X-ray and molecular structure

To date, six single-crystal X-ray molecular structures of alkynyliodonium compounds have been reported four aIkynyl(phenyl)iodonium salts including the substituted cyanoethynyl salt, one heterocyclic and one dialkynyliodonium salt, all with oxyanions. Key structural data for these compounds are summarized in Table 3-1. 

The data in Thble 3-1 indicate that alkynyliodonium salts, like the related 10—1—3 species PhICl2, PhI(OAc)2, and HTIB (5), can be considered as distorted pseudo-trigonal-bipyrami-dal (39), or approximately T-shaped in the solid state. 

In other words, there are two apical ligands, an equatorial ligand and two lone-pair electrons also in the equatorial position around the central iodine(III) atom. As expected by simple electrostatic considerations, the most electronegative groups occupy apical positions and the least electronegative group is in the equatorial position. Hence, in all known alkynyl(phe-nyl)iodonium species to date the alkyne and counter-anion occupy the apical sites whereas the less electronegative phenyl resides in the equatorial position. 

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Toda, F., Tanaka, K., Infantes, L., Forces-Forces, C., Claramunt, R. M., and Elguero, J. (1995), Optical Resolution of 1,3-Dimethyl-5-phenyl-V2-pyrazoline by Diastereo- isomeric Complex Formation with an Optically Active Host Compound X-Ray and Molecular Structure of the Complex, J. Chem. Soc., Chem. Commun., 1453-1454. 

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