Understanding the effects of intermolecular interactions on metal-to-metal charge transfer (MMCT) is crucial to develop molecular devices by grafting MMCT-based molecular arrays.H erein, we report as eries of solvent-free {Fe 2 Co 2 } compounds sharing the same cationic tetranuclear {[Fe(PzTp)-(CN) 3 ] 2 [Co(dpq) 2 ] 2 } 2+ (PzTp À = tetrakis(pyrazolyl)borate, dpq = dipyrido[3,2-d:2',3'-f]quinoxaline) square units but having anions with different size, including BF 4 À ,PF 6 À ,OTf À ,and [Fe(PzTp)(CN) 3 ] À .I ntermolecular p···p interactions between dpq ligands,w hichc oordinate to cobalt ions in the {[Fe-(PzTp)(CN) 3 ] 2 [Co(dpq) 2 ] 2 } 2+ units,c an be modulated by introducing different counterions,r egulating the distortion of the CoN 6 octahedron and ligand field around the cobalt ions. This change results in different MMCT behavior.C omputational analyzes reveal the substantial role of the intermolecular interactions tuned by the presence of different counteranions on the MMCT behavior.

The on/off-switching of single-chain magnetic behavior tuned through bidirectional light irradiation.

Electron transfer in solid is crucial to switchable magnetic, electrical, optical and mechanical properties. However, it is a formidable challenge to control electron-transfer behaviors via manipulation of crystalline phases, especially through dynamic crystalline transformation. Herein, three crystalline phases of an {Fe2Co2} compound were obtained via enhancement of intermolecular π···π interactions inducing successive single-crystal-to-single-crystal transformations, from solvated 1·2CH3OH·4H2O, to desolvated 1 and its polymorph 1a accompanying electron transfer. 1·2CH3OH·4H2O showed thermally induced reversible intermetallic electron transfer in mother liquor. No electron-transfer behavior was observed in 1. 1a showed reversible intermetallic electron transfer upon thermal treatment or alternative irradiation with 808- and 532-nm lasers at cryogenic temperatures. The electron-transfer behaviors significantly change the magnetic and optical properties, providing a strategy to realize different electron-transfer behaviors and switchable functions via π···π interactions manipulated dynamic crystalline transformation.