Interactions of halogens

Abstract

As an analogue of the ubiquitous hydrogen bond, interest in halogen bonding has garnered interest since the turn of the twenty-first century. The orthogonal nature and occasionally surprising characteristics of halogen bonds (compared to better-understood hydrogen bonds) has seen them find useful application in a wide range of disciplines.

Chapter 1 summarises key literature characterising the halogen bond, including the identification of the sigma-hole. The novel character of halogen bonds and the role played by a verity of physiochemical forces are discussed; with an in-depth review of recreant advances pertaining to anti-electrostatic halogen bonds. Other closely related sigma-hole interactions such as chalcogen and pnictogen bonding are also introduced with key similarities and novel characteristics being highlighted.

Chapter 2 presents an experimental and theoretical investigation of halogen-arene interactions using molecular torsion balances. Thermodynamic double mutant cycles are used to future dissect the energetics halogen-arene from the background noise. A broad solvent screen reveals the solvent-dependent nature of such dispersion-driven contacts. This is supported by a number of computational experiments that further characterise the various energetic contributions and used to study their angular and geometric dependencies.

Chapter 3 examines bifurcated halogen bonds and hydrogen bonds using a combined solution-phase and computational approach. The binding properties of a series of halogen bonded host-guest complexes are compared with hydrogen-bonded analogues. Experimental changes in free energy for the host-guest complexes were determined by 1H NMR titration. Bi- and trifurcated interactions were found to be energetically cooperative, but the nature of said cooperativity differs between hydrogen and halogen bonds. Computational methodologies including SAPT and NBO calculations were used to partition energetic contributions and to rationalise the experimentally observed experimental trends and rationalize the differences between the interaction types.