Polymorphism of urea–barbituric acid co-crystals

Abstract

The crystal structures of three polymorphs found for the addition complex of urea and barbituric acid are described and compared. Two polymorphs are monoclinic, space groups P2(1)/c and Cc, whereas the third is triclinic, P1. The displacement of electron density towards the mesomeric forms, corresponding to the tautomeric forms of higher stability, of the barbituric acid molecule seem to influence the type of hydrogen bonds formed, which in turn determines the different packing topology in the polymorphs. While the polymorphic forms can be easily differentiated at the first-level graph-set analysis of their hydrogen-bonding patterns, a higher-level analysis enables important features of the mutual spatial arrangement of the structural components to be revealed.

Co-crystal/salt crystal structure disorder of trichloroacetic acid–N-methylurea complex with double system of homo- and heteronuclear O–H···O/N–H···O hydrogen bonds: X-ray investigation, ab initio and DFT studies

“…There are known many acid-urea multicomponent crystal structures among them are neutral complexes and ionic structures as well [35][36][37][38][39][40][41][42]. Moreover, the urea is of interest in experimental and theoretical investigations because of simplicity of its molecule [43][44][45][46], interesting highly symmetrical crystal structure [47,48] or physical properties [49,50].…”

Transferability of cocrystallization propensities between aromatic and heteroaromatic amides

“…Also many other physicochemical properties can be modulated by cocrystallization including stability [21][22][23][24], hygroscopicity [25] and prolonged shelf life [26]. Among many drugs, aromatic amides acting either as APIs or as excipients attract nowadays substantial attention [27][28][29][30][31][32][33][34][35]. These compounds are known for their important roles in medical applications.…”

“…Although many pharmaceutical cocrystals containing amides have been studied [27][28][29][30][31][32][33][34][35], the data deposited in the Cambridge Structural Database (CSD) [41] are rather variable in the sense that many coformers were used for synthesis of diverse cocrystals. For example cocrystals of fumaric acid with benzamide, isonicotinamide or nicotinamide are known under refcodes YOPBUB, LUNNOX and EDAPOQ, respectively, but there is no information about solids of these coformers with temozolomide.…”

Polymorphism Solvatomorphism 2008

“…Besides the papers just discussed, the 2008 literature contained a large number of additional reports on the polymorphism associated with a wide variety of organic compounds. While some of these substances may be of limited pharmaceutical interest, the references summarized in Table 1 66–110 will be of interest to suitably directed investigators.…”