Pavel A. Abramov

Synthetic Tuning of Redox, Spectroscopic, and Photophysical Properties of {Mo6I8}4+ Core Cluster Complexes by Terminal Carboxylate Ligands

The reactions between the tetra-n-butylammonium salt of [{Mo6I8}I6](2-) and silver carboxylates RCOOAg (R = CH3 (1), C(CH3)3 (2), α-C4H3O (3), C6H5 (4), α-C10H7 (5), or C2F5 (6)) in CH2Cl2 afforded new carboxylate complexes [{Mo6I8}(RCOO)6](2-). The complexes were characterized by X-ray single-crystal diffraction and elemental analysis, cyclic/differential pulse voltammetry, and IR, NMR, and UV-visible spectroscopies. The emission properties of the complexes 1-6, and those of the earlier reported complexes with R = CF3 (7) and n-C3F7 (8), were studied both in acetonitrile solution and in the solid state. In deaerated CH3CN at 298 K, all of the complexes 1-8 exhibit intense and long-lived emission with the quantum yield and lifetime being 0.48-0.73 and 283-359 μs, respectively. The oxidation (Eox)/reduction (Ered) potentials of the complexes correlate linearly with the pKa value of the terminal carboxylate ligands L = RCOO (pKa(L)). Reflecting the pKa(L) dependences of Eox/Ered, the emission energy (νem) of the complexes was also shown to correlate with pKa(L). The present study successfully demonstrates synthetic tuning of the redox, spectroscopic, and photophysical characteristics of a {Mo6I8}(4+)-based cluster complex with pKa(L).

Photogeneration of Hydrogen from Water by Hybrid Molybdenum Sulfide Clusters Immobilized on Titania

Two new hybrid molybdenum(IV) Mo3 S7 cluster complexes derivatized with diimino ligands have been prepared by replacement of the two bromine atoms of [Mo3 S7 Br6 ](2-) by a substituted bipyridine ligand to afford heteroleptic molybdenum(IV) Mo3 S7 Br4 (diimino) complexes. Adsorption of the Mo3 S7 cores from sample solutions on TiO2 was only achieved from the diimino functionalized clusters. The adsorbed Mo3 S7 units were reduced on the TiO2 surface to generate an electrocatalyst that reduces the overpotential for the H2 evolution reaction by approximately 0.3 V (for 1 mA cm(-2) ) with a turnover frequency as high as 1.4 s(-1) . The nature of the actual active molybdenum sulfide species has been investigated by X-ray photoelectron spectroscopy. In agreement with the electrochemical results, the modified TiO2 nanoparticles show a high photocatalytic activity for H2 production in the presence of Na2 S/Na2 SO3 as a sacrificial electron donor system.

Supramolecular assemblies of triblock copolymers with hexanuclear molybdenum clusters for sensing antibiotics in aqueous solutions via energy transfer

The work introduces the supramolecular assembly of triblock copolymers, namely (PEO)13(PPO)30(PEO)13 (L64), (PPO)14(PEO)24(PPO)14 (17R4), (PPO)8(PEO)22(PPO)8 (10R5) and (PEO)21(PPO)67(PEO)21 (P123) with novel cluster complexes [K(diglyme)(CH3CN)]2[Mo6I14] (1) and [K2(diglyme)(CH3CN)5][Mo6I14] (2) as a route to increase their water solubility. Dynamic light scattering and photophysical measurements reveal the decisive influence of the arrangement of PEO and PPO blocks and of their length on both colloidal and photophysical properties of these solutions. ES-MS data reveal [Mo6I14]2− clusters as the predominant form in aqueous solutions of L64 and P123. The steady state and time resolved luminescence data indicate concentration dependent sensitizing of the Mo-centered luminescence through the energy transfer from difloxacin to [Mo6I14]2− mediated by the ion-pairing. The impact of both arrangement and length of PEO and PPO blocks in the luminescent response of [Mo6I14]2− to difloxacin is discussed. The aqueous solutions of L64 at pH 4 provide the optimal conditions for the sensing of difloxacin through the cluster luminescence.

Coordination-Induced Condensation of [Ta6O19]8–: Synthesis and Structure of [{(C6H6)Ru}2Ta6O19]4– and [{(C6H6)RuTa6O18}2(μ-O)]10−

Reaction of [(C6H6)RuCl2]2 and Na8[Ta6O19] gives two new hybrid organometallic POM complexes, Na10[{(C6H6)RuTa6O18}2(μ-O)]·39.4H2O (Na10-1) and Na4(trans-[{(C6H6)Ru}2Ta6O19]·20H2O (Na4-2). In both cases the half-sandwich fragments {(C6H6)Ru}(2+) are coordinated as additional vertices to the {Ta3(μ2-O)3} triangles of the hexatantalate. According to NMR and ESI-MS data, the dimeric complex [{(C6H6)RuTa6O18}2(μ-O)](10-) dissociates in water with the formation of monomeric [(C6H6)RuTa6O19](6-) species (1a). X-ray structural characterization and aqueous speciation of the complexes by (13)C, (1)H, and DOSY NMR; ESI-MS; and capillary electrophoresis (CE) have been carried out.

Polyoxometalate, Cationic Cluster, and γ-Cyclodextrin: From Primary Interactions to Supramolecular Hybrid Materials

Herein, we report on a three-component supramolecular hybrid system built from specific recognition processes involving a Dawson-type polyoxometalate (POM), [P2W18O62]6-, a cationic electron-rich cluster [Ta6Br12(H2O)6]2+, and γ-cyclodextrin (γ-CD). Such materials have been investigated using a bottom-up approach by studying the specific interactions between γ-CD and both types of inorganic units. Their ability to interact has been investigated in the solid state by single-crystal X-ray diffraction (XRD) and in solution using multinuclear NMR methods (including DOSY, EXSY, and COSY), electrospray ionization mass and UV-vis spectroscopies, electrochemistry, and isothermal titration calorimetry experiments. Single-crystal XRD analysis reveals that POM:γ-CD constitutes a highly versatile system which gives aggregates with 1:1, 1:2, and 1:3 stoichiometry. Surprisingly, these arrangements exhibit a common feature wherein the γ-CD moiety interacts with the Dawson-type POMs through its primary face. We present also the first structural model involving an octahedral-type metallic cluster with γ-CD. XRD study reveals that the cationic [Ta6Br12(H2O)6]2+ ion is closely embedded within two γ-CD units to give a supramolecular ditopic cation, suitable to be used as a linker within extended structure. Solution study demonstrates clearly that pre-associations exist in solution, for which binding constants and thermodynamic parameters have been determined, giving preliminary arguments about the chaotropic nature of the inorganic ions. Finally, both building blocks, i.e., the ditopic supramolecular cation {[Ta6Br12(H2O)6]@2CD}2+ and the Dawson-type anion, react together to give a three-component, well-ordered hybrid material derived either as a supramolecular hydrogel or single crystals. The solid-state structure shows an unprecedented helicoidal tubular chain resulting from the periodic alternation of POM and supramolecular cation, featuring short hydrogen-bonding contacts between the electron-poor POM and electron-rich cluster. The 1D tubular ionic polymer observed in the single crystals should make it possible to understand the long-range ordering observed within the hydrogel hybrid material. The supramolecular chemical complementarities between the γ-CD-based ditopic cation and POM open a wide scope for the design of hybrid materials that accumulate synergistic functionalities.

New polyoxotantalate salt Na 8 [Ta 6 O 19 ]·24.5H 2 O and its properties

The interaction of Ta2O5 with sodium hydroxide at 400°C yields Na8[Ta6O19], which can be recrystallized from an aqueous solution in the form of Na8[Ta6O19]·24.5H2O. The complex is characterized by IR spectroscopy, thermogravimetry, powder XRD, and single crystal XRD: hexagonal system, P63 space group, a = 12.3622(2) Å, c = 31.4305(7) Å, V = 4159.81(13) Å3, dx = 3.217 g/cm3, R = 0.0195.

Halogen Contacts‐Induced Unusual Coloring in BiIII Bromide Complex: Anion‐to‐Cation Charge Transfer via Br⋅⋅⋅Br Interactions

A yellow bromobismuthate {(2-BrPy)2 H}[BiBr4 ] (1, 2-BrPy=2-bromopyridinium) transforms into the unusually deeply colored cherry-red (2-BrPyH)2 [BiBr5 ] (2). A combination of structural studies and theoretical calculations confirms that the appearance of short non-covalent Br⋅⋅⋅Br interactions (≈3.3 Å) in 2 is responsible for the anion-to-cation charge transfer (LP(Brligand )→σ*(Br-C)), yielding dramatic changes in optical behavior. This effect opens the way towards novel halogen bonding-templated halometalate-based hybrid materials with enhanced optical properties.

First heteroleptic Mo3S7 clusters containing non-innocent phenanthroline ligands

Reaction of the thiobromide [Mo3S7Br6]2− cluster anion with 5,6-dimethyl-1,10-phenanthroline (Me2Phen) in solution leads to the substitution of two bromide ligands and the subsequent formation of a new mixed-ligand neutral complex [Mo3S7Br4(Me2Phen)] (I). Reaction of [Mo3S7Br6]2− with 5,6-dimethyl-1,10-phenanthroline in CH2Cl2 followed by treatment of I with Na(Dtc) · 3H2O (Dtc = diethyldithiocarbamate) results in the new mixed-ligand cluster complex [Mo3S7(Dtc)2(Me2Phen)]2+ (IIa). Slow evaporation of the CHCl3 solution of the complex in the presence of PF6− gives crystals of {[Mo3S7(Dtc)2(Me2Phen)]Br}PF6 · 3CHCl3 (II) characterized by X-ray structural analysis. Close contacts S...S result in the formation of cationic dimers {[Mo3S7(Dtc)2(Me2Phen)]2}4+ which form infinite chains through additional Sax...Br contacts. All compounds were characterized by IR, elemental analysis and ESI-MS. Synthesized complexes represent the first examples of heteroleptic Mo3S7 clusters containing phenanthroline ligands.

Crystal structures of two solvates of molybdenum octahedral clusters: (Bu4N)2[Mo6Cl8(O3SC6H4CH3)6]·2CH3CN and (Bu4N)2[Mo6Cl8(O3SC6H4CH3)6]·2CH2Cl2

Crystal structures of two solvates (Bu4N)2[Mo6Cl8(O3SC6H4CH3)6]·2CH3CN (1) and (Bu4N)2[Mo6Cl8(O3SC6H4CH3)6]·2CH2Cl2 (2) are determined. Both compounds contain cluster [Mo6Cl8(O3SC6H4CH3)6]2− anions. Molybdenum atoms are coordinated with monodentate carboxylate ligands (Mo-O 2.101(3)–2.110(3) Å in 1; 2.088(7)–2.109(2) Å in 2).

Nonconventional Three-Component Hierarchical Host–Guest Assembly Based on Mo-Blue Ring-Shaped Giant Anion, γ-Cyclodextrin, and Dawson-type Polyoxometalate

In this communication, we report on a noteworthy hybrid supramolecular assembly built from three functional components hierarchically organized through noncovalent interactions. The one-pot synthesis procedure leads to the formation of large Mo-blue ring-shaped anion {Mo154}, which contains the supramolecular adduct based on the symmetric encapsulation of the Dawson-type [P2W18O62]6- anion by two γ-cyclodextrin units. Such a nanoscopic onion-like structure, noted [P2W18O62]@2γ-CD@{Mo154} has been characterized by single-crystal X-ray diffraction, thus demonstrating the capability of the giant inorganic torus to develop relevant supramolecular chemistry, probing the strong affinity of the inner and outer faces of the γ-CD for the polyoxometalate surfaces. Furthermore, interactions and behavior in solution have been studied by multinuclear NMR spectroscopy, which supports specific interactions between γ-CD and POM units. Finally, the formation of this three-component hybrid assembly from one-pot procedure, in water and using nearly stoichiometric conditions, is discussed in terms of the driving forces orchestrating this highly efficient multilevel recognition process.