organic compounds
Methylammonium hydrogen maleate, CH6N+.C4H3O4-, crystallizes in space group Pnam with two independent anions in the asymmetric unit having crystallographic mirror planes bisecting the C=C bonds. Dimethylammonium hydrogen maleate, C2H8N+.C4H3O4-, crystallizes in space group P21/n without crystallographic symmetry constraints on the hydrogen maleate ion and this anion possesses also almost perfect mirror-plane symmetry. One of the anions in the methylammonium salt displays significant deviation from planarity [-12.00 (9)°]. The symmetry of the three anions and the difference in their conformations are rationalized from the hydrogen-bond interactions in the two salts.