No abstract

No abstract

Magnesium ammonium arsenate hexahydrate, MgNH4AsO4.6HzO (arsenstruvite), is isostructural with the phosphate struvite and crystallizes in the orthorombic system, space group Pmn21. Unit-cell parameters are: a0 = 7.054 (4), b0 = 6.205 (3), Co = 11.368 (6) A; Z= 2. The crystal structure was refined anisotropically to R=0-030, using 1110 non-zero hkl and hkl (equivalent by Laue symmetry) reflexions measured on an automatic three-circle diffractometer (Cu Kc~ radiation). Corrections for absorption, secondary extinction and anomalous scattering, which allowed the determination of the correct polarity, were applied. The hydrogen atoms were located from a difference map; one of the four independent water molecules ('all coordinated by Mg) is very weakly hydrogen bonded and the ammonium group shows disorder around a fixed N-H direction. The Mg and As polyhedra are fairly regular and connected by hydrogen bonds only; the crystal structure, built up from Mg octahedra and ammonium groups sandwiched between As tetrahedra, is discussed in the light of bond-length and bond-strength correlations.

No abstract

No abstract