Two polymorphs and the diethyl­ammonium salt of the barbiturate eldoral

Polymorph (Ia) of eldoral [5-ethyl-5-(piperidin-1-yl)barbituric acid or 5-ethyl-5-(piperidin-1-yl)-1,3-diazinane-2,4,6-trione], C₁₁H₁₇N₃O₃, displays a hydrogen-bonded layer structure parallel to (100). The piperidine N atom and the barbiturate carbonyl group in the 2-position are utilized in N-H...N and N-H...O=C hydrogen bonds, respectively. The structure of polymorph (Ib) contains pseudosymmetry elements. The two independent mol­ecules of (Ib) are connected via N-H...O=C(4/6-position) and N-H...N(piperidine) hydrogen bonds to give a chain structure in the [100] direction. The hydrogen-bonded layers, parallel to (010), formed in the salt di­ethyl­ammonium 5-ethyl-5-(piperidin-1-yl)barbiturate [or di­ethyl­ammonium 5-ethyl-2,4,6-trioxo-5-(piperidin-1-yl)-1,3-di­azinan-1-ide], C₄H₁₂N⁺·C₁₁H₁₆N₃O₃^-, (II), closely resemble the corresponding hydrogen-bonded structure in polymorph (Ia). Like many other 5,5-disubstituted derivatives of barbituric acid, polymorphs (Ia) and (Ib) contain the R₂²(8) N-H...O=C hydrogen-bond motif. However, the overall hydrogen-bonded chain and layer structures of (Ia) and (Ib) are unique because of the involvement of the hydrogen-bond acceptor function in the piperidine group.