Complexes of nickel(II) and copper(II) with 1,2,4-triazole-3-carboxylic acid and of cobalt(III) with 3-amino-1,2,4-triazole-5-carboxylic acid.

Because of their versatile coordination modes and strong coordination ability for metals, triazole ligands can provide a wide range of possibilities for the construction of metal-organic frameworks. Three transition-metal complexes, namely bis(μ-1,2,4-triazol-4-ide-3-carboxylato)-κN,O:N;κN:N,O-bis[triamminenickel(II)] tetrahydrate, [Ni(CHNO)(NH)]·4HO, (I), catena-poly[[[diamminediaquacopper(II)]-μ-1,2,4-triazol-4-ide-3-carboxylato-κN:N,O-[diamminecopper(II)]-μ-1,2,4-triazol-4-ide-3-carboxylato-κN,O:N] dihydrate], {[Cu(CHNO)(NH)(HO)]·2HO}, (II), (μ-5-amino-1,2,4-triazol-1-ide-3-carboxylato-κN:N)di-μ-hydroxido-κO:O-bis[triamminecobalt(III)] nitrate hydroxide trihydrate, [Co(CHNO)(OH)(NH)](NO)(OH)·3HO, (III), with different structural forms have been prepared by the reaction of transition metal salts, i.e. NiCl, CuCl and Co(NO), with 1,2,4-triazole-3-carboxylic acid or 3-amino-1,2,4-triazole-5-carboxylic acid hemihydrate in aqueous ammonia at room temperature. Compound (I) is a dinuclear complex. Extensive O-H...O, O-H...N and N-H...O hydrogen bonds and π-π stacking interactions between the centroids of the triazole rings contribute to the formation of the three-dimensional supramolecular structure. Compound (II) exhibits a one-dimensional chain structure, with O-H...O hydrogen bonds and weak O-H...N, N-H...O and C-H...O hydrogen bonds linking anions and lattice water molecules into the three-dimensional supramolecular structure. Compared with compound (I), compound (III) is a structurally different dinuclear complex. Extensive N-H...O, N-H...N, O-H...N and O-H...O hydrogen bonding occurs in the structure, leading to the formation of the three-dimensional supramolecular structure.