Effect of Ligand Substituent Coordination on the Geometry and the Electronic Structure of Cu(II)-Diradical Complexes

Two
organic moieties, known as ligands, having −OMe and
−SePh as the ortho substituent attached to the aniline moiety
of the parent 2-anilino-4,6-di-tert-butylphenol ligand,
were synthesized. The ligands reacted with CuCl2·2H2O in a 2:1 ratio in CH3CN in the presence of Et3N and provided the corresponding mononuclear Cu­(II)-diradical
complexes 1 (−OMe) and 2 (−SePh).
Complex 1 was square planar, while complex 2 was in distorted square planar geometry due to the secondary coordination
between the Se atom and the central Cu­(II) center. Both complexes
were comprised of multi-paramagnetic centers and exhibited an St = 1/2 ground state as established by variable-temperature
magnetic susceptibility measurements. X-band electron paramagnetic
resonance measurements indicated the presence of an unpaired electron
at the Cu­(II) center in complex 1 and at the ligand center
(π-radical) in complex 2. The extent of the secondary
interaction was found to be dependent on the “softness”
of the donor atom belonging to the ortho substituent.