ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES, vol.61, no.9, pp.1094-1100, 2006 (SCI-Expanded)
Preparations, crystal structures, thermal properties, IR and UV/vis spectroscopic studies and magnetic moments of tris(1,10-phenanthroline)cobalt(II) squarate octahydrate, [Co(phen)(3)]sq (.) 8H(2)O (1) ;and diaquabis(picolinamide)cobalt(II) squarate, [Co(H2O)(2)(pia)(2)]sq (2) are described. 1 crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.9832(5), b = 21.4569(12), c = 17.0649(7) angstrom, beta = 98.159(3)degrees and Z = 8, while 2 crystallizes in the triclinic system, space group P (1) over bar, with a = 6.9624(9), b = 7.9224(11), c = 8.0501 (11) angstrom, alpha = 107.404 degrees, beta = 93.340(11)degrees, gamma = 93.266 degrees and Z = 1. Both 1 and 2 have slightly distorted octahedral coordination geometry, involving six N atoms from bidentately chelating phen ligands and trans-[CoN2O4] coordination geometry, in which the Co atom is located at a center of symmetry. There are significant hydrogen-bonding interactions in the structure of 1. The squarate dianions are linked to the eight solvent water molecules by means of hydrogen-bonding interactions. Moreover, there are links between the complex cation and the squarate dianion via C-H center dot center dot center dot O hydrogen bonds. These interactions hold the crystal structure of 1 in a three-dimensional network, while O-H center dot center dot center dot O, N-H center dot center dot center dot O, weak pi center dot center dot center dot pi and pi center dot center dot center dot ring interactions lead to a three-dimensional crystal structure for 2. The thermal decomposition pathways of 1 and 2 have been investigated by the help of thermal analyses data (TG and DTA).