Synthesis and X-ray crystal structures of some mononuclear and dinuclear complexes of 4-isobutyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole

In order to probe the ability of the bis-bidentate ligand 4-isobutyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole (ibdpt) to form mononuclear complexes of the 1:2 type, [M-II(ibdpt)2(X)(2)](y+), a metal-to-ligand molar ratio of 1:2 has been employed in reactions with Co(ClO4)(2).6H(2)O, Ni(ClO4)(2).6H(2)O and Zn(ClO4)(2)-6H(2)O. A high yield of the pure mononuclear complex [Zn-II(ibdPt)(2)(ClO4)(2)] is obtained when Zn(ClO4)(2).6H(2)O is employed. In contrast, when Co(ClO4)(2).6H(2)O is employed a mixture of mono- and dinuclear complexes, [Co-II(ibdPt)(2)(X)(2)](y+). and [Co-2(II) (ibdPt)(2)(X)(4)](y+), respectively, results. Even more dramatically, when Ni(ClO4)(2).6H(2)O is employed, no mononuclear [Ni-II(ibdpt)(2)(X)(2)](y+) complex is obtained despite the 1:2 ratio. It is clear from these studies that stoichiometry alone does not control the outcome of such complexation reactions but that other factors, including the nature of the N-4 substituent and the relative solubility of the various possible products, also influenced by the N-4 substituent, are also important. The X-ray crystal structures of the mononuclear complexes [Co-II(ibdpt),(H2O)(2)](ClO4)(2).Et2O, [Zn-II(ibdPt)(2)(ClO4)(2)] and [Zn-II(ibdPt)(2)(H2O)(2)](ClO4)(2).3MeCN and of the dinuclear complex [Zn-2(ibdPt)(2)(H2O)(4)](ClO4)(2) are presented. In all of these complexes the metal centres are octahedrally N4O2 coordinated by two in-plane ibdpt molecules and axial H2O or ClO4-, co-ligands. The trans-(N',N')(2) coordination mode is adopted in all three mononuclear complexes and the trans-(N',N-1,N-2,N '')(2) double bridging coordination mode is adopted in the dinuclear complex. (c) 2006 Elsevier Ltd. All rights reserved.