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1. 1-Methyl-5-nitroimidazolium chloride

   https://doi.org/10.1107/S2414314622008781  

   Bellia, Sophia; Anderson, Grace; Zeller, Matthias; Mirjafari, Arsalan; Hillesheim, Patrick C. (September 2022, IUCrData)

   The title salt, C 4 H 6 N 3 O 2 + ·Cl − , exhibits multiple hydrogen-bonding interactions involving the nitroimidazolium cation and the chloride anion. Strong hydrogen bonds between the amine hydrogen atom and the chloride anion link the ionic moieties. Of note, with respect to H...Cl interactions, the central aromatic hydrogen atom displays a shorter interaction than the other aromatic hydrogen atom. Finally, interactions are observed between the nitro moiety and methyl H atoms. While no π–π stacking is observed, anion-π interactions are present. The crystal was refined as a two-component twin. 

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2. π-Complexation and C—H hydrogen bonding in the formation of colored cocrystals

   https://doi.org/10.1107/S2053229623002231  

   Bosch, Eric; Moreno, Bryce S.; Bowling, Nathan P. (April 2023, Acta Crystallographica Section C Structural Chemistry)

   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. 

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3. 1,1′-Methylenebis{4-[( E )-2-(pyridin-4-yl)ethenyl]pyridinium} dibromide dihydrate

   https://doi.org/10.1107/S2414314622005259  

   Neal, Henry C.; Nesterov, Volodymyr V.; Smucker, Bradley W. (May 2022, IUCrData)

   The chevron-shaped cations of the title hydrated salt, C 25 H 22 N 4 2+ ·2Br − ·2H 2 O, are arranged in back-to-back alternating directions to form a zigzag ribbon propagating along the [010] direction. Intermolecular interactions comprising these ribbons are π–π interactions between the pyridinium and adjacent pyridyl rings, as well as O—H...O hydrogen bonding between water molecules and two adjacent pyridyl N atoms. Half of the cation is generated by the mirror plane. The water O atoms, the central C atom and one Br atom are located on this mirror plane while the other Br atom is on a twofold screw axis. 

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4. Geometrical variations of two manganese(II) complexes with closely related quinoline-based tripodal ligands

   https://doi.org/10.1107/S2056989021009786  

   Frey, Steven T.; Ballot, Jasper G.; Hands, Allison; Cirka, Haley A.; Rinaolo, Katheryn C.; Phalkun, Nich N.; Kaur, Manpreet; Jasinski, Jerry P. (October 2021, Acta Crystallographica Section E Crystallographic Communications)

   Structural analyses of the compounds di-μ-acetato-κ 4 O : O ′-bis{[2-methoxy- N , N -bis(quinolin-2-ylmethyl)ethanamine-κ 4 N , N ′, N ′′, O ]manganese(II)} bis(tetraphenylborate) dichloromethane 1.45-solvate, [Mn 2 (C 23 O 2 ) 2 (C 23 H 23 N 3 O) 2 ](C 24 H 20 B)·1.45CH 2 Cl 2 or [Mn(DQMEA)(μ-OAc) 2 Mn(DQMEA)](BPh 4 ) 2 ·1.45CH 2 Cl 2 or [1] (BPh 4 ) 2 ·1.45CH 2 Cl 2 , and (acetato-κ O )[2-hydroxy- N , N -bis(quinolin-2-ylmethyl)ethanamine-κ 4 N , N ′, N ′′, O ](methanol-κ O )manganese(II) tetraphenylborate methanol monosolvate, [Mn(CH 3 COO)(C 22 H 21 N 3 O)(CH 3 OH)](C 24 H 20 B)·CH 3 OH or [Mn(DQEA)(OAc)(CH 3 OH)]BPh 4 ·CH 3 OH or [2] BPh 4 ·CH 3 OH, by single-crystal X-ray diffraction reveal distinct differences in the geometry of coordination of the tripodal DQEA and DQMEA ligands to Mn II ions. In the asymmetric unit, compound [1] (BPh 4 ) 2 ·(CH 2 Cl 2 ) 1.45 crystallizes as a dimer in which each manganese(II) center is coordinated by the central amine nitrogen, the nitrogen atom of each quinoline group, and the methoxy-oxygen of the tetradentate DQMEA ligand, and two bridging-acetate oxygen atoms. The symmetric Mn II centers have a distorted, octahedral geometry in which the quinoline nitrogen atoms are trans to each other resulting in co-planarity of the quinoline rings. For each Mn II center, a coordinated acetate oxygen participates in C—H...O hydrogen-bonding interactions with the two quinolyl moieties, further stabilizing the trans structure. Within the crystal, weak π – π stacking interactions and intermolecular cation–anion interactions stabilize the crystal packing. In the asymmetric unit, compound [2] BPh 4 ·CH 3 OH crystallizes as a monomer in which the manganese(II) ion is coordinated to the central nitrogen, the nitrogen atom of each quinoline group, and the alcohol oxygen of the tetradentate DQEA ligand, an oxygen atom of OAc, and the oxygen atom of a methanol ligand. The geometry of the Mn II center in [2] BPh 4 ·CH 3 OH is also a distorted octahedron, but the quinoline nitrogen atoms are cis to each other in this structure. Hydrogen bonding between the acetate oxygen atoms and hydroxyl (O—H...O) and quinolyl (C—H...O and N—H...O) moieties of the DQEA ligand stabilize the complex in this cis configuration. Within the crystal, dimerization of complexes occurs by the formation of a pair of intermolecular O3—H3...O2 hydrogen bonds between the coordinated hydroxyl oxygen of the DQEA ligand of one complex and an acetate oxygen of another. Additional hydrogen-bonding and intermolecular cation–anion interactions contribute to the crystal packing. 

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5. Crystal structure of 8-hydroxyquinoline: a new monoclinic polymorph

   https://doi.org/10.1107/S1600536814016110  

   Castañeda, Raúl; Antal, Sofia A.; Draguta, Sergiu; Timofeeva, Tatiana V.; Khrustalev, Victor N. (September 2014, Acta Crystallographica Section E Structure Reports Online)

   In an attempt to grow 8-hydroxyquinoline–acetaminophen co-crystals from equimolar amounts of conformers in a chloroform–ethanol solvent mixture at room temperature, the title compound, C 9 H 7 NO, was obtained. The molecule is planar, with the hydroxy H atom forming an intramolecular O—H...N hydrogen bond. In the crystal, molecules form centrosymmetric dimers via two O—H...N hydrogen bonds. Thus, the hydroxy H atoms are involved in bifurcated O—H...N hydrogen bonds, leading to the formation of a central planar four-membered N 2 H 2 ring. The dimers are bound by intermolecular π–π stacking [the shortest C...C distance is 3.2997 (17) Å] and C—H...π interactions into a three-dimensional framework. The crystal grown represents a new monoclinic polymorph in the space group P 2 1 / n . The molecular structure of the present monoclinic polymorph is very similar to that of the orthorhombic polymorph (space group Fdd 2) studied previously [Roychowdhury et al. (1978). Acta Cryst. B 34 , 1047–1048; Banerjee & Saha (1986). Acta Cryst. C 42 , 1408–1411]. The structures of the two polymorphs are distinguished by the different geometries of the hydrogen-bonded dimers, which in the crystal of the orthorhombic polymorph possess twofold axis symmetry, with the central N 2 H 2 ring adopting a butterfly conformation. 

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