Synthesis and crystal structure of Sr(AsO3OH) and Ba(AsO3OH):: crystal chemistry of related MHXO4 (X = As, P, S) compounds

Crystals of M(AsO3OH) (M = Sr and Ba) were synthesized under hydrothermal conditions; single-crystal X-ray structure investigations were performed. The average structure of Sr(ASO(3)OH) exhibits three crystallographically different hydrogen bonds; two of them are related by 1 symmetry [space group P1, a = 7.349(2) angstrom, b = 7.057(2) angstrom, c = 7.460(2) angstrom, alpha = 95.20(3)degrees, beta = 104.78(3)degrees, gamma = 88.11(3)degrees, Z = 4]. Weak superstructure reflections were detected which are responsible for a larger cell volume [space group P1, a = 9.038(2) angstrom, b = 11.732(2) angstrom, c = 15.356(3) angstrom, alpha = 71.66(3)degrees, beta = 75.16(3)degrees, gamma = 89.11(3)degrees, Z = 16]. All inversion centres restricting the hydrogen bonds are avoided in the super cell. As a result, a completely ordered atomic arrangement is obtained. The arsenate tetrahedra are linked by hydrogen bonds to polar chains with branches in [110] and [110], respectively; they are linked by the Sr atoms. The compounds CaHPO4 (monetite), CaHAsO4 (weilite), a-SrHPO4 alpha-NaHSO4, and HgHPO4 have roughly the same arrangements of the M(= Ca, Sr, Na, Hg) and X(= P, As, S) atoms; however their hydrogen-bonding schemas are principally different. For the detailed comparison, the non-standard- unit cell was chosen for Sr(AsO3OH) [space group F1, a = 14.697(3), b = 28.230(5), c = 14.920(3) angstrom, alpha = 95.20(3)degrees, beta = 104.78(3)degrees, gamma = 88.11(3)degrees, Z = 64]. The structural refinement of Ba(AsO3OH) confirmed isotypy with gamma-Sr(PO3OH), K(SO3OH), and K(SeO3OH) [space group Pbca a = 8.581(2), b = 9.896(2), c = 19.417(4) angstrom, Z = 16]. Sr(AsO3OH) and Ba(AsO3OH) are characterized by short (strong) hydrogen bonds.