Halogen bonding bond geometry

Figure 5.1 (a) Radial and angular descriptors of the halogen-bond geometry (b) example of... 

Ouvrard, C., Le Questel, J.Y., Berthelot, M. and Laurence, C. (2003) Halogen-bond geometry a crystallographic database investigation of dihalogen complexes. Acta Crystallogr, Sect. B, B59, 512-526. 

Keywords Lewis bases Dihalogens Halogen bond Angular geometry ... 

Fig. 1 Comparison of the experimentally determined geometries of the hydrogen-bonded complex H3N-- -HC1 and its halogen-bonded analogue H3N- C1F (both drawn to scale) with a non-bonding electron-pair (n-pair) model of NH3. Here, and in other figures, the n-pair electron distribution is drawn in the exaggerated style favoured by chemists. The key to the colour coding of atoms used in this and similar figures is also displayed...

Fig. 6 The experimentally determined geometries of oxirane- -HC1 and oxirane- -ClF drawn to scale. The n-pair model of oxirane is shown for comparison. While the angle

The equilibrium angular geometry of a halogen-bonded complex B- XY can be predicted by assuming that the internuclear axis of a XY or X2 molecule bes ... 

The rules for predicting angular geometries of halogen-bonded complexes B- XY have recently received support from a wide ranging analysis of X-ray diffraction studies in the solid state by Laurence and co-workers [205]. This study not only confirms the validity of the rules in connection with complexes B- XY, where XY is Cl2, Br2, I2, IC1 and IBr, with many Lewis bases B but also reinforces the conclusion that halogen bonds Z- X - Y show a smaller propensity to be non-linear that do hydrogen bonds Z- H — X. 

In addition to halogen bonded complexes or ionic salts, it is also possible for sulfur and selenium electron donors to form complexes in which the electron donor atom inserts into the X2 bond, giving a hypervalent donor atom with a T-shaped geometry. It has been recently reported [147] that for dibromine and selenium, this type of complex is favored over halogen bonded complexes. While no purely halogen bonded complex is reported for dibromine, there is one complex (IRABEI) in which one selenium atom of each of several selenanthrene molecules in the asymmetric unit does insert into a Br2 bond, but for one of the molecules, the other selenium atom forms a halogen bond with a Br2 molecule to form a simple adduct (A). 

As discussed above, XBs tend to be Unear, namely to be formed along the C - X bond axis on the XB donor module and along the lone pair axis of the heteroatom on the XB acceptor module. The angles between these axes determine the halogen-bonded adducts geometry. 

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