Weak antiferromagnetism in carboxylato copper(II) complexes of bipyridines

Three new members of the copper/carboxylato/heterocyclic diimine family, namely [Cu(GLYO)(2,2'-bipy)](2) . nH(2)O (n = 4 (1) or 6 (2), H(2)GLYO = glycolic acid, 2,2'-bipy = 2,2'-bipyridine) and {[Cu(AcO)(2)(4,4'-bipy)] . 3H(2)O}(n) (3) (AcO = acetato, 4,4'-bipy = 4,4-bipyridine), have been synthesized and characterized by IR and electronic absorption spectroscopy, and the crystal structures have been determined by single crystal X-ray analysis. 1 and 2 are composed of discrete dinuclear units in which each Cu-II atom is coordinated in a square pyramidal arrangement to the two nitrogen atoms of a bipyridine ligand, to bridging non-carboxy oxygen atoms belonging to two glycolato ligands, and to one of the carboxy oxygen atoms of one of these glycolato ligands. The Cu..Cu distance is 3.0666(5) Angstrom. Compound 3 consists of linear chains of dinuclear units in which each Cu-II is coordinated to one non-bridging monodentate acetato ligand, to two acetato ligands that each bridge via a single oxygen atom, and to one nitrogen atom of each of two mutually trans bis-monodentate 4,4'-bipyridine ligands that link the repeat units of the polymer. The coordination polyhedra are square pyramids, and the Cu..Cu distance within each dimeric repeat unit is 3.502(2) Angstrom. The temperature dependence of their magnetic susceptibilities shows there to be weak antiferromagnetic interaction between the metal atoms of each dimer in all three complexes, with Fitting parameter values of -2J = 1.3 cm(-1) and g = 2.09 for 1 and 2, and -2J = 1.4 cm(-1) and g = 2.15 for 3. The X-band EPR spectra show signals corresponding to the dinuclear units.