VERSATILE BEHAVIOR OF THE CYCLOHEXANE-1,2-DIONE BIS(SEMICARBAZONE) LIGAND IN MONONUCLEAR AND DINUCLEAR METAL-COMPLEXES

The chelating properties of cyclohexane-1,2-dione bis(semicarbazone) (H-2chds) were considered by means of IR spectroscopy and the crystal structures of [Co2(H-2chds)2(OH2)3(NO3)][NO3]3 1, [Ni(H-2chds)2][NO3]2.2H2O 2 and H-2chds.H2O. The structure of 1 is triclinic, space group P1BAR, with a = 13.616(2), b = 12.694(2), c = 11.537(2) angstrom, alpha = 68.13(1), beta = 63.37(1), gamma = 70.01(1)-degrees, Z = 2 and R = 0.0778. The crystals of 2 are also triclinic, space group P1BAR, a = 13.504(4), b = 13.221(5), c = 8.333(5) angstrom; alpha = 98.00(3), beta = 77.71(4), gamma = 106.43(3)-degrees, Z = 2 and R = 0.0688. The H-2chds.H2O molecule crystallizes in the space group P2(1)/c with a = 7.350(1), b = 15.469(3), c = 10.270(3) angstrom; beta = 93.98(2)-degrees, Z = 4 and R = 0.0372. The behaviour of the ligand is different in each structure: in 1 nearly planar tetradentate and accommodated in the equatorial positions of pentagonal bipyramids; in 2 distorted-octahedral co-ordination is provided by two tridentate ligand molecules having one urea group free. The free molecule is nearly planar with a different conformation: its arms are folded in such a way that an intramolecular N-H ... O hydrogen bond is allowed. The structure of 1 is quite original: dimers are formed by means of two carbonylic bridges; the apices of the two polyhedra are occupied by two water molecules and a nitrate ion and one water molecule respectively.