Experimental Electron Density Study of NaH₂PO₄ at 30 K

The deformation electron density of sodium dihydrogen phosphate, NaH₂PO₄, 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 (0.3–0.6 e Å⁻³) are seen in the middle of each P—O bond and electron deficiency (−0.2 to −0.4 e Å⁻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 deformation-density peaks of around 0.2 e Å⁻³ appear in the middle of the O—H bond, followed by a deeper electron depletion of around −0.4 e Å⁻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 deformation-density peaks and the depth of the negative peak of the H atom with the hydrogen-bond distance are discussed.

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