The first open-framework cadmium phosphate, K4[Cd3(HPO4)4(H2PO4)2],with a layered structure

A layered cadmium phosphate of the formula K-4[Cd-3(HPO4)(4)(H2PO4)(2)], I, containing six-membered apertures, constituting the first example of an open-framework cadmium phosphate, has been synthesized under hydrothermal conditions. Crystal data: monoclinic, P2(1)/n (No. 14), a = 9.0698(3), b = 6.7341(3), and c = 18.2663(7) Angstrom, beta = 93.092(1)degrees, V= 1114.03 Angstrom(3), Z = 4. The structure consists of a network of CdO6 octahedra and PO3(OH) and PO2(OH)(2) tetrahedra forming a spiro unit, which are connected through Cd2O2 two-membered rings forming one-dimensional chains. The chains are further connected forming two-dimensional macroanionic layers with six-membered apertures possessing hanging phosphate units on either side of the layer. The layers are stabilized by strong hydrogen bond interactions between the terminal P-OH groups forming pseudo channels in which the charge-compensating extraframework K+ ions are located. The presence of the spiro unit and the infinite one-dimensional Cd-O-Cd chains, along with the hanging phosphates are noteworthy structural features. (C) 2001 Elsevier Science.