Solvomorphs of tyraminium 5,5-diethylbarbiturate: a rare example of the barbiturate R33(12) hydrogen-bond motif and a crystal structure with Z' = 4.

In the past two decades, the solvomorphism phenomenon in organic materials has attracted much attention, especially in the pharmaceutical and materials industries. Cocrystallization with solvent molecules can lead to modified physical and chemical properties of materials. We present here two new solvomorphs (pseudopolymorphs) of tyraminium 5,5-diethylbarbiturate [2-(4-hydroxyphenyl)ethanaminium 5,5-diethyl-2,4,6-trioxotetrahydro-2H-pyrimidin-1-ide, C8H12NO+·C8H11N2O3-] with unusual structural features. Pseudopolymorph (I) follows the symmetry of the P21/n space group and has four tyraminium cations, four barbitalate anions and four molecules of chloroform in the asymmetric unit. Pseudopolymorph (II) crystallizes in the space group R-3c with one tyraminium cation, one barbitalate anion and a small amount of disordered solvent (ethanol and water) located in the cavities. Hirshfeld surface analysis and the Non-Covalent Interaction (NCI) index were used to examine and compare the crystal packing features and intermolecular interactions in (I) and (II). Both materials crystallize with large unit cells and contain nontypical barbitalate ions formed through deprotonation of the barbital N3 position. Pseudopolymorph (I) is an example of a crystal structure with a rarely observed value of Z' = 4. Analysis of the hydrogen-bond patterns in (II) showed an unusual arrangement of three barbitalate anions in R33(12) rings, which is the first example of such a hydrogen-bond motif in barbital structures. The mutual arrangement of the ions in the crystal structure of (II) leads to the formation of specific cavities along the c direction.