Crystal structures of sodium magnesium selenate decahydrate, Na2Mg(SeO4)(2)center dot 10H(2)O, a new selenate salt, and sodium magnesium selenate dihydrate, Na2Mg(SeO4)(2)center dot 2H(2)O

摘要

Metal selenates crystallize in many instances in isomorphic structures of the corresponding sulfates. Sodium magnesium selenate decahydrate, Na2Mg(SeO4)(2)center dot 10H(2)O, and sodium magnesium selenate dihydrate, Na2Mg(SeO4)(2)center dot 2H(2)O, were synthesized by preparing solutions of Na2SeO4 and MgSeO4 center dot 6H(2)O with different molar ratios. The structures contain different Mg octahedra, i.e. [Mg(H2O)(6)] octahedra in the decahydrate and [MgO4(H2O)(2)] octahedra in the dihydrate. The sodium polyhedra are also different, i.e. [NaO2(H2O)(4)] in the decahydrate and [NaO6(H2O)] in the dihydrate. The selenate tetrahedra are connected with the chains of Na polyhedra in the two structures. O-H center dot center dot center dot O hydrogen bonding is observed in both structures between the coordinating water molecules and selenate O atoms.