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 34

Fig. 9 The experimentally determined geometries of thiirane ··· HCl and thiirane ··· ClF

φ

drawn to scale. The n-pair model of thiirane is shown for comparison. The angle is

slightly different in the two complexes for reasons discussed in [69]. The non-linearity θ
of the hydrogen bond is again greater than that of the halogen bond. See Fig. 1 for key to
thecolourcodingofatoms

slightly smaller angle in the case of (CH 2 ) 2 S ··· ClF is discussed in [69]. It is

clear that the hydrogen bond in (CH 2 ) 2 S ··· HCl deviates significantly from

= 21.0(5) ◦ ]whilethehalogenbondin(CH 2 ) 2 S linearity [ φ ··· ClF is close to

=3.5(2) ◦ ]. The hydrogen bonds in the complexes (CH 2 ) 2 S

linear[ φ ··· HF [124]

and (CH 2 ) 2 S ··· HBr [28, 125] are also significantly non-linear.

3.1.3
B Carries Two Inequivalent n-Pairs

Sulfur dioxide is an example of a simple Lewis base that carries two sets of in-
equivalent n-pairs, one set on each O atom. The n-pair model (in which the

π
bonding pairs are not drawn and are ignored here) is shown in Fig. 10. The
geometries of SO 2 ClF [70]

have all been determined from investigations of their rotational spectra. Each
molecule is planar and belongs to the C S point group. Scale drawings for
SO 2 ···

··· HF [126, 127], SO 2 ··· HCl [28, 126] and SO 2 ···

HCl and SO 2 ··· ClF are displayed in Fig. 10.

We note that the HCl and ClF molecules attach, approximately at least,
along the axis of the cis n-pair, as required by rule 1, with angles of 143.0(1) ◦

and 131.9(6) ◦ , respectively, although the former value may be influenced by

φ