Crystal Structure of Copper Fluoride Dihydrate, CuF2·2H2O

Abstract

The crystal structure of copper fluoride dihydrate, CuF₂·2H₂O, has been determined from single crystal x‐ray data. The monoclinic unit cell, space group C_2h(3)—12/m, with a=6.416, b=7.397, c=3.301, all ±0.005 A, β=99.6±0.1°, contains two formula units. The atoms are in the following positions: Cu(II) in 2(a): (0, 0, 0; ½, ½, ½): F^— in 4(i): (0, 0, 0; ½, ½, ½)±(x, 0, z) with x= —0.222, z=0.311; O in 4(g): (0, 0, 0; ½, ½, ½)±(0, y, 0) with y=0.261. The estimated parameters of the H atoms in 8(j): (0, 0, 0; ½, ½, ½)±(x, y, z; x, y, z) are x=0.107, y=0.340, z= —0.073. In this structure the Cu(II) atoms have two fluorine neighbors at 1.89 A, two (water) oxygen neighbors at 1.93 A, and two fluorine neighbors at 2.47 A. These form a highly distorted octahedron about the Cu(II), and in fact, the distance of the two further fluorine atoms implies that the Cu(II) prefers square coordination. The distance 2.66 A between an oxygen and a fluorine associated with a neighboring lattice point implies appreciable hydrogen bonding between these atoms .Comparisons are made with other Cu(II) halide compounds and the observed antiferromagnetism is discussed. The morphology and optic axes have been investigated. The refractive indices (NaD) are α=1.51, β=?, γ=1.54. The optic angle 2V≅46° and the optic axes lie in the (010) plane between +a and +c, one optic axis making an angle of 16° with the c axis.