HYDROTHERMAL SYNTHESIS AND CRYSTAL-STRUCTURE OF A NEW LAYERED PHOSPHATE, K2CO3(P2O7)2.2H2O

A novel pyrophosphate, K2Co3(P2O7)2 · 2H2O, has been synthesized by hydrothermal techniques and characterized by single crystal X-ray diffraction. Crystals suitable for structure determination were grown by slow cooling from 700°C under an external pressure of 3 kbar, though the phase may be synthesized in pure polycrystalline form under much milder conditions (220°C and 30 bar). The compound adopts the monoclinic space group P21/a with a = 9.229(2), b = 8.110(1), c = 9.122(4) Å, β = 99.31(4)°. The structure was solved by Patterson and Fourier methods, and refined to final agreement factors R = 0.023, Rw = 0.025. The structure has a layered nature, composed of cis-edge-sharing chains of CoO6 octahedra running parallel to the b-direction, linked together by P2O7 groups to form two-dimensional sheets in the ab plane. Adjacent sheets are separated in the c-direction by potassium ions. The ammonium analog of the title compound has also been synthesized. © 1990 Academic Press, Inc.