Boat and Chair Shaped Hexahalogen Synthons

Abstract

Non‐covalent halogen bonding interactions are quintessential in crystal engineering for the construction of distinctive supramolecular synthons. Here, we report the first crystalline evidences of unique boat and chair shaped cyclic hexahalogen synthons in the crystal structures of α,α,α′,α′,4‐pentabromo‐o‐xylene (PBX) and α,α,α′,α′,4,5‐hexabromo‐o‐xylene (HBX) respectively. Nature and stability of constituent interactions in the supramolecular synthons are scrutinized with the help of quantum‐chemical calculations. Pendás’ interacting quantum atoms approach confirmed the stability of Br⋅⋅⋅Br interactions leading to boat and chair shaped synthons with major contribution from exchange‐correlation. Although both the molecules are achiral in nature, the packing forces guide PBX to crystallize in the chiral space group P21 with a helix‐like orientation while HBX packs in a centrosymmetric P21/n space group. The extended furcations in the pentabromo derivative construct a molecular framework consisting of macrocycles realized through halogen bonding.

Unveiling the topology of partially disordered micro-crystalline nitro-perylenediimide with X-aggregate stacking: an integrated approach

“…The stacking of one molecule above another with zero angle between the planes of two molecules results in steric hindrance between the tails, which is considered geometrically unfavourable. 68,69 The alkyl tail also contributes to disorder, in addition to the NO 2 group at the bay substituent, which will be discussed in the following sections.…”

“…67 The electrostatic surface potential (ESP) map of NO 2 -PDI was computed to explain the critical role played by the electrostatic component in dictating the solid-state packing of NO 2 -PDI. 71,72 NO 2 -PDI displays an intermediate positive potential at the aromatic core (Fig. S18 †).…”

Triiodide-Based Chair-Like Copper Complex Assembled by Halogen Bonding

“…These chains include the 10-membered cyclic noncovalent motif {I 3 – ·I 2 ·I 3 – ·I 2 }, which are assembled to give extended architectures via the copper­(I) site, which is mutual for each I 3 – ligands. The occurrence of the cyclic HaB-based motif is rather typical for halogen compounds; for example, different conformations of such HaB-based cycles were recently observed . The neighboring chains are connected via π–π stacking interactions between the Xyl rings (interplane distances range from 3.435(5) to 3.520(6) Å).…”

“…The occurrence of the cyclic HaB-based motif is rather typical for halogen compounds; for example, different conformations of such HaB-based cycles were recently observed. 46 The neighboring chains are connected via π−π stacking interactions between the Xyl rings (interplane distances range from 3.435(5) to 3.520(6) Å). In addition, I 2 forms short contact with Cu (I5− Cu1 and I4−Cu1 distances are 4.0900(6) and 4.0059(7) Å, respectively; I−I bond to Cu distance is 3.8084(6) Å; Figure S9), which can be attributed to semicoordination bonding.…”

Polyoxometalate-Induced Preorganization of Halogenated Ligands in Supramolecular Assemblies

“…A similar Br 6 type of synthon was reported recently by Hariharan et al, where the tetrameric unit consists of four types of dimers arranged in an antiparallel fashion, whereas the X 6 synthon reported here consists of a dimeric unit with the halogen atoms arranged in an octahedral fashion. 12 Surprisingly, the X−X separations for 1_Cl and 1_Br fall out of the range to classify them as halogen interactions (see Table S7) despite geometrically resembling bifurcated type-I interactions (Figure 1a). Following postsynthetic thermal treatment and completion of the SC−SC transition, X−X distances in (2_Cl and 2_Br) are notably decreased to fulfill the ≤ sum of vdW radii +0.4 Å criteria for halogen−halogen interactions, and 2_I shows a decreased distance well within this value.…”