Gradual two-step and room temperature spin crossover in Mn(III) complexes with nitro-substituted ligand

The syntheses, crystal structures and magnetic properties of spin crossover (SCO) salts of formula [Mn(5-NO2-sal-N-1,5,8,12)]AsF6 (1) and [Mn(5-NO2-sal-N-1,5,8,12)]SbF6 (2) and [Mn(5-NO2-sal-N-1,5,8,12)]BF4.3H(2)O (3..3H(2)O) have been reported in this paper, where (5-NO2-sal-N-1,5,8,12)(2-) 2,2'-((1Z,13Z)-2,6,9,13-tetraaza-tetradeca-1,13-diene-1,14-diyl)bis(4-nitrophenol) is synthesized by 5-nitrosalicylaldehyde and 1,2-bis(3-aminopropylamino)ethane and possess a stronger ligand field. The magnetic susceptibilities demonstrated that complexes 1-3 showed a gradual two-step SCO between the high-spin (HS, S = 2) and low-spin (LS, S = 1) states without thermal hysteresis. The transition temperature T-1/2 of the AsF6 (1) and SbF6 (2) salts estimated from the magnetic susceptibility measurements decreased with increasing the size of the anions. The temperatures of the second transition step are close to room temperature during the heating process of 2-400 K, which are 319, 317 and 305 K, respectively. The existence of the crystalizing solvents of complex 3 changes the supramolecular packing, weakening the cooperative interaction in the crystal and it stabilizes in the HS state in the temperature range of 2-400 K.