Experimental Electron Density study of NaH2PO4 at 30 K

The deformation electron density of sodium dihydrogen phosphate, NaHzPO4, at 30 K has been studied as a reference for the electron-density characteristics of hydrogen-bonded ferroelectrics containing phosphate ions. Clear peaks of deformation electron density (0.30.6 e A -3) are seen in the middle of each P--O bond and electron deficiency (-0.2 to -0.4 e A -3) on the opposite side of each P--O bond peak. The peak height is higher and the peak shape is more distinct in P--O bonds than in P---O(H) bonds as a whole; the distribution of deformation density in the region of lone-pair electrons is more diffuse. The O--H...O bond deformationdensity peaks of around 0.2 e A -3 appear in the middle of the O--H bond, followed by a deeper electron depletion of around -0.4 e A -3 on the H...O contract, just outside the H atom. The effective charges, defined as the integral of the deformation electron density, have the following values: around +0.2 for Na, +1.8 for P, -0.8 for O and +0.6 for H. The correlation of the deformationdensity peaks and the depth of the negative peak of the H atom with the hydrogen-bond distance are discussed.