title: 5-Fluorouracil and thymine form a crystalline solid solution.
abstract: The crystal structure of a 5-fluorouracil-thymine [5-fluoropyrimidine-2,4(1H,3H)-dione-5-methylpyrimidine-2,4(1H,3H)-dione, C(4)H(3)FN(2)O(2)xC(5)H(6)N(2)O(2)] solid solution has been determined. Both of the crystallographically independent sites can accommodate either 5-fluorouracil or thymine molecules, leading to occupational disorder [C(5-x)H(6-3x)F(x)N(2)O(2)xC(5-y)H(6-3x)F(y)N(2)O(2), with x = 0.52 and y = 0.7 for determination (I), x = 0.55 and y = 0.69 for (II), and x = 0.67 and y = 0.76 for (III)]. The 5-fluorouracil-thymine ratio in the crystal structure is influenced by the 5-fluorouracil-thymine ratio in the crystallization solution, though it does not exactly mirror it. The crystal structure comprises interpenetrating hydrogen-bonded nets, containing four independent hydrogen bonds.
authors.affiliation: Christopher Ingold Laboratory, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, England.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Barnett
authors.forename: Ashley T
authors.initials: AT
authors.lastname: Hulme
authors.forename: Derek A
authors.initials: DA
authors.lastname: Tocher