Structural characterization of selenium and selenium-diiodine analogues of the antithyroid drug 6-n-propyl-2-thiouracil and its alkyl derivatives

The structures of four selenium analogues of the antithyroid drug 6‐n‐propyl‐2‐thiouracil [systematic name: 2,3‐dihydro‐6‐n‐propyl‐2‐thioxopyrimidin‐4(1H)‐one], namely 6‐methyl‐2‐selenouracil, C5H6N2OSe (1), 6‐ethyl‐2‐selenouracil, C6H8N2OSe (2), 6‐n‐propyl‐2‐selenouracil, C7H10N2OSe (3), and 6‐isopropyl‐2‐selenouracil, C7H10N2OSe (4), are described, along with that of the dichloromethane monosolvate of 6‐isopropyl‐2‐selenouracil, C7H10N2OSe·CH2Cl2 (4·CH2Cl2). The extended structure of (1) is a two‐dimensional sheet of topology 63 with a brick‐wall architecture. The extended structures of (2) and (4) are analogous, being based on a chain of eight‐membered R86(32) hydrogen‐bonded rings. In (3) and (4·CH2Cl2), R22(8) hydrogen bonding links molecules into chains. 6‐n‐Propyl‐2‐selenouracil·I2, C7H10N2OSe·I2 (7), is a charge‐transfer complex with a `spoke' structure, the extended structure of which is based on a linear chain formed principally by intermolecular N—H⋯O hydrogen bonds. Re‐crystallization of 6‐ethyl‐2‐selenouracil or (7) from acetone gave crystals of the diselenides [N‐(6′‐ethyl‐4′‐pyr­imidone)(6‐ethyl‐2‐selenouracil)2(Se—Se)]·2H2O (9·2H2O) or [N‐(6′‐n‐propyl‐4′‐pyrimidone)(6‐n‐propyl‐2‐selenouracil)2(Se—Se)] (10), respectively: these have similar extended chain structures formed via N—H⋯O and C—H⋯O hydrogen bonds, stacked to give two‐dimensional sheets. Re‐crystallization of (7) from methanol/acetonitrile led via deselenation to the formation of crystals of 6‐n‐propyl‐2‐uracil (11), in which six symmetry‐related molecules combine to form a six‐membered R66(24) hydrogen‐bonded ring, with each pair of molecules linked by an R22(8) motif.