Three hexahydropyridopyrimidine-spiro-cyclohexanetriones: supramolecular structures generated by O-H...O, N-H...O, C-H...O and C-H...π hydrogen bonds, and π...π stacking interactions

4',4'-Dimethyl-2-methylsulfanyl-3,4,5,6,7,8-hexahydropyrido-[2,3-d] pyrimidine-6-spiro-1'-cyclohexane-2',4,6'-trione, C15H19N3O3S, (I), has a markedly polarized molecular-electronic structure, and the molecules are linked into a three-dimensional framework by a combination of N-H...O, C-H...O and C-H...pi hydrogen bonds. 8-Hydroxymethyl-4',4'-dimethyl-2-methylsulfanyl-3,4,5,6,7,8-hexahydropyrido[2,3-d] pyrimidine-6-spiro-1'-cyclohexane-2',4,6'-trione, C16H21N3O4S, (II), where the hydroxymethyl substituent is disordered over two sets of sites, has a much less polarized structure than (I); the molecules are linked by a combination of O-H...O and N-H...O hydrogen bonds into chains containing alternating R-2(2)(8) and R-2(2)(16) rings, and these chains are linked into sheets by a combination of a pi-pi stacking interaction and a C-H...O hydrogen bond. 8-Ethoxymethyl-2-methoxy-4',4'-dimethyl-3,4,5,6,7,8-hexahydropyrido-[2,3-d]-pyrimidine-6-spiro-1'-cyclohexane-2',4,6'-trione, C18H25N3O5, (III), has an unpolarized electronic structure, and a combination of N-H...O, C-H...O and C-H...pi hydrogen bonds links the molecules into sheets.