Polymorph-Dependent Molecular Valence Tautomerism Synchronized with Crystal-Melt Phase Transitions

摘要

This paper describes a molecular valence tautomeric (VT) testability synchronized with polymorphic crystal-melt phase transitions of a newly designed VT complex, Co(C9Espy)2(3,6-DTBQ)2 (CoC9Espy, C9Espy = dinonyl-pyridine-3,5-dicarboxylate and 3,6-DTBQ = 3,6-di-tert-butyl-semiquinonate (3,6-DTBSQ) or catecholate (3,6-DTBCat)). Two polymorphic crystals which are the thermodynamically stable phase (K1) and the kinetically stable phase (K2), commonly containing a low spin-Co~(III)(C9Espy)2(3,6-DTBSQ)(3,6-DTBCat) (ls-Co~(III)) tautomer with a low-spin Co~(III) atom and mixed-valence ligands. These polymorphic crystals show a molecular VT interconversion that is synchronized with crystal-to-melt phase transitions at different temperatures, 368.2 and 362.6 K for the ls-Co~(III)is contained in K1 and the ls-Co~(III)is contained in K2 phases, respectively. Interestingly, the ls-Co~(III)is contained in K2 obtained from a melt of a high spin-Co~(II)(C9Espy)2(3,6-DTBSQ)2 (hs-Co) tautomer with a high-spin Co atom with two 3,6-DTBSQ exhibits a double-melting phenomenon that includes, in part, the thermodynamically unfavorable hs-Co~(II)-to-ls-Co~(III) VT interconversion. Eventually, three types of VT interconversions synchronized with macroscopic crystal-melt phase transitions appear either in equilibrium or nonequilibrium conditions: (1) the thermodynamically stable Zs-Co~(III)is contained in K1 to the hs-Cois contained in melt, (2) the metastable Zs-Co~(III)is contained in K2 to the hs-Co~(II)is contained in melt, and (3) the relaxing process of the metastable hs-Cois contained in melt to the thermodynamically stable ls-Co~(III)is contained in K1. A new strategy for simultaneous control of molecular states and macroscopic phases using thermodynamically and kinetically formed polymorphic crystalline phases is presented.