Interlayer interactions in M(OH)2: a neutron diffraction study of Mg(OH)2

Abstract

Magnesium hydroxide, Mg(OH)2: Mr = 58.3, trigonal, P{\bar 3}m1, a = 3.148 (1), c = 4.779 (2) Å, V = 41.015 Å3, Dx = 2.36 g cm−3 at room temperature; a = 3.145 (1), c = 4.740 (2) Å, V = 40.602 Å3, Dx = 2.39 g cm−3 at 70 K; Z = 1, λ = 0.8330 (5) Å, μ = 1.78 cm−1, F(000) = 9.503 fm; final R = 2.42, wR = 2.40, S = 3.22 for 82 unique reflections at room temperature; R = 1.84, wR = 1.82, S = 2.54 for 81 unique reflections at 70 K. Refinements have been carried out using anisotropic thermal coefficients for all atoms. To interpret the very large thermal motion of the H atom, subsequent refinements have been carried out with an anharmonic model and with a three-site split-atom model, and results are compared with those previously reported for Ca(OH)2. By comparing the interatomic distances O...O, H...H and H...O in the interlayer spacing of Mg(OH)2 and Ca(OH)2, as well as their temperature dependence, the nature and the strength of interlayer interactions in both compounds are discussed.