Spin crossover (SCO) is a spin-state switching phenomenon observed for transition metals with the 3d4-3d7 electronic configuration. The switching can be triggered by the application of external stimuli such as temperature, pressure, pulsed magnetic field, or light. The spin sensitivity to the various perturbation accompanied by the changes in M-L bonds, color, and unit cell volume, that makes these materials useful for the preparation of sensors, displays, and memory devices. Many reported SCO complexes are known for Fe (II) ions with {N6} coordination environment. There are several SCO complexes that feature the unusual coordination that contains mixed N,S-donor atoms. The SCO-induced changes in the crystal lattice are larger in a case with N,S mixed donor set due to large changes in Fe-S bond length accompanying the LS«HS spin transitions. However, based on our knowledge, there are no reported examples SCO Fe (II) complexes with abrupt hysteretic spin transitions. In the current work, we report the influence of structural changes on spin-crossover behavior in a series of Fe(II) complexes with N,S-coordinating ligands 1,2-bis(2-pyridylmethylthio)ethane (bpte), 1,2-bis((pyridin-2-ylmethyl)thio)benzene (bptPh), and bis(2-pyridylmethyl)sulfide (bpt). A homoleptic complex [Fe(bpt)2](ClO4) with the tridentate thioether ligand bpt, which coordinates in fac-configuration, exhibits gradual two-step SCO, while its analogue, [Fe(bpt)2](BF4)2, displays an abrupt spin transition with a 7-K hysteresis loop. We also report the synthesis of new heteroleptic complexes [Fe(bpte)(xnap-bim)](ClO4)2 and [Fe(bptPh)(bim)](ClO4)2, where bim = 2,2’-biimidazole and xnap-bim = 2,3-dimethyl-naphthalene-2,2’-biimidazole. Both complexes display gradual SCO. We discuss the structural, magnetic, and optical properties of these new SCO materials.

Designing FeII complexes with abrupt hysteretic spin transitions in N,S-mixed coordination

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.