Layered iron(II) spin crossover complex constructed by NH⋯Br− hydrogen bonds with 2 K wide thermal hysteresis, [FeIIH3LMe]Br·CF3SO3 (H3LMe = tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

► We synthesized four Br− complexes [FeIIH3LMe]Br·Y for comparing with Cl− analogues. ► Only [FeIIH3LMe]Br·CF3SO3 is isomorphous of related Cl− complex. ► [FeIIH3LMe]Br·CF3SO3 shows abrupt SCO with hysteresis, frozen-in and LIESST effects. ► At 296 and 93 K, CF3SO3 complex has a same NH⋯Br− hydrogen bonded layered assembly. ► The complexes with Y− (PF6-,AsF6-,SbF6-) contain one methanol and show no SCO.