Formation, Structures, and Magnetic and EPR Spectroscopic Properties of Dicobalt(III)-Dicopper(II) Complexes Featuring Heterotetranuclear Cations of a Puckered Cyclic Structure with Diethanolamine and Diethanolamine(2−) as Bridging Ligands

Abstract

The compounds [CuII2CoIII2(H2dea)2(dea)4]X2(Solv)n [X = Cl (1), Br (2), SCN (3), O2CMe (4), I (5); Solv = H2O or/and CH3OH, DMF, n = 1−4] were synthesised by the reaction of zero-valent copper with cobalt(II) salts in non-aqueous (CH3OH, DMF, DMSO) solutions of diethanolamine (H2dea) in air. Crystallographic investigations of 1−4 reveal that the complexes contain the centrosymmetric cation [Cu2Co2(H2dea)2(dea)4]2+ in which the four metal atoms are linked together by bridging oxygen atoms of the six ligand groups to form a parallelogram with the length of the short edge (Cu···Co) being ca. 2.83 A and a short diagonal distance (Cu···Cu) at approximately 3.23−3.29 A. The copper atom is five-coordinate with a square-pyramidal geometry; the geometry at the trivalent cobalt ion is almost octahedral. The tetranuclear units are further stabilized by intramolecular O−H···O and N−H···O hydrogen bonds. The hydrogen-bonded network that involves the OH and NH groups of the ligands, uncoordinated anions, and solvent molecules links the tetranuclear units together and results in the formation of extended two- and three-dimensional networks. Variable-temperature magnetic susceptibility measurements of 1−3 and 5 show no significant exchange coupling between the copper centres. The frozen-solution and solid-state EPR spectra at 77 K are characteristic of a triplet state with the hyperfine structure distinctly resolved in solution. On the assumption of noncoaxiality of the g and D tensors the spectra were interpreted with the zero-field-splitting parameters D = 0.0560(1) (2−5) and D = 0.0712(1), E= 0.0028(2) cm−1 (1). Dominant contributions to the observed EPR zero-field splitting are presumed to be dipole-dipole in origin. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)