Crystal structures of (E)-2-amino-4-methyl­sulfanyl-6-oxo-1-(1-phenyl­ethyl­idene­amino)-1,6-di­hydro­pyrimidine-5-carbo­nitrile and (E)-2-amino-4-methyl­sulfanyl-6-oxo-1-[1-(pyridin-2-yl)ethyl­idene­amino]-1,6-di­hydro­pyrimidine-5-carbo­nitrile

The title compounds 3a, C(14)H(13)N(5)OS, and 3b, C(13)H(12)N(6)OS, both show an E configuration about the N=C bond and a planar NH(2) group. The mol­ecules, which only differ in the presence of a phenyl (in 3a) or pyridyl (in 3b) substituent, are closely similar except for the different orientations of these groups. The amino hydrogen atoms form classical hydrogen bonds; in 3a the acceptors are the oxygen atom and the cyano nitro­gen atom, leading to ribbons of mol­ecules parallel to the b axis, whereas in 3b the acceptors are the oxygen atom and the pyridyl nitro­gen, leading to a layer structure perpendicular to ([Image: see text]01).