Halogen Bonding Fundamentals and Applications

Halogen atoms in organiccompounds can typically be foundat the periphery of molecules. For this reason, they are ideally positioned to be involved in intermolecular interactions. Indeed, halogen atoms are frequently involved in awide varietyofnon-covalent interactions whichcanberemarkably different regarding their energetic and geometric features. Theoretical studies predict thattheelectrondensitydistributionaroundhalogenatomsformsanellipsoid elongated in the direction perpendicular to the covalent bond axis. A clear trend ofincreasing electropositive potential develops alongthe covalent bond axisuponincreasingthepolarizabilityandatomicmassofthehalogen. Exp- imentalresultscon?rmthisanisotropicdistributionandprovetheamphoteric characterofhalogens. Thiscanproduceinteractionsinadirectionperpend- ular to the covalent bond axis when the halogen is the electron donor (Lewis base), and along the axis when the halogen is the electron acceptor (Lewis acid). This book focuses on the interactions wherein halogens work as el- trophilicspecies and interact with electron rich sites (namely, electronegative partners). Ofthenumerousnon-covalentinteractionsinvolvinghalogens, this particular subset istypically referredto ashalogen bonding. The bookbegins byintroducingtheoreticalcalculationsonthecharacteristicsofhalogenbo- ing (A. Karpfen), then focuses on the adducts wherein the electron donor is a lone pair possessing species (n donor). The complexes formed by halogens andinterhalogensinthegas(A. Legon)andsolidphase(W.T. Penningtonetal.) arepresentedandtheroleofhalocarbonsinhalogenbonding-basedcrystal- gineeringisdiscussed(P. Metrangolo, G. Resnatietal.). Achapterexploringthe complexesinwhichhalogenatomsinteractwith? electrondonors(J.K. Kochi etal.)concludesthepartofthebookthatdealswiththegeneralitiesofhalogen bonding. Incontrast, thelasttwochaptersofthisbookdiscusshalogenbonded adducts endowed with useful applicative properties. Among the many novel applications of halogen bonding, liquid crystals(D. Bruce) and conducting or magnetic materials (M. Fourmigue)are discussed as prototypicalexamples.