Abstract
The hydroxyl orientations in Sr(OH)2 have been determined by electrostatic-energy calculations. In this structure, the hydroxyls lie on a mirror plane so that starting models were obtained by first arbitrarily choosing a reasonable orientation for one of the two hydrogens, OH(1), and then calculating the electrostatic energy for the other, OH(2), as a function of its orientation in the plane. This resulted in two minima each of which was used in turn as an orientation for OH(2) while OH(1) was similarly rotated. This produced a total of seven structure models. For each, the electrostatic energy was minimized as a function of hydroxyl orientation. In the minimum-energy structure, OH(1) lies nearly in the edge of the coordination polyhedron about strontium (CN = 7). The Sr–H(1) distance of 2.388 Å is much less than the average Sr–O distance of 2.598 Å. This and considerations of the ionic radii indicate that the hydrogen is in contact with the strontium. The hydroxyl orientations are more strongly influenced by Sr–H repulsion than by H–H repulsion since the minimum-energy has the least total Sr–H repulsion.
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