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

Abstract

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)Å, 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)Å, 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)Å, 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.