Non-oxo vanadium(iv) alkoxide chemistry: Solid state structures, aggregation equilibria and thermochromic behaviour in solution

摘要

The reversible thermochromic behaviour of homoleptic [{V(OR) _4}_n] complexes in solution [R = Pr~i (product I), Bu~s (B~s), Nep (N) and Cy (C)] is accounted for the existence of an aggregation equilibrium involving dimeric and monomeric species in which vanadium(iv) is respectively five- and four-coordinate. Bulky R groups such as Bu~t and Pe~t (tert-pentoxide) prevent aggregation and therefore give rise to exclusively mononuclear compounds (B~t and P~t, respectively) that are not thermochromic. The complexes and their temperature-dependent interconversion were characterised by single crystal X-ray diffractometry, magnetic susceptibility measurements and electronic, FTIR and EPR spectroscopies in a wide temperature range. Equilibrium constants and enthalpy and entropy changes for the dimerization reactions have been determined and compared with literature data.