Steric Quenching of Mn(III) Thermal Spin Crossover: Dilution of Spin Centers in Immobilized Solutions

Structural and magnetic properties of a new spin crossover complex [Mn(4,6-diOMe-sal(2)323)](+) in lattices with ClO4-, (1), NO3-, (2), BF4-, (3), CF3SO3-, (4), and Cl- (5) counterions are reported. Comparison with the magnetostructural properties of the C-6, C-12, C-18 and C-22 alkylated analogues of the ClO4- salt of [Mn(4,6-diOMe-sal(2)323)](+) demonstrates that alkylation effectively switches off the thermal spin crossover pathway and the amphiphilic complexes are all high spin. The spin crossover quenching in the amphiphiles is further probed by magnetic, structural and Raman spectroscopic studies of the PF6- salts of the C-6, C-12 and C-18 complexes of a related complex [Mn(3-OMe-sal(2)323)](+) which confirm a preference for the high spin state in all cases. Structural analysis is used to rationalize the choice of the spin quintet form in the seven amphiphilic complexes and to highlight the non-accessibility of the smaller spin triplet form of the ion more generally in dilute environments. We suggest that lattice pressure is a requirement to stabilize the spin triplet form of Mn3+ as the low spin form is not known to exist in solution.

Automated summary

This study reports the structural and magnetic properties of a new spin crossover complex in lattices with different counterions. Comparison experiments show that alkylation effectively inhibits the thermal spin crossover pathway. Further investigations confirm the stability of the high spin state in dilute environments.