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Synthesis and structural characterization of some metal thiocyanate complexes with nicotinamide

In thiocyanate metal complexes containing additional ligands the coordination mode of thiocyanate group is influenced by steric factors, by polarizing activity of the central metal atom, by symbiosis of the &laquo ; soft&raquo ; and &laquo ; hard&raquo ; ligands in the coordination sphere as well as by the solvent. We have chosen nicotinamide as additional/competitional ligand, due to its biological importance, to halide or pseudohalide ligands towards coordination sites of the 12th group metal ions although generally there is a lack of data in this area. Mercury(II) salts, HgX2 (X = Cl, Br), in aqueous media react with nicotinamide and give complexes of the formula: HgX2L2 (L = nicotinamide) irrespectively of molar ratio of the reactants (1:1 or 1:2). On the contrary, Hg(SCN)2 in methanol solution forms HgX2L In the structure of catena[(mi2-thiocyanato-S, N)-(thiocyanato-S)-nicotinamide-mercury(II)] tetrahedral coordination of mercury atom is established. In distorted tetrahedron mercury atom is coordinated by two sulphur atoms (Hg – S1 2.458(2) and Hg – S2 2.421(3) &Aring ; ) from thiocyanate ions and two nitrogen atoms (Hg – N3 2.325(8) and Hg – N1b 2.366(8) &Aring ; ) one originated from thiocyanate ion and the other one from nicotinamide molecule. Thiocyanate ions act as ambidentate ligand. One of them bridges two mercury atoms forming polymeric chains in [0 1 0]direction, while the other one is terminal, yet forming intermolecular hydrogen bonds where thiocyanate nitrogen atom, as expected, accepts more than one hydrogen bond: N-H... Ni and C-H... Ni, 3.07(2) &Aring ; , 172o and 3.37(2) &Aring ; , 175o respectively ; i = x, y+0.5, z). Amide groups from two symmetrically related molecules form R22(8) centrosymmetrical dimers of N-H...O type, 2.93(1) &Aring ; , 160o.

Mercury(II); nicotinamide; crystal ctructure; hydrogen bonding

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