title: Magic electron counts and bonding in tubular boranes.
abstract: Ring stacking in some closo-borane dianions and the hypothetical capped borane nanotubes, predicted to be stable earlier, is analyzed in a perturbation theoretic way. A "staggered" building up of rings to form nanotubes is explored for four- and five-membered B(n)H(n) rings. Arguments are given for the stacking of B(5)H(5) rings being energetically more favorable than the stacking of B(4)H(4) rings. Elongated B[bond]B distances in the central rings are predicted for some nanotubes, and the necessity to optimize ring-cap bonding is found to be responsible for this elongation. This effect reaches a maximum in B(17)H(17)(2-); the insertion of additional rings will reduce this elongation. These closo-borane nanotubes obey Wade's n + 1 rule, but the traditional explanation based on a partitioning into radial/tangential molecular orbitals is wanting.
authors.affiliation: Department of Chemistry and Biochemistry, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Musiri M
authors.initials: MM
authors.lastname: Balakrishnarajan
authors.forename: Roald
authors.initials: R
authors.lastname: Hoffmann
authors.forename: Pattath D
authors.initials: PD
authors.lastname: Pancharatna
authors.forename: Eluvathingal D
authors.initials: ED
authors.lastname: Jemmis