Solid-State Hydrogen-Bond Alterations in a [Co Fe ] Complex with Bifunctional Hydrogen-Bonding Donors.

A hydrogen-bonding donor-acceptor system, Co Fe (bpy*) (CN) (tp*) ⋅2ABA⋅4BN⋅2PE (1 s ), was prepared by co-crystallization of an external stimuli-responsive cyanide-bridged tetranuclear [Co Fe ] complex and bifunctional hydrogen-bonding donors, p-aminobenzoic acid. Compound 1 s exhibited a gradual electron-transfer-coupled spin transition (ETCST), and the removal of solvent molecules led to an abrupt thermal ETCST behavior with increased transition temperature. X-ray structural analysis revealed that the modification of ETCST was caused by a significant alteration of a hydrogen-bonding mode between the tetranuclear [Co Fe ] cations and ABA molecules. Variable temperature IR measurements indicated that the desolvated form, 1 d , showed dynamic alteration of hydrogen-bonding interactions coupled with thermal ETCST behavior. These results suggested that the tetranuclear [Co Fe ] complex shows solid-state modulations of hydrogen-bond strengths by external stimuli.