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 Al2[SiO4]F2, using high‐precision X‐ray diffraction data. The electron deformation 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 the Laplacian of the electron density are displaced towards the close‐packed plane owing to the mutual repulsion of the anion valence shells. The relationship between the topological features of the electron density and the close‐packing concept is discussed. Shifts of the critical points from the internuclear vectors reflect the strain in the structure.