The Relationship Between Spin Crossover (SCO) Behaviors, Cation and Ligand Motions, and Intermolecular Interactions in a Series of Anionic SCO Fe(III) Complexes with Halogen-Substituted Azobisphenolate Ligands.

To investigate the halogen substitution effect on the anionic spin crossover (SCO) complexes, azobisphenolate ligands with 5,5'-dihalogen substituents from fluorine to iodine were synthesized, and their anionic Fe complexes , , , and were isolated. The temperature dependence of magnetic susceptibility and crystal structure revealed that , , and are all isostructural and exhibit SCO with the rotational motion of the cation and ligands, whereas shows incomplete SCO. Note that and showed irreversible and reversible cooperative SCO transitions, respectively.

Cooperative spin-crossover transition from three-dimensional purely π-stacking interactions in a neutral heteroleptic azobisphenolate Fe complex with a NO coordination sphere.

A novel neutral heteroleptic Fe complex from two kinds of π-extended tridentate ligands was designed and prepared. The π-ligands formed a three-dimensional purely π-stacking interaction network. The present complex proved to be the first neutral spin-crossover (SCO) Fe complex with a NO coordination sphere exhibiting an abrupt SCO transition with a thermal hysteresis of 10 K and the light-induced excited spin-state trapping effect.