Synthesis, crystal structure and magnetic studies of tetranuclear hydroxo and ligand bridged [Co-4(mu(3)-OH)(2)(mu(2)-dea)(2)(L-L)(4)](4)Cl.8H(2)O [L-L=2,2 '-bipyridine or 1,10-phenanthroline] complexes with mixed valence defect dicubane core

X-ray crystallography of the title complexes indicates a discrete mixed valence (Co-2 (II)-Co-2 (III)) defect dicubane molecular unit where each cobalt nucleus attains a distorted octahedral geometry. The alpha-diimine (L-L) chelator coordinated to each cobalt ion stops further polymerization or nuclearization. The water molecules in the lattice play a crucial role in the formation of the supramolecular architectures. Magnetic data were analyzed using the effective spin-1/2 Hamiltonian approach and the parameters are, J = 115(6) Delta J = -57.0(1.2) Delta g(xy) = 3.001(25), and g(z) = 7.214(7) for 1 and J = 115(12) Delta J = -58.5(2.5) Delta g(xy) = 3.34(5), and g(z) = 6.599(12) for 2 suggesting that only the g matrices are prone to the change of alpha-diimine chelator.