Influence of Intermolecular Interactions on Valence Tautomeric Behaviors in Two Polymorphic Dinuclear Cobalt Complexes.

Two polymorphic structures have been well determined in a valence tautomeric (VT) dinuclear cobalt complex. These polymorphs showdistinct thermal and photo magnetic behaviors, and are thus, ideal for studyingthe "pure" intermolecular factors to VT transitions. In polymorph 1A, the VT cations are arranged head-to-waist with their neighbors and exhibit weak pai-pai interactions, resulting in a gradual and incomplete thermal VT transition. In contrast, the cations in polymorph 1B are arranged head-to-tail and exhibit relatively strong pai-pai interactions, leading to an abrupt and complete thermal VT transition with adjustable hysteresis loop at around room temperature. The VT process for both polymorphs can be induced by light, but the light-excited state of 1B*2H2O has a higher thermal relaxation temperature than that of 1A*3H2O.