Generation of polymeric structures of cadmium(II) complexes by a flexible double betaine: [{Cd 4(L) 2X 8(H 2O) 2} n [X Cl, Br, I; L= −O 2CCH(N +Me 3)CH 2CH 2(N +Me 3)CO 2−

Abstract

Three polymeric cadmium(II) complexes of a flexible double betaine, namely [{Cd 4(L) 2Cl 8(H 2O) 2} n ] ( 1), [{Cd 4(L) 2Br 8(H 2O) 2} n ] ( 2) and [{Cd 4(L) 2I 8(H 2O) 2} n ] ( 3) [L= −O 2CCH(N +Me 3)CH 2CH 2CH(N +Me 3)CO 2 −], have been prepared and characterized by X-ray crystallography. Complex 1 consists of a two-dimensional polymeric layer structure corresponding to the (020) plane, in which neighbouring chains constructed from corner-sharing CdCl 3O 3 and CdCl 4O 2 octahedra are alternatively cross-linked by two different double betaines in the end-to-end mode. Complexes 2 and 3 constitute an isomorphous pair exhibiting a three-dimensional network, in which polymeric zig-zag chains composed of centrosymmetric Cd 2X 2 quadrilaterals and the bridging carboxylate groups are intercrossed by chelating and bridging double betaine ligands in different directions, and the two cadmium(II) atoms independently adopt distorted octahedral and square-pyramidal coordination geometries. The OCO angles of the carboxylate groups in the three complexes increase according to the mode of ligation: chelating [123.5(9)–124.1(8)° < syn-anti bridging [124.8(5), 125.0(8)°] < syn-syn bridging [127.0(8)°].