Methylamine and Dimethylamine Salts of the Hydrogen Maleate Ion

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.

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