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The structures of a series of 2:1 cocrystals formed between 4-(dimethylamino)pyridine and each of 1,2,4,5-tetrachloro-3,6-diiodobenzene, 2C₇H₁₀N₂·C₆Cl₄I₂, 1,2,4,5-tetrabromo-3,6-diiodobenzene, 2C₇H₁₀N₂·C₆Br₄I₂, 1-bromo-4-iodo-2,3,5,6-tetrafluorobenzene, 2C₇H₁₀N₂·C₆BrF₄I, and 1,2-dibromo-4,5-difluoro-3,6-diiodobenzene, 2C₇H₁₀N₂·C₆Br₂F₂I₂, are reported. In all five structures, the core halogen-bonded 2:1 trimolecular units have geometrically similar parameters, with the central halogen-bond donor flanked by two pyridine halogen-bond acceptors twisted with respect to the central halogen-bond donor at angles ranging from 76 to 86°. The I...N halogen-bond separations are all short, ranging from 73.3 to 76.7% of the sum of the van der Waals radii, while the C—I...N bond angles are essentially linear. The Br...N halogen-bond separation in the cocrystal formed with 1-bromo-4-iodo-2,3,5,6-tetrafluorobenzene is 80.4% of the sum of the van der Waals radii. Subtle differences in the crystal packings are attributed to the role of secondary C—H...π and weak π-type interactions with chloro and bromo substituents. The cocrystals 2C₇H₁₀N₂·C₆Cl₄I₂and 2C₇H₁₀N₂·C₆Br₄I₂are isomorphous. 

The formation of a halogen-bonded co-crystal based upon 1,2-bis(2-pyridyl)ethylene along with iodoperchlorobenzene is reported. The co-crystal undergoes a nearly quantitative [2 + 2] cycloaddition reaction in the organic solid state. 

The formation of a series of isostructural three-component co-crystals between 1,2,4,5-tetrachloro-3-iodobenzene and each of three isosteric bipyridines is reported. 

The present study evaluates the potential combination of charge-transfer electron-donor–acceptor π–π complexation and C—H hydrogen bonding to form colored cocrystals. The crystal structures of the red 1:1 cocrystals formed from the isomeric pyridines 4- and 3-{2-[4-(dimethylamino)phenyl]ethynyl}pyridine with 1-[2-(3,5-dinitrophenyl)ethynyl]-2,3,5,6-tetrafluorobenzene, both C 14 H 4 F 4 N 2 O 4 ·C 15 H 14 N 2 , are reported. Intermolecular interaction energy calculations confirm that π-stacking interactions dominate the intermolecular interactions within each crystal structure. The close contacts revealed by Hirshfeld surface calculations are predominantly C—H interactions with N, O, and F atoms. 

The formation and crystal structure of a zigzag network held together by I...N halogen bonds is reported. In particular, the halogen-bond donor is 1,3-diiodoperchlorobenzene ( C 6 I 2 Cl 4 ) while the acceptor is the photoproduct rtct -tetrakis(pyridin-4-yl)cyclobutane ( TPCB ). Curiously, within the resulting co-crystal ( C 6 I 2 Cl 4 )·( TPCB ), the photoproduct accepts only two halogen bonds between neighbouring 4-pyridyl rings and as a result behaves as a bent two-connected node rather than the expected four-connected centre. In addition, the photoproduct, TPCB , is also found to engage in C—H...N hydrogen bonds, forming an extended zigzag chain. 

1,3-Diiodo-5-nitrobenzene, C₆H₃I₂NO₂, and 1,3-dibromo-5-nitrobenzene, C₆H₃Br₂NO₂, crystallize in the centrosymmetric space groupP2₁/m, and are isostructural with 1,3-dichloro-5-nitrobenzene, C₆H₃Cl₂NO₂, that has been redetermined at 100 K for consistency. While the three-dimensional packing in all three structures is similar, the size of the halogen atom affects the nonbonded close contacts observed between molecules. Thus, the structure of 1,3-diiodo-5-nitrobenzene features a close Type 1 I...I contact, the structure of 1,3-dibromo-5-nitrobenzene features a self-complementary nitro-O...Br close contact, while the structure of 1,3-dichloro-5-nitrobenzene also has a self-complementary nitro-O...Cl interaction, as well as a bifurcated C—H...O(nitro) close contact. Notably, the major energetically attractive intermolecular interaction between adjacent molecules in each of the three structures corresponds to a π-stacked interaction. The self-complementary halogen...O(nitro) and C—H...O(nitro) interactions correspond to significant cohesive attraction between molecules in each structure, while the Type 1 halogen–halogen contact is weakly cohesive. 

The rapid evaporation of 1:1 solutions of diethynylpyridines and N -halosuccinimides, that react together to form haloalkynes, led to the isolation of unreacted 1:1 cocrystals of the two components. The 1:1 cocrystal formed between 2,6-diethynylpyridine and N -iodosuccinimide (C 4 H 4 INO 2 ·C 9 H 5 N) contains an N -iodosuccinimide–pyridine I...N halogen bond and two terminal alkyne–succinimide carbonyl C—H...O hydrogen bonds. The three-dimensional extended structure features interwoven double-stranded supramolecular polymers that are interconnected through halogen bonds. The cocrystal formed between 3,5-diethynylpyridine and N -iodosuccinimide (C 4 H 4 INO 2 ·C 9 H 5 N) also features an I...N halogen bond and two C—H...O hydrogen bonds. However, the components form essentially planar double-stranded one-dimensional zigzag supramolecular polymers. The cocrystal formed between 3,5-diethynylpyridine and N -bromosuccinimide (C 4 H 4 BrNO 2 ·C 9 H 5 N) is isomorphous to the cocrystal formed between 3,5-diethynylpyridine and N -iodosuccinimide, with a Br...N halogen bond instead of an I...N halogen bond. 

The treatment of 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine with a threefold excess of 1,2,3,5-tetrafluoro-4,6-diiodobenzene in dichloromethane solution led to the formation of the unexpected 1:2 title co-crystal, C 14 H 13 N 3 ·2CF 4 I 2 . In the extended structure, two unique C—I...N halogen bonds from one of the 1,2,3,5-tetrafluoro-4,6-diiodobenzene molecules to the pyrimidine N atoms of the 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine molecule generate [110] chains and layers of these chains are π-stacked along the a- axis direction. The second 1,2,3,5-tetrafluoro-4,6-diiodobenzene molecule resides in channels formed parallel to the a -axis direction between stacks of 5-{[4-(dimethylamino)phenyl]ethynyl}pyrimidine molecules and interacts with them via C—I...π(alkyne) contacts.