The crystal chemistry of doyleite, Al(OH)3

Abstract

Abstract The structure of doyleite, a rare polymorph of Al(OH)3, has been determined by a three-dimensional single-crystal diffraction study as triclinic, space group P[unk], a = 4.9997(8) Å, b = 5.1681(6) Å, c = 4.9832(6) Å, α = 97.444(10)°, β = 118.688(12)°, γ = 104.661(12)°, V = 104.39(3) Å3, Z = 2. Doyleite has a similar bilayer structure to the other modifications of Al(OH)3, comprising double layers of hcp O atoms with Al atoms occupying two-thirds of the octahedral interstices but is distinct from the other forms in its lateral displacement of adjacent layers and in aspects of the hydrogen bonding pattern. A good correspondence exists between the calculated structure and AFM images of doyleite's (010) surface. The OH-stretching Raman spectrum shows a single broad band centred near 3345 cm−1 with a weaker shoulder at 3615 cm−1 in some spectra. Intra-layer interactions between hydroxyl groups appear to involve limited, if any, bonding between a hydrogen and the next-nearest-neighbour oxygen and show no Raman scattering, in contrast to other Al(OH)3 polymorphs. The ∼100 cm−1 width of doyleite's OH-stretching band is taken as describing the time-averaged hydrogen bondstrength distribution throughout the crystal, with a continuous range of bond strengths consequential upon interchanging positional disorder of the hydrogen atoms and their varying involvement in interplane hydrogen bonds.