APPLICATION OF IGLO AND GIAO STRUCTURE NMR ANALYSES TO A NOVEL ISOMEROF THE DICARBAOCTABORANE(11) ANION, [ARACHNO-2,6-C2B6H11]-, PREPARED FROM THE REACTION OF CLOSO-1,6-C2B7H9 WITH FLUORIDE-ION

The structure of a new carborane anion [arachno-2,6-C2B6H11]-, prepare d from the reaction of closo-1,6-C2B7H9 with tetrabutylammonium fluori de in tetrahydrofuran, is determined from a combination of experimenta lly observed B-11, 2D B-11-B-11, and C-13 NMR results and the applicat ion of ab-Initio/IGLO/NMR and ab-Initio/GIAO/NMR methods. The skeletal structure of the new ion is related to both the known C2B6H10 and the proposed [2,3-C2B6H11]-ion, but with a single bridging hydrogen betwe en the borons 3 (3k) and 4 (4k) of the six-atom open face, a BH2 group at position 5 (3k), and a CH2 group at position 6 (3k). The 2D NMR ob servations are consistent with the B-B bond distance trends derived fr om ab Initio optimized geometries obtained at both the 3-21G and 6-31G levels of theory.