Spin-Crossover Phenomenon in a Pentanuclear Iron(II) Cluster Helicate

The first spin-crossover cluster helicate [{Fe(II)(μ-bpt)3}2Fe(II)3(μ3-O)][Fe(II)2(μ-Cl)(μ-bpt)(NCS)4(H2O)]·2H2O·C2H5OH [Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole] was reported, in which one spin-crossover unit and one low-spin triple-stranded [Fe(II)(bpt)3](-) unit wrapped a rare planar [Fe(II)3(μ3-O)](4+) core to form a bis(triple-helical) cation with trigonal-bipyramidal topology. The origin of different magnetic behaviors of two [Fe(II)(bpt)3](-) units could be ascribed to their different intermolecular interactions.