Hydrothermal syntheses, characterizations and crystal structures of three new cadmium (II) amino-diphosphonates: effects of substitute groups on the structures of metal phosphonates

Abstract

Hydrothermal reactions of cadmium(II) chloride with three amino-diphosphonic acids, C 6H 5CH 2N(CH 2PO 3H 2) 2 (H 4L 1), C 6H 5CH 2CH 2N(CH 2PO 3H 2) 2 (H 4L 2) and 4-CH 3–C 6H 4CH 2N (CH 2PO 3H 2) 2) (H 4L 3) resulted in three new metal amino-diphosphonates, namely, Cd(H 3L 1) 2, 1 Cd(H 3L 2) 2·2H 2O 2 and Cd(H 3L 3) 2 3. In all three complexes, the Cd(II) ion is octahedrally coordinated by six phosphonate oxygen atoms from six ligands. Complexes 1 and 3 have a similar structure in which the CdO 6 octahedra are cross-linked by bridging ligands into a double chain along the c-axis, such double chains are further interlinked via hydrogen bonds between non-coordinated phosphonate oxygen atoms to form 〈100〉 and 〈200〉 layers with the phenyl groups of the ligands orientated toward the interlayer space. The structure of complex 2 features a 〈100〉 cadmium(II) diphosphonate layer. The effects of the substitute groups attached to the amine groups on the structures of the metal phosphonates are also discussed.