unusual Crystal Packing in a Family of [Fe{2,6-bis(pyrazol-3-yl)pyridine}2]2+ Compounds and the Effect on the Occurrence of Spin Crossover and Its Cooperative Character

The crucial relationship between the spin-crossover (SCO) phenomenon and the crystal lattice can be investigated by tuning the intermolecular interactions of a complex with little change to the electronic environment of the metal. With this aim, the synthesis of the new ligand 2,6-bis[5-(naphth-2-yl)-pyrazol-3-yl]pyridine (H2L) and four different forms (1–4) of the corresponding [Fe(H2L)2]2+ complex cation are presented. H2L exhibits an increased number of aromatic rings with respect to previous analogues to augment the density of ?···? contacts within the system. The four compounds group into three different structural arrangements that coincide with two different SCO behaviour types and a locked high-spin state. The intermolecular interactions that embody the various crystallographic organisations have been analysed through Hirshfeld plots, and the SCO properties of 1–4 are also discussed in light of the local structural analysis around the FeII centres. The enhanced aromaticity of a naphthyl-substituted 2,6-di(pyrazol-3-yl)pyridine-type (3bpp-type) ligand (H2L) is explored in the preparation of four [FeIIL2]X2 compounds with three different crystal packing modes that lead to three spin-crossover (SCO) patterns.

Posted on 10 November 2014 | 1:30 pm

Synthesis and Characterization of Diaminobisfuroxane

The synthesis of 3,3?-diamino-4,4?-bisfuroxane and its isomer 4,4?-diamino-3,3?-bisfuroxane was explored for the first time. In addition, the structure of highly dense (2.007 g?cm–3 at 100 K) and energetic 4,4?-dinitro-3,3?-bisfuroxane was determined. The energetic properties of the compounds, including their thermal behavior and sensitivities, were determined, and their heat of formation and explosive properties were calculated. The two isomers of diaminobisfuroxane are isolated and characterized for the first time. The crystal structure of the very dense and energetic CNO compound 4,4?-dinitro-3,3?-bisfuroxane is determined.

Posted on 7 November 2014 | 12:10 pm

Synthesis and Biological Activity of Gold(I) N-Heterocyclic Carbene Complexes with Long Aliphatic Side Chains

Seven imidazolium salts have been synthesized from octadecylimidazole (Im18). These salts differ in the length of the alkyl chain length bound to the second nitrogen atom of the imidazolium ring [R = Me, Et, iPr, Pr, Bu, decyl (Dec), octadecyl] and were used as synthetic precursors to obtain two series of gold(I) carbene complexes (AuNHC). The first series contains one labile ligand at the second coordinative position {monocarbene, [AuCl(NHC)]}, and the second one comprises dicarbene complexes. Their biological activity has been evaluated with respect to two different cell lines, and thioredoxin reductase (TrxR) inhibition has also been evaluated for selected examples. Distinct effects have been observed for the imidazolium salts and monocarbene derivatives. The syntheses of a series of imidazolium salts and mono- and dicarbene gold(I) complexes are reported together with a study of their cytotoxicity and inhibition of the thioredoxin reductase enzyme.

Posted on 7 November 2014 | 12:10 pm

3d Metal Complexes Supported by a Bis(imidazolin-2-imino)pyridine Pincer Ligand – Synthesis, Structural Characterisation, and Magnetic Properties

The coordination chemistry of the tridentate pincer ligand TLtBu, which contains two electron-rich imidazolin-2-imine moieties, has been explored. The reaction of TLtBu with metal dihalides gave complexes of the general formula [(TLtBu)MX2] (M = Mn, Fe, Co, Ni; X = Cl, Br). These complexes were characterized by X-ray diffraction analysis, which showed them to have different geometries in the solid state. Although [(TLtBu)MnCl2] (1) is best described as distorted square-pyramidal, the complexes [(TLtBu)FeCl2] (2) and [(TLtBu)CoCl2] (3) show distorted tetrahedral geometries with the TLtBu ligand bound in a ?2 fashion and one of its imidazolin-2-imine fragments not coordinated to the metal atom. [(TLtBu)NiBr]Br (4) crystallizes with a slightly distorted square-planar cation. The reaction of the triflate (OTf) salts [M(OTf)2·nMeCN] (M = Mn, n = 1; M = Fe, Co, n = 2; OTf = CF3SO3) with TLtBu resulted in [(TLtBu)M(OTf)][OTf] (M = Mn, 5; M = Fe, 6) and [(TLtBu)Co(NCMe)][OTf]2 (7). Complexes 6 and 7 were characterized by X-ray diffraction analysis, and both showed distorted square-planar geometries. Magnetic measurements of 5, 6 and 7 showed them to possess a S = 5/2, 2 and 1/2 ground states, respectively. The bromide ions in complex 4 were exchanged by reaction with AgBF4 to afford [(TLtBu)Ni(NCMe)][BF4]2 (8), which showed a distorted square-planar geometry in the solid state. The reactions of 1 and 6 with AgOTf resulted in the oxidation of the complexes and the formation of [(TLtBu)MnCl(OTf)][OTf] (9) and [(TLtBu)Fe(OTf)2][OTf] (10), respectively. Complexes 9 and 10 both display distorted square-pyramidal geometries in the solid state. The ground state of 10 was found to be S = 5/2 by superconducting quantum interference device (SQUID) magnetometry measurements. The oxidation of 5, 6 and 7 with the iodosobenzene derivative (tBuSO2)C6H4IO was investigated. Although the reactions of 6 and 7 gave no evidence for the formation of transient oxo species, crystals were obtained from the reaction of 5. These crystals showed the formation of [TLtBu*Mn(OH)](OTf)2 (11), in which one of the tBu groups of the TLtBu ligand has undergone a C–H activation by a putative MnIV=O bond. The complex shows a distorted square-pyramidal geometry in the solid state, and the carbon atom of the CH-activated tBu group occupies the apical position. The coordination chemistry of the tridentate pincer ligand TLtBu, which contains a bridging pyridine moiety and two electron-rich imidazolin-2-imine moieties, is explored. The TLtBu ligand strongly favours square-planar geometries. The FeII complex [(TLtBu)Fe(OTf)][OTf] contains a cation with an unusual high-spin (S = 2) electronic ground state.

Posted on 7 November 2014 | 12:10 pm

Mechanistic Insights into Phenol Oxidation by a Copper(II) Complex of a Pyridine- and Amide-Containing Copolymer in an Aqueous Medium

A CuII complex of a pyridine- and amide-containing copolymer (Cu-P1) exhibits effective activity toward phenol hydroxylation in 50?% aqueous methanol solution at apparent pH 8.0 and 25 °C. The complex shows significant first-order rate accelerations of 4.2?×?105 and 1.4?×?105 relative to phenol autoxidation in air and in the presence of 20 mM H2O2, respectively. The reaction mechanisms with H2O2 and air are different on the basis of (a) the different activity profiles for Cu binding, (b) the different deuterium kinetic isotope effects (2.8 in 20 mM H2O2 and 1.2 aerobically), and (c) the formation of a dinuclear substrate–(Cu-P1) complex with H2O2 but a mononuclear one aerobically. The mechanism in the presence of H2O2 is consistent with that of the type-3 dicopper tyrosinase. Although oxidized di-CuII tyrosinase can only use H2O2 for phenol hydroxylation, CuII-P1 can use either air or H2O2 for this process. The studies herein introduce a versatile chemical system for the further exploration of Cu–oxygen chemistry and other types of metal-centered chemistry and for the aerobic degradation of aromatic compounds in environmental and green chemistry. A CuII complex of a pyridine- and amide-containing copolymer catalyzes phenol hydroxylation/oxidation in aqueous methanol at pH 8.0 and 25 °C. First-order rate accelerations by factors of 4.2?×?105 and 1.4?×?105 and deuterium kinetic isotope effects of 2.8 and 1.2, respectively, were observed with and without H2O2. The results suggest that different mechanisms apply for oxidation by O2 and H2O2.

Posted on 7 November 2014 | 11:40 am

Low Activation Barriers in N2 Reduction with H2 at Ruthenium Pincer Complexes Induced by Ligand Cooperativity: A Computational Study

The catalytic reduction of dinitrogen (N2) with dihydrogen (H2) was investigated by means of DFT calculations [MN12-L/def2-TZVP(ECP)] using ruthenium pincer complexes of the general formula [Ru{4,6-bis(di-tert-butylphosphanyl)dibenzo[b,d]furan}(H)(X)] (X = H, Me, iPr, Br, I). One tBu group of one of the two phosphorus atoms was augmented with a CH2BH2 group to introduce a borane moiety that is needed for the cooperative stabilization of intermediates and transition states. By optimizing a representative amount of local minima and transition states, it was possible to identify closed catalytic cycles that show surprisingly low activation barriers. As an example, for X = Me after reoptimization in the solvent phase (toluene), transition states with a maximum height in the energy profile of only 36.2 kcal?mol–1 were obtained and with the largest single barrier of 29.2 kcal?mol–1! It was also observed that the stabilities of amide complexes, which occur late in the catalytic cycle, are very pronounced. Accordingly, they contribute to the overall energy span (ES) in an unfavourable way. However, despite this fact, the calculated ES in the solvent phase for X = I amounts to only 48.4 kcal?mol–1 and indicates clearly that the computationally guided design process of the catalyst is a suitable approach to identify elements of a catalyst structure that enables hydrogen-transfer processes with comparatively low barriers. Ligand cooperativity induced by borane side arms in ruthenium pincer complexes help stabilize local minima and transition states in N2/H2 reduction chemistry and leads to comparatively low activation barriers.

Posted on 7 November 2014 | 11:40 am

One-Step Synthesis and Polyacrylic Acid Functionalization of Multifunctional Europium-Doped NaGdF4 Nanoparticles with Selected Size for Optical and MRI Imaging

Multifunctional Eu:NaGdF4 nanospheres functionalized with polyacrylic acid (PAA) polymer have been prepared for the first time by a simple one-pot method that consists of a homogeneous precipitation reaction at 120 °C. The size of the nanospheres, which were polycrystalline and crystallized into a hexagonal structure, could be altered in the 60–95 nm range by adjusting the amount of polyacrylic acid added. The effects of Eu content and particle size of these nanomaterials on their optical properties (emission intensity and lifetime) as well as on their relaxivity (r1 and r2) values were also analyzed to find the optimum system for optical bioimaging and as a positive contrast agent for magnetic resonance imaging (MRI) applications. Finally, such optimum nanoparticles showed negligible cytotoxicity for Vero cells for concentrations up to 0.5 mg?mL–1 and a high colloidal stability in 2-morpholinoethanesulfonic acid solutions, thereby satisfying the most important requirements for their use in biotechnological applications. Multifunctional Eu:NaGdF4 nanospheres functionalized with polyacrylic acid and tunable sizes in the 95–60 nm range have been synthesized by a one-pot procedure. These nanoparticles presented red luminescence when excited with ultraviolet light, and the smaller nanospheres showed great potential as a positive contrast agent for magnetic resonance imaging.

Posted on 6 November 2014 | 9:33 am

Nitrogen-Rich Energetic Salts of Bis-Heterocycle-Substituted 1,2,3-Triazole (HTANFT)

Energetic salts based on bis-heterocycle-substituted 1,2,3-triazole (HTANFT) were synthesized and characterized by 1H and 13C NMR spectroscopy, infrared spectroscopy, and elemental analysis. The crystal structure of neutral HTANFT (4) was confirmed through single-crystal X-ray diffraction. The density of 4 and its salts ranged from 1.60 to 1.83 g?cm–3, their nitrogen contents ranged from 56.4 to 65.2?% and their decomposition temperatures ranged between 187 and 236 °C. The determined sensitivities towards impact, friction and electrostatic discharge suggest that all salts are much less sensitive than 1,3,5-trinitro-1,3,5-triazinane (RDX). Moreover, the detonation pressures and velocities were calculated to be 24.6 to 32.9 GPa and 7956 to 8757 m?s–1, respectively. Therefore salts 9, 11 and 12 are potential alternatives to RDX in explosive applications. Energetic salts based on bis-heterocycle-substituted 1,2,3-triazole (HTANFT) exhibit high density, good thermal stability and low impact sensitivity. In particular, the hydrazinium, 3,4,5-triamino-1,2,4-triazolium and hydroxylammonium salts that display excellent detonation performances are potential alternatives to 1,3,5-trinitro-1,3,5-triazinane (RDX).

Posted on 6 November 2014 | 9:33 am

Na2(smbipy) – A Bipyridine-Derived Ligand with Chelating Sulfonate Tags and Its 3d Metal Complexes

The sulfonated bipyridine derivative disodium 6,6?-bis(sulfonatomethyl)-2,2?-bipyridine [Na2(smbipy)] was synthesized, and its complexation behaviour towards divalent 3d metals in aqueous solution was explored. The complexes of late 3d metals [M(smbipy)(H2O)2]·H2O (M = Co, Ni, Zn) and [Cu(smbipy)(H2O)] are sparingly soluble in water, and their crystal structures show fourfold equatorial coordination (?4N,N?,O,O?) of the smbipy ligand. Ammonia-rich solutions of the NiII and CuII aqua complexes yield the decomplexation products [Ni(NH3)6](smbipy), [Ni(NH3)5(H2O)](smbipy) and [Cu(NH3)4](smbipy)·2H2O. Buffered solutions with a reduced ammonia content lead to [Ni(smbipy)(NH3)2] and [Cu(smbipy)(NH3)3]·2H2O, and the latter shows twofold coordination of the smbipy ligand through the nitrogen atoms only (?2N,N?). When nearly quantitative amounts of ammonia are applied, two closely related complexes with the core motif [(smbipy)Cu(?-OH)2Cu] form. Crystal structures of all complexes were obtained, and their features are discussed. The sulfonated bipyridine ligand disodium 6,6?-bis(sulfonatomethyl)-2,2?-bipyridine [Na2(smbipy)] shows pronounced chelating behaviour of the sulfonate tags towards CoII, NiII, CuII and ZnII ions in aqueous solution. In the presence of ammonia, sequential decomplexation enables the isolation of a nitrogen-only-ligated smbipy–copper complex.

Posted on 6 November 2014 | 9:33 am

Hydrolytic Stability and Hydrogen Peroxide Activation of Zirconium-Based Oxoclusters

The hydrolytic stability of [Zr6(OH)4O4{O(O)CC(CH3)=CH2}12] (Zr6), and [Zr6O4(OH)4{O(O)CCH2CH=CH2}12]2·6[CH2=CHCH2C(O)OH] (Zr12) oxoclusters in different environments was thoroughly investigated by FTIR, Raman, and X-ray photoelectron spectroscopy (XPS). Specific information about the local structures around the Zr centers during the stability tests was achieved by in situ extended X-ray absorption fine structure (EXAFS) measurements, and the exact compositions were determined by inductively coupled plasma MS (ICP-MS) and elemental analysis. By this multidimensional spectroscopic approach, an overview on the structures formed after different treatments could be gained. The stability of the oxoclusters was then investigated in the presence of hydrogen peroxide, and the formation of peroxo–metal complexes was detected. Thus, a kinetic study was performed in acetonitrile to evaluate the performances of the oxoclusters as oxygen transfer catalysts. The oxidation of methyl p-tolyl sulfide to the corresponding sulfoxide and sulfone was chosen as a model reaction; in some cases, an interesting selectivity towards the formation of the sulfone was found over more than 4700 catalytic cycles. The hydrolytic stability and reactivity of Zr6 and Zr12 oxoclusters are investigated by FTIR, Raman, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The clusters are stable in water at neutral pH, and peroxo complexes are detected in the presence of hydrogen peroxide. A kinetic study highlights the catalytic potential of the clusters for the oxidation of methyl p-tolyl sulfide.

Posted on 6 November 2014 | 9:33 am

Complexes of Copper(I) Thiocyanate with Monodentate Phosphine and Pyridine Ligands and the P(,N)-Donor Diphenyl(2-pyridyl)phosphine

Copper(I) thiocyanate derivatives were prepared by the reaction of CuNCS with pyridine (py) and tertiary monophosphine ligands [PR3 in general; in detail: PPh3, triphenylphosphine, P(4-FPh)3, tris(4-fluorophenyl)phosphine)], as well as the potentially bidentate ligand diphenyl(2-pyridyl)phosphine (PPh2py). Mechanochemical methods were used in some cases to investigate stoichieometries that were not easily accessible by conventional solution syntheses. Three forms of the resulting adducts of CuNCS/PR3/py-base (1:3–n:n) stoichiometry?all containing four-coordinate copper(I) atoms and monodentate N-thiocyanate groups?were confirmed crystallographically. Mononuclear arrays are defined for [(PPh2py)3–n(py)nCuNCS], n = 0, 1, 2, the monodentate thiocyanate being N-coordinated in all; two polymorphs are observed for the n = 2 complex, both crystallizing in monoclinic P21 (Z = 2) cells with similar cell dimensions, but with aromatic components eclipsed about the Cu–P bond in the PPh3 complex, and staggered in the PPh2py complex. Bridging thiocyanate groups are found in the 1:1:1 CuNCS/PPh2py/2-methylpyridine (mpy) and P(4-FPh)3/mpy complexes, wherein centrosymmetric dimers with eight-membered central rings are obtained: [(R3P)(mpy)Cu(NCS)2Cu(PR3)(mpy)], as is also the case in the parent 1:2 CuNCS/PPh2py adduct [(pyPh2P)2Cu(NCS)2Cu(PPh2py)2]. For the 1:1:1 CuNCS/P(4-FPh)3/py and PPh3/Brmpy (Brmpy = 3-bromo-4-methylpyridine) adducts, and, likely, CuNCS/PPh2py/py (1:1:1), single-stranded polymers of the form [···Cu(NCS)(PR3)(py-base)(Cu)···](?|?) with linearly bridging NCS ligands were obtained. Some derivatives, representative of all forms, display medium to strong green to blue luminescence when excited with radiation at 365 nm. The 31P CPMAS NMR spectroscopic data clearly differentiate the inequivalent phosphorus positions within each system, showing a wide range of 1J(31P,63/65Cu) values ranging from 965 Hz for [Cu(NCS)(PPh2py)3] to 1540 Hz for dimeric [(4-FPh)3P(mpy)Cu(NCS)2Cu(P(4-FPh)3)(mpy)], reflecting the large variations in the Cu–P bond length. Mononuclear [(PR3)xCuSCN(py)2], dinuclear [{(PR3)CuSCN(py)}2], and single-stranded polymers of the form [···Cu(PR3)(py-base)(SCN)Cu···] were synthesized and have been characterized by IR spectroscopy, single-crystal X-ray diffraction and 31P CPMAS NMR spectroscopic studies.

Posted on 6 November 2014 | 9:33 am

One- versus Two-Electron Oxidation of Complexed Guanidino-Functionalized Aromatic Compounds

Herein, we report a rational synthetic access to dinuclear CuII complexes with radical monocationic guanidine ligands. The starting point was the first directed synthesis of a dinuclear CuII complex of the redox-active, neutral guanidino-functionalized aromatic (GFA) compound 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1) as ligand by treatment of 1 with Cu(OAc)2. The neutral complex [1{Cu(OAc)2}2] was then oxidized with several oxidizing reagents. With I2 two-electron oxidation occurred, thus leading to green salts of the dication [1{Cu(OAc)2}2]2+. In contrast, with AgPF6 or AgSbF6 one-electron oxidation was observed to yield red salts of the monocation [1{Cu(OAc)2}2]+, which is a three-spin system with one unpaired electron at each copper atom and at the ligand unit. Superconducting quantum interference device (SQUID) magnetometric measurements confirm a quartet electronic ground state that arises from strong ferromagnetic copper–ligand coupling. Intense charge-transfer transitions in the visible region (576 and 536 nm) were observed in the electronic absorption spectra and assigned to strong ligand–ligand (1·+OAc) charge-transfer (LLCT) excitations. These LLCT bands open up the possibility of photoinduced redox reactions with [1{Cu(OAc)2}2]+ driven by restoration of the aromatic system at the GFA ligand. One-electron oxidation of a neutral dicationic CuII complex with a redox-active guanidine ligand leads to red salts of the monocationic complex with a high-spin (quartet) electronic ground state and strong ligand–ligand charge-transfer transitions.

Posted on 6 November 2014 | 9:33 am

Tris(borane) Adducts of Diphosphanylmethanides: The [H3BCH(PPh2BH3)2]– Anion and Its Alkali Metal Complexes

The reactivity of lithium complexes that contain the borane-modified diphoshanylmethanide ligand [CH(PPh2BH3)2]– towards different Lewis base adducts of BH3 was studied to gain further insight into the mechanism of the isomerization of this derivative, which formally proceeds through a shift of one BH3 group from the phosphorus atom to the carbon atom. Whereas the use of BH3·THF in THF only resulted in the thf adduct of the starting material, [Li{CH(PPh2BH3)2}(thf)2] (1), the application of BH3·SMe2 in toluene resulted in the formation of the novel compound [(Li{H3BCH(PPh2BH3)2})?] (2). The subsequent addition of ethereal ligands led to the isolation of [Li{H3BCH(PPh2BH3)2}(Me4thf)] (3) and [Li{H3BCH(PPh2BH3)2}(thf)3] (4). Treatment of these complexes with stronger Lewis bases such as N,N,N?,N?-tetramethylethane-1,2-diamine (tmeda) results in the removal of one phosphorus-bound BH3 molecule and the formation of the [Ph2PCH(BH3)PPh2BH3]– anion. These results indicate that the isomerization of [CH(PPh2BH3)2]– requires an additional BH3 source and a rather strong Lewis base. Complexes 1–4 and the related derivatives [Li{CH(PPh2BH3)2}(Me4THF)] (5) and [K{H3BCH(PPh2BH3)2}(dme)2] (6; dme = 1,2-dimethoxyethane) were characterized by multinuclear NMR spectroscopy and by single-crystal X-ray diffraction analysis. A series of ether-ligated lithium complexes that contain the [H3BCH(PPh2BH3)2]– anion was synthesized by the reaction of the related bis(borane) adduct [(Li{CH(PPh2BH3)2})n] with different BH3 sources. Coordination modes and stability of the formed methanide ligand were investigated. The relevance of these complexes in the isomerization of the lithium precursor is discussed.

Posted on 6 November 2014 | 9:33 am

Coordination Behavior and Reactivity of ?-Heterosubstituted Trimethylsilylalkynes at Titano- and Zirconocene

The coordination behavior of the ?-donor-atom-substituted (trimethylsilyl)alkynes OC4H8N–C?C–SiMe3 (2), EtO–C?C–SiMe3 (3), and Me2P–C?C–SiMe3 (4) towards group 4 metallocene generators [Cp2Ti(?2-btmsa)] (1a), [Cp2Zr(py)(?2-btmsa)] (1b), and [Cp*2Ti(?2-btmsa)] (1c) [Cp = ?5-cyclopentadienyl; btmsa = bis(trimethylsilyl)acetylene; py = pyridine; Cp* = ?5-pentamethylcyclopentadienyl] was investigated. By using 1a and 1b, metallacyclopropenes were obtained for alkyne 2, a titanacyclopentadiene for alkyne 3, and dimeric-stabilized metallacyclopropenes for alkyne 4. Employing the sterically demanding metallocene 1c resulted in monomeric metallacyclopropenes for alkynes 3 and 4. The reactivity of the obtained complexes towards CO2 and acetone was explored as well, thus leading to regioselective formation of metallafuranones and metalladihydrofurans. Adding a donor atom (D) in the ? position of the triple bond of an alkyne causes a strong polarization, which is retained in the metallacyclopropenes formed by reaction with early-transition metallocene fragments (Ti, Zr). This polarization in turn governs the regioselectivity for the further insertion of alkynes and carbonyls such as acetone.

Posted on 6 November 2014 | 9:33 am

The First Late-Transition-Metal Cyclopentadienyl Chelate Complexes with Silylphosphane or Secondary Phosphane Tethers

While phosphane-tethered cyclopentadienyl complexes with tertiary phosphane moieties have extensively been investigated for many metals, this is not the case for such complexes with a secondary phosphane tether. Only a few representatives of such complexes with early-transition-metals are known. Here, we report the first late-transition-metal cyclopentadienyl chelate complexes with silylphosphane or secondary phosphane tethers. The respective ligand system is generated by nucleophilic opening of spiro[2.4]hepta-4,6-diene with lithium tert-butylphosphide. The anionic ligand is trapped with iron(II) chloride with formation of the respective ferrocene derivative. Treatment of lithium tert-butylphosphide with tert-butylchlorodimethylsilane or with chlorotriisopropylsilane affords the respective secondary silylphosphanes. Deprotonation, reaction with spiro[2.4]hepta-4,6-diene, followed by treatment with nickel dihalide complexes affords the respective nickel cyclopentadienylalkylsilylphosphane chelates as the first representatives of their kind. Their halide ligands can easily be exchanged by methylation with methyllithium or by reaction with trimethylsilyl cyanide to give the respective cyano chelate. Under the chromatographic conditions applied, this complex undergoes a protiodesilylation to give the first secondary cyclopentadienylalkylphosphane chelate of a late-transition-metal, which has been characterized by X-ray crystallographic analysis. Alternatively, deprotonation of the extremely sterically crowded primary (2,4,6-tri-tert-butylphenyl)phosphane followed by nucleophilic ring opening of spiro[2.4]hepta-4,6-diene and reaction of the anionic ligand system with NiBr2(thf)2 directly affords the respective cyclopentadienylalkylphosphane nickel chelate with a secondary phosphane ligand. The first late-transition-metal cyclopentadienylalkylphosphane chelates with a secondary phosphane tether are reported.

Posted on 6 November 2014 | 9:33 am

Theoretical Search for an Iron-Based Magnetic Superhalogen with Halogen or Interhalogen as Ligand

By using density functional theory, we have investigated the geometrical structures, electrophilic properties, magnetic properties, and fragmentation channels of FeXn (X = Cl, Br; n = 1–6) clusters as well as the “mixed species” that contain interhalogen compounds. Our main objectives are to design new iron-based magnetic superhalogens and to explore whether the interhalogen compounds are suitable for the superhalogen ligand. By calculating their adiabatic electron affinities (AEAs) and vertical detachment energies (VDEs), we found that both FeCln and FeBrn can be classified as superhalogens for n???3. Among mixed species, FeClF3, FeBrF3, FeClF5, and FeBrF5 are superhalogens, but their AEA values are still smaller than those of the correspondingly sized FeFn clusters. Their superhalogen properties are further supported by the natural population analysis (NPA) charge distribution and the HOMO of anions. However, in mixed species, the extra electron and HOMO do not uniformly delocalize over the different halogen atoms. This might be the reason why FeXYn possesses relatively small AEA values. In addition, we also studied the superhalogen salts formed with these superhalogen anions and Na+, which greatly enhance the reliability of our obtained superhalogens. To explore new magnetic superhalogens, we have performed a systematic investigation on the neutral and anionic FeCln, FeBrn (n = 1–6), and “mixed species” (FeClF, FeClF3, FeClF5, FeBrF, FeBrF3, FeBrF5, and FeBrCl) clusters. Their superhalogen properties are explained by the natural population analysis charge distribution and the HOMO of the anion.

Posted on 5 November 2014 | 11:10 am

Evaluation of the Formate Dehydrogenase Activity of Three-Legged Pianostool Complexes in Dilute Aqueous Solution

Formic acid is an attractive means to reversibly store dihydrogen. In this context, d6 pianostool complexes rank among the most-effective formate dehydrogenase catalysts. With biologically generated formic acid in mind, we evaluated the performances of iridium-based pianostool complexes bearing a cooperative ligand, which are known to catalyze formate decomposition. Interestingly, the phenylpyrazole-derived catalyst [Cp*Ir(phenpz)(OH2)]+ (7, Cp* = pentamethylcyclopentadienyl, phenpz = 1-phenylpyrazole) compares favourably with the very best systems [Cp*Ir(phenpzCO2H)H2O]+ [8, phenpzCO2H = 4-(pyrazol-1-yl)benzoic acid] and [Cp*Ir(imim)H2O]2+ [11, imim = 2,2?-bis(4,5-dimethylimidazole)]. These catalysts display remarkable air tolerance, recyclability and activity under dilute aqueous conditions. The catalytic activity of d6 Ir pianostool complexes for formic acid decomposition was evaluated under dilute conditions. Both [Cp*Ir{phenpz(CO2H)}H2O]+ (Cp* = pentamethylcyclopentadienyl, phenpz = 1-phenylpyrazole) and [Cp*Ir(imim)H2O]2+ [imim = 2,2?-bis(4,5-dimethylimidazole)] display excellent activity, recyclability and air tolerance under the tested conditions.

Posted on 5 November 2014 | 11:10 am

Monothiolato-Bridged Dinuclear Arene Ruthenium Complexes: The Missing Link in the Reaction of Arene Ruthenium Dichloride Dimers with Thiols

The monothiolato complexes [(?6-p-MeC6H4iPr)2Ru2Cl2(?-Cl)(?-SR)] with R = CH2C6H5 (1), p-CH2C6H4NO2 (2), C10H15 (3), m-9-B10C2H11 (4) were synthesized by treating [(?6-p-MeC6H4iPr)2Ru2Cl2(?-Cl)2] with the corresponding thiols RSH. The reaction of p-cymene ruthenium dichloride dimer with thiols is well known to give the cationic trithiolato complexes [(?6-p-MeC6H4iPr)2Ru2(?-SR)3]+, but recently the intermediary dithiolato complexes [(?6-p-MeC6H4iPr)2Ru2Cl2(?-SR)2] could also be isolated and characterized in some cases. The monothiolato complexes 1–4 now observed represent the missing link in the stepwise formation of the trithiolato complexes. The single-crystal X-ray structure analyses of complexes 1 and 2 show the two ruthenium atoms to be bridged by a chlorido ligand and by the thiolato ligand without a metal–metal bond, which is in accordance with the eighteen-electron rule. Four complexes of the type [(?6-p-MeC6H4iPr)2Ru2Cl2(?-Cl)(?-SR)] were synthesized by treating p-cymene ruthenium dichloride dimer with thiols. These complexes, containing one thiolato and one chlorido bridge, represent the missing link in the stepwise formation of the well-known diruthenium trithiolato complexes [(?6-arene)2Ru2(?-SR)3]+.

Posted on 5 November 2014 | 11:10 am

Slow Exchange of Bidentate Ligands between Rhodium(I) Complexes: Evidence of Both Neutral and Anionic Ligand Exchange

The phosphine double exchange process involving [RhCl(COD)(TPP)] and [Rh(acac)(CO)(TMOPP)] (TPP = PPh3, TMOPP = P(C6H4-4-OMe)3) to yield [RhCl(COD)(TMOPP)] and [Rh(acac)(CO)(TPP)] is very rapid but is followed by a much slower process where the bidentate ligands are exchanged to yield [Rh(acac)(COD)] and a mixture of [RhCl(CO)(TPP)2], [RhCl(CO)(TMOPP)2], and [RhCl(CO)(TPP)(TMOPP)]. The exchange involving [RhCl(COD)(L)] and [Rh(acac)(CO)(L)] yields [Rh(acac)(COD)] and [RhCl(CO)(L)2], where the reaction is much faster when L = TPP than when L = TMOPP. The mixed-metal system comprising [IrCl(COD)(TPP)] and [Rh(acac)(CO)(TPP)] yields all four complexes [M(acac)(COD)] and [MCl(CO)(TPP)2], where M = Rh and Ir. This illustrates that both a neutral ligand exchange and an anionic ligand exchange occur. Possible pathways for these processes are discussed. Complexes [Rh(acac)(CO)(L1)] and [RhCl(COD)(L2)] undergo a very rapid double exchange of the monodentate phosphine ligands followed by a much slower exchange process involving the bidentate ligands.

Posted on 30 October 2014 | 1:10 pm

Photochemical Reactions of [(?5-C5R5)Re(CO)3] (R = Me or H) with Aryl Halides in Benzene: Stoichiometric Formation of Biphenyl

Photolysis of [Cp*Re(CO)3] (Cp* = ?5-C5Me5) with bromobenzene or chlorobenzene in benzene results in biphenyl and the corresponding rhenium hydride halide complex trans-[Cp*Re(CO)2H(X)], which further converts into the dihalide complexes cis/trans-[Cp*Re(CO)2X2] (X = Br, Cl). Additional experiments, including isotopic labeling experiments, indicate that one phenyl ring in biphenyl comes from the aryl halide and the other one comes from solvent benzene. Photolysis of [CpRe(CO)3] (Cp = ?5-C5H5) with aryl halide in benzene similarly generates biphenyl, the corresponding rhenium hydride halide complex. Furthermore, the reaction also affords small amounts of rhenium dihydride complex [CpRe(CO)2H2]. Plausible mechanisms for the formation of the different types of products are proposed that involve intermolecular C–X and C–H activation. Molecular structures of trans-[Cp*Re(CO)2(Br)(Cl)] (trans-6) and trans-[CpRe(CO)2(Br)(Cl)] (trans-12) determined by X-ray diffraction are also presented. Photolysis of [Cp*Re(CO)3] with bromo- or chlorobenzene in benzene results in the formation of biphenyl and the corresponding rhenium hydride halide complex trans-[Cp*Re(CO)2H(X)]. Isotopic labeling experiments indicate that one phenyl ring in the resulting biphenyl comes from the aryl halide and the other one from the solvent benzene. Plausible mechanisms are proposed that involve intermolecular C–X and C–H activation.

Posted on 30 October 2014 | 1:10 pm

Quantitative UV/Vis Spectroscopic Investigations of the In Situ Synthesis of Neutral ?2-Chloro-Bridged Dinuclear (Diphosphine)rhodium Complexes

The stepwise in situ formation of neutral ?2-chloro-bridged dinuclear (diphosphine)rhodium complexes of the type [{Rh(PP)(?2-Cl)}2] (PP = chelating diphosphine) following the reaction of [{Rh(COD)(?2-Cl)}2] (COD = cyclooctadiene) with the ligands BINAP, SegPhos, DM-SegPhos and DiFluorPhos was investigated quantitatively by stopped-flow UV/Vis spectroscopy at 25.0 °C. The second-order rate constants of each step of the consecutive reactions were determined. The investigations were hindered by an unexpected equilibrium reaction between starting and target complex on one side and an intermediate species formed during the ligand-exchange process on the other. The rate constants of this equilibrium were also determined. The results reveal that the in situ formation of neutral ?2-chloro-bridged dinuclear (diphosphine)rhodium complexes, which are commonly applied in homogeneous catalysis as catalyst precursors, requires longer reaction times than is generally expected. The in situ formation of neutral ?2-chloro-bridged dinuclear (diphosphine)rhodium complexes from the corresponding diolefin complexes by a twofold ligand-exchange reaction was investigated kinetically. The second-order rate constants of each step of the consecutive reactions were determined for the ligands BINAP, SegPhos, DM-SegPhos and DiFluorPhos by stopped-flow UV/Vis spectroscopy.

Posted on 30 October 2014 | 1:10 pm

Acyl-Functionalized Molybdenum Compounds [(?3-C3H5)(?5-Cp?)Mo(CO)2]: An Experimental Study Including the X-ray Structure of a Rare endo Conformer

A series of new acyl-functionalized molybdenum(II) complexes [(?3-C3H5)(?5-C5H4COR)Mo(CO)2] have been successfully synthesized and crystallographically characterized, and the relationship between the reactivity and electronic properties of these organometallic compounds has been studied in detail. The X-ray analysis revealed [(?3-C3H5)(?5-C5H4COCF3)Mo(CO)2] to exist as a rare endo conformer, the first time that this structure has been observed in the crystal lattice of a [(?3-C3H5)(?5-Cp?)Mo(CO)2] (Cp? = substituted Cp) complex without any disorder. It has also been demonstrated that the derivatives bearing very strong electron-withdrawing acyl groups (e.g., -CHO, -COCF3) show different outcomes in the protonation reactions compared with the parent cyclopentadienyl compound or derivatives bearing less electron-withdrawing groups (e.g., -COMe, -COPh). This study has also revealed the increased reactivity of the formyl derivative [(?3-C3H5)(?5-C5H4CHO)Mo(CO)2] towards aromatic amines. An IR spectroscopic analysis revealed that the aldimine-functionalized products formed very quickly even under the mild conditions that fulfill the basic rules of click chemistry. A series of new acyl-functionalized molybdenum(II) complexes [(?3-C3H5)(?5-Cp?)Mo(CO)2] (Cp? = substituted Cp) have been synthesized. X-ray diffraction analysis of the CF3CO derivative revealed a rare endo conformer. In addition, it was found that the electronic properties of the acyl substituents have a strong effect on the outcome of protonation reactions.

Posted on 30 October 2014 | 1:10 pm

O–S Bond Activation in Structures Isoelectronic with Ferric Peroxide Species Known in O–O-Activating Enzymes: Relevance for Sulfide Activation and Sulfite Reductases

The interactions of H2S with FeIVO porphyrin radical-cation structures and of peroxide-like H2OS systems with ferric heme have been investigated by DFT. The data are relevant for the formation of sulfheme in globins and for the catalytic cycle of sulfite reductases. Heme FeOS systems (and their protonated versions) feature relatively accessible potential energy surfaces for O–S bond formation and cleavage, and for the insertion of S at the meso position of the heme; O–S bond cleavage is thermodynamically favorable only in diprotonated versions of the FeOS unit, FeIVO?+ H2S, or the ferric–HOSH isomer. The insertion at the meso position is reminiscent of heme oxygenase meso-hydroxylation via a ferric–hydroperoxo intermediate. Although axial imidazole and methylthiolate yield similar reaction profiles in all themodels studied, the FeIVO?+ H2S reaction is another case of our previously advocated “thiolate obstruction”, in which thiolate hinders rather than favors reactions at the heme center. Described herein is the proton-driven activation of O–S bonds at heme centers, which is of relevance for sulfite reductases and globins, and contrasts with peroxidases, heme oxygenases, and cytochrome P450.

Posted on 30 October 2014 | 1:10 pm

Switching the Macrocycle Conformation from Nonplanar to Planar in Cobalt(II) and Copper(II) ?-Tetra-2?-thienyl-meso-tetraphenylporphyrin Cocrystallates with C60

Crystal structures of cobalt(II) and copper(II) complexes of 2,3,12,13-tetra-2?-thienyl-5,10,15,20-tetraphenylporphyrin/C60 cocrystallates were determined by single-crystal XRD analysis. The crystal structures of the two cocrystallates, MTPP(2?-thienyl)4·C60·(toluene)2 (M = CoII and CuII; TPP = tetraphenylporphyrin), compounds 1 and 2, respectively, are isomorphous and reveal a one-dimensional (1D) supramolecular structure. In these cocrystallates, the macrocycle is almost planar within ±0.08 Å, as evidenced by comparing the value of ?Cb (the average deviation of the ?-pyrrole carbon from the porphyrin ring mean plane) with those for the nonplanar parent structures, CoTPP(2?-thienyl)4 [±0.710(5) Å] and CuTPP(2?-thienyl)4 [±0.546(2) Å]. This difference has been ascribed to intermolecular interactions and/or crystal packing forces. Two new porphyrin/C60 cocrystallates, MTPP(2?-thienyl)4·C60·(toluene)2 (M = CoII and CuII; TPP = tetraphenylporphyrin), were examined by single-crystal XRD analysis. These cocrystallates exhibited essentially 1D supramolecular structure. In both the structures, an unusual dramatic decrease in nonplanarity of the macrocycle to near planarity was observed.

Posted on 28 October 2014 | 10:20 pm

Color Tuning and Noteworthy Photoluminescence Quantum Yields in Crystalline Mono-/Dinuclear ZnII Complexes

A series of ZnII complexes with an O,N,O tridentate core is reported. Four species of the general formula ZnLiPy2 were obtained from pyridine, where Li is a substituted 4-[(aroylhydrazono)methyl]-3-hydroxyphenyl 4-(octyloxy)benzoate group. Crystal structures were solved by single-crystal X-ray diffraction. Nematogenic phase behavior was detected only for the ligands. Photoluminescence spectra were recorded both in solution and in the solid state, and the complexes showed noteworthy photoluminescence in the solid state with wavelengths tunable by varying the aroyl group. Medium to very high photoluminescence quantum yields (PLQY) were recorded on the crystalline complexes obtained in their mononuclear coordination environments. In the case of a 4-nitrobenzoyl substituent on the ligand, a dinuclear complex with formula Zn2L42Py2 showed an unprecedented and exceptionally high PLQY value for a crystalline zinc complex. Molecular and periodic calculations were performed by using Density Functional Theory (DFT). Complexes ZnLiPy2 were obtained in pyridine. A bulky benzoyloxy moiety was introduced in the tridentate ligands Li. Tuning of emission was achieved, and noteworthy photoluminescence quantum yields (PLQY) were recorded on crystalline species. Specific conditions afforded O-bridged dinuclear complexes with an unprecedented 64?% PLQY. Discussions are supported with XRD and DFT calculations.

Posted on 28 October 2014 | 10:20 pm

Electrochemical Conversion of Bicarbonate to Formate Mediated by the Complex RuIII(edta) (edta4– = ethylenediamine­tetraacetate)

In this paper, we present the first example of a ruthenium(III) complex, [RuIII(edta)] (edta = ethylenediaminetetraacetate), that catalyzes the electrochemical conversion of hydrogen carbonate to formate selectively. The formation of an [RuIII(edta)(HCO3)]2– species through the reaction of the [RuIII(edta)(H2O)]– catalyst and hydrogen carbonate (HCO3–) was studied kinetically by using the stopped-flow technique. The value of the second-order rate constant for the formation of the [RuIII(edta)(HCO3)]2– complex was 82?±?7 M–1?s–1 at 25 °C and pH = 6.4. Electrochemical reduction of hydrogen carbonate (HCO3–) was achieved by carrying out constant-potential bulk electrolysis at –0.4 V (vs. SCE) with a mercury-pool cathode at pH = 6.4. The formation of formate as the only reduction product was evidenced by a 13C NMR analysis of the reaction mixture obtained after electrolysis. [RuIII(edta)(H2O)]– (edta = ethylenediaminetetraacetate) mediates the electrochemical conversion of hydrogen carbonate to formate through the formation of an [RuIII(edta)(HCO3)]2– species, which undergoes electrochemical reduction at –0.4 V (vs. SCE) at a mercury-pool cathode at pH = 6.4. This results in the formation of formate as the only product.

Posted on 28 October 2014 | 10:20 pm

Synthesis and Characterization of a Linear Dinitrosyl-Triiron Complex

Nitric oxide is released during the immune response by the host during bacterial infection. To counteract this response, bacteria have evolved nitric oxide reductases to convert NO to N2O. Some of these nitric oxide reductases contain a flavodiiron active site that has bridging carboxylates and hydroxides. Only a handful of synthetic complexes currently exist as models for the protein reactivity. Here, we report the reaction of [Fe2(?-OH)(?-Ph4DBA)(TMEDA)2(OTf)] (4) with NO(g) and Ph3CSNO to prepare the dinitrosyl-triiron complex [Fe3(?-OH)2(?-Ph4DBA)2(TMEDA)2(NO)2](OTf) (5). The reaction was monitored by UV/Vis and ReactIR spectroscopy, and compound 5 was characterized by X-ray crystallography, 57Fe Mössbauer spectroscopy, Evan's method, and FTIR spectroscopy. The IR spectrum of compound 5 compares favorably to experimental spectroscopic data obtained for the proposed mononitrosylated intermediate of the protein. The complex [Fe3(?-OH)2(?-Ph4DBA)2(TMEDA)2(NO)2](OTf) was synthesized and spectroscopically characterized. Its properties resemble those of a proposed intermediate observed during the catalytic reduction of nitric oxide by flavodiiron reductases.

Posted on 28 October 2014 | 10:11 pm

?2P,O-Hybrid Ligands: Synthesis of the First 4-Hydroxy-1,3-benzazaphospholes by ortho-Lithiation of m-Amidophenyl Diethyl Phosphates

The m-phosphorylanilides 2 are available from anilides 1 by the Atherton–Todd reaction; the selective ortho-lithiation of the o?-methyl-protected phosphorylpivalanilide 2b with tBuLi proceeded in high yield in the presence of ClSiMe3. The ortho-lithiation is followed by rapid 1,3-migration of the PO3Et2 group to yield the phosphonoanilide cis/trans-3b. This compound mainly reacts with excess LiAlH4 by reductive cyclization to form the 4-hydroxy-1H-1,3-benzazaphosphole 6. The lithiation of the o?-unprotected phosphorylpivalanilide 2a with LDA was unselective and led to 3a and 4a in low yields, whereas additional ortho-lithiation of the benzoyl group occurred for the lithiation of the o?-protected phosphonobenzanilide 2c with tBuLi/LDA to give 7 in rather low yield. The reduction of crude 7 led to (benzylamino)phenol 8 and the 4-hydroxy-1H-1,3-benzazaphosphole 9 as a minor product. The properties, NMR spectroscopy data, and crystal structures of 5b, 6, and 8 are reported. The reactions of 2-methyl-protected 5-(pivaloylamino)phenyl phosphates with tBuLi in the presence of ClSiMe3 to trap lithium species gave high yields of ortho-lithiation/rearrangement products. The reductive cyclization of the [2-hydroxy-6-(pivaloylamino)phenyl]phosphonates with LiAlH4 furnished 4-hydroxybenzazaphosphole, a new ?2P,O-hybrid ligand with relatively high ?-density at the phosphorus atom.

Posted on 28 October 2014 | 10:11 pm

Synthesis, Structures, and Reactivity of Copper(I) Complexes Supported by a Rigid Dinucleating Ligand

Herein, we report the diverse CuI chemistry of a dinucleating ligand L that features two iminopyridine chelates bridged by a 1,8-diaminoxanthene linker {L = (1E,1?E)-N,N?-(2,7-di-tert-butyl-9,9-dimethyl-9H-xanthene-4,5-diyl)bis[1-(pyridin-2-yl)methanimine]}. The ligand L leads to the formation of discrete bimetallic species, or metallopolymers, as a result of syn-parallel or anti-parallel mutual disposition of the chelating units. The reaction of L with [Cu(NCMe)4]+ forms the discrete bimetallic complexes [Cu2(L)(NCMe)2]2+ (1) or [Cu2(L)2]2+ (2), depending on the solvent and the ligand-to-metal ratio. In contrast, the reaction of L with CuX (X = Cl, Br) forms the metallopolymers [Cu2(L)(Br)2]n (3) and {[Cu3(L)2Cl2][CuCl2]}n (4). The compounds were characterized by X-ray crystallography, NMR spectroscopy, mass spectrometry, electrochemistry, and DFT calculations. The reaction of compound 1 with O2 in CH2Cl2 was found to lead to a mixture of CuII products of which tetrametallic [Cu4(L)4(OH)3(Cl)]4+ and [Cu4(L)2(OH)4]4+ were identified by X-ray crystallography. We report the CuI chemistry of a rigid dinucleating ligand that forms a discrete bimetallic complex [Cu2(L)(NCMe)2]2+ or metallopolymer [Cu2(L)(Br)2]n owing to the syn-parallel or anti-parallel mutual disposition of the chelating units. The bimetallic complex reacts with O2 to form a mixture of CuII–hydroxide clusters of which [Cu4(L)4(OH)3(Cl)]4+ and [Cu4(L)2(OH)]4+ were characterized by XRD.

Posted on 28 October 2014 | 10:11 pm

Tuning CuII Coordination Polymers ­Derived from a Bis(pyrazolecarboxylate) Ligand by Solvothermal C–H Bond Activation: Synthesis, Structures, Catalysis, and Magnetic Properties

A new bis(pyrazolecarboxylate) ligand, 1,3-phenylenebis(1H-pyrazole-5-carboxylic acid) (H2PBPC) has been synthesized to study the structure and intriguing properties of the resultant coordination polymers synthesized under solvothermal conditions. The reaction of H2PBPC with Cu(ClO4)2 in the presence of NaOH at two different temperatures (80 and 120 °C) resulted in two coordination polymers, namely, [{Cu2Na(H2OPBPC)}]? (1) and [{Cu4Na2(H2OPBPC)2}]? (2), which display 2D corrugated sheet and 3D staircase architectures, respectively; in these structures, the aromatic C–H bond flanked by the pyrazolecarboxylate moieties was oxidized to form a C–O bond. When 2,2?-bipyridine (2,2?-bpy) was used instead of NaOH, [{Cu2(2,2?-bpy)2(H2PBPC)}(H2O)]? (3) formed, and such C–H bond activation was not observed. Interestingly, one of the coordination polymers, namely, 1, displayed catecholase and phosphatase activity. Variable-temperature magnetic susceptibility data in the range 2–300 K showed that there is antiferromagnetic coupling between the metal centers of 1 and 2 that is mediated through the phenoxo and pyrazole bridges, whereas 3 revealed dominant ferromagnetic interactions between the bis(pyrazolato)-bridged CuII centers owing to its very unusual Cu–N–N–Cu torsion angles of 75.28 and 69.52°. A new bis(pyrazolecarboxylate) ligand undergoes C–H bond activation in the presence of Cu(ClO4)2 under mild basic conditions. The resulting coordination polymers exhibit interesting structural features with promising catalytic and magnetic properties.

Posted on 28 October 2014 | 10:11 pm

Synthetic Strategies for Variably Substituted Ruthenium–Imidazophenanthrolinium Complexes

The synthesis of several symmetric and asymmetric substituted imidazophenanthrolinium ligands and their corresponding ruthenium polypyridyl complexes was achieved by applying a newly designed synthetic concept. By testing different moieties, the advantages and limits of the synthetic approach could be defined. The substitution pattern on the imidazolium moiety has no significant influence on the structural aspects of the imidazophenanthrolinium backbone or on the photophysical properties of the ruthenium compounds. Given that imidazolium salts act as precursors for N-heterocyclic carbenes, the reported results provide the basis for the design of highly efficient oligonuclear photocatalysts. Different synthetic strategies are investigated for the synthesis of variably substituted ruthenium–imidazophenanthrolinium complexes. Structural and preliminary photochemical characterizations suggest that substitution patterns can be altered without influencing the photochemical properties.

Posted on 28 October 2014 | 10:11 pm

Two Supramolecular Inorganic–Organic Hybrids of 12-Silicotungstic Acid Heteropolyoxometalate and Trinuclear Lanthan­ide Clusters: Syntheses, Structures, and Magnetic Properties

Hydrothermal synthesis of two novel inorganic–organic hybrid assemblies, {Na[Ln(pydc-OH)(H2O)4]3}[SiW12O40]·15H2O [Ln = Nd (1) and Ln = Sm, (2); pydc-OH = 4-hydroxypyridine-2,6-dicarboxy], and their characterization is described. Structural characterizations by single-crystal X-ray diffraction reveal that these compounds are isostructural, and each consists of [SiW12O40]4– Keggin-type polyoxometalates (POMs) linked by three lanthanide ions to yield discrete trinuclear lanthanide clusters. These discrete molecules are further packed into 3D supramolecular assemblies by means of hydrogen-bonding and anion–? interactions. Both compounds exhibit remarkable thermal stability. The temperature variation in the magnetic susceptibility ?m and of the ?mT product and Bohr magnetons of the NdIII (1)- and SmIII (2)-based compounds are considered. The magnetic data have been interpreted relative to data presented in the literature. Hydrothermal synthesis of two inorganic–organic hybrid assemblies and their characterization by single-crystal X-ray diffraction reveals that these compounds consist of [SiW12O40]4– Keggin-type polyoxometalates linked by three lanthanide ions to yield discrete trinuclear lanthanide clusters. The magnetic properties of the NdIII (1)- and SmIII (2)-based compounds are considered.

Posted on 28 October 2014 | 10:10 pm

Two Layerlike Supramolecular Assemblies Based on B-Anderson-Type Polyanionic Clusters and Their Adsorption Property

Two layerlike supramolecular assemblies that consist of Ag-supported B-Anderson-type clusters (H2bpp)[Ag{AlMo6(OH)6O18}]·2.5H2O (1) and (H2bpe)[Ag(OH2){AlMo6(OH)6O18}] (2) [bpp = 1,3-di(4-pyridyl)propane; bpe = 1,2-di(4-pyridyl)ethylene] have been synthesized and characterized. X-ray diffraction analysis reveals that the supramolecular structures of two compounds are built upon alternative arrangements of inorganic anionic and organic cationic layers. In 1 and 2 the oxophile silver centers have different coordination modes to bridge Anderson-type clusters into 2D inorganic anionic layers. There are extensive noncovalent forces among inorganic anions and organic cations to construct 3D supramolecular frameworks of compounds 1–2. The preliminary experiments show that the two crystals possess an adsorption–desorption property for methylene blue (MB). Crystal 2 shows a very fast adsorption rate towards MB, and a relatively high value (ca. 90?%) can be reached within 15 min. Two layerlike supramolecular assemblies that consist of Ag-supported B-Anderson-type clusters have been synthesized. They possess an adsorption–desorption property for methylene blue with a very fast adsorption rate.

Posted on 28 October 2014 | 10:10 pm

Role of the Isolable Hydride Intermediate in the Hydrosilylation of Carbonyl Compounds Catalyzed by the High-Valent Mono-Oxido–Rhenium(V) Complex

The hydrosilylation of carbonyl compounds catalyzed by high-valent mono-oxido–rhenium(V) complex [Re(O)Cl3(PPh3)2] (1) and its hydride [Re(O)(H)Cl2(PPh3)2] (1H) was theoretically investigated using density functional theory. Our calculations indicated that the most energetically favorable process for 1-catalyzed hydrosilylation was the “ionic mechanistic pathway”. The catalytic cycle is initiated by carbonyl substrate nucleophilic attacks on the ?1-silane rhenium adduct, which results in the heterolytic cleavage of the Si–H bond and generation of a siloxy carbenium ion paired with an anionic rhenium hydride, [ReOCl3(H)(PPh3)]–[Me3SiOCHPh]+. The ionic mechanistic pathway is more favorable than the ?-bond metathesis pathway that involves the generation of rhenium hydride (23.8 versus 31.5 kcal?mol–1). Therefore, our results indicated that an undetected ?1-silane rhenium adduct was the real intermediate rather than the isolable hydride intermediate 1H in the hydrosilylation catalyzed by 1. An undetected ?1-silane rhenium adduct rather than the isolable rhenium hydride was the real intermediate in the hydrosilylation of carbonyl compounds catalyzed by the mono-oxido–rhenium(V) complex [Re(O)Cl3(PPh3)2] (1). The formed isolable hydride intermediate 1H was not the activated intermediate for the carbonyl hydrosilylation catalyzed by the mono-oxido–rhenium(V) complex.

Posted on 28 October 2014 | 9:40 pm

S = 2 Spin Ladders in the Sulfide Oxide BaFe2S2O

Pure powder and small single crystals of BaFe2S2O were obtained by solid-state reaction between BaO, Fe, and S in closed silica ampoules. The crystal structure contains a magnetic ladderlike sublattice of high-spin Fe2+ (d6) tetrahedrally coordinated by three S and one O atoms. Strong antiferromagnetic spin interactions are observed far above the Néel transition (TN = 260 K). 57Fe Mössbauer spectra show typical features of Fe2+ as a doublet with large quadrupole splitting above TN and combined electric and magnetic hyperfine interaction in the magnetically ordered phase. A structural transition upon the magnetic order is discussed. The sulfide oxide BaFe2S2O contains spin ladders of tetrahedrally coordinated high-spin Fe2+ (d6). The Fe ion is thereby surrounded by three S and one O atoms. Below the Néel transition (TN = 260 K), it is assumed that the crystal lattice distorts and the geometrical frustration between the spin ladders is cancelled.

Posted on 21 October 2014 | 10:10 am

Synthesis, Characterisation and Modelling of a Ferromagnetically Coupled Chromium(III) Dimer: Di-?-hydroxobis[tetrakis(isothiocyanato)chromate(III)]

A rare example of a ferromagnetically coupled dinuclear chromium(III) complex, the di-?-hydroxobis[tetrakis(isothiocyanato)chromate(III)] anion, is reported. This complex has been synthesised from the oxo-bridged acetonitrile complex [(CH3CN)5CrOCr(NCCH3)5](BF4)4 and isolated as the solvated tetraphenylphosphonium salt, (Ph4P)4[(SCN)4Cr(OH)2Cr(NCS)4]·2CH3CN (1). From magnetometry the coupling constant, J, was determined to be –5.17 cm–1 (in an H = JSA·SB scheme). The X-band EPR spectra were measured in the temperature range 2–305 K and the data were modelled. The spectra, which are very rich, are the first reported for a ferromagnetically coupled Cr-diol, and they allow for detailed modelling that encompasses zero-field splittings (ZFS) and fourth-order spin-Hamiltonian parameters for the coupled system. The structural parameters that determine the magnitude and sign of the exchange coupling were studied with broken-symmetry DFT. These results are discussed in terms of and compared to existing angular overlap model (AOM)-based magneto-structural correlations. This furnishes qualitative as well as quantitative insight into the coupling mechanisms. The di-?-hydroxobis[tetrakis(isothiocyanato)chromate(III)] ion has been isolated and investigated by EPR spectroscopy. The magnetic susceptibility was measured in the temperature range 2–300 K. Both experiments show this system to be ferromagnetically coupled with a septet ground state. This is the third example of a ferromagnetically coupled CrIII dimer, the first to be investigated by EPR.

Posted on 21 October 2014 | 10:10 am

1D Heterometallic Oxalate Compounds as Precursors for Mixed Ca–Cr Oxides – Synthesis, Structures, and Magnetic Studies

The heterodimetallic compounds {[CaCr2(L)2(C2O4)4]·xH2O}n [L = 2,2?-bipyridine (bpy), x = 0.83 (1); L = 1,10-phenanthroline (phen), x = 0.33 (2)] were synthesized and characterized by IR spectroscopy, X-ray diffraction and magnetic measurements. The crystal structure of 2 is reported: the chelation of a [Cr(phen)(C2O4)2]– units towards Ca cations results in 1D double zigzag chains. The ability of 1 and 2 to act as single-source precursors for the formation of Ca–Cr oxides is explored by thermal analysis, powder X-ray diffraction and IR spectroscopy. The thermal processing of 1 and 2 at 1100 °C in air led to the appearance of the ?-CaCr2O4 phase as the major crystalline oxide. By heating the samples up to 1100 °C in nitrogen, only the ?-CaCr2O4 phase formed, whereas heating at 1400 °C caused the crystallization of two polymorphs, ?- and ?-CaCr2O4. The magnetic behaviour of ?-CaCr2O4 pointed to the freezing of magnetic moments in coexistence with a weak ferromagnetic order. The heat treatment of {[CaCr2(L)2(C2O4)4]·xH2O}n [L = 2,2?-bipyridine, x = 0.83 (1) and 1,10-phenanthroline, x = 0.33 (2)] at 1100 °C in a nitrogen flow resulted in the isolation of the ?-CaCr2O4 phase, whereas heating at 1400 °C caused the crystallization of two polymorphs, ?-CaCr2O4 and ?-CaCr2O4. The spectroscopic, structural and magnetic properties of the single-source precursors and the ? phase are investigated.

Posted on 15 October 2014 | 4:11 pm

Lithium Complexes of Asymmetric Hydrogen Tetraimido Sulfate

Two novel monolithiated complexes, [(thf)2Li(NtBu)2(NHtBu)S(Ndipp)] (3) and [(thf)2Li(NtBu)2(NHtBu)S(Ndmp)] (4), are presented from the reaction of the neutral tri(tert-butyl)sulfur triimide S(NtBu)3 (1), nBuLi, and diisopropylaniline and dimethylaniline, respectively. These asymmetrically substituted hydrogen tetraimido sulfate complexes of lithium provide the opportunity to switch the metal in a transmetalation reaction and to introduce another substituent at the protonated imide function. Asymmetrically substituted hydrogen tetraimido sulfate ligands provide two opportunities to generate metal complexes. Firstly, the lithium metal can be exchanged in a transmetalation reaction, and secondly, the proton can be replaced by an additional substituent or another metal. This gives access to heterobimetallic complexes.

Posted on 15 October 2014 | 4:11 pm

Mono-Oxido-Bridged Heterobimetallic and Heterotrimetallic Compounds Containing Titanium(IV) and Chromium(III)

A series of oxido-bridged heterobi- and heterotrimetallic complexes, [(tmtaa)Ti=OCr(Por)Cl] and [(tmtaa)Ti=OCr(Por)O=Ti(tmtaa)]+ (tmtaa = 7,16-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine; Por = 5,10,15,20-tetraarylporphyrin), have been synthesized. To the best of our knowledge, these complexes are the first structurally characterized examples to contain a Ti=OCr or Ti=OCrO=Ti structural motif. Crystal structures of representative heterobimetallic compounds, including the Ti=OCr binuclear complex 2 and two separate trimers, [Ti=OCrO=Ti]SbF6 (10) and [Ti=OCrO=Ti]Cl (12), are reported. The bi- and trimetallic molecules have similar structural parameters, including Ti–O, Cr–O, and Ti–O–Cr bond lengths and angles with a linear Ti=OCr geometry. Magnetic studies showed that a high-spin CrIII (S = 3/2) center is present in both the bi- and trinuclear molecules. The redox potentials for CrIV/III (?E = 320 mV) and Por/Por·– (?E = 260 mV) can be tuned by modifying the porphyrin ligand. By determining the thermodynamics and kinetics of the formation of these complexes by titration experiments and electrochemistry, it was found that the bi- and trimetallic species undergo isomerization in solution, allowing easy substitution of the apical chlorido ligand. A series of heterobi- and heterotrimetallic molecules containing an unsupported oxido bridge have been synthesized. The molecular structures are controlled by the stoichiometry of the reagents, and the heterotrimetallic structural motif Ti=OCrO=Ti is hitherto unknown. Electrochemistry and magnetic studies were performed to identify the intermediates and their thermodynamic properties.

Posted on 15 October 2014 | 4:11 pm

Structurally Characterized Antipyrine-Based Dual Fluorescent Probe: Enhanced AlIII Selectivity of a Dinuclear ZnII Complex for Intracellular Sensing by a Displacement Approach

The antipyrine-based fluorescence probe daph, structurally characterized by single-crystal X-ray diffraction, can recognize both Zn2+ (at 520 nm, yellow) and Al3+ (at 490 nm, green). However, Al3+ selectivity is enhanced significantly when the dinuclear ZnII-daph complex is used as a sensor, which senses Al3+ by a displacement approach. The binding constants of daph for Zn2+ and Al3+ are (4.9?±?0.2)?×?104 and (3?±?0.1)?×?105 M–1, respectively. The higher water solubility of the ZnII-daph complex allows the detection of Al3+ in a greener way (0.1 M HEPES buffer, ethanol/water = 1:9, v/v, pH 7.4). Moreover, the detection limit of the ZnII-daph complex for Al3+ is higher (2.5?×?10–9 M) than that of free daph (4.6?×?10–8 M). Alkali and alkaline-earth metal ions, Cd2+, Hg2+, and Pb2+, and 3d metal ions do not interfere. Both daph and the ZnII-daph complex are capable of intracellular Al3+ detection. The antipyrine-based fluorescent probe daph recognizes both Zn2+ and Al3+ at two different wavelengths. However, Al3+ selectivity is enhanced significantly when the corresponding ZnII-daph complex is used as a sensor. Moreover, the detection limit of the ZnII-daph complex for Al3+ is higher than that of free daph. Both daph and ZnII-daph are capable of intracellular Al3+ detection.

Posted on 15 October 2014 | 4:11 pm

Generation of Group VI Piano-Stool and Triple-Decker Complexes from [(IMes)2PtH(Cl-boratabenzene)] Species

Species [(IMes)2Pt(H)(1-Cl-2-SiMe3–BC5H4)] (1) was used as the source of the Cl-boratabenzene anion for coordination to group VI transition metals, resulting in the formation of piano-stool complexes [(?6-1-Cl-2-SiMe3–BC5H4)M(CO)3]– [M = Cr (2), Mo (4), W (5)] and a homodimetallic triple-decker complex [(CO)3Cr(?6-1-Cl-2-SiMe3–BC5H4)Cr(CO)3]– (3). All species were spectroscopically characterized and the first X-ray structure of a Cl-boratabenzene species is reported. Group VI piano-stool and triple-decker complexes of a Cl-boratabenzene ligand were prepared. All species were spectroscopically characterized and the first X-ray structure of the Cl-boratabenzene triple-decker complex is reported.

Posted on 15 October 2014 | 4:11 pm

A Tetradentate ?-Diiminato Ligand Containing Phenolate Substituents: Flexivalent Coordination to MnIII, CoIII, NiII, and CuII

A functionalized ?-dialdimine was prepared, bearing a 3,3-dimethylindoleninyl group at the meso-position and two N-phenolic groups. The structure contains three labile protons, which can be lost or migrate through tautomerism to provide an N2O2 coordination core. A number of divalent and trivalent metal ions (CuII, NiII, CoII/III, and MnIII) were accommodated inside the core, forming a series of intensely colored products consisting of a tricyclic MN2O2 chelate. In the resulting divalent metal complexes, the dialdimine ligand is deprotonated only at the two phenolic oxygen atoms and is thus dianionic, whereas in the trivalent metal complexes, the dialdiminato ligand is triply deprotonated. The copper and nickel complexes adopt square-planar geometries, whereas in the trivalent cobalt and manganese complexes, two neutral ancillary ligands complete an octahedral geometry around the metal center. In each case, the denticity of the diimino–diiminato ligand is four. The electrochemical oxidation of the copper and nickel complexes was studied by cyclic voltammetry. meso-Substituted dialdimine/dialdiminate acts as a di- or trianionic N2O2 ligand and exhibits redox-non-innocent character.

Posted on 14 October 2014 | 3:10 pm

On the Preparation and Structure of Caesium Aluminium Tetrahydride

A new tetragonal phase of CsAlH4 was observed after the precipitation of CsAlH4 from a diglyme solution with an inert solvent. This new phase and the previously described orthorhombic phase were characterized by a combination of X-ray powder diffraction analysis and 27Al and 133Cs solid-state NMR spectroscopy. The transformation of the tetragonal CsAlH4 phase into the orthorhombic CsAlH4 phase can be induced by thermal treatment, whereas the opposite process can be stimulated by mechanical treatment. The phase transformation processes are almost completely reversible and can be performed several times without any observable decomposition of CsAlH4. The structure of the tetragonal CsAlH4 phase (space group I41/a) was solved from X-ray powder diffraction data, and the lattice parameters were determined to be a = 5.6732(4) and c = 14.2795(11) Å. The transformation of a newly observed tetragonal polymorph of CsAlH4 into the previously described orthorhombic CsAlH4 phase can be induced by thermal treatment. The reverse transformation can be induced by mechanical treatment. Both phases were characterized by X-ray diffraction and 27Al and 133Cs MAS NMR spectroscopy.

Posted on 14 October 2014 | 3:10 pm

High Adsorption Capacity for Cationic Dye Removal and Antibacterial Properties of Sonochemically Synthesized Ag2WO4 Nanorods

?-Ag2WO4 nanorods with an average diameter of 15 to 25 nm and a surface area of ca. 115.0?±?0.2 m2/g have been synthesized by a facile sonochemical technique. These nanorods have been used for the adsorption of various cationic dyes (rhodamine B, methylene blue, and malachite green) from aqueous solution. The adsorption process is fast, and ca. 100?% adsorption of a 20 ppm mixture of all three dyes occurs within 10 min. The adsorption process was studied by varying different regulating parameters such as the solution pH and the initial dye and Ag2WO4 concentrations, and the results were analyzed with various isotherm and kinetic models. The mechanistic pathway for the selective adsorption of cationic dyes has been explained through zeta potential studies. Moreover, the thermal regeneration of the sorbent was possible by furnace heating at 250 °C, and the nanorods were efficient for multicyclic use. X-ray photoelectron spectroscopy (XPS) has been performed on the thermally regenerated samples to ascertain their surface purity. The Ag2WO4 nanorods have a bactericidal effect and are active against both Gram-negative and -positive bacterial strains of Escherichia coli and Bacillus subtilis, respectively. However, the efficiency is more pronounced for Gram-positive bacteria. Thus, these sonochemically synthesized Ag2WO4 nanorods have great potential for the treatment of dye industry effluents as a promising adsorbent for cationic dyes from aqueous solution and are also useful as an antibacterial agent. Sonochemically synthesized ?-Ag2WO4 nanorods exhibit superior sorption affinity for cationic dyes such as rhodamine B and methylene blue and also display good antibacterial activity.

Posted on 14 October 2014 | 3:10 pm

Seleno-Nucleobases and Their Water-Soluble Ruthenium–Arene Half-Sandwich Complexes: Chemistry and Biological Activity

Half-sandwich organometallic ruthenium complexes of seleno-nucleobases, 3 and 4, were synthesized and characterized. The structures of both complexes were determined by X-ray crystallography and are the first crystal structures of ruthenium complexes with seleno-nucleobases. Interestingly, 3 self-assembles aided by adventitious water in DMF to give a tetranuclear square 3a·6H2O. Complex 4 is active against Jurkat and Molt-4 cell lines but inactive against the K562 cell line, whereas 3 is completely inactive against all three cell lines. The free ligand 6-selenopurine (1) and 6-selenoguanine (2) are highly active against these cell lines. Compound 2, like its thio analogue, is unstable under UVA light, whereas 4 is stable under similar conditions, which suggests that the ruthenium complex could reduce problems associated with the instability of the free ligand, 2, under irradiation. Water-soluble bioorganometallic ruthenium complexes with seleno-nucleobases have been studied. The complex with 6-selenoguanine is shown to be more stable, although less cytotoxic, relative to the free ligand.

Posted on 14 October 2014 | 2:40 pm

Ionic Liquid Based Approaches to Carbon Materials Synthesis

Ionic liquids (ILs) have attracted continuous interest because of their remarkable physicochemical properties, including high thermal and chemical stability, nonflammability, negligible vapor pressure, designable cation/anion pairs, electrical and ionic conductivity, low melting points, and affinity towards many compounds. These properties make ionic liquids valuable in the creation of new materials and new processes throughout almost the entire field of materials chemistry. An emerging field is the use of ionic liquids in carbon-based nanomaterials. Initially, ionic liquids were used as self-templating carbon sources for the generation of unusual carbon materials in which homogeneous heteroatom doping (e.g., N, B, S) can be accomplished fairly easily. Later, ionic liquids were recognized as suitable for use in the conversion of biomass into porous carbon materials, acting as both reaction media and porosity-directing regulator. Such applications open the door towards the synthesis and accurate tuning of carbon nanostructures, for example, pore structure, morphology, heteroatom doping, and surface functionality. In addition, the hybridization of ionic liquids and nanocarbons enables the development of composites by combining the properties of the ionic liquid (e.g., ionic conductivity or catalytic activity) and those of a host (e.g., chemical or mechanical stability). Currently, although the research of this topic is rapidly expanding, the rational design and synthesis of carbon-based materials, particularly their applications in energy storage and transformation, is still in its infancy. In this review, we focus on several aspects of ionic liquid derived carbons with the aim of shedding light on this new topic: 1) Ionic liquids as an advanced medium for carbon synthesis, 2) ionogels derived from nanocarbon, 3) ionic liquids as fluid precursors for functional carbons, and 4) ionic liquid derived carbons for heterogeneous catalysis. Ionic liquids are currently established solvents, precursors for carbon materials, and components of carbon-based ionogels. The unique properties of ionic liquids are beneficial for the formation of unusual carbon materials or composites with homogeneous heteroatom doping (e.g., N, B, S) and controllable porosity.

Posted on 14 October 2014 | 2:40 pm

An Insight into the Complexation of Pyrazine-Functionalized Calix[4]arenes with Am3+ and Eu3+ – Solvent Extraction and Luminescence Studies in Room-Temperature Ionic Liquids

The complexation behaviour of six pyrazine-functionalized calix[4]arenes, containing substituents such as carbamoyl dioctyl (L-1, L-2), diisopropyl phosphonate (L-3, L-4) and diphenyl phosphoryl (L-5, L-6), with Am3+ and Eu3+ ions was investigated by solvent extraction as well as by luminescence spectroscopy (only for Eu3+) in room-temperature ionic liquids (RTILs), [Cnmim][NTf2] (1-alkyl-3-methylimidazolium, n = 4, 6, and 8). The spectacular enhancement in the extraction values of the trivalent metal ions in RTILs, as compared to those reported in a molecular diluent from 3 M HNO3, was rather unusual and was further investigated by luminescence studies. Luminescence studies involving Eu3+ and performed with L-4 and L-6 confirmed the 1:1 stoichiometry of the extracted species (Eu3+?L) with log?? values of 4.42?±?0.51 and 5.18?±?0.38 for L-4 and L-6, respectively. Judd–Ofelt parameters, which give information about the nature of bonding as well as the coordinating environment, were computed from the emission spectra of the Eu3+?L-4 and Eu3+?L-6 complexes. Complexation of Am3+ and Eu3+ with six pyrazine-functionalized calix[4]arene ligands was investigated in room-temperature ionic liquids (RTIL) by carrying out solvent extraction as well as luminescence (only for Eu3+) studies. Solvent extraction with RTIL resulted in a large enhancement in D values, and the nature of the complexes was investigated by luminescence spectroscopy.

Posted on 10 October 2014 | 1:11 pm

Palladium(II) and Platinum(II) Complexes Containing Six-Membered N-Heterocyclic Ligands: Synthesis, Characterization, Interaction with DNA, DFT Calculation, and Cytotoxicity

Four novel complexes based on the ligand piperazine (Pip) in a chair conformation have been synthesized, namely [Pd(5,5?-dcbpy)Pip]·4H2O (1), [Pt(5,5?-dcbpy)Pip]·3H2O (2), [Pd(4,4?-dcbpy)Pip]·4H2O (3), and [Pt(4,4?-dcbpy)Pip]·2H2O (4; 4,4?-dcbpy = 2,2?-bipyridyl-4,4?-dicarboxylate, 5,5?-dcbpy = 2,2?-bipyridyl-5,5?-dicarboxylate). The four complexes were characterized by elemental analysis, FTIR spectroscopy, 1H and 13C NMR spectroscopy, and single-crystal X-ray diffraction analysis. In addition, gel electrophoresis was performed on the four complexes and further insight into these complexes was gained by quantum chemistry calculations. The interaction of these complexes with fish sperm DNA (FS-DNA) was studied by UV/Vis and fluorescence spectroscopy, which revealed that they have the ability to bind to FS-DNA. The IC50 values of the four complexes range from 8.3 to 32.5 ?M. Finally, we studied the cytotoxic activities of complexes 1–4 against two different cancer cell lines. A series of bioactive experiments have revealed four Pd and Pt complexes exhibit good biological activity towards DNA. The in vitro cytotoxicity of these complexes was investigated against two different cancer cell lines, showing good cytotoxic activity.

Posted on 10 October 2014 | 12:40 pm

Assemblies of Alkaline-Earth-Metal Ions with o-Tetramethyl-Substituted Cucurbituril in the Presence of the Cadmium Tetrachloride Anion

o-Tetramethyl-substituted cucurbituril (o-TMeQ[6]), a polydentate ligand, has been synthesized and isolated in a controlled manner by using a dimer of dimethyl-substituted glycoluril and a dimer of unsubstituted glycoluril. Coordination assemblies have been investigated by reactions between alkaline earth cations and o-TMeQ[6] in the presence of [CdCl4]2–, a structure inducer, in HCl aqueous solution. X-ray diffraction analysis revealed that o-TMeQ[6] coordinates with Ca2+ or Sr2+ and forms centrosymmetric tetranuclear assemblies in the presence of [CdCl4]2–. [CdCl4]2– typically produces the “honeycomb effect” by forming honeycomb-like frameworks, which assist metal ions in coordinating to o-TMeQ[6]. The driving forces of this effect are the “outer-surface interactions” of cucurbit[n]urils. Coordination assemblies have been investigated by reactions between alkaline earth cations and o-tetramethyl-substituted cucurbituril (o-TMeQ[6]) in the presence of [CdCl4]2–, a structure inducer, in HCl aqueous solution. [CdCl4]2– forms honeycomb-like frameworks, which assist metal ions in coordinating to o-TMeQ[6].

Posted on 9 October 2014 | 7:13 pm

Copper(II) Clusters of Two Pairs of 2,3-Dihydroxybutanedioyl Dihydrazones: Synthesis, Structure, and Magnetic Properties

Condensation reactions of (2R,3R)- and (2S,3S)-2,3-dihydroxybutanedihydrazide with salicylaldehyde and 3-methoxysalicylaldehyde gave two enantiomeric pairs, (2R,3R)/(2S,3S)-2,3-dihydroxybutanedioylbis(salicylaldehydehydrazone) [(2R,3R)-BSH and (2S,3S)-BSH] and (2R,3R)/(2S,3S)-2,3-dihydroxybutanedioyl bis(3-methoxysalicylaldehydehydrazone) [(2R,3R)-MBSH and (2S,3S)-MBSH]. Their reactions with CuII salts provided two chiral hexanuclear clusters [Cu6L2(C5H5N)10]2[C5H6N]3(ClO4)7·(CH3OH)·(C5H5N) [L = (2R,3R)-BSH; (2S,3S)-BSH] and four chiral tridecanuclear clusters [Cu13L3(OH)2(CH3COO)6(C5H5N)6(DMF)3]·6DMF·3H2O [L = (2R,3R)-BSH; (2S,3S)-BSH] and [Cu13X3(OH)2(CH3COO)6(C5H5N)2(DMF)8]·6H2O [X = (2R,3R)-MBSH, (2S,3S)-MBSH]. Their structures were determined by single-crystal X-ray diffraction analysis. All six compounds are enantiomers of each other. The two hexanuclear clusters exhibit two orthogonal linear trinuclear units. The two pairs of tridecanuclear clusters display esthetic structures with different symmetries; they feature rare heptanuclear vertex-sharing dicubane cores and their six unshared CuII vertexes are linked to another six CuII ions. These represent the first examples of chiral clusters bearing dicubane cores. Magnetic studies revealed the presence of overall antiferromagnetic interactions in these compounds. Six chiral clusters of two pairs of 2,3-dihydroxybutanedioyl dihydrazones, four of which represent the first examples of chiral clusters bearing dicubane cores, are presented. All six compounds are enantiomers of each other. Magnetic studies reveal the presence of overall antiferromagnetic interactions in these compounds.

Posted on 8 October 2014 | 12:23 pm

?-Tetrasubstituted meso-Tetra(4?-n-butylphenyl)porphyrins and Their Metal Complexes: Synthesis and Structural Properties

A new family of -tetrasubstituted porphyrins, 2,3,12,13-tetra[phenylethynyl (PE)/4-methoxyphenyl (4?-CH3OPh)/4-carboxy methylesterphenyl (4?-CH3CO2Ph)]-5,10,15,20-tetrakis(4?-n-butylphenyl)porphyrin, H2T(4?-BuPh)P(R)4 and their metal (CoII, CuII and ZnII) complexes were synthesized using H2T(4?-BuPh)PBr4 as the precursor. These porphyrins show red-shifted absorption bands and follow the nature of the ?-pyrrole substituent, R: PE > Br > 4?-CO2CH3Ph ? 4?-OCH3Ph. Crystal structures of MT(4?-BuPh)P(PE)4 (M = 2H, CoII, CuII and ZnII) derivatives were determined by single-crystal XRD and they are isomorphous. The normal coordinate structure decomposition analysis of these structures reveal a slight wave-type of distortion of the macrocycle. Electrochemical redox properties of these derivatives show an anodic shift in potentials relative to their metallotetraphenylporphyrins (MTPPs), and this has been ascribed mainly to the electronic effect of the substituents. The synthesis of a series of ?-tetra(phenylethynyl/4?-methoxyphenyl/4?-carboxymethylesterphenyl)-meso-tetra(4?-n-butylphenyl)porphyrins and their metal complexes is reported. Single-crystal XRD analysis show interesting structural and intermolecular interactions in the solid state, and electrochemical redox properties show an anodic shift in redox potentials relative to their corresponding MTPPs (metallotetraphenylporphyrins).

Posted on 8 October 2014 | 12:20 pm

A Mononuclear Manganese Complex of a Tetradentate Nitrogen Ligand – Synthesis, Characterizations, and Application in the Asymmetric Epoxidation of Olefins

A new chiral manganese complex (C1) bearing a tetradentate nitrogen ligand containing chiral bipyrrolidine and benzimidazole moieties was prepared. The structure of C1 was confirmed by ESI-MS and crystallography. This manganese complex is an active catalyst for the asymmetric epoxidation of various olefins with excellent conversion (up to 99?%) and high enantiomeric excess (up to 96?%?ee) with hydrogen peroxide as the oxidant in the presence of 2-ethylhexanoic acid or acetic acid. Compared with previous structurally similar manganese complexes with different diamine backbones (C2, cyclohexanediamine; C3, diamine from L-proline), C1 showed improved asymmetric induction, especially for simple olefins such as styrene derivatives and substituted chromene. The possible reasons for the improvement of the ee values are discussed in the text on the basis of the crystal structures of the manganese complexes. A chiral manganese complex bearing a tetradentate nitrogen ligand with chiral bipyrrolidine and benzimidazole moieties is an active catalyst for the asymmetric epoxidation of various olefins with excellent conversions (up to 99?%) and up to 96?%?ee with hydrogen peroxide as the oxidant in the presence of 2-ethylhexanoic acid or acetic acid.

Posted on 8 October 2014 | 12:20 pm

Preparation of Alginate/Graphene Oxide Hybrid Films and Their Integration in Triboelectric Generators

Sodium alginate/graphene oxide (Al/GO) nanocomposite films were prepared by solvent casting. The structure, morphology, and electrical properties of Al/GO films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and thermal analysis. The utilization of such an Al/GO film for a device that uses friction as the charging process to convert mechanical energy into electric power is reported. The triboelectric generator (TEG) was fabricated by stacking a drop-cast Al/GO film bewteen indium–tin oxide (ITO)-coated poly(ethylene terephthalate) (PET) and a PET sheet. Furthermore, the utilization of such a TEG as a pressure sensor is also illustrated. Sodium alginate/graphene oxide nanocomposite films were prepared by a solvent-casting method. We report the proof of concept that such a hybrid system can be used as the active component of a triboelectric generator. The involvement of a biodegradable polymer might introduce new applications in biodegradable/biocompatible electronics.

Posted on 6 October 2014 | 11:10 am

Nanostructuring of Bridged Organosilane Precursors with Pendant Alkyl Chains

The copper-catalyzed alkyne azide cycloaddition (CuAAC) reaction was combined with sol-gel reactions for the production of bridged silsesquioxanes (BSs) in which hexyl and icosanyl chains are pendant and anchored on a single position to a triazole ring. The influence of the alkyl chain length on the structure of the BSs, represented by the notation Cn/siloxane (where n = 6 and 20), was examined. The C20/siloxane hybrid is a hydrophobic material that exhibits a hierarchically structured lamellar bilayer organization, a texture composed of microplates of nanometer thickness, and a reversible time-independent order/disorder phase transition (onset at 60 °C). The driving forces for self-assembly are van der Waals interactions between the icosanyl chains and ?-? interactions between the triazole rings. In the essentially amorphous C6/siloxane hybrid, the latter contribution promotes the genesis of a pre-lamellar phase similar to that found in C20/siloxane. A new bridged silsesquioxane with hierarchically structured lamellar bilayer structure and a texture composed of microplates of nanometer thickness was obtained by sol-gel and self-assembly by using a bridged organosilane carrying a pendant icosanyl chain produced by click chemistry. The hybrid exhibits a time-independent reversible order/disorder phase transition in a heating-cooling cycle.

Posted on 1 October 2014 | 7:23 pm

Constitutional Hybrid Materials – Toward Selection of Functions

This microreview reveals a new strategy to transcribe supramolecular architectures in self-organized constitutional hybrids. In particular, the use of communicating reversible-covalent and supramolecular hydrophobic interfaces between organic/supramolecular and inorganic/siloxane networks represents a useful approach for improving their compatibility. Interpenetrated hybrid components lead, after the sol–gel process, to materials in which the features of supramolecular and inorganic networks are expressed through cross-over and linear processing schemes. Such a “dynamic marriage” between the processes of supramolecular self-assembly and inorganic sol–gel polymerization, which communicate synergistically, leads to higher self-organized hybrid materials on increased micrometric scale. Considering the simplicity of this strategy, possible applications in membranes and sensors are effective, reaching close to novel expressions of complex matter. This review will focus on the implementation of constitutional dynamic chemistry (CDC) toward constitutional hybrid materials, emphasizing recent developments in biomimetic ion channels, membranes, and constitutional hybrid materials.

Posted on 29 September 2014 | 11:30 am

Conformational Changes and Phase Behaviour in the Protic Ionic Liquid 1-Ethylimidazolium Bis(trifluoromethylsulfonyl)imide in the Bulk and Nano-Confined State

We report a Raman spectroscopic study of conformational changes to the TFSI anion in the protic ionic liquid 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide, [C2HIm][TFSI], in its bulk and nano-confined state. We show that the TFSI anion is found as a mixture of cis and trans conformations at room temperature and in the liquid state, whereas this equilibrium shifts towards an increased cis population upon confinement in silica. In addition, the strong Raman signature at ca. 743 cm–1 assigned to TFSI is found at systematically higher frequencies in the confined state. These findings suggest a higher packing efficiency, or density, for the ionic liquid at the silica surface. Moreover, the enthalpy of conformational change is only marginally affected upon confinement (4.32?±?1.30 vs. 5.27?±?1.09 kJ?mol–1), and the entropy is found to be a few J?mol–1?K–1 higher in the confined state. Raman spectra recorded upon heating from very low temperatures show that the phase behaviour of the ionic liquid is also affected by confinement, with crystallization upon cooling being frustrated in favour of an amorphous glassy phase. To summarize, our results indicate that the interaction established in the ionogels between the silica surface and the protic ionic liquid [C2HIm][TFSI] favours local structural disorder, in conceptual agreement with the slightly higher experimentally estimated entropy. Conformational changes of the TFSI anion in the protic ionic liquid C2HImTFSI have been monitored by temperature-dependent Raman spectroscopy for the bulk and nano-confined states. Phase behaviours have also been spectroscopically investigated at a range of temperatures. In the nano-confined state the cis form predominates and the enthalpic term was higher.

Posted on 29 September 2014 | 11:30 am

Prussian Blue Films Produced by Pentacyanidoferrate(II) and Their Application as Active Electrochemical Layers

Iron complexes such as ferri/ferrocyanides are usually employed as electrochemical mediators in portable devices for the quick diagnosis of diseases. Stable complexes designed for the electrochemical active layer may render devices with better performance and lifetimes than conventional devices. In this work we have synthesized and characterized spectroscopically, electrochemically, and by DFT the complex Na4[Fe(CN)5(isn)] (isn = isonicotinate). This complex was used as a single-source precursor of Prussian Blue (PB) in solution at pH 2.0 and 3.0, as confirmed by UV/Vis spectroscopy. Potentiostatic deposition of PB onto glassy carbon electrodes provided stable films at pH 3.0 and 5.0, with electrocatalytic activity for ascorbic acid oxidation with a linear response in the range 20–200 ?M and an limit of detection of 12 ?M. The anodic peak potential of the modified electrodes varied with solution pH with a minimum value of 0.350 V versus NHE at pH 5.0. Prussian Blue is widely used in electrochemical sensors due to its ability to catalyze H2O2 reduction. Glucose meters are common point-of-care devices that employ ferricyanide as a redox mediator. The sensitivity, selectivity, and specificity of these devices can be improved by using Prussian Blue produced by pentacyanidoferrate(II) as an electroactive species rather than a redox mediator.

Posted on 24 September 2014 | 12:10 pm

Organic–Inorganic Hybrid Membranes Based on Sulfonated Poly(ether ether ketone) and Tetrabutylphosphonium Bromide Ionic Liquid for PEM Fuel Cell Applications

Ionic liquids (ILs), with their inherent ionic conductivity and negligible vapor pressure, can be exploited in proton exchange membrane (PEM) fuel cells for which thermal management is a major problem and the cell operation temperature is limited by the boiling point of water. In this work, sulfonated poly(ether ether ketone) (SPEEK) membranes were modified by the incorporation of tetrabutylphosphonium bromide ([P4 4 4 4]Br) by solvent-casting. Electrochemical impedance spectroscopy (EIS) was used to study the electrical properties of the modified membranes. Simultaneous TGA and FTIR studies were used to evaluate the thermal stability and chemical structure of the modified membranes, respectively. 1H NMR spectroscopy was applied to probe the changes in the chemical environment due to the interaction between the ionic liquid and the polymer. Mechanical properties were studied by dynamic mechanical analysis. The temperature-dependent behavior of the viscosity of the [P4 4 4 4]Br ionic liquid was observed to obey the Vogel–Fulcher–Tammann (VFT) equation, and was correlated to the ion-conducting properties of the IL-doped SPEEK membranes. Polymer–ionic liquid electrolyte membranes were fabricated from tetrabutylphosphonium bromide ([P4 4 4 4]Br) and sulfonated poly(ether ether ketone) (SPEEK). Their thermal, mechanical, structural and electrical properties show promise for their use in high-temperature fuel cell applications.

Posted on 19 September 2014 | 10:20 am

Investigating the Formation Mechanism of Arene Ruthenium Metallacycles by NMR Spectroscopy

The stereochemical properties of twelve dinuclear arene ruthenium complexes have been studied in solution. The dinuclear complexes of the general formula [(p-cymene)2Ru2(OO?OO)(Ln)2](CF3SO3)2 (OO?OO = oxalato, 2,5-dioxido-1,4-benzoquinonato, 5,8-dioxido-1,4-naphthoquinonato; Ln = 4-phenylpyridine, 4-styrylpyridine, 4-methylpyridine, 4-tert-butylpyridine) have been isolated as mixtures of the cis and trans isomers. All of the complexes showed lability of the pyridyl-based ligands (Ln) in solution and rapid exchange between the cis and trans isomers. The equilibrium between the cis and trans isomers was confirmed by 1H NMR spectroscopy, and the intermediate species were identified and, thus, provided valuable insights into the formation mechanism of arene ruthenium metalla-assemblies. The stereochemical properties of twelve dinuclear arene ruthenium complexes have been studied in solution by NMR spectroscopy. All complexes showed lability of the pyridyl-based ligands in solution and rapid exchange between the cis and trans isomers. The intermediate species have been identified and, thus, provided insights into the formation mechanism of arene ruthenium metalla-assemblies.

Posted on 12 September 2014 | 10:10 am

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