New Open-Framework Ammonium and Amine Cadmium Zirconium Oxalates with Helical Structures

Two new open-framework cadmium zirconium oxalates containing ammonium or ethylenediamine have been prepared from precipitation methods at room pressure. The crystal data of these oxalates are as follows:  <BO>I</BO>, 2[NH<INF>4</INF>]⁺[CdZr(C<INF>2</INF>O<INF>4</INF>)<INF>4</INF>]^2-·3.9H<INF>2</INF>O, trigonal, space group P6<INF>4</INF>22 (no. 181), a = 9.061(5) Å, c = 23.394(5) Å, V = 1663(1) ų, Z = 3, R<INF>1</INF> = 0.03; <BO>II</BO>, [C<INF>2</INF>N<INF>2</INF>H<INF>10</INF>]²⁺[CdZr(C<INF>2</INF>O<INF>4</INF>)<INF>4</INF>]^2-·4.4H<INF>2</INF>O, trigonal, space group P3<INF>1</INF>12 (no. 151), a = 9.105(5) Å, c = 23.656(5) Å, V = 1698(1) ų, Z = 3, R<INF>1</INF> = 0.04. The two structures are built from MO<INF>8</INF> (M = Cd, Zr) distorted antiprisms connected by oxalate groups to give rise to chains based on the sequence ...−Cd−oxalate−Zr−oxalate−... that display a helical wire arrangement. Each helix is connected to six neighboring ones to form an anionic three-dimensional framework [CdZr(C<INF>2</INF>O<INF>4</INF>)<INF>4</INF>]^2- balanced by the cations NH<INF>4</INF>⁺ or [NH<INF>3</INF>−(CH<INF>2</INF>)<INF>2</INF>−NH<INF>3</INF>]²⁺ located in tunnels parallel to the c axis that also contain water molecules. The apertures have hexagonal and square cross sections of ~5.7 Å and ellipsoidal cross sections of 5.7 × 12 Å. There is extensive hydrogen bonding among the ammonium and amine groups, water molecules, and framework. The thermal decomposition of the two compounds into cadmium and zirconium oxides is described.