Regularities of thermal decay of carbonyl chalcogenide metal clusters

The thermal decay of 19 individual carbonyl homo- and heterochalcogenide clusters with different M/X ratios (M = Fe, Mn, Pt, Cr, W, Mo, Re, Ru; X = S, Se, Te) was studied by differential scanning calorimetry and thermogravimetry. The process is stepwise and occurs at relatively low temperatures (100—350 °C). The general fact of incomplete removal of carbon monoxide (due to the formation of carbide and oxide impurities) during thermolysis of narbonyl chalcogenide clusters with the M : X ratio greater than 1 was elucidated. Conversely, when M : X 1 (or at any M/X ratio for clusters containing methylcyclopentadienyl groups), pure metal chalcogenides are formed.     

Synthesis and molecular structure of niobocene(tricarbonyl)(π-cyclopentadienyl)molybdenum with metalmetal bond and unusual coordination of carbonyl groups

(C₅H₅)₂NbBH₄ reacts with C₅H₅M(CO)₃Me in toluene solution in the presence of Et₃N to give binuclear complexes (C₅H₅)₂NbM(CO)₃C₅H₅ where M is Mo or W (IV and V, respectively). The structure of IV has been studied by X-ray diffraction (the crystals are orthorhombic, a 12.748(5), b 16.745(6), c 14.314 $\text{A/ac>}\text{?}$;; Z = 8, space group of Pbca, automatic difractometer Syntex P2_I, λ(Mo-K_α, 1382 reflections, R = 0.056, R_w = 0.058). Molecule IV contains a wedge-like sandwich (π-C₅H₅)₂Nb (NbC 2.37–2.48, CC (av) 1.42 $\text{A/ac>}\text{?}$;, angle between ring planes 49°) linked with the (π-C₅H₅)Mo(CO) fragment by a direct NbMo bond (3.073 $\text{A/ac>}\text{?}$;) and two bridging CO groups, one nonsymmetrically bonded through the carbon atom only (CO 1.17, NbC 2.53, MoC 2.02 $\text{A/ac>}\text{?}$;) and the other σ-bonded to Mo (MoC 1.944 $\text{A/ac>}\text{?}$;) and π-bonded to Nb (CO 1.22, NbC 2.22, NbO 2.26 $\text{A/ac>}\text{?}$;). Three types of carbonyl groups present in IV give rise to strong IR bands at 1870, 1700 and 1560 cm^?1 assigned to the terminal, μ-bridging and σ, π-bridging CO groups respectively. Complex IV has a similar structure. The electronic structure of IV and its dissociation across the NbMo bond are discussed.     

Synthesis,structure, and properties of a new trinuclear iron cluster, [(MeOH)(H2O)2Fe3(μ3-O)(μ-OOCC6H4OCH2C5H4NH)6] (ClO4)7 · · 8MeOH · 3.5H2O

Reactions of iron(m) salts with a new bidentate ligand, which is potentially capable of forming binuclear iron complexes upon complexation, were studied. Under various conditions, we succeeded in isolating only the trinuclear cationic complex (Fe^III ₃(O₂CR)6(₃-)17+ (1), where RCO₂ is 2-(pyrid-2-ylmethoxy)benzoic acid protonated at the pyridyl moiety. The structure of 1 was established by spectral, magnetic, and X-ray structural studies. Cyclic voltammetry in McCN in the temperature range from -35 to 20 °C demonstrated that 1 undergoes successive Fe^IIIFe^II reduction in three one-electron stages, which is indicative of the electronic interaction between iron atoms in the complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2086–2092, August, 1996.     

CO oxidation at platinum-molybdenum electrodes

CO oxidation at Pt-Mo electrodes prepared by different procedures is studied. When CO is oxidized from its saturated solutions at Mo-containing electrodes, catalysis is observed at lower potentials (<0.4 V (RHE)); inhibiting, at higher potentials (>0.7 V). When adsorbed CO is oxidized in supporting electrolyte, no oxidation current is observed at lower potentials; the current observed on platinum at higher potentials (>0.7 V) is also lowered in the presence of molybdenum. Depending on the preparation procedure, catalysts with different phase structure were obtained, namely, as the Pt and Mo separate phases, alloys with the platinum-type crystal lattice, or mixed amorphous deposits. The catalyst phase structure did not affect the general picture of observed processes; however, it had influence on the magnitude of the catalytic and inhibiting effects. The presence of crystallinity made the catalyst more stable against oxidation. Amorphous structures were unstable during the potential cycling and the catalyst storage.     

Tolerant-to-methanol cathodic electrocatalysts based on organometallic clusters

A new approach to the fabrication of catalytic systems based on hetero-and homometal-chalcogenide clusters of Pt-M-X type (M: Fe, Mn; X: S, Se, Te), which provides the reproducibility of catalyst composition and uniform distribution of catalyst over the carbon support, is proposed. Thus obtained catalysts are characterized using the XRD, TEM, and EDAX methods. The electrocatalytic activity of these systems in the oxygen reduction reaction, the role of the nature of chalcogenide atom and the atom of the second metal, which is the platinum partner, and the electrochemical behavior of nonplatinum chalcogenide systems are studied.