Reporting a New Class of Divanadium(V) Compounds Connected by an Unsupported Hydroxo Bridge

• Published in: Inorganic chemistry 2008-05, Vol.47 (9), p.3709-3718
• Main Authors: Chatterjee, Pabitra Baran, Mandal, Debdas, Audhya, Anandalok, Choi, Ki-Young, Endo, Akira, Chaudhury, Muktimoy
• Format: Article
• Language: English
• Subjects: Derivatives; Electrodes; Molecular structure; Reduction; Reporting; Silver; Vanadium; Voltammetry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic702286h

Dinuclear oxovanadium(V) compounds [LVVO(μ-OH)OVVL](PF6) [H2L = N,N′-tert-ethylene bis(salicylideneimine) (H2Salen) and its derivatives] (1–3) have been obtained by aerial oxidation of VIVOL precursors in THF in the presence of added NH4PF6. The oxidized vanadium(V) probably extracts an OH− ligand from the residual moisture in the solvent and is retained as an unsupported hydroxo-bridge between the metal centers of these compounds as confirmed by single-crystal X-ray diffraction analyses. The molecules of 1–3 have centrosymmetric structures with each vanadium center having a distorted octahedral geometry. The bridging OH− group is located trans to the terminal VO t bond. The latter exerts strong trans labilizing influence to set the participating vanadium centers apart by about 4.1 Å. These separations are by far the largest (e.g., V···V#, 4.131 Å in 1) among all binuclear compounds containing an unsupported hydroxo bridge reported to date. The complexes retain their identity also in solution as established by 1H NMR spectroscopy. Electrochemically, the behaviors of 1–3 are quite interesting as studied by cyclic voltammetry in acetonitrile, each undergoing three (except 3) nearly reversible metal-based reductions, all in the positive potential range (e.g., at E ½ = 0.57, 0.39, and 0.04 V versus Ag/AgCl reference for 1) as indicated by steady state voltammetry. The electrode process at 0.39 V appears to involve a single-step two-electron transfer as revealed from the normal and differential pulse voltammetric data and probably includes a combination of VV−VIV ↔ VIII−VIV mixed oxidation states. Compounds 1–3 thus provide a unique example of divanadium compounds in which the metal centers are linked by an unsupported hydroxo-bridge.