The Interaction of Dihalogens and Hydrogen Halides with Lewis Bases in the Gas Phase: An Experimental Comparison of the Halogen Bond and the Hydrogen Bond - Halogen Bonding: Fundamentals and Applications - page 16

The Interaction of Dihalogens and Hydrogen Halides
with Lewis Bases in the Gas Phase:
An Experimental Comparison of the Halogen Bond
and the Hydrogen Bond

A. C. Legon
School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
[e-mail]

1 Introduction .................................. 18

1.1 HistoricalBackground............................. 18

1.2 DefinitionsandNomenclature......................... 19

1.3 Summary .................................... 21

2 Properties of Isolated Complexes B ··· XY: How to Measure Them .... 21

3 Comparison of the Angular and Radial Geometries

of Halogen-Bonded Complexes B XY

and their Hydrogen-Bonded Analogues B ··· HX

···

.............. 23

3.1 Angular Geometries of B HCl

inWhichBisan-PairDonor .........................

··· ClF and B ···

25

3.1.1 BCarriesaSinglen-Pair............................ 25

3.1.2 BCarriesTwoEquivalentn-Pairs....................... 26

3.1.3 BCarriesTwoInequivalentn-Pairs...................... 35

3.2 Angular Geometries of B ··· ClF and B ··· HCl

in Which B is a π -PairDonor......................... 36

3.2.1 B Carries a Single- π -Pair ........................... 36

3.2.2 B Carries Pseudo- π -Pairs ........................... 38

3.2.3 B Carries Several- π -Pairs ........................... 39

3.3 Angular Geometries of B ··· ClF and B ··· HCl

in Which B is a Mixed n-Pair/ π -PairDonor ................. 43

3.4 Radial Geometries of Complexes B ··· XY and B ··· HX: A Summary . . . . 47

4 Intermolecular Binding Strength in Halogen-Bonded Complexes:

Systematic Behaviour of k σ .......................... 47

···

5 Extent of Electron Transfer in Halogen-Bonded Complexes B XY ... 50

5.1 Electron Transfer in Weak (Outer) Complexes B ··· XY ........... 50

5.2 Do Mulliken Inner Halogen-Bonded Complexes Exist in the Gas Phase? . 54

6 Conclusions: A Model for the Halogen Bond in B ··· XY .......... 56

References ....................................... 59

Abstract This chapter is concerned exclusively with the experimentally determined prop-
erties of halogen-bonded complexes of the type B ··· XY in isolation in the gas phase and
their relationship with those of the corresponding hydrogen-bonded complexes B ··· HX.