Alkali-metal hydrogen selenate-phosphates M2H3(SeO4)(PO4) (M = Rb or K) and M4H5(SeO4)(3)(PO4) (M = K or Na)

Crystalline hydrogen selenate-phosphates M2H3(SeO4)(PO4) [M = Rb(I) or K(II )] and M4H5(SeO4)(3)(PO4) [M = K (III) Or Na (IV)] were obtained by reactio ns of Rb, K, and Na carbonates with mixtures of selenic and phosphoric acid solutions. The X-ray structure study of single crystals revealed that I an d II are isostructural (sp. gr. Pn). In these structures, SeO4 and H3PO4 te trahedra are linked by hydrogen bonds to form corrugated layers. Structures In and IV (sp. gr. P (1) over bar) have similar arrangements of non-hydrog en atoms but different hydrogen-bond systems. In III = K-4(HSeO4)(2) {H[H(S e,P)O-4](2)}, the HSeO4 groups branch from the infinite anionic {H[H(Se,P)O -4](2)} chains. In IV = Na-4[H(SeO4)(2)] {H[H-1.5(Se,P)O-4](2)}, the anioni c {H[H-1.5(Se,P)O-4](2)} chains are crosslinked by hydrogen bonds formed by the [H(SeO4)(2)] dimers. (C) 2000 MAIK "Nauka/Interperiodica".