title: Cocrystals of 6-chlorouracil and 6-chloro-3-methyluracil: exploring their hydrogen-bond-based synthon motifs with several triazine and pyrimidine derivatives.
abstract: In order to obtain complexes held together by hydrogen as well as halogen bonds, 6-chlorouracil [6-chloropyrimidin-2,4(1H,3H)-dione; 6CU] and its 3-methyl derivative [6-chloro-3-methylpyrimidin-2,4(1H,3H)-dione; M6CU] were cocrystallized with 2,4,6-triaminopyrimidine and the three triazine derivatives 2,4,6-triamino-1,3,5-triazine (melamine), 2,4-diamino-6-methyl-1,3,5-triazine and 2-chloro-4,6-diamino-1,3,5-triazine, which all offer complementary hydrogen-bonding sites. Three of these compounds form cocrystals with 6CU; however, melamine yielded only a new pseudopolymorph with 6CU, but formed a cocrystal with M6CU. All six cocrystals contain solvent molecules (N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidin-2-one), whose intermolecular interactions contribute significantly to the stabilization of the crystal packing. Each of these structures comprises chains, which are primarily formed by strong hydrogen bonds with a basic framework built by R2(2)(8) hydrogen bonds of either pure N-H...N or mixed patterns. Solvent molecules are aligned to the border of these chains via N-H...O hydrogen bonds. Two of the reported crystal structures containing 6CU show additional Cl...O halogen bonds, which connect the chains to two-dimensional layers, while one weak and one strong Cl...Cl interaction are observed in the two structures in which molecules of M6CU are present.
authors.affiliation: Institut für Organische Chemie und Chemische Biologie, Goethe-Universität Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt am Main, Germany.
authors.forename: Valeska
authors.initials: V
authors.lastname: Gerhardt
authors.affiliation: Institut für Organische Chemie und Chemische Biologie, Goethe-Universität Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt am Main, Germany.
authors.forename: Ernst
authors.initials: E
authors.lastname: Egert
mesh_terms: D003460:Crystallization; D003461:Crystallography; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011743:Pyrimidines / Q000737:chemistry*; D014227:Triazines / Q000737:chemistry*; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D011743:Pyrimidines; D014227:Triazines; C012070:2,4,6-triaminopyrimidine; C044976:6-chlorouracil; D014498:Uracil; C055991:3-methyluracil; C011907:melamine
keywords: cocrystals; crystal engineering; halogen bonds; hydrogen bonds