Computational and Experimental Characterization of Five Crystal Forms of Thymine: Packing Polymorphism, Polytypism/Disorder and Stoichiometric 0.8-Hydrate.

New polymorphs of thymine emerged in an experimental search for solid forms, which was guided by the computationally generated crystal energy landscape. Three of the four anhydrates (AH) are homeoenergetic ( - ) and their packing modes differ only in the location of oxygen and hydrogen atoms. and are ordered phases, whereas shows disorder (X-ray diffuse scattering).

Polythia-zide.

The crystal structure of the title compound, C(11)H(13)ClF(3)N(3)O(4)S(3) (systematic name: 6-chloro-2-methyl-3-{[(2,2,2-trifluoro-eth-yl)sulfan-yl]meth-yl}-3,4-dihydro-2H-1,2,4-benzothia-diazine-7-sul-f-on-amide 1,1-diox-ide; CRN: 346-18-9), exhibits a two-dimensional network of hydrogen-bonded mol-ecules parallel to (01). The NH and NH(2) groups act as donor sites and the sulfonyl O atoms as acceptor sites in N-H⋯O hydrogen bonds, and a C-H⋯O interaction also occurs. The thiadiazine ring adopts an envelope conformation with the N atom bonded to sulfur at the tip of the flap, and the methyl substituent is in an axial position.