Crystal structure of dicalcium sodium monohydrogen diarsenate hexahydrate, Ca2Na[HAsO4][AsO4] · 6H2O

Abstract

As2Ca2H13NaO14, triclinic, P1 (no. 2), a = 6.680(5) Å, b = 8.223(4) Å, c = 12.537(3) Å, = 73.46(5)°, = 78.89(4)°, = 87.47(5)°, V = 647.7 Å3 , Z = 2, Rgt(F) = 0.062, wRref(F2 ) = 0.197, T = 293 K. Source of material Crystallization of Ca2Na(HAsO4)(AsO4) · 6H2O was carried out by mixing CaCl2 (0.01 M) and Na2HAsO4 (1 M) aqueous solutions in a thermostated (25(1) °C) polypropylene vessel. 50 cm3 of each parent solution were placed in the reacting vessel, which was then sealed with a polypropylene cap to avoid evaporation. After mixing, the pH reached a value of ca. 8.90. The obtained crystals are tabular (ca. 100 m) with well-defined polygonal contours. Experimental details Hydrogen atoms were geometrically placed and refined using distance restraints. Odd anisotropic displacement parameters were found probably due to crystal size and shape. The range of Ca/As and Na/As ratios measured by EDS seems to exceed the analytical error, suggesting the possibility of a coupled substitution of Ca2+ + AsO4 3 for Na+ + HAsO42.