One-step and two-step spin crossover binuclear iron(III) complexes bridged by 4,4′-bipyridine

► Two binuclear iron(III) complexes bridged by 4,4′-bipyridine were synthesized. ► They showed one-step and two-step spin crossover behaviors. ► They consist of one and two crystallographically inequivalent Fe sites. ► Some saturated six-membered chelate rings suffer from disorder, but some does not. ► The difference in the disorder gives their structural and magnetic differences.