Probing halogen–halogen interactions in solution

Abstract

a Halogen-halogen interactions are a particularly interesting class of halogen bonds that are known to be essential design elements in crystal engineering. In solution, it is likely that halogen-halogen interactions also play a role, but the weakness of this interaction makes it difficult to characterize or even simply detect. We have designed a supramolecular balance that allows to detect Br … Br interactions between CBr3 groups in solution and close to room temperature. The sensitivity and versatility of the chosen platform has allowed to accumulate consistent data.In halogenoalkane solvents, we propose estimates for the free energy of these weak halogen bond interactions. In toluene solutions, we show that the interactions between Br atoms and the solvent aromatic groups dominate over the Br … Br interactions.

A Competing Hydrogen Bonding Pattern to Yield a Thermo‐Thickening Supramolecular Polymer

“…[41] In the range from 15 to 60 8 8C, the FTIR spectra are similar, but the NH vibration band is significantly less broadened. [41] In the range from 15 to 60 8 8C, the FTIR spectra are similar, but the NH vibration band is significantly less broadened.…”

“…We call this structure g.Ithas previously been shown by small-angle neutron scattering (SANS) to correspond to al ong and rigid SP with as ingle monomer in the cross-section. [41] In the range from 15 to 60 8 8C, the FTIR spectra are similar, but the NH vibration band is significantly less broadened. SANS analysis previously confirmed the structural transition and showed that this SP (called b)isalso long and rigid, but contains two molecules in the crosssection, [41] that is,S Pb is twice the thickness of g.M ore interestingly,b elow 15 8 8C, ap reviously unreported band appears that corresponds to weakly bonded NH (3350 cm À1 ).…”

“…[30,31] However,achange in the properties of the supramolecular assemblies at the macroscale has been reported for very few cases. [41,42] We later realized that the ester linkage that is introduced is not innocent:i tallows as ubtle modification of the hydrogen bond pattern and thus pathway complexity. [33] In particular,w hen two competing SPs can assemble from the same monomer, [25] the transition between the two structures can result in noticeable macroscopic property changes.…”

“…[20] Thei ntroduction of competing interactions in the design of as upramolecular assembly is al ogical approach to create pathway complexity.I np ractice,t his can be done through solvents [21,34,35] and additives [19,33,36,37] or by introducing functional groups that can interfere with the main sticker.O ften, this latter approach will weaken the main assembly, [38,39] but it can also lead to an ew structure with ac ompetitive thermodynamic stability. [41,42] We later realized that the ester linkage that is introduced is not innocent:i tallows as ubtle modification of the hydrogen bond pattern and thus pathway complexity. [41,42] We later realized that the ester linkage that is introduced is not innocent:i tallows as ubtle modification of the hydrogen bond pattern and thus pathway complexity.…”

“…[40] Along this line,w ep reviously reported that introducing an aminoester synthon in the classical bisurea scaffold provides an efficient access to functionalized assemblies. [41,42] We later realized that the ester linkage that is introduced is not innocent:i tallows as ubtle modification of the hydrogen bond pattern and thus pathway complexity. Indeed, we now report that such ester-bis-urea monomers self-assemble into three structurally different and competing SPs.A ll three structures are thermodynamically stable in their respective temperature range and can be accessed reversibly.R emarkably,t his competition between supramolecular assemblies is responsible for at hermo-thickening effect, that is,a ni ncrease of viscosity while temperature is raised.…”