Lattice Effects on the Spin-Crossover Profile of a Mononuclear Manganese(III) Cation

Six solvated salts of a mononuclear manganese(III) complex with a chelating hexadentate Schiff base ligand are reported. One member of the series, [MnL]PF6 center dot 0.5CH(3)OH (1), shows a rare low-spin (LS) electronic configuration between 10-300 K. The remaining five salts, [MnL]NO3 center dot C2H5OH (2), [MnL]BF4 center dot C2H5OH (3), [MnL]CF3SO3 center dot C2H5OH (4), [MnL]ClO4 center dot C2H5OH (5) and [MnL]ClO4 center dot 0.5 CH3CN (6), all show gradual incomplete spin-crossover (SCO) behaviour. The structures of all were determined at 100 K, and also at 293 K in the case of 36. The LS salt [MnL]PF6.0.5CH3OH is the only member of the series that does not exhibit strong hydrogen bonding. At 100 K two of the four SCO complexes (2 and 4) assemble into 1D hydrogen-bonded chains, which weaken or rupture on warming. The remaining SCO complexes 3, 5 and 6 do not form 1D hydrogen-bonded chains, but instead exhibit discrete hydrogen bonding between cation/counterion, cation/solvent or counterion/solvent and show no significant change on warming.