Formation of nickel(II) coordination polymers by a double betaine: [{Ni(L)(H2O)(4)}(n)]Cl-2n center dot 2nH(2)O and [{Ni(L)(2)(H2O)(2)}(n)](ClO4)(2n)center dot 4nH(2)O [L=(O2CCH2N+)-O--(CH2CH2)(3)N+CH2CO2-]

Two novel polymeric nickel(II) complexes of a double betaine with a rigid tris(ethylene) bridge between the pair of nitrogen atoms, namely [{Ni(L)(H2O)(4)}(n)] Cl-2n.2nH(2)O (1) and [{Ni(L)(2)(H2O)(2)}(n)] (ClO4)(2n).4nH(2)O (2) [L = (O2CCH2N+)-O--(CH2CH2)(3)N+CH2CO2-], have been prepared and characterized by X-ragi crystallography. The nickel(II) atom in either complex is coordinated by unidentate carboxylate groups and aqua ligands in a distorted octahedral geometry. The crystal structure of (1) features an infinite zigzag chain composed of an alternate arrangement of metal atoms and double betaine ligands, and hydrogen bonding among adjacent chains leads to a three-dimensional network. Complex (2) exhibits a wave-like layer structure corresponding to the (200) family of planes.