Coordination studies of copper(II), nickel(II), cobalt(II) and zinc(II) salts with pyridyl-tetrazole ligands containing alkyl or alkyl halide pendant arms

The reaction of 2-(2H-tetrazol-5-yl)pyridine (L1) with 1,n-dibromoalkane (n = 3, 4, 6 or 8) results in the formation of the isomers 2-(n″-bromoalkyl- (1-tetrazol-5-yl)pyridine (L2A-D) and 2-(n″-bromoalkyl-(2-tetrazol-5-yl) pyridine (L3A-D). The reaction of L1 with 1-bromoalkanes also resulted in the formation of isomeric materials, namely 2-(n″-alkyl-(1-tetrazol-5-yl) pyridine (L4A-C) and 2-(n″-alkyl-(2-tetrazol-5-yl)pyridine (L5A-C). Complexation reactions of these ligands with the transition metal salts CuCl₂·2H₂O, Co(NCS)₂, NiCl ₂·2H₂O and ZnCl₂ were carried out in methanol and resulted in complexes containing a 1:1 metal:ligand stoichiometry except in the cases of the cobalt complexes where a 1:2 metal:ligand stoichiometry was obtained. The ¹H NMR spectra of the zinc complexes showed that the ligands containing the pendant arm in the 2-N position of the tetrazole ring bind the zinc ion more strongly than those containing the pendant arm in the 1-N position. The X-ray structures of two cobalt salts, Co(L5A) ₂(NCS)₂ and Co(L5C)₂(NCS)₂, are also discussed.