The Synergetic Effect in Beryllium Sulfate Tetrahydrate- an Experimental Electron-Density Study*

The electron density in piezoelectric beryllium sulfate tetrahydrate has been determined by multipole refinement of single-crystal X-ray data collected at 30 K. Hydrogen positional and displacement parameters have been taken from a refinement using single-crystal neutron data. Structural parameters are also given based on single-crystal neutron data collected at 100 and 295 K. The Be 2+ ion causes a strong polarization of the lone-pair density of the water O atom. Only a single maximum of the deformation density is observed in this region