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Divanadium(V) and Trapped Valence Linear Tetravanadium(IV,V,V,IV) Complexes
Author(s) -
Sarkar Anindita,
Pal Samudranil
Publication year - 2009
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200900680
Subject(s) - chemistry , pyrazole , crystallography , acetonitrile , valence (chemistry) , imidazole , coordination sphere , metal , electron paramagnetic resonance , octahedron , crystal structure , medicinal chemistry , stereochemistry , physics , organic chemistry , chromatography , nuclear magnetic resonance
In an acetonitrile/water mixture, reactions of the N , N ′‐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(μ‐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(μ‐O)VO(hc)(μ‐diah)(hc)OV(μ‐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 ligand diah 2– is in trans configuration. Metal‐centred bond parameters are consistent with the localized electronic structure of the two trans ‐bent {OV(μ‐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 O 6 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 –0.90 V and 0.96 to 1.12 V (vs. Ag/AgCl), respectively, for the tetravanadium species 4 – 6 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)