HYDROTHERMAL SYNTHESIS AND CRYSTAL-STRUCTURES OF SR2V(PO4)2(H2PO4) AND SR2FE(PO4)2(H2PO4)

Two new phosphates, Sr2M(PO4)2(H2PO4) (M = V(III) or Fe(III)), have been synthesised hydrothermally at 230-degrees-C and characterized by single-crystal X-ray diffraction and thermal analysis. Crystal data: Sr2V(PO4)2(H2PO4), monoclinic, space group C2/c, a = 11.078(3), b = 11.742(3), c = 8.951(3) angstrom, beta = 125.35(2)-degrees, Z = 4 and R = 0.0356; Sr2Fe(PO4)2(H2PO4), as above except a = 11.082(2), b = 11.737(2), c = 8.961 (2) angstrom, beta = 125.45(l)-degrees and R = 0.0273. The two compounds are isostructural. The structure consists of infinity/1[M(PO4)4/2(H2PO4)2/2] units along the [101] direction, held together by hydrogen bonding and O-Sr-O bonds. The interaction between the structural unit and the interstitial species has been evaluated using the valence-matching principle to account for the presence of an interstitial H2O in the structure of the related compound Ca2V(PO4)(HPO4)2-H2O. Dehydration of the compounds at 750 and 650-degrees-C yields Sr2V(PO4)(P2O7) and Sr2Fe(PO4)(P2O7), respectively.