STRUCTURAL STUDIES OF SYSTEMS WITH VERY SHORT HYDROGEN-BONDS - STRUCTURES OF METHYLAMMONIUM HYDROGEN SUCCINATE MONOHYDRATE AND DIMETHYLAMMONIUM HYDROGEN SUCCINATE AT 110-K

Methylammonium hydrogen succinate monohydrate, CH6N+.C4H5O4-.H2O, M(r) = 167.16, monoclinic, P2(1)/m, a = 4.9788 (5), b = 13.077 (1), c = 6.133 (2) angstrom, beta = 92.34 (1)degrees, V = 399.0 (2) angstrom 3, Z = 2, D(x) = 1.391 g cm-3, lambda(Mo K-alpha-BAR) = 0.71073 angstrom, mu = 1.164 cm-1, F(000) = 180, T = 110 K, R = 0.035 for 2627 observed reflections. Dimethylammonium hydrogen succinate, C2H8N+.C4H5O4-, M(r) = 163.17, orthorhombic, Cmcm, a = 6.7863 (9), b = 8.069 (2), c = 14.284 (3) angstrom, V = 782.2 (4) angstrom 3, Z = 4, D(x) = 1.386 g cm-3, lambda(Mo K-alpha-BAR) = 0.71073 angstrom, mu = 1.086 cm-1, F(000) = 352, T = 110 K, R = 0.028 for 1142 observed reflections. In both compounds the hydrogen succinate ions are linked by 'very short' hydrogen bonds resulting in infinite chains. The O atoms involved in the short hydrogen bond are related by crystallographic symmetry in both salts, making the short hydrogen bond symmetric in a crystallographic sense. The H atom in the short hydrogen bond seems to be best described by two equally populated sites on each side of the centre of the hydrogen bond.