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.

The compounds [(Cu2Co2III)-Co-II(H(2)dea)(2)(dea)(4)]X-2(Solv)(n) [X = Cl (1), Br (2), SCN (3), O2CMe (4), 1 (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 (H(2)dea) in air, Crystallographic investigations of 1-4 reveal that the complexes contain the centrosymmetric cation [Cu2Co2(H(2)dea)(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 Angstrom and a short diagonal distance (Cu...Cu) at approximately 3.23-3.29 Angstrom. 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(l) (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. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.