Unusual chelating properties of the ligand 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo). Crystal structures of Ni(bddo)(NCS)2, Zn(bddo)(NCS)2 and Cd2(bddo)(NCS)4

The synthesis and characterization of the ligand 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo) and its co-ordination compounds with zinc, cobalt, nickel, and cadmium thiocyanate are described. The general formula is M(bddo)(NCS)2 with M = Ni, Co, or Zn. With cadmium, Cd2(bddo)(NCS)4 was found. X-Ray structure determinations were performed on crystals of the compounds Zn(bddo)(NCS)2, Ni(bddo)(NCS)2, and Cd2(bddo)(NCS)4. The cobalt compound was found to be isomorphous to the zinc compound. The compound Zn(bddo)(NCS)2 crystallizes from ethanol in the orthorhombic space group Pbcn with unit-cell dimensions a= 9.521(1), b= 14.835(5), c= 16.840(4)A, for Z= 4. The structure was refined to R= 0.058 and R′= 0.069 for 1 072 unique reflections with I > 2σ(I). The compound consists of chains of zinc atoms linked by ligand molecules. The zinc ion is tetrahedrally co-ordinated by two pyrazole nitrogen atoms and two thiocyanate nitrogen atoms. The sulphur atoms of the ligand bddo do not co-ordinate. The compound Ni(bddo)(NCS)2 crystallizes from ethanol in the tetragonal space group P41212 with a= 9.370(3), c= 26.524(7)A, for Z= 4. The structure was refined to R= 0.041 and R′= 0.034 for 1 441 unique reflections with I > 3σ(I). The compound consists of monomeric units of octahedral nickel(II) ions with a trans,cis,cis-NiN2N′2S2 chromophore. The compound Cd2(bddo)(NCS)4 crystallizes from ethanol in the triclinic space group P with a= 8.695(3), b= 9.083(5), c= 10.008(3)A, β= 91.10(3), β= 99.34(3), γ= 108.23(2)°, for Z= 1. The structure was refined to R= 0.029 and R′= 0.033 for 2 794 unique reflections with I > 3σ(I). The cadmium ions are octahedrally co-ordinated with a CdNSN′2S′2 chromophore. Each cadmium ion is linked to two other cadmium ions by double thiocyanate bridges and to a third cadmium ion by one ligand molecule in such a manner that a two-dimensional structure results.