Multipole analysis of the electron density in topaz using X-ray diffraction data

The static deformation electron density, Laplacian of the electron density and critical points in the electron density were analyzed in topaz Al-2[SiO 4]F-2, using high-precision X-ray diffraction data. The electron deformatio n density, positive values of the Laplacian at (3,-1) bond critical points and the net atomic charges indicate a closed-shell-type interaction in the polyhedra. Anion valence-shell charge depletions are revealed. Maxima in th e Laplacian of the electron density are displaced towards the close-packed plane owing to the mutual repulsion of the anion valence shells. The relati onship between the topological features of the electron density and the clo se-packing concept is discussed. Shifts of the critical points from the int ernuclear vectors reflect the strain in the structure.