Coordination Chemistry of Amine Bis(phenolate) Cobalt(II), Nickel(II), and Copper(II) Complexes

Cobalt(II), nickel(II), and copper(II) (1, 2, and 3) complexes of the dianionic form of the bis(phenolate) ligand
N,N-bis(3,4-dimethyl-2-hydroxybenzyl)-N‘,N‘-dimethylethylenediamine (H2L) have been synthesized by electrochemical
oxidation of the appropriate metal in an acetonitrile solution of the ligand. When copper is used as the anode, the
addition of 1,10-phenanthroline to the electrolytic phase gave rise to a different compound [CuL]2·2CH3CN (4). The
compounds [CoL]2·2CH3CN (1), [Ni2L2(H2O)]·H2O (2), [CuL]2·3H2O (3), and [CuL]2·2CH3CN (4) were characterized
by microanalysis, IR, electronic spectroscopy, FAB mass spectrometry, magnetic measurements and by single-crystal X-ray diffraction. The crystal structures show that the complexes have a dinuclear structure. In compounds
1, 3, and 4, two metal ions are coordinated by the two amine nitrogens and the two phenol oxygen atoms of a
deprotonated pendant phenol ligand, with one phenolic oxygen atom from ligand acting as a bridge. In compounds
1 and 3, each metal center has a geometry that is closest to trigonal bipyramidal. Magnetic susceptibility data for
both compounds show an antiferromagnetic coupling with 2J = −15 cm-1 for the cobalt(II) complex and a strong
antiferromagnetic coupling with 2J = −654 cm-1 for the copper(II) complex. However, in 4 the geometry around
the metal is closer to square pyramidal and the compound shows a lower antiferromagnetic coupling (2J = −90
cm-1) than in 3. The nickel atoms in the dimeric compound 2 are hexacoordinate. The NiN2O4 chromophore has
a highly distorted octahedral geometry. In this structure, a dianionic ligand binds to one nickel through the two
amine nitrogen atoms and the two oxygen atoms and to an adjacent nickel via one of these oxygen atoms. The
nickel atoms are linked through a triple oxygen bridge involving two phenolic oxygens, each from a different ligand,
and an oxygen atom from a water molecule. The two nickel ions in 2 are ferromagnetically coupled with 2J = 19.8
cm-1.