Triclinic and monoclinic polymorphs of meso-(E,E)-1,1'-[1,2-bis(4-chlorophenyl)ethane-1,2-diyl]bis(phenyldiazene): the high-yield synthesis of an unexpected product, concomitant polymorphism and configurational disorder.

Pyrazolidine-3,5-diones and their derivatives exhibit a wide range of biological activities. Seeking to explore the effect of combining a hydrocarbyl ring substituent, as present in sulfinpyrazone (used to treat gout), with a chlorinated aryl ring, as present in muzolimine (a diuretic), we explored the reaction between 1-phenylpyrazolidine-3,5-dione and 4-chlorobenzaldehyde under mildly basic conditions in the expectation of producing the simple condensation product 4-(4-chlorobenzylidene)-1-phenylpyrazolidine-3,5-dione. However, the reaction product proved to be meso-(E,E)-1,1'-[1,2-bis(4-chlorophenyl)ethane-1,2-diyl]bis(phenyldiazene), C26H20Cl2N4, and a tentative mechanism is proposed. Crystallization from ethanol produces two concomitant polymorphs, i.e. a triclinic form, (I), in the space group P-1, and a monoclinic form, (II), in the space group C2/c. In both polymorphs, the molecules lie across centres of inversion, but in (II), the molecules are subject to whole-molecule disorder equivalent to configurational disorder with occupancies of 0.6021 (19) and 0.3979 (19). There are no hydrogen bonds in the crystal structure of polymorph (I), but the molecules of polymorph (II) are linked by C-H...π(arene) hydrogen bonds into complex chains, which are further linked into sheets by C-H...N interactions.

The interplay of solvation, molecular conformation and supramolecular assembly in 1,1'-({[(ethane-1,2-diyl)dioxy](1,2-phenylene)}bis(methanylylidene))bis(thiosemicarbazide) and its N,N-dimethylformamide disolvate.

The wide diversity of applications of thiosemicarbazones and bis(thiosemicarbazones) has seen them used as anticancer and antitubercular agents, and as ligands in metal complexes designed to act as site-specific radiopharmaceuticals. Molecules of 1,1'-({[(ethane-1,2-diyl)dioxy](1,2-phenylene)}bis(methanylylidene))bis(thiosemicarbazide) {alternative name: 2,2'-[ethane-1,2-diylbis(oxy)]dibenzaldehyde bis(thiosemicarbazide)}, C18H20N6O2S2, (I), lie across twofold rotation axes in the space group C2/c, with an O-C-C-O torsion angle of -59.62 (13)° and a trans-planar arrangement of the thiosemicarbazide fragments relative to the adjacent aryl rings. The molecules of (I) are linked by N-H...S hydrogen bonds to form sheets containing R(2)4(38) rings and two types of R(2)2(8) ring. In the N,N-dimethylformamide disolvate, C18H20N6O2S2·2C3H7NO, (II), the independent molecular components all lie in general positions, but one of the solvent molecules is disordered over two sets of atomic sites having occupancies of 0.839 (3) and 0.161 (3). The O-C-C-O torsion angle in the ArOCH2CH2OAr component is -75.91 (14)° and the independent thiosemicarbazide fragments both adopt a cis-planar arrangement relative to the adjacent aryl rings. The ArOCH2CH2OAr components in (II) are linked by N-H...S hydrogen bonds to form deeply puckered sheets containing R(2)2(8), R(2)4(8) and two types of R(2)2(38) rings, and which contain cavities which accommodate all of the solvent molecules in the interior of the sheets. Comparisons are made with some related compounds.

2,2'-[Ethane-1,2-diylbis(-oxy)]dibenz-alde-hyde.

In the title compound, C16H14O4, the benzene rings are inclined at a dihedral angle of 75.14 (9)°. The torsion angle of the bridging O-C-C-O group is -76.50 (11)°. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds, forming C(6) chains along [100]. Furthermore, C-H⋯π inter-actions and π-π stacking inter-actions [centroid-centroid distances = 3.6957 (7) and 3.6735 (8) Å] contribute to the stability of the crystal packing.

2-(Piperidin-1-yl)-6-(1H-pyrrol-1-yl)pyridine-3,5-dicarbonitrile.

The piperidine ring of the title compound, C(16)H(15)N(5), adopts a chair conformation. The pyridine ring is essentially planar, with a maximum deviation of 0.035 (3) Å. The pyrrole and pyridine rings are almost coplanar, forming a dihedral angle of 3.48 (14)°. In the crystal, no classical hydrogen bonds were found. In the crystal, the molecules are linked by aromatic π-π stacking [centroid-centroid separations = 3.4984 (16) and 3.9641 (15) Šbetween pyrrole and pyridine rings and between pyridine rings, respectively].

2-Amino-6-(dimethyl-amino)pyridine-3,5-dicarbonitrile.

The title compound, C(9)H(9)N(5), is slightly twisted from planarity, with a maximum deviation of 0.0285 (13) Šfrom the pyridine plane for the C atom bearing the amino group. The cyano groups are on different sides of the pyridine plane, with C- and N-atom deviations of 0.072 (3)/0.124 (4) and -0.228 (4)/-0.409 (5) Šfrom the pyridine plane. In the crystal, N-H⋯N and C-H⋯N hydrogen bonds connect the mol-ecules into zigzag chains running along the c axis.

2-(Morpholin-4-yl)-6-(1H-pyrrol-1-yl)-pyridine-3,5-dicarbonitrile.

In the title compound, C(15)H(13)N(5)O, the morpholine ring adopts a chair conformation. The dihedral angle between the pyrrole ring and the pyridine ring is 28.93 (14)°. In the crystal, the molecules are linked by C-H⋯O hydrogen bonds occur, and aromatic weak π-π stacking [centroid-centroid separation = 4.178 (2) Å] and C-H⋯π inter-actions consolidate the packing.