The impact of solvent on spin crossover is explored with T _1/2 varying by 200 K and hysteresis up to 80 K.

[Fe(qsal-Br)₂]NO₃·2MeOH is reported which undergoes abrupt two step symmetry breaking spin crossover, T½(1st step) = 136 K and T½(2nd step) = 232 K with a hysteresis of 16 K and 5 K, respectively, and an unprecedented [HS–LS] plateau of 96 K.

The first Fe(III) qsal-X complex exhibiting abrupt complete spin crossover at 228 K with a hysteresis of 8 K, [Fe(qsal-I)₂]OTf is reported. Structural studies of the MeOH solvate in the LS and HS state and at the spin transition are described.

Four iron(iii) spin crossover complexes with halogen substituted ligands are reported. The halogen is correlated with T_1/2 and controls the degree of spin crossover while extensive C–H⋯X and X⋯π interactions increase cooperativity.