Supramolecular modulation of spin crossover profile in manganese(III)

Six salts of mononuclear manganese(III) complexes with Schiff-base ligands L3-L5 are reported. Solvated complexes with L3, [MnL3]ClO4 center dot 0.5MeOH, 3a, and [MnL3]NO3 center dot EtOH, 3b, are low spin (LS) at 80 K and exhibit a gradual and incomplete spin crossover (SCO) on warming to 281 K. Complexes with L4, [MnL4]ClO4, 4a, and [MnL4] NO3, 4b, are predominantly high spin (HS) at RT and undergo gradual and incomplete SCO on cooling. Complexes [MnL5]NO3, 5b, and [MnL5]PF6, 5c, are fully HS over the measured temperature range. Both salts with the dihalogenated ligand L3, 3a and 3b, crystallise with alcohol solvent molecules and exhibit discrete cation-counterion hydrogen bonding and a hydrogen-bonded macrocyclic anion-cation-solvent dimer, respectively. Complex 4a contains two unique complex sites, each with internal rotation symmetry, which assemble into 1D hydrogen-bonded chains at 100 K, which persist on warming to RT. Complex 4b also contains two unique cation sites, without internal symmetry, one of which shows a discrete cation-anion hydrogen bond similar to that of 3a, which dissociates on warming. Complex 5c forms a weak hydrogen bond between complex and counterion, whereas 5b does not participate in any hydrogen bonding.