title: Four cocrystals of thymine with phenolic coformers: influence of the coformer on hydrogen bonding.
abstract: Cocrystals are molecular solids composed of at least two types of neutral chemical species held together by noncovalent forces. Crystallization of thymine [systematic name: 5-methylpyrimidine-2,4(1H,3H)-dione] with four phenolic coformers resulted in cocrystal formation, viz. catechol (benzene-1,2-diol) giving thymine-catechol (1/1), C5H6N2O2·C6H6O2, (I), resorcinol (benzene-1,3-diol) giving thymine-resorcinol (2/1), 2C5H6N2O2·C6H6O2, (II), hydroquinone (benzene-1,4-diol) giving thymine-hydroquinone (2/1), 2C5H6N2O2·C6H6O2, (III), and pyrogallol (benzene-1,2,3-triol) giving thymine-pyrogallol (1/2), C5H6N2O2·2C6H6O3, (IV). The resorcinol molecule in (II) occupies a twofold axis, while the hydroquinone molecule in (III) is situated on a centre of inversion. Thymine-thymine base pairing is common across all four structures, albeit with different patterns. In (I)-(III), the base pair is propagated into an infinite one-dimensional ribbon, whereas it exists as a discrete dimeric unit in (IV). In (I)-(III), the two donor N atoms and one carbonyl acceptor O atom of thymine are involved in thymine-thymine base pairing and the remaining carbonyl O atom is hydrogen bonded to the coformer. In contrast, in (IV), just one donor N atom and one acceptor O atom are involved in base pairing, and the remaining donor N atom and acceptor O atom of thymine form hydrogen bonds to the coformer molecules. Thus, the utilization of the donor and acceptor atoms of thymine in the hydrogen bonding is influenced by the coformers.
authors.affiliation: X-ray Crystallography Division, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, India.
authors.forename: Balasubramanian
authors.initials: B
authors.lastname: Sridhar
authors.affiliation: X-ray Crystallography Division, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, India.
authors.forename: Jagadeesh Babu
authors.initials: JB
authors.lastname: Nanubolu
authors.affiliation: X-ray Crystallography Division, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, India.
authors.forename: Krishnan
authors.initials: K
authors.lastname: Ravikumar
mesh_terms: D020029:Base Pairing; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry*; D011748:Pyrogallol / Q000737:chemistry*; D012118:Resorcinols / Q000737:chemistry*; D013941:Thymine / Q000737:chemistry*
chemical_list: D010636:Phenols; D012118:Resorcinols; D011748:Pyrogallol; D013941:Thymine; C031389:resorcinol
keywords: catechol; cocrystals; coformers; crystal structure; hydrogen bonding; nucleobases; pyrogallol; resorcinol; thymine; thymine–thymine base pairing