Two new layer structures of zinc(II) or strontium(II) diphosphonates based on N,N-dimethylaminomethane-1,1-diphosphonate ligand

Hydrothermal reactions of Zn2+ or Sr2+ ion with N,N-dimethylaminomethane-1,1-diphosphonic acid (H4L) afforded two new layered metal diphosphonates, namely, [Zn2(H2L)2]·2H2O (1) and [Sr3(H2L)2(H3L)2(H2O)2]·2H2O (2). The layer structure in 1 features a square-grid unit with Zn1O6 octahedra acting as nodes, which tetradentately traps one Zn2 ion inside it. On the other hand, the layer architecture of 2 exhibits an unusual corner-sharing Sr3O17 tri-polyhedra unit; and such trimer unit is edge-shared with two neighboring trimers, which further chelate a third trimer to form a square-grid ring with two aqua molecules residing in it. The diphosphonate ligand in the two compounds manifests diversified coordination modes accompanying with a cooperative coordination effect of its two closely linked phosphonate moieties.