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The title crystals are isomorphous, and form centrically stacked planar sheets formed by CN⋯I and NC⋯I short contacts., The title crystals, C7H2I3N, are isomorphous. Both mol­ecules lie across two crystallographic mirror planes and a twofold axis. The principal supra­molecular inter­action is centric R 2 2(10) CN/NC⋯I short contacts involving both ortho I atoms, with two contacts bis­ecting each cyano and iso­cyano group. These form ribbons along [010] and give rise to a planar sheet structure parallel to (100). All pairs of adjacent sheets have centric stacking, a mode not previously reported for sheets of this type. This study completes the series of homo-2,4,6-trihalobenzo­nitriles, in which I atoms give the strongest CN⋯X and NC⋯X inter­actions (X = F, Cl, Br, I).

In the title compound, the 1,3-dioxane ring has an envelope conformation. In the crystal, classical O—H⋯O and N—H⋯O hydrogen bonds link mol­ecules into a sheet structure, and a weak inter­molecular C—H⋯Cl inter­action extends the sheet structure into a three-dimensional network., In the title compound, C10H14Cl3NO5, the five-membered dioxolane ring adopts an envelope conformation with the C atom bonded to the butenoate side chain as the flap. It deviates from the mean plane of the other atoms in the ring by 0.446 (6) Å. In the crystal, mol­ecules are connected by O—H⋯O hydrogen bonds into helical chains running along the b-axis direction. The chains are linked into a sheet structure parallel to (001) by an N—H⋯O hydrogen bond. These classical hydrogen bonds enclose an R 4 4(24) graph-set motif in the sheet structure. Furthermore, a weak inter­molecular C—H⋯Cl inter­action expands the sheet structures into a three-dimensional network.

In the title dimedone derivative, the 4-hy­droxy-3-meth­oxy­benzyl substituent adopts a sofa conformation. In the crystal, mol­ecules are assembled into a sheet structure parallel to the ab plane via O—H⋯O hydrogen bonds., In the title compound, C16H20O4, a new starting compound for the synthesis of various heterocycles, the partially saturated six-membered ring adopts a sofa conformation. An intra­molecular O—H⋯O hydrogen bond is observed in the guaiacol residue. In the crystal, mol­ecules are assembled into a sheet structure parallel to the ab plane via O—H⋯O hydrogen bonds. The hydrogen-bond pattern is described by an R 4 4(28) graph-set motif. The sheets are further linked by C—H⋯O hydrogen bonds into a three-dimensional network.

The title compound shows two packing polymorphs, in which the mol­ecular structures are planar and essentially similar. One crystal shows inter­molecular C—H⋯O and π–π inter­actions, while the other crystal exhibits several modes of inter­molecular C—H⋯O inter­actions., The title compound, C11H13NO6, shows two polymorphs, orange and yellow forms, both of which crystallize in the space group P21/c. The mol­ecular structures in the two polymorphs are essentially similar and adopt a planar structure, the maximum deviations for the non-H atoms being 0.1836 (13) and 0.1276 (13) Å, respectively, for the orange and yellow forms. In the orange crystal, mol­ecules are linked by an inter­molecular C—H⋯O inter­action into a helical chain along the b-axis direction. The chains are stacked along the c axis through a π–π inter­action [centroid–centroid distance = 3.6087 (11) Å], forming a layer parallel to the bc plane. In the yellow crystal, mol­ecules are connected through C—H⋯O inter­actions into a sheet structure parallel to (-302). No significant π–π inter­action is observed. The unit-cell volume of the orange crystal is larger than that of the yellow one, and this accounts for the predominant growth of the yellow crystal.

In the title compound, C12H12N2O2, the dihedral angle between the planes of the two pyridine rings is 5.8 (1)°. Neighbouring molecules are linkedviaC(Me)—H...N interactions, generating a two-dimensional sheet structure; C—H...π interactions further link the molecules into a three-dimensional network. An overlapped arrangement of parallel pyridine rings in neighbouring molecules [centroid-to-centroid distance = 3.6655 (15) Å] is observed in the crystal structure.