EXPERIMENTAL CHARGE-DENSITY STUDY OF METHYLAMMONIUM HYDROGEN SUCCINATE MONOHYDRATE - A SALT WITH A VERY SHORT O-H-O HYDROGEN-BOND

A charge density study of the crystalline salt of methylammonium hydrogen succinate monohydrate has been carried out based on combined use of neutron and X-ray diffraction data at 110 K. The neutron data of a deuterated crystal showed that the O-D(H)-O hydrogen bond in the crystal is symmetrical with D(H) at a crystallographic inversion center. A charge density from the X-ray data with hydrogen positional and thermal parameters based on the neutron data proved to be informative on the topological properties of chemical bonding in the crystal. The Laplacian of the density was calculated and analyzed, and some of-the (3,-1) critical points in the crystal unit cell have been isolated and characterized. These results show that the short hydrogen bond has covalent character. The X-ray data also indicate that the electrostatic potential in the crystal adds to the stability of the short O-H-O hydrogen bond.