Hypervalent Bonding and General Structural Features

The definition of hypervalent species as ions or molecules of the elements of Groups 15—18 bearing more than eight electrons within a valence shell was proposed byj. I. Musherin 1969 (1969AGE54). General aspects of bonding 

Structural aspects of polyvalent iodine compounds were previously summarized in several books and reviews (1983MI4, 2013MI2, 2008CR5299, 2003MI3). In general, molecular structure of and X -iodanes is predetermined by the nature of the hypervalent bonding. Key structural features of hypervalent organoiodine compounds can be summarized as follows  

The I—C bond lengths in iodonium salts R2l X and X -iodanes RIX2 are approximately equal to the sum of the covalent radii of iodine and carbon, ranging generally from 2.00 to 2.10 A. 

Iodonium salts R2l X generally have a typical distance of 2.6—2.8 A between iodine and the nearest anion X and in principle can be considered as ionic compounds with pseudotetrahedral geometry about the central iodine atom. However, with consideration of the anionic part of the molecule, the overall experimentally determined geometry is a distorted T-shaped structure similar to the X -iodanes RIX2. 

Intramolecular positional isomerization (Berry pseudorotation) resulting in an exchange between the apical and the equatorial Hgands occurs rapidly in both X - and X -iodanes. This process is important in explanation of the mechanisms of hypervalent iodine reactions. 

---