Empirical and ab initio energy/architectural patterns for 73 nido-6<V>-carborane isomers, from B(6)H(9)(-) to C(4)B(2)H(6).
Qualitative rules governing carbon and bridge-hydrogen placement permit the prediction of the most stable isomeric structures for the various carboranes. Seventy-three isomeric boron hydride and carborane structures, from B(6)H(9)(-) to C(4)B(2)H(6), were computed at the ab initio MP2(fc)/6-31G level to determine their relative stabilities quantitatively. Specific architectural features, recognized to be unfavorable, were assigned "energy penalty" values that allow the projection of comprehensive thermodynamic stability values via a simple additivity procedure. These values match the ab initio results with surprising precision. Our study includes Siebert's nido-2,3,5-C(3)B(3)H(7) and Wrackmeyer's nido-2,4-C(2)B(4)H(8) nido-6<V> carboranes, which contain "unusual" CH-B-bridge hydrogens.
Hofmann
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Loker Hydrocarbon Research Institute, University of Southern California, University Park, Los Angeles, California 90089-1661, USA.
Fox
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Greatrex
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Schleyer
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Williams
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