Extended Hypervalent Bonds mc-ne

If an interaction of the X- -E-E 3c-4e type occurs in both sides of an E-E bond, the X- -E-E- -X interaction is expected to be symmetric or close to symmetric under suitable conditions. The interaction is no more treated as 

Extended hypervalent bonds containing chalcogens have been substantially discussed in the last decade, however. 

Flypervalent ra(E)—cr (E-E) 3c-4e interactions are expected to be much stronger than n(E)—ct (E-C) for E = S, Se, and Te, since ct (E-E) must work much more effectively as acceptors than cj (E-C). This idea led to design 4c-6e of four E atoms (E4 4c-6e E = Se and S) in naphthalene system. 

Flow do E4 4c-6e stabilize the linear forms Energies of linear and Z-shaped forms are calculated for naphthalene and benzene systems. The results are 

T able 4 Energies of linear and Z-shaped conformers in naphthalene and benzene systemsa 

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The hypervalent chalcogen chemistry has been developed to higher coordinated species with various ligands,7 10 where TBP changes to square pyramidal (SP) or octahedral (Oh), etc. Additional atomic orbitals of E, such as an 5-orbital, may operate to stabilize the structures.10b The concept is also extended over linear a-bonds constructed by m ( > 4) atoms with n electrons (extended hypervalent bonds mc-ne (in > 4)).11 14 The approximate molecular orbital model for mc-ne (m > 4) is also exhibited in Scheme la, exemplified by 4c-6e. 

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