Interlayer interactions in <i>M</i>(OH)₂: a neutron diffraction study of Mg(OH)₂

Abstract

Magnesium hydroxide, Mg(OH) 2 : M r = 58.3, trigonal, P {\bar 3} m 1, a = 3.148 (1), c = 4.779 (2) Å, V = 41.015 Å 3 , D x = 2.36 g cm −3 at room temperature; a = 3.145 (1), c = 4.740 (2) Å, V = 40.602 Å 3 , D x = 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.