Divanadium(V) and Trapped Valence Linear Tetravanadium(IV,V,V, IV) Complexes

作者：Sarkar Anindita; Pal Samudranil^*

来源：European Journal of Inorganic Chemistry, 2009, 2009(35): 5391-5398.

DOI：10.1002/ejic.200900680

• Vanadium
• Mixed-valent compounds
• EPR spectroscopy
• Redox chemistry
• Localized valence

In an acetonitrile/water mixture, reactions of the NN'-bis(diacetyl)hydrazine (H(2)diah), bis(acetylacetonato)oxidovanadium(IV)[VO(acac)(2)] and monodentate N-coordinating heterocycles (hc) in a 1:2:2 mol ratio provide yellow divanadium(V) complexes of formula [(hc)O(2)V(mu-diah)VO(2)(hc)] (1, hc = imidazole; 2, hc = pyrazole; 3, hc = 3,5-dimethyl pyrazole). On the other hand, in the same solvent mixture reactions of the same reagents in a 1:4:2 mol ratio produce green linear tetravanadium(IV,V,V,IV) complexes of formula [(acaC)(2)OV(mu-O)VO-(hc)(mu-diah)(hc)OV(mu-O)VO(acaC)(2)] (4, hc = imidazole; 5, hc pyrazole; 6, hc = 3,5-dimethyl pyrazole). The complexes 1-6 have been characterized by elemental analysis, magnetic susceptibility, and various spectroscopic and electrochemical measurements. The X-ray crystal structures of 1, 3 and 6 have been determined. In all three structures, the diazine Iigand diah 2- is in trans configuration. Metal-centred bond parameters are consistent with the localized electronic structure of the two trans-bent {OV(mu-O)VO}(3+) cores present in 6. The pentavalent metal centres in 1, 3 and 6 are in a distorted trigonal-bipyramidal N(2)O(3) coordination environment, while the terminal tetravalent metal centres in 6 are in a distorted octahedral 06 coordination sphere. The eight-line EPR spectra of the tetravanadium species (4-6) in dimethyl sulfoxide at ambient temperature indicate the rare valence localized electronic structure in the fluid phase. All the complexes are redox active and display metal-centred electron transfer processes in dimethyl sulfoxide solution. A reduction within -0.78 to -0.94 V (vs. Ag/AgCl) is observed for the divanadium(V) species 1-3, while a reduction and an oxidation are observed in the potential ranges -0.82 to -0.90V and 0.96 to 1.12 V (vs. Ag/AgCl), respectively, for the tetravanadium species 4-6.

• 出版日期2009-12