Crystal structures, magnetic and spectroscopic properties of manganese(II), cobalt(II), nickel(II) and zinc(II) dichloro complexes bearing two 2-pyridyl-substituted imino nitroxides

Four new complexes of formula [MCl₂(IM2py)₂], where M = Mn(II), Co(II), Ni(II) or Zn(II); IM2py = 4,4,5,5-tetramethyl-2-(2-pyridyl)-imidazolin-1-oxyl, have been prepared, and examined from viewpoints of the crystal structures, magnetic and spectroscopic properties. All the complexes crystallize in an isomorphous space group C2/c with Z = 4, and exist as discrete mononuclear molecules with OC-6-22 [cis(Cl)-trans(py)] geometrical structure in the crystal. In the zinc(II) complex a moderate intramolecular IM2py-IM2py antiferromagnetic interaction (2J′ = -19.1(1) cm^-1) is estimated by the magnetic susceptibility measurement. The magnetic interactions between Mn(II) and IM2py are found to be antiferromagnetic, J = -23.8(2) cm^-1. Ferromagnetic interactions of the complexes of Ni(II) and Co(II) are inferred from the magnetic susceptibility. These magnetic properties are substantiated by the variable temperature UV-vis-NIR spectra of which the intensities increase for Mn(II) or decrease for Ni(II) and Co(II) with decreasing temperature for the spin-forbidden d-d transition and/or the metal(II) dσ to IM2py SOMO π* CT transition.