Hydrogen and halogen bonding drive the orthogonal self-assembly of an organic framework possessing 2D channels

Orthogonal self-assembly of an open organic framework showing 2D channels has been obtained by combining hydrogen and halogen bonding. The framework is able to host various guest molecules with a diverse set of steric demands and substitution patterns, and survives single-crystal-to-single-crystal guest exchanges from liquid and gas phases

Dynamic Characterization of Crystalline Supramolecular Rotors Assembled through Halogen Bonding

A modular molecular kit for the preparation of crystalline molecular rotors was devised from a set of stators and rotators to gain simple access to a large number of structures with different dynamic performance and physical properties. In this work, we have accomplished this with crystalline molecular rotors self-assembled by halogen bonding of diazabicyclo[2.2.2]octane, acting as a rotator, and a set of five fluorine-substituted iodobenzenes that take the role of the stator. Using variableerature 1H T1 spin-lattice relaxation measurements, we have shown that all structures display ultrafast Brownian rotation with activation energies of 2.4-4.9 kcal/mol and pre-exponential factors of the order of (1-9) × 1012 s-1. Line shape analysis of quadrupolar echo 2H NMR measurements in selected examples indicated rotational trajectories consistent with the 3-fold or 6-fold symmetric potential of the rotator

Multinuclear Solid-State Magnetic Resonance as a Sensitive Probe of Structural Changes upon the Occurrence of Halogen Bonding in Co-crystals

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well-developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (13C, 14/15N, 19F, and 127I) solid-state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen-bonded co-crystalline product materials. Single-crystal X-ray diffraction (XRD) structures of three novel co-crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH3)3N+(CH 2)10N+(CH3)3][2 I -]) and different para-dihalogen-substituted benzene moieties (i.e., p-C6X2Y4, X=Br, I; Y=H, F) are presented. 13C and 15N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co-crystal complexes in the solid state. Long-range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using 14N NMR spectroscopy, with a systematic decrease in the 14N quadrupolar coupling constant (CQ) observed upon halogen bond formation. Attempts at 127I solid-state NMR spectroscopy experiments are presented and variable-temperature 19F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge-including projector augmented-wave (GIPAW) or relativistic zeroth-order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond

Supramolecular amplification of amyloid self-assembly by iodination

Amyloid supramolecular assemblies have found widespread exploitation as ordered nanomaterials in a range of applications from materials science to biotechnology. New strategies are, however, required for understanding and promoting mature fibril formation from simple monomer motifs through easy and scalable processes. Noncovalent interactions are key to forming and holding the amyloid structure together. On the other hand, the halogen bond has never been used purposefully to achieve control over amyloid self-assembly. Here we show that single atom replacement of hydrogen with iodine, a halogen-bond donor, in the human calcitonin-derived amyloidogenic fragment DFNKF results in a super-gelator peptide, which forms a strong and shape-persistent hydrogel at 30-fold lower concentration than the wild-type pentapeptide. This is remarkable for such a modest perturbation in structure. Iodination of aromatic amino acids may thus develop as a general strategy for the design of new hydrogels from unprotected peptides and without using organic solvents

Halogen Bonding in Perovskite Solar Cells A New Tool for Improving Solar Energy Conversion

Hybrid organic inorganic halide perovskites HOIHPs have recently emerged as a flourishing area of research. Their easy and low cost production and their unique optoelectronic properties make them promising materials for many applications. In particular, HOIHPs hold great potential for next generation solar cells. However, their practical implementation is still hindered by their poor stability in air and moisture, which is responsible for their short lifetime. Optimizing the chemical composition of materials and exploiting non covalent interactions for interfacial and defects engineering, as well as defect passivation, are efficient routes towards enhancing the overall efficiency and stability of perovskite solar cells PSCs . Due to the rich halogen chemistry of HOIHPs, exploiting halogen bonding, in particular, may pave the way towards the development of highly stable PSCs. Improved crystallization and stability, reduction of the surface trap states, and the possibility of forming ordered structures have already been preliminarily demonstrate

Definition of the Chalcogen Bond (IUPAC Recommendations 2019)

This recommendation proposes a definition for the term “chalcogen bond”; it is recommended the term is used to designate the specific subset of inter- and intramolecular interactions formed by chalcogen atoms wherein the Group 16 element is the electrophilic site

Solid-state synthesis of mixed trihalides via reversible absorption of dihalogens by non porous onium salts

1,6-Bis(trimethylammonium) hexane bis(trihalides) and mixed bis(trihalides) have been synthesized by treating the corresponding dihydrated halides with molecular dihalogens under gas-solid and solution conditions. Despite the starting halides being non-porous, the trihalide syntheses occur homogeneously, in quantitative yields, and reversibly. In all cases halogen bond prevails over hydrogen bond, dihalogens substitute for the hydration water of starting halide anions and trihalides are formed. The stability of the obtained trihalides is mainly due to cooperative halogen bond and cation templation effect. Hexamethonium halides are proven effective solids for the clathration and storage of molecular dihalogens. While the starting salts are not isostructural, all the formed trihalides and mixed trihalides are isostructural

A synthetically modified hydrophobin showing enhanced fluorous affinity

Hydrophobins are natural surfactant proteins endowed with exceptional surface activity and film-forming capabilities and their use as effective “fluorine-free fluorosurfactants” has been recently reported. In order to increase their fluorophilicity further, here we report the preparation of a unique fluorous-modified hydrophobin, named F-HFBI. F-HFBI was found to be more effective than its wild-type parent protein HFBI at reducing interface tension of water at both air/water and oil/water interfaces, being particularly effective at the fluorous/water interface. F-HFBI was also found to largely retain the exceptionally good capability of forming strong and elastic films, typical of the hydrophobin family. Further studies by interface shear rheology and isothermal compression, alongside Quartz Crystal Microbalance and Atomic Force Microscopy, demonstrated the tendency of F-HFBI to form thicker films compared to the wild-type protein. These results suggest that F-HFBI may function as an effective compatibilizer for biphasic systems comprising a fluorous phase

Metal Hydrides Form Halogen Bonds: Measurement of Energetics of Binding

The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η5-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η5-cyclopentadienyl) is demonstrated by 1H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = −10.9 ± 0.4 and −11.8 ± 0.3 kJ/mol; ΔS° = −38 ± 2 and −34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = −7.3 ± 0.1 kJ/mol, ΔS° = −24 ± 1 J/(mol·K)). For the more reactive complexes 2–5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M–1, respectively