LAYERED, NETWORK AND CHAIN STRUCTURES OF CADMIUM(II) MALONATE - CRYSTAL-STRUCTURE AND CD-113 NUCLEAR-MAGNETIC-RESONANCE STUDIES

Three structurally non-identical cadmium(II) malonate compounds have b een obtained: polymeric tetraaquabis(malonato)dicadmium(II) 1, polymer ic monoaqua(malonato)cadmium(II) monohydrate 2 and polymeric triaqua(m alonato)cadmium(II) monohydrate 3. The layered-structure compound 1 is the initial product formed at room temperature, and has two cadmium s ites in distinct chemical and magnetic environments: six- and eight-co -ordinate cadmium involving oxygen donors including two water molecule s, characterized by two Cd-113 NMR resonances at delta 18 and -107 res pectively: Compound 2, which has a three-dimensional network structure , is formed irreversibly when 1 is heated at 60 degrees C or exposed t o sunlight: its seven-co-ordinate cadmium site involves one six-member ed and two four-membered chelate rings and one water molecule (delta-4 7). Compound 3 has an unusual chain structure and is formed reversibly when 2 is heated at 100 degrees C: a different seven-co-ordinated cad mium site involves two four-membered rings and three water molecules ( delta-53). The results of the cross polarization magic angle spinning Cd-113 NMR study of the six-; seven- and eight-co-ordination sites sho w that cadmium atoms with higher co-ordination numbers tend to be more shielded.