Ammonium cyamelurates: synthesis and crystalline structures

Contradictory literature on the alkali-assisted exfoliation of the melon and searching for the best precursors for different heptazine derivative synthesis led us to the synthesis of two cyameluric acid salts, (NH4)2[C6N7O3H] (ECN3) and (NH4)2(H9O4)[C6N7O3] (ECN5). These salts were characterized by single-crystal X-ray diffractometry for the first time. Ammonium cations bind C6N7O3H2− anions (ECN3) by means of Coulombic compression and hydrogen bonds. In ECN5, stability of the columns consisting of C6N7O33− anion triads is provided by Coulombic compression and hydrogen bonds between anions, ammonium cations, and hydroxonium (H9O4+). The planar cyamelurate anions of one triad are located strictly above each other with the distance of 3.710(3) A between the neighbor anions. Each triad is twisted relative to the adjacent one by an angle of 60° and is distant by 3.605(3) A.