Reaction of nitrogen and sulphur donor ligands with the antitumour complex [{CuL(MeCo2)}2](HL = 2-formylpyridine thiosemicarbazone) and the single-crystal X-Ray structure of [CuL(bipy)]ClO4(bipy = 2,2′-bipyridyl)

Abstract

The preparation of N- and S-donor ligand adducts with CuL⁺(HL = 2-formylpyridine thiosemicarbazone) is described. The N-donors, 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen) and 4-dimethylaminopyridine (dmap) give the complexes [CuL(bipy)]X (X = ClO₄ or PF₆), [CuL(bipy)]₂SO₄·8H₂O, [CuL(phen)]PF₆ and [CuL(dmap)₂]PF₆, which have been characterized by physical and spectroscopic techniques. The structure of one of the complexes, [CuL(bipy)]ClO₄, has been determined by the single-crystal X-ray diffraction method: triclinic, space group P with a= 8.560(3), b= 9.452(4), c= 13.078(4)Å, α= 106.35(3), β= 94.66(3), γ= 95.27(3)° and Z= 2. The complex contains discrete [CuL(bipy)]⁺ cations and ClO₄^– anions. The copper atom environment exhibits a distorted five-co-ordinate geometry. Three donor atoms (NNS) from L form a tricyclic ligating system with the remaining positions being occupied by bipy N atoms giving significantly different Cu–N distances of 1.986(4) and 2.179(4)Å. Pentafluoro-(pftp), pentachloro-(pctp) and 4-nitro-thiophenolate (ntp) give S-donor complexes [{CuL(SR)}₂]·nH₂O (SR = pftp, n= 4; pctp, n= 0; ntp, n= 6). Thiolato co-ordination is proposed on the basis of spectroscopic evidence. With 2-mercaptobenzothiazole (Hmbt), 2-mercaptoimidazole (Hmi), 2-mercapto-1-methylimidazole (Hmmi) and 3-mercapto-4-methyl-1,2,4-triazole (Hmmt), either deprotonated ligand adducts of the type [CuL(A)](A = mbt, mi or mmt) or neutral ligand adducts [CuL(HA)₂]PF₆(HA = Hmmi or Hmi) are isolated. It is suggested that the thioamides co-ordinate via the imine nitrogen atom. The relevance of the results to proposed mechanisms for the antitumour activity of CuL⁺ is discussed.