Frontispiece: Metal Centers as Nucleophiles: Oxymoron of Halogen Bond‐Involving Crystal Engineering

Halogen bond interactions, which take place between an electrophilic halogen and the electron-pair of a Lewis base and exhibit high directionality (approximately 180°), are non-covalent bond interactions similar to the hydrogen bond interaction. Many reports on halogen bond interactions have been published thus far, but many of them discuss halogen bond in the context of crystal engineering of supramolecular architecture. Since a seminal report by Bolm in 2008, halogen bond-assisted or -promoted organic synthesis has received significant attention. This review aims to introduce the molecular design of suitable halogen bond donors and organic transformations involving halogen bond interactions to afford a variety of organic compounds.

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1,3,5-Tri(iodoethynyl)-2,4,6-trifluorobenzene: halogen-bonded frameworks and NMR spectroscopic analysis

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520617000944 ◽

2017 ◽

Vol 73 (2) ◽

pp. 153-162 ◽

Cited By ~ 10

Author(s):

Patrick M. J. Szell ◽

Bulat Gabidullin ◽

David L. Bryce

Keyword(s):

Solid State ◽

Crystal Engineering ◽

Halogen Bond ◽

Halogen Bonding ◽

Lewis Base ◽

Phosphonium Salts ◽

Covalent Interaction ◽

Framework Materials ◽

Engineering Strategy ◽

Triphenylphosphonium Bromide

Halogen bonding is the non-covalent interaction between the region of positive electrostatic potential associated with a covalently bonded halogen atom, named the σ-hole, and a Lewis base. Single-crystal X-ray diffraction structures are reported for a series of seven halogen-bonded cocrystals featuring 1,3,5-tris(iodoethynyl)-2,4,6-trifluorobenzene (1) as the halogen-bond donor, and bromide ions (as ammonium or phosphonium salts) as the halogen-bond acceptors: (1)·MePh3PBr, (1)·EtPh3PBr, (1)·acetonyl-Ph3PBr, (1)·Ph4PBr, (1)·[bis(4-fluorophenyl)methyl]triphenylphosphonium bromide, and two new polymorphs of (1)·Et3BuNBr. The cocrystals all feature moderately strong iodine–bromide halogen bonds. The crystal structure of pure [bis(4-fluorophenyl)methyl]triphenylphosphonium bromide is also reported. The results of a crystal engineering strategy of varying the size of the counter-cation are explored, and the features of the resulting framework materials are discussed. Given the potential utility of (1) in future crystal engineering applications, detailed NMR analyses (in solution and in the solid state) of this halogen-bond donor are also presented. In solution, complex13C and19F multiplets are explained by considering the delicate interplay between variousJcouplings and subtle isotope shifts. In the solid state, the formation of (1)·Et3BuNBr is shown through significant13C chemical shift changes relative to pure solid 1,3,5-tris(iodoethynyl)-2,4,6-trifluorobenzene.

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N—H...X (X = Cl and Br) hydrogen bonds in three isomorphous 3,5-dichloropyridinium salts

Acta Crystallographica Section C Structural Chemistry ◽

10.1107/s2053229617013201 ◽

2017 ◽

Vol 73 (10) ◽

pp. 803-809 ◽

Cited By ~ 2

Author(s):

Ai Wang ◽

Ulli Englert

Keyword(s):

Hydrogen Bonds ◽

Small Molecules ◽

Crystal Engineering ◽

Electrostatic Interactions ◽

Halogen Bond ◽

Halogen Bonds ◽

Dipole Orientation ◽

Halide Ligand ◽

Van Der Waals Radii ◽

Short Contacts

Specific short contacts are important in crystal engineering. Hydrogen bonds have been particularly successful and together with halogen bonds can be useful for assembling small molecules or ions into crystals. The ionic constituents in the isomorphous 3,5-dichloropyridinium (3,5-diClPy) tetrahalometallates 3,5-dichloropyridinium tetrachloridozincate(II), (C5H4Cl2N)2[ZnCl4] or (3,5-diClPy)2ZnCl4, 3,5-dichloropyridinium tetrabromidozincate(II), (C5H4Cl2N)2[ZnBr4] or (3,5-diClPy)2ZnBr4, and 3,5-dichloropyridinium tetrabromidocobaltate(II), (C5H4Cl2N)2[CoBr4] or (3,5-diClPy)2CoBr4, arrange according to favourable electrostatic interactions. Cations are preferably surrounded by anions and vice versa; rare cation–cation contacts are associated with an antiparallel dipole orientation. N—H...X (X = Cl and Br) hydrogen bonds and X...X halogen bonds compete as closest contacts between neighbouring residues. The former dominate in the title compounds; the four symmetrically independent pyridinium N—H groups in each compound act as donors in charge-assisted hydrogen bonds, with halogen ligands and the tetrahedral metallate anions as acceptors. The M—X coordinative bonds in the latter are significantly longer if the halide ligand is engaged in a classical X...H—N hydrogen bond. In all three solids, triangular halogen-bond interactions are observed. They might contribute to the stabilization of the structures, but even the shortest interhalogen contacts are only slightly shorter than the sum of the van der Waals radii.

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Crystal Engineering with Iodoethynylnitrobenzenes: A Group of Highly Effective Halogen-Bond Donors

Crystal Growth & Design ◽

10.1021/acs.cgd.5b00478 ◽

2015 ◽

Vol 15 (8) ◽

pp. 3853-3861 ◽

Cited By ~ 52

Author(s):

Christer B. Aakeröy ◽

Tharanga K. Wijethunga ◽

John Desper ◽

Marijana Đaković

Keyword(s):

Crystal Engineering ◽

Halogen Bond ◽

Highly Effective

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Anion Templated Crystal Engineering of Halogen Bonding Tripodal Tris(halopyridinium) Compounds

10.26434/chemrxiv.11862900.v1 ◽

2020 ◽

Author(s):

Emer Foyle ◽

Nicholas White

Keyword(s):

Crystal Engineering ◽

Self Assembly ◽

Halogen Bond ◽

Halogen Bonding ◽

Halogen Bonds ◽

X Ray ◽

X Ray Crystallography ◽

H Nmr ◽

Structural Database ◽

Van Der Waals Radii

<div>In this work four new tripodal tris(halopyridinium) receptors containing potentially halogen</div><div>bonding groups were prepared. The ability of the receptors to bind anions in competitive</div><div>CD<sub>3</sub>CN/d<sub>6</sub>-DMSO was studied using <sup>1</sup>H NMR titration experiments, which revealed that the</div><div>receptors bind chloride anions more strongly than more basic acetate or other halide ions.</div><div>The solid state self–assembly of the tripodal receptors with halide anions was investigated by</div><div>X-ray crystallography. The nature of the structures was dependent on the choice of halide</div><div>anion, as well as the crystallisation solvent. Halogen bond lengths as short as 80% of the sum</div><div>of the van der Waals radii were observed, which is shorter than any halogen bonds involving</div><div>halopyridinium receptors in the Cambridge Structural Database.</div>

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Anion Templated Crystal Engineering of Halogen Bonding Tripodal Tris(halopyridinium) Compounds

10.26434/chemrxiv.11862900 ◽

2020 ◽

Author(s):

Emer Foyle ◽

Nicholas White

Keyword(s):

Crystal Engineering ◽

Self Assembly ◽

Halogen Bond ◽

Halogen Bonding ◽

Halogen Bonds ◽

X Ray ◽

X Ray Crystallography ◽

H Nmr ◽

Structural Database ◽

Van Der Waals Radii

<div>In this work four new tripodal tris(halopyridinium) receptors containing potentially halogen</div><div>bonding groups were prepared. The ability of the receptors to bind anions in competitive</div><div>CD<sub>3</sub>CN/d<sub>6</sub>-DMSO was studied using <sup>1</sup>H NMR titration experiments, which revealed that the</div><div>receptors bind chloride anions more strongly than more basic acetate or other halide ions.</div><div>The solid state self–assembly of the tripodal receptors with halide anions was investigated by</div><div>X-ray crystallography. The nature of the structures was dependent on the choice of halide</div><div>anion, as well as the crystallisation solvent. Halogen bond lengths as short as 80% of the sum</div><div>of the van der Waals radii were observed, which is shorter than any halogen bonds involving</div><div>halopyridinium receptors in the Cambridge Structural Database.</div>

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Application of Halogen Bonding to Organocatalysis: A Theoretical Perspective

Molecules ◽

10.3390/molecules25051045 ◽

2020 ◽

Vol 25 (5) ◽

pp. 1045 ◽

Cited By ~ 7

Author(s):

Hui Yang ◽

Ming Wah Wong

Keyword(s):

Crystal Engineering ◽

Lewis Acids ◽

Halogen Bond ◽

Theoretical Perspective ◽

Halogen Bonding ◽

Catalyst Design ◽

Methodology Development ◽

Wide Range ◽

Promising Area ◽

Organocatalytic Reactions

The strong, specific, and directional halogen bond (XB) is an ideal supramolecular synthon in crystal engineering, as well as rational catalyst and drug design. These attributes attracted strong growing interest in halogen bonding in the past decade and led to a wide range of applications in materials, biological, and catalysis applications. Recently, various research groups exploited the XB mode of activation in designing halogen-based Lewis acids in effecting organic transformation, and there is continual growth in this promising area. In addition to the rapid advancements in methodology development, computational investigations are well suited for mechanistic understanding, rational XB catalyst design, and the study of intermediates that are unstable when observed experimentally. In this review, we highlight recent computational studies of XB organocatalytic reactions, which provide valuable insights into the XB mode of activation, competing reaction pathways, effects of solvent and counterions, and design of novel XB catalysts.

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