Flip-type disorder in 3-substituted 2,2′:5′,2′′-terthio­phenes

In the crystal structures of four thio­phene derivatives, (E)-3′-[2-(anthracen-9-yl)ethen­yl]-2,2′:5′,2′′-terthio­phene, C₂₈H₁₈S₃, (E)-3′-[2-(1-pyren­yl)ethen­yl]-2,2′:5′,2′′-terthio­phene, C₃₀H₁₈S₃, (E)-3′-[2-(3,4-dimethoxy­phen­yl)­ethen­yl]-2,2′:5′,2′′-terthio­phene, C₂₂H₁₈O₂S₃, and (E,E)-1,4-bis­[2-(2,2′:5′,2′′-terthio­phen-3′-yl)­ethen­yl]-2,5-dimethoxy­benzene, C₃₆H₂₆O₂S₆, at least one of the terminal thio­phene rings is disordered and the disorder is of the flip type. The terthio­phene fragments are far from being coplanar, contrary to terthio­phene itself. The central C—C=C—C fragments are almost planar but the bond lengths suggest slight delocalization within this fragment. The crystal packing is determined by van der Waals inter­actions and some weak, relatively short, C—H...S and C—H...π directional contacts.

Crystal packing of two 5-substituted 2-methyl-4-nitro-1H-imidazoles

Infinite chains connected by N—H...N hydrogen bonding form the primary packing motif in two closely related 4-­nitro­imidazole derivatives, viz. 5-bromo-2-methyl-4-nitro-1H-imidazole, C₄H₄BrN₃O₂, (I), and 2-methyl-4-nitro-1H-imidazole-5-carbonitrile, C₅H₄N₄O₂, (II). These chains are almost identical, even though in (II) there are two symmetry-independent mol­ecules in the asymmetric unit. The differences appear in the inter­actions between the chains; in (I), there are strong C—Br...O halogen bonds, which connect the chains into a two-dimensional grid, while in (II), the cyano group does not participate in specific inter­actions and the chains are only loosely connected into a three-dimensional structure.

Two different modes of halogen bonding in two 4-nitro­imidazole derivatives

In the crystal structures of the two imidazole derivatives 5-chloro-1,2-dimethyl-4-nitro-1H-imidazole, C₅H₆ClN₃O₂, (I), and 2-chloro-1-methyl-4-nitro-1H-imidazole, C₄H₄ClN₃O₂, (II), C-Cl...O halogen bonds are the principal specific inter­actions responsible for the crystal packing. Two different halogen-bond modes are observed: in (I), there is one very short and directional C-Cl...O contact [Cl...O = 2.899 (1) Å], while in (II), the C-Cl group approaches two different O atoms from two different mol­ecules, and the contacts are longer [3.285 (2) and 3.498 (2) Å] and less directional. In (I), relatively short C-H...O hydrogen bonds provide the secondary inter­actions for building the crystal structure; in (II), the C-H...O contacts are longer but there is a relatively short [pi]-[pi] contact between mol­ecules related by a centre of symmetry. The mol­ecule of (I) is almost planar, the plane of the nitro group making a dihedral angle of 6.97 (7)° with the mean plane of the imidazole ring. The mol­ecule of (II) has crystallographically imposed mirror symmetry and the nitro group lies in the mirror plane.

N,N'-Bis(2-hydroxy­benzyl­idene)pentane-1,5-diamine

In the title potential O,N,N',O'-tetra­dentate Schiff base ligand {systematic name: 2,2'-[pentane-1,5-diylbis(nitrilo­methyl­idyne)]diphenol}, C₁₉H₂₂N₂O₂, the mutual orientation of the three planar fragments determines the conformation of the mol­ecule. The dihedral angles between the planes of the two salicyl­idene groups and the plane of the central extended pentane chain are 78.4 (2) and 62.0 (3)°, and the angle between the terminal ring planes is 55.4 (1)°. Strong intra­molecular O-H...N hydrogen bonds close almost-planar six-membered rings, and the O-H bonds are elongated as a result of hydrogen-bond formation.

Two 9-[(E)-nitro­phenyl­vinyl]-9H-carbazoles

The crystal structures of 9-[(E)-(4-nitro­phenyl)vinyl]-9H-carbazole and 9-[(E)-(3-nitro­phenyl)vinyl]-9H-carbazole, both C₂₀H₁₄N₂O₂, are determined mainly by van der Waals forces and [pi]-[pi] inter­actions between the carbazole and benzene systems. However, the packing modes are different. In the 4-nitro derivative, the mol­ecules in the weakly bound stack are related by a unit-cell translation, while in the 3-nitro derivative there are centrosymmetric pairs of mol­ecules joined by [pi]-[pi] inter­actions and also pairs of mol­ecules, related by another centre of symmetry, connected by eight relatively short C-H...O inter­actions.

Three 9-[(E)-2-(4-halogenophen­yl)vin­yl]-9H-carbazoles

The crystal structures of 9-[(E)-2-(4-fluoro­phen­yl)vin­yl]-9H-carbazole, C₂₀H₁₄FN, (I), 9-[(E)-2-(4-chloro­phen­yl)vin­yl]-9H-carbazole, C₂₀H₁₄ClN, (II), and 9-[(E)-2-(4-bromo­phen­yl)vin­yl]-9H-carbazole, C₂₀H₁₄BrN, (III), are determined mainly by van der Waals forces. The chloro and bromo derivatives are highly isomorphous, while the fluoro derivative has a different packing mode. Weak C—H...X inter­actions are also involved in the crystal packing. The mol­ecular structures of the three compounds are similar, with relatively large twist angles of ca 55° between the carbazole and benzene planes.