The first thermochromic vanadium(IV) alkoxide system

When the dark green, crystalline [V2(μ-OPri)2(OPri)6] is dissolved in hexane, toluene, dichloromethane, tetrahydrofuran or propan-2-ol at room temperature, a royal blue solution is formed, which changes to gold yellow upon cooling to 210 K. Allowing the system to warm again to 300 K reversibly restores the blue colour. This solution thermochromic behaviour can be accounted for by an equilibrium between a blue, monomeric, hot form (V(OPri)4) and a yellow, dimeric vanadium(IV) cold form (V2(OPri)8).