Structure−function correlations in mononuclear manganese(III) spin crossover system with big conjugated hexadentate Schiff-base ligands

This paper reports the syntheses, crystal structures and magnetic properties of spin crossover (SCO) salts of formula [Mn(naphth-sal-N-1,5,8,12)]SbF6 (1), [Mn(naphth-sal-N-1,5,8,12)]AsF6 (2), [Mn(naphth-sal-N-1,5,8,12)]PF6•1/2CH3OH (3) and [Mn(naphth-sal-N-1,5,8,12)]ClO4 (4), where (naphth-sal-N-1,5,8,12)2− (2,2'-((1E,14E)-2,6,10,14-tetraazapentadeca-1,14-diene-1,15-diyl)diphenolate) is a big conjugated hexadentate Schiff-base ligand. The magnetic susceptibilities demonstrated that complexes 1 and 2 showed a gradual one-step SCO between the high-spin (HS, S = 2) and low-spin (LS, S = 1) states without thermal hysteresis. The transition temperature T1/2 of the SbF6 (1) and AsF6 (2) salts estimated from the magnetic susceptibility measurements are 164 and 171 K, respectively. The existence of the crystal solvent of complex 3 changes the supramolecular packing, leading to the close π•••π stackings between phenyl groups from ligands. These close stackings hinder the flexibility of the whole ligand, precluding the spin transformation of complex 3 and it stabilizes in the HS state in the temperature range of 2–300 K. For 4, crystal structural analysis indicates that the reduction in anion size leading to close contacts between the naphthalene rings. These C-H•••π interactions provide a means for preventing the spin crossover occurring at low temperatures.