Bioctahedral structures

They have edge-sharing bioctahedral structures [37],... 

W2C19]3 has the confacial bioctahedral structure with a W—W bond length of 2.418 A. (This structure was first solved in 1958272 and then re-refined in 1983).273 This experimental result coupled with the electronic configuration of the metals is consistent with a W—W bond order of three. 

For the Tlli ion,13 the stability of the iodide in contact with Tl111 is a result of the stability of the ion, since T1I3 is itself unstable relative to Tl F). Thallium also forms the ion T Clj, which has the confacial bioctahedral structure. 

V— V Bonding. Since its congeners, Nb and Ta, as well as its neighbor Cr form numerous compounds with strong M—M bonds, similar behavior by vanadium might have been expected, but so far only a few are known. A triple bond (V—V = 2.20 A) occurs in V2(2,6-dimethoxyphenyl)4, which has an edge-sharing bioctahedral structure shown schematically in 17-B-VIII. 

A few monoadducts have been reported for Nb. These are favored by bulky ligands thus tetrahydrothiophene formed diadducts with NbCU, while the bulkier methyl and ethyl sulfides provided monoadducts and unstable diadducts. Monoadducts were also obtained with HMPA, NEts and PBus they are only slightly paramagnetic, and halogen-bridged bioctahedral structures with M—bonds have therefore been postulated. The monoadducts are stabler for the chlorides than for the iodides, illustrating the importance of M—bonding. 

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