The crystal structure of sodium trihydrogen selenite

Abstract

Sodium trihydrogen selenite is ferroelectric below -79°C. At room temparature this compound crystallizes in the monoclinic space group P2₁/n with two formula units in a unit cell of dimensions a= 10.35, b = 4.84, c = 5.84 Å and β = 89°. The structure was solved by the interpretation of an unsharpened three dimensional Patterson synthesis and was refined from photographic X-ray data by the structure-factor least-squares method to an R index of 0.134 for 491 independent observed reflexions. In the structure, the selenine ions have idoalized 3m (C_3r) symmetry. The coordination of oxygen atoms around the sodium ion is slightly distorted octahedron. The selenite ions are held together by a system of strong hydrogen bonds. These hydrogen bonds form closed loops and may work as switching mechanisms in the ferroelectric phase.