Other homoleptic derivatives of hypervalent Group 15 elements

6 Other homoleptic derivatives of hypervalent Group 15 elements 

Arsenic forms a gaseous pentafluoride and a solid pentachloride which decomposes at temperatures above -50°C. Antimony forms a pentachloride which may be vaporized without decomposition, and a pentafluoride which is tetrameric in the solid phase and trimeric in the gas phase. The structures of the trimer will be described in Chapter 16. The heaviest element in the group (Bi) forms a pentafluoride which is polymeric in the solid phase. The gas phase structure is unknown. 

Pentamethylphospforane, P(CH3)5, is unknown, but both arsenic and antimony form stable pentamethyl derivatives. Bi(CH3)5 explodes on warming to room temperature. P, As, Sb and Bi all from solid pentaphenyl derivatives, the least stable of these compounds is BiPhj. 

The properties of known homoleptic compounds of hypervalent Group 15 elements, EB5 where B is a singly bonded ligand, are summarized in Table 15.2. The properties of the homoleptic derivatives of hypervalent Group 16 and 17 elements are described in Sections 

7 and 18.2 respectively. No hypervalent compound where the central atom carries only hydrogen or iodine substituents is known, and only one where it carries only Br atoms. Altogether there are five homoleptic hypervalent compounds with methyl substituents, live with phenyl and four with chlorine atoms. By far the largest number of hypervalent compounds (15) are fluorides. This tally suggests that the ability of singly bonded ligands to stabilize hypervalent molecules increases in the order 

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