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The isomeric derivatives 1,2-bis(iodomethyl)benzene, (I), and 1,3-bis(iodomethyl)benzene (II), both C8H8I2, were prepared by metathesis from their dibromo analogues. The ortho-derivative, (I), lies about a crystallographic twofold axis that bisects the C—C bond between the two iodomethyl substituents. The packing in (I) relies solely on C—H...I hydrogen bonds supported by weak parallel slipped π–π stacking interactions [inter-centroid distance = 4.0569 (11) Å, inter-planar distance = 3.3789 (8) Å and slippage = 2.245 Å]. While C—H...I hydrogen bonds are also found in the packing of (II), type II, I...I halogen bonds [I...I = 3.8662 (2) Å] and C—H...π contacts feature prominently in stabilizing the three-dimensional structure.

The title molecular salt, C18H21N2+·I−, consists of a pyridinium cation and an I− anion. The cation exists in an E,E conformation with respect to the two C=C double bonds, and is roughly planar with the pyridinium ring being inclined to the benzene ring by 10.8 (2) °. In the crystal, the ions are linked by a C—H...I hydrogen bond, and the cations are linked by C—H...π interactions, forming zigzag chains propagating along [010].

In the cation of the title salt, C18H20N3+·I−, the mesityl and phenyl rings are inclined to the central triazolium ring by 61.39 (16) and 30.99 (16)°, respectively, and to one another by 37.75 (15)°. In the crystal, molecules are linked via C—H...I hydrogen bonds, forming slabs parallel to the ab plane. Within the slabs there are weak π–π interactions present involving the mesityl and phenyl rings [inter-centroid distances are 3.8663 (18) and 3.8141 (18) Å].

N-Heterocyclic carbene (NHC) based systems are usually exploited in the exploration of catalytic mechanisms and processes in organocatalysis, and homo- and heterogeneous catalysis. However, their molecular structures have not received adequate attention. The NHC proligand methylenebis( N-butylimidazolium) has been synthesized as the acetonitrile solvate of the diiodide salt, C15H26N42+·2I−·CH3CN [1,1′-methylenebis(3-butylimidazolium) diiodide acetonitrile monosolvate], and fully characterized. An interesting cation-anion connection pattern has been identified in the crystal lattice, in which three iodide anions interact simultaneously with the cisoid-oriented cation. A Hirshfeld surface analysis reveals the predominance of hydrogen bonding over anion-π interactions. This particular arrangement is observed in different methylene-bridged bis(imidazolium) cations bearing chloride or bromide counter-anions. Density functional theory (DFT) calculations with acetonitrile as solvent reproduce the geometry of the title cation. [ABSTRACT FROM AUTHOR]