Polyhalide anions bonding

Much of the current research into halogen bonding involves organohalogen or inorganic halide acceptors. However, the dihalogens (X2) and inter halogens (XY) continue to attract attention. This review will focus specifically on structural and theoretical studies of such systems over the past decade. While polyhalide anions are closely related to the neutral donor-acceptor concepts that are the focus here, they will be discussed only when necessary to elaborate on the central theme of the review. 

The halides participate as terminal and bridge ligands and can be included in inner and external spheres of this kind of complex. A few examples of compounds with such terminal ligands are the boron ammines [BX3 NH3], [BX2(NH3)2]X, BX(NH3)3]X2, and [B(NH3)4]X3 (X = F, Cl, Br, I). Halides form part of many mixed-ligand carbonyl complexes, for example, Fe(CO)4I2 and polyhalide anions with various elements [4], In this respect, the structure of the anion [Re2Clx]2 provides important information the Re — Re bond is present and the chlorine atoms have a bridge function [4]. 

The halogens are known lo form reasonably stable chains in polyhalide anions, the best-known example being the triiodide ion, I,. They are considered separately in Chapter 17. A great number of nonmelals form simple X—X bonded molecules B,C14. N,H4. P.Ij. As,R4, H,0,. S.CU. X, (halogens), etc. In general these are relatively stable, although all are susceptible to attack by reagents that can cleave the X—X bond ... 

Many other polyhalide anions can be formed by reactions of the type shown in Equation 6.61. If CsF reacts with ClF3(g) at 100 °C, CsClF4(s) is formed a similar reaction with BrFs gives CsBrF. In these reactions, CIF3 and BrF5 act as Lewis acids, accepting a non-bonding pair from the F" ion in CsF ... 

In a polyhalide ion two or more halogen atoms are covalently bonded into a polyatomic anion, e.g., 13 . 

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