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2n framework electron clusters: Diamagnetic polyhedral boron chlorides, BnCln (n = 8-12), from the thermal disproportionation of diboron tetrachloride
Davan,Morrison
, p. 2366 - 2372 (2008/10/08)
In the presence of elemental mercury, diboron tetrachloride, B2Cl4, is generated from the radio frequency discharge of BCl3 at the rate of 250-350 mg/h. The disproportionation of undiluted B2Cl4 has been examined at a variety of temperatures and found to occur in five stages. The amounts of the polyhedral diamagnetic products, B8Cl8, B9Cl9, B10Cl10, B11Cl11, B12Cl12, and (B9Cl8)2, formed during the reaction are highly dependent upon the thermal history of the sample. In undiluted B2Cl4 the maximum yield of B9Cl9 (29%) occurs at elevated temperatures, 400-450°C, whereas the most B8Cl8 (38%) is produced at 100°C. At temperatures below 100°C, more B12Cl12 than B10Cl10 is observed whereas the reverse is true above 100°C. At ambient temperature the 11B NMR resonances of the polyhedral boron chlorides BnCln (n = 8-12) are all deshielded singlets, 58-78 ppm from BF3·OEt2. The relative thermal stabilities of these compounds, B9Cl9 > B10Cl10 > B11Cl11 > B12Cl12 > B8Cl8, do not correspond to the relative thermal stabilities of 2n + 2 framework electron clusters, such as the borane dianions.
