Iron(II) complexes containing thiophene-substituted “bispicen” ligands — Spin-crossover, ligand rearrangements, and ferromagnetic interactions

Abstract

The synthesis and characterization of three new tetradentate “bispicen-type” ligands containing a substituted thiophene heterocycle are described [2,5-thienyl substituents = H (7), Ph (8), or 2-thienyl (9)]. Iron(II) bis(thiocyanate) coordination complexes containing 7–9 were prepared, and the electronic and variable-temperature magnetic properties of complexes containing 7 (10) and 9 (12) are described. Complex 10 features a gradual and incomplete spin crossover in the solid state, and 12 remains high-spin over the entire temperature range. Complex 11 is extremely unstable and rearranges to another iron(II) complex (13), which was structurally characterized. The temperature-dependent magnetic properties of 13 are described as a one-dimensional ferromagnetic chain, with interchain antiferromagnetic interactions and (or) zero-field splitting dominant at low temperatures. The magnetic analysis is corroborated by the molecular packing and density functional theory calculations, which suggest intermolecular interactions between coordinated thiocyanate ligands bearing a significant spin density.