Hydrothermal syntheses, crystal structures and luminescence properties of three new metal diphosphonates with layered structure

Three new divalent metal(II) diphosphonates with layered structure, [Cd2.5(L)(H2O)2F]·H2O (1), [Cd3.5(HL)(L)] (2) and [Sn3O(L)] (3) (H4L = C6H11N(CH2PO3H2)2), have been hydrothermally synthesized and structurally characterized by X-ray single-crystal diffraction, X-ray powder diffraction as well as with infrared spectroscopy, elemental and thermogravimetric analysis. For compound 1, each Cd(II) atoms are octahedrally coordinated [Cd(1)O4NF, Cd(2)O5F, Cd(3)O6]. These cadmium octahedra form a 1D chain along the b-axis through edge- and corner-sharing, and such chains are further interlinked by CPO3 tetrahedra via corner-sharing to form a 2D layer. In compound 2, the interconnection of Cd(1)O6, Cd(2)O5N(1), Cd(3)O6 and Cd(4)O5N(2) polyhedra via bridging diphosphonate ligands leads to a 2D Cd(II) phosphonate layer, which is analogous to that of compound 1. The structure of compound 3 shows a novel layered structure, in which the interconnection of three SnO3 trigonal pyramids via the bridging oxygen atom forms a trimer, the so-built trimers are bridged by the diphosphonate ligands into a 2D Sn(II) phosphonate layer. In all three compounds, the organic groups of the ligands are oriented toward the interlayer space. Luminescence properties of compounds 1 and 2 have also been studied.