Zinc(II) and cadmium(II) chloride complexes with 4,4'-bi-1,2,4-triazole.

New coordination compounds with the 4,4'-bi-1,2,4-triazole ligand (btr), namely tetraaqua-2kappa(4)O-di-mu(2)-4,4'-bi-1,2,4-triazole-1:2kappa(2)N(1):N(1');2:3kappa(2)N(1):N(1')-hexachlorido-1kappa(3)Cl,3kappa(3)Cl-trizinc(II), [Zn(3)Cl(6)(C(4)H(4)N(6))(2)(H(2)O)(4)], (I), and poly[cadmium(II)-mu(2)-4,4'-bi-1,2,4-triazole-kappa(2)N(1):N(2)-di-mu(2)-chlorido], [CdCl(2)(C(4)H(4)N(6))](n), (II), reveal an unprecedented molecular zwitterionic structure for (I) and a polymeric two-dimensional layer structure for (II). Differences between these products, which involve the formation of either charge-separated chlorometallate/aquametal fragments or complementary organic and inorganic bridges, are attributable to the hardness-softness characters of the metal cations. In (I), two N(1),N(1')-bidentate btr molecules connect one [Zn(H(2)O)(4)](2+) cation and two [ZnCl(3)](-) anions into a linear trizinc motif (the Zn atom of the cation occupies a centre of inversion in an N(2)O(4) coordination octahedron, whereas the Zn atom of the anion possesses a distorted tetrahedral Cl(3)N environment). In (II), the distorted vertex-sharing CdCl(4)N(2) octahedra are linked into binuclear [Cd(2)(mu(2)-Cl)(mu(2)-btr)(2)](3+) fragments by unprecedented N(1):N(2)-bidentate btr double bridges and bridging chloride ligands, while the additional chloride anions are also bridging, providing further propagation of the fragments into a two-dimensional network [Cd-Cl = 2.5869 (2)-2.6248 (7) A].