Spatial dispersion of lone electron pairs?--experimental charge density of cubic arsenic(III) oxide

The first experimental charge density study of arsenolite, a cubic polymorph of arsenic(III) oxide, extended by periodic DFT calculations is reported. The presence of weak AsO interactions is confirmed and their topological characterization based on experimental electron density is provided. Spatial dispersion of arsenic lone electron pairs into three domains is observed in the Laplacian of electron density as well as in the electron localization function. It results from the clustering of As atomic cores in the crystal structure and/or from the presence of strong As-O bonds. A similar phenomenon is recognized in the crystal structures of antimonates(III) and bismuthates(III) of alkaline metals indicating that this could be a more general feature worthy of further investigations.