Dramatic Remote Substitutent Effects on the Electronic Spin State of Bis(scorpionate) Iron(II) Complexes

A molecular vise: The purple-colored bis(tert-butylscorpionate) iron(II) complex is fully low-spin at room temperature, despite the steric hindrance brought about by the six methyl groups in the equatorial belt. The remotely situated bulky tert-butyl substituent on boron acts like a locking screw for a vise, forcing the tripod-shaped ligand to close, thus favoring low-spin complex formation.