The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Quinones, which are ubiquitous in nature, can act as sustainable and green electrode materials but face dissolution in organic electrolytes, resulting in fast fading of capacity and short cycle life. We report that quinone electrodes, especially calix[4]quinone (C4Q) in rechargeable metal zinc batteries coupled with a cation-selective membrane using an aqueous electrolyte, exhibit a high capacity of 335 mA h g-1 with an energy efficiency of 93% at 20 mA g-1 and a long life of 1000 cycles with a capacity retention of 87% at 500 mA g-1. The pouch zinc batteries with a respective depth of discharge of 89% (C4Q) and 49% (zinc anode) can deliver an energy density of 220 Wh kg-1 by mass of both a C4Q cathode and a theoretical Zn anode. We also develop an electrostatic potential computing method to demonstrate that carbonyl groups are active centers of electrochemistry. Moreover, the structural evolution and dissolution behavior of active materials during discharge and charge processes are investigated by operando spectral techniques such as IR, Raman, and ultraviolet-visible spectroscopies. Our results show that batteries using quinone cathodes and metal anodes in aqueous electrolyte are reliable approaches for mass energy storage.

High-capacity aqueous zinc batteries using sustainable quinone electrodes

The use of 'water-in-salt' electrolytes has considerably expanded the electrochemical window of aqueous lithium-ion batteries to 3 to 4 volts, making it possible to couple high-voltage cathodes with low-potential graphite anodes1-4. However, the limited lithium intercalation capacities (less than 200 milliampere-hours per gram) of typical transition-metal-oxide cathodes5,6 preclude higher energy densities. Partial7,8 or exclusive9 anionic redox reactions may achieve higher capacity, but at the expense of reversibility. Here we report a halogen conversion-intercalation chemistry in graphite that produces composite electrodes with a capacity of 243 milliampere-hours per gram (for the total weight of the electrode) at an average potential of 4.2 volts versus Li/Li+. Experimental characterization and modelling attribute this high specific capacity to a densely packed stage-I graphite intercalation compound, C3.5[Br0.5Cl0.5], which can form reversibly in water-in-bisalt electrolyte. By coupling this cathode with a passivated graphite anode, we create a 4-volt-class aqueous Li-ion full cell with an energy density of 460 watt-hours per kilogram of total composite electrode and about 100 per cent Coulombic efficiency. This anion conversion-intercalation mechanism combines the high energy densities of the conversion reactions, the excellent reversibility of the intercalation mechanism and the improved safety of aqueous batteries.

Aqueous Li-ion battery enabled by halogen conversion–intercalation chemistry in graphite

Halogen bonding is the electron density donation based weak interaction of halogens with Lewis bases Its applicability for molecular recognition processes long remained unappreciated and has so far mostly been studied in silico and in solid state As most physiological processes and chemical reactions take place in solution, investigations in solutions are of highest relevance for its use in the pharmaceutical and material scientific toolboxes Following a short discussion of the phenomenon of halogen bonding, this tutorial review presents an overview of the methods hitherto applied for gaining an improved understanding of its behaviour in solutions and summarizes the gained knowledge in order to indicate the scope of the techniques and to facilitate exciting future developments

Halogen bonding in solution

Molecular dynamics calculations have been carried out for model liquid systems of N (=108 or 256) molecules interacting through two Lennard-Jones (12–6) centres coinciding with the positions of the atomic masses (the ‘atom-atom’ pair potential). The objectives were (a) to study the dependence of the properties on the molecular anisotropy defined by the reduced distance l*=l/σ between the centres in the range 0·5–0·8; and (b) to compare the computed quantities with those of real liquids (F2, Cl2, Br2, CO2). This paper deals with thermodynamic and structural features. Time-dependent correlations will be treated in a future communication. In the liquid region not too far from the triple point the energy and pressure isochores are well represented by straight lines, the slopes of which increase with density and anisotropy. Thermodynamically consistent expressions for the energy and pressure as functions of density and temperature have been obtained for each system. With Lennard-Jones parameters adjusted so as...

Thermodynamic and structural properties of liquids modelled by ‘2-Lennard-Jones centres’ pair potentials

The vibrational spectrum of the dichromate ion

The infrared and Raman spectra for the polyhalide ions (ICl2−, ICl4−, BrCl2−, and Br3−) are presented. From these data, the X—Y stretching force constant fr, the interaction force constants frr between bond stretching coordinates at 180° to each other, and the interaction force constant frr′ for bond stretching coordinates at an angle of 90° (for ICl4−) have been calculated. The values of fr for the trihalide ions are roughly one‐half the values for the free halogens, and the values of the interaction force constants frr are very large (approximately 35% the value of the stretching constant fr). These rather unusual force constants have been interpreted in terms of the description of the bonding in these ions using p orbitals, which was first suggested by Pimentel. In fact, these results offer rather strong support for the recent evidence from nuclear quadrupole coupling constant measurements of Cornwell and Yamasaki favoring this structure. Attention is drawn to the qualitative similarity between these f...

Infrared and Raman Spectra, Force Constants, and the Structures of Some Polyhalide Ions: ICl2−, ICl4−, BrCl2−, and Br3−

The Raman spectra of the ions Co(CO)4—, Fe(CO)42—, and HFe(CO)4— have been studied in aqueous solutions of the corresponding sodium salts. The spectra of Co(CO)4— and Fe(CO)42—, excited by the helium radiations 5875.6 and 6678.1 A are in full agreement with the expected Td symmetry of these ions; all observed frequencies were assigned to fundamental vibrational modes. A normal coordinate treatment was carried out under the assumption of a simplified valence force field model making use of only two interaction constants. The values of the fundamental frequencies of the tetrahedral ions, calculated by means of the potential constants of this model, were found to be in satisfactory agreement with the observed Raman shifts.The Raman spectrum of HFe(CO)4—, put in correlation with that of Fe(CO)42—, points strongly to a C3v symmetry of the former ion.

H. Stammreich

Papers

The vibrational spectrum of the dichromate ion

Infrared and Raman Spectra, Force Constants, and the Structures of Some Polyhalide Ions: ICl2−, ICl4−, BrCl2−, and Br3−

Raman Spectra of Metal Carbonyl Compounds. II. Raman Spectra, Structure, and Force Constants of Cobalt and Iron Tetracarbonylate Anions

Technique and results of excitation of Raman spectra in the red and near infra-red region

Raman spectrum and force constants of the chromate ion