Electron-density study of m-nitrophenol in the orthorhombic structure

Abstract

m-Nitrophenol (m-NPH) occurs at room temperature in two solid modifications: monoclinic P21/n and orthorhombic P212121 [Pandarese, Ungaretti & Coda (1975). Acta Cryst. B31, 2671–2675]. The thermal vibrations and electronic-density distribution of the molecule in the orthorhombic structure have been analyzed in terms of Stewart's rigid pseudoatom model, using restricted Slater radial functions and angular multipole terms extending to actapoles for C, N and O and dipoles for H pseudoatoms. The net atomic charge and the in-crystal molecular dipole moment have been determined in order to understand the nature of the inter- and intramolecular charge transfer. The analysis suggests that aspherical pseudoatoms are essential for modeling the charge distribution in a noncentrosymmetric crystal. Careful consideration must also be given to the treatment of the H atoms, in the absence of complementary neutron diffraction data.