CH/? hydrogen bonds in crystals

Abstract

The nature and characteristics of the CH/p interaction are discussed by comparison with other weak molecular forces such as the CH/O and OH/p interaction. The CH/p interaction is a kind of hydrogen bond operating between a soft acid CH and a soft base p-system (double and triple bonds, C 6 and C 5 aromatic rings, heteroaromatics, convex surfaces of fullerenes and nanotubes). The consequences of CH/p hydrogen bonds in supramolecular chemistry are reviewed on grounds of recent crystallographic findings and database analyses. The topics include intramolecular interactions, crystal packing (organic and organometallic compounds), host/ guest complexes (cavity-type inclusion compounds of cyclodextrins and synthetic macrocyclic hosts such as calixarenes, catenanes, rotaxanes and pseudorotaxanes), lattice-inclusion type clathrates (including liquid crystals, porphyrin derivatives, cyclopentadienyl compounds and C 60 fullerenes), enantioselective clathrate formation, catalytic enantioface discriminating reactions and solid-state photoreaction. The implications of the CH/p concept for crystal engineering and drug design are evident.

Structural and Photophysical Properties of (Phosphane)gold(I)‐Decorated 4,4′‐Diethynyl‐2,2′‐bipyridine Ligands

“…Et 2 O, similar close contacts are observed between molecules of 2, but this time involving the methyl group of one tolyl substituent (C7...H212 ii = 2.85 Å, C7...C21 ii = 3.764(3) Å, symmetry code ii = -1 + x, y, z). Packing motifs based on C-H....C alkyne contacts are well established in the solid state structures of alkynes with aromatic substituents, [44][45][46][47][48][49] and C-H....C alkyne interactions are ubiquitous among compounds containing R 3 PAuC≡C units (CSD v 5.3 with May 2009 updates, Conquest v. 1.11), [17] involving both aromatic and aliphatic C-H units. There are no significant intermolecular Au...Au contacts in either 1 or 2, the closest separations being Au2...Au2 i = 4.763(1) Å in 1 (symmetry code i = 2 -x, -y, -z), and Au1...Au1 iii = 5.303(1) Å in 2 (symmetry code iii = 1 -x, 1 -y, -z).…”

Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

“…Although weak interactions have been detected in synthetic molecules, it is difficult to quantify them experimentally because of very weak nature vis-à-vis conventional hydrogen bonds. Recently, some weak noncovalent interactions like C-H/p, [11][12][13] C-H/F-C, 14 C-H/O, 15,16 N/O¼ ¼C, 17 X/X (Cl, Br, S, Se), [18][19][20] C-H/ N, 21 X-H/p, [22][23][24] and Se/F 25 have been explored for stabilizing specific conformations of man-made small molecules and molecular assemblies.…”

Synthesis, Crystal Structure and in vitro DNA Binding Studies of Combretastatin A-4 Analogue

“…The measured π-π distances of 3.704 and 3.253 Å respectively suggests π-π stacking and C-H-π interaction. [20,21] The distances of 2.614 and 2.734 Å respectively indicate a good hydrogen bonding of phenyl hydrogen with carbonyl oxygen and nitrogen atoms in compound 1.…”