Isocyanide and Cyanide Entities Form Isostructural Halogen Bond-Based Supramolecular Networks Featuring Five-Center Tetrafurcated Halogen···C/N Bonding

Abstract

A typical halogen bond (HaB) donor, 1,4-dibromo-2,3,5,6-tetrafluorobenzene (FBB), was cocrystallized with the isocyanide CNMes and the cyanide NCMes to give two isostructural cocrystals, (CNMes)•FBB and (NCMes)•FBB. Their solid-state architecture exhibits a close similarity between the isocyanide and cyanide groups in their HaB-accepting role. This similarity and particular bonding features of the HaBs were additionally verified by theoretical calculations (molecular electrostatic potential analysis, electron density/ electrostatic potential profiles, atoms-in-molecules charge analysis, and calculations of pK a values and binding energies). Remarkably, both cocrystals form unusual heterohexamers where one Br atom of FBB simultaneously forms four contacts with two C (or N) and two Br atoms of neighboring molecules. On the basis of the geometric parameters and the theoretical data, these contacts can be defined as five-center tetrafurcated μ 4 -Br•••(C, Br, C, Br) and μ 4 -Br•••(N, Br, N, Br) HaBs; this is the first observation of the tetrafurcated HaB involving four disunited HaB acceptors.

Halogen and Hydrogen Bonding Interplay Triggered Reversible Phase Transformations through Water Release/Uptake: X-ray Powder Diffraction Studies on Halogen-Substituted 1,4-Bis(4,5-diphenyl-imidazolyl)benzene

“…For both Cl-BDPI-IB and Br-BDPI-IB, the bifurcated halogen bond was found to be asymmetric as both N···X distances and C–X···N angles are different (Figures d and S9a). It was reported earlier that the asymmetrically bifurcated halogen bonds exhibit longer N···X distances than monocoordinated halogen bonds. , Moreover, the molecular geometry and the molecular stacking were slightly altered by the dehydration process. The interplanar angle between the central phenylene ring and the imidazole ring revealed that the X-BDPI moiety became more planar after water removal (Figure S10).…”

Halogen bonding with carbon: directional assembly of non-derivatised aromatic carbon systems into robust supramolecular ladder architectures

“…[24][25][26][27][28][29][30][31][32][33][34] While cocrystals exhibiting individual XBs to carbon have been reported or theoretically studied, the possibility of using such interactions for the predictable assembly of supramolecular architectures based on PAHs has not been established. [35][36][37][38][39][40][41][42] Recently, 43 we observed that cocrystals of azulene with XB donors 1,4-diiodotetrauorobenzene (tb) or trans-octauoro-4,4 ′ -diiodoazobenzene (oab) (Fig. 1b and c) exhibit a ladder-like halogen-bonded motif involving aromatic carbon, in which the PAHs act as the rungs and the XB donors as rails, identical to the motif seen in a cocrystal of naphthalene 30 with 14tb.…”

Factors contributing to halogen bond strength and stretch or contraction of internal covalent bond

“…The halogen bond (XB) [52][53][54][55][56][57] is one of a family of noncovalent bonds, including also chalcogen, pnicogen, and tetrel bonds, [58][59][60][61][62][63][64][65] in which the bridging proton of the HB is replaced by any of a large group of other elements. Because most of the halogen atoms are more electronegative than H, one cannot assign an overall positive charge to X as one can for H. Nonetheless, there is a high degree of anisotropy of electron density around X, which leads in turn to a positive region of the electrostatic potential that is focused along the extension of the A-X bond.…”