The cooperative effects of ligand substituent positions and solvents on spin crossover in Mn(III) complexes based on hexadentate Schiff-base ligands

Abstract

Spin crossover (SCO), as a molecular bistable phenomenon, has attracted extensive interest. In this paper, the syntheses, crystal structures and magnetic properties of three Mn(III) hexadentate Schiff-base complexes [Mn(3-OMe-sal-N-1,5,8,12)]AsF6·H2O (1), [Mn(4-OMe-sal-N-1,5,8,12)]AsF6·H2O (2) and [Mn(5-OMe-sal-N-1,5,8,12)]AsF6(3) have been reported. The substituent positions of ligands and solvent molecules have a cooperative effect on SCO behavior. Complex 1 shows a complete SCO between the high-spin (HS, S = 2) and low-spin (LS, S = 1) states without thermal hysteresis, and complex 2 shows a gradual incomplete SCO behavior. The transition temperatures of 2 (T1/2 = 241 K) is 98 K higher than that of 1 (T1/2 = 143 K), which indicates that the ligand field strength of (4-OMe-sal-N-1,5,8,12)2– is stronger than that of (3-OMe-sal-N-1,5,8,12)2–. Due to the absence of crystallizing solvent water molecule, complex 3 maintains a HS state in the test temperature range.