Cooperative effects of ligands and Counteranions in mononuclear Manganese(III) Schiff-base spin crossover complexes

Abstract

The flexible hexadentate Schiff-base ligands (R-sal-N-1,5,8,12)2− can be easily obtained by modifying the different substituents at the 5 or 3,5 positions on the phenyl rings of the salicylaldehyde. We report in this paper the syntheses, crystal structures and magnetic properties of three new mononuclear manganese(III) complexes [Mn(R-sal-N-1,5,8,12)]Y (R = 5-H, Y = BF4 (1); R = 3,5-diCl, Y = SbF6 (2); R = 5-tBu, Y = ClO4 (3)). All the complexes have an analogous monocationic MnN4O2 surrounding offered by the flexible hexadentate ligand in a distorted octahedral geometry. Magnetic susceptibility measurements demonstrated that complex 1 maintains a high-spin (HS) state between 2 and 400 K due to the closing packing, while complex 2 shows a cooperative and complete one-step thermo-induced spin state switching with T1/2 of 194 K. As for complex 3, single-crystral X-ray structural studies show the existence of a large amount of HS manganese(III) ions at 100 K and it exhibits a surprisingly gradual SCO process with a hysteresis width of 6 K at lower temperature.