Zinc 4-Carboxyphenylphosphonates with Pillared Layered Framework Structures Containing Large 12-Membered Rings Built Up from Tetranuclear Zn<sub>4</sub> Clusters and CPO<sub>3</sub> Linkages

Two isostructural zinc phosphonates [Zn(H<sub>2</sub>O)<sub>6</sub>][Zn<sub>8</sub>(OOCC<sub>6</sub>H<sub>4</sub>PO<sub>3</sub>)<sub>6</sub>(4,4′-bipy)] (<b>1</b>) and (dabcoH)<sub>2</sub>[Zn<sub>8</sub>(OOCC<sub>6</sub>H<sub>4</sub>PO<sub>3</sub>)<sub>6</sub>]·6H<sub>2</sub>O (<b>2</b>) (dabco = 1,4-diazabicyclo[2.2.2]octane) have been obtained by hydrothermal reactions of zinc sulfate and 4-carboxyphenylphosphonic acid in the presence of additional organic ligands 4,4′-bipyridine and 1,4-diazabicyclo[2.2.2]octane, respectively. Both show pillared layered open framework structures. The inorganic layers are of particular interest in which the highly symmetric tetranuclear clusters, composed of corner-sharing {ZnO<sub>4</sub>} and {ZnO<sub>3</sub>N} tetrahedra, are linked by {CPO<sub>3</sub>} tetrahedra through corner-sharing, forming an inorganic layer containing large 12-membered windows. The [Zn(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> cations (for <b>1</b>) or lattice water (for <b>2</b>) reside in the cavities generated by the 12-membered windows and the organic pillars.