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(1 H )‐one], namely 6‐methyl‐2‐selenouracil, C 5 H 6 N 2 OSe (1), 6‐ethyl‐2‐selenouracil, C 6 H 8 N 2 OSe (2), 6‐ n ‐propyl‐2‐selenouracil, C 7 H 10 N 2 OSe (3), and 6‐isopropyl‐2‐selenouracil, C 7 H 10 N 2 OSe (4), are described, along with that of the dichloromethane monosolvate of 6‐isopropyl‐2‐selenouracil, C 7 H 10 N 2 OSe·CH 2 Cl 2 (4·CH 2 Cl 2 ). The extended structure of (1) is a two‐dimensional sheet of topology 6 3 with a brick‐wall architecture. The extended structures of (2) and (4) are analogous, being based on a chain of eight‐membered R 8 6 (32) hydrogen‐bonded rings. In (3) and (4·CH 2 Cl 2 ), R 2 2 (8) hydrogen bonding links molecules into chains. 6‐ n ‐Propyl‐2‐selenouracil·I 2 , C 7 H 10 N 2 OSe·I 2 (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)]·2H 2 O (9·2H 2 O) 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 R 6 6 (24) hydrogen‐bonded ring, with each pair of molecules linked by an R 2 2 (8) motif.