Z and E isomers of butenedioic acid with 2-amino-1,3-thiazole: 2-amino-1,3-thiazolium hydrogen maleate and 2-amino-1,3-thiazolium hydrogen fumarate.

Maleic acid and fumaric acid, the Z and E isomers of butenedioic acid, form 1:1 adducts with 2-amino-1,3-thiazole, namely 2-amino-1,3-thiazolium hydrogen maleate (2ATHM), C(3)H(5)N(2)S(+) x C(4)H(3)O(4)(-), and 2-amino-1,3-thiazolium hydrogen fumarate (2ATHF), C(3)H(5)N(2)S(+) x C(4)H(3)O(4)(-), respectively. In both compounds, protonation of the ring N atom of the 2-amino-1,3-thiazole and deprotonation of one of the carboxyl groups are observed. The asymmetric unit of 2ATHF contains three independent ion pairs. The hydrogen maleate ion of 2ATHM shows a short intramolecular O-H...O hydrogen bond with an O...O distance of 2.4663 (19) A. An extensive hydrogen-bonded network is observed in both compounds, involving N-H...O and O-H...O hydrogen bonds. 2ATHM forms two-dimensional sheets parallel to the ab plane, extending as independent parallel sheets along the c axis, whereas 2ATHF forms two-dimensional zigzag layers parallel to the bc plane, extending as independent parallel layers along the a axis.