EXPERIMENTAL ELECTRON-DENSITY IN CRYSTALLINE H3PO4

X-ray diffraction data for H3PO4 crystals have been measured to d(min) = 0.46 Angstrom resolution, and used to model the electron-density distribution with the hydrogen structure of the crystals adopted from an earlier neutron diffraction analysis. The molecule is asymmetric in the crystal with site symmetry 1 (C-1), but the local symmetries of the pseudoatomic densities are, within experimental error, equivalent as they would be under idealized 3m (C-3v) molecular symmetry. Although the experimental analysis entailed substantial problems with absorption and extinction corrections, the static deformation density from the experiment agrees very well with that from a polarized split-valence molecular orbital wavefunction for an isolated molecule with the crystallographic molecular geometry. Hydrogen bonding in the crystal polarizes the molecule's P = O acceptor group towards p(+)-O-, and appears to relocalize the lone-pair density of the P-OH donor groups. Crystal data: anhydrous orthophosphoric acid, H3PO4, M(r) = 98.00, room temperature, P2(1)/c, a = 5.7572 (13), b = 4.8310 (17), c = 11.5743 (21)Angstrom, beta = 95.274 (12)circle, V = 320.55 (25)Angstrom(3), Z = 4, d(x) = 2.030 mg mm(-3) mu = 0.660 mm(-1) for lambda(Mo Kappa alpha) = 0.7107 Angstrom, F(000) 200 e(-), R(\F\) = 0.026 for 3512 unique reflections.