Jemmis, Eluvathingal D. ; Balakrishnarajan, Musiri M. ; Pancharatna, Pattath D. (2001) A unifying electron-counting rule for macropolyhedral boranes, metallaboranes, and metallocenes Journal of the American Chemical Society, 123 (18). pp. 4313-4323. ISSN 0002-7863
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Official URL: http://pubs.acs.org/doi/abs/10.1021/ja003233z
Related URL: http://dx.doi.org/10.1021/ja003233z
Abstract
A generally applicable electron-counting rule-the mno rule-that integrates macropolyhedral boranes, metallaboranes, and metallocenes and any combination thereof is presented. According to this rule, m+n+o number of electron pairs are necessary for a macropolyhedral system to be stable. Here, m is the number of polyhedra, n is the number of vertices, and o is the number of single-vertex-sharing condensations. For nido and arachno arrangements, one and two additional pairs of electrons are required. Wade's n+1 rule is a special case of the mno rule, where m = 1 and o = 0. B20H16, for example has m = 2 and n = 20, leading to 22 electron pairs. Ferrocene, with two nido polyhedral fragments, has m = 2, n = 11, and o = 1, making the total 2+11+1+2 = 16. The generality of the mno rule is demonstrated by applying it to a variety of known macropolyhedral boranes and heteroboranes. We also enumerate the various pathways for condensation by taking icosahedral B12 as the model. The origin of the mno rule is explored by using fragment molecular orbitals. This clearly shows that the number of skeletal bonding molecular orbitals of two polyhedral fragments remains unaltered during exohedral interactions. This is true even when a single vertex is shared, provided the common vertex is large enough to avoid nonbonding interactions of adjacent vertices on either side. But the presence of more than one common vertex results in the sharing of surface orbitals thereby, reducing the electronic requirements.
Item Type: | Article |
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Source: | Copyright of this article belongs to American Chemical Society. |
ID Code: | 13506 |
Deposited On: | 12 Nov 2010 15:27 |
Last Modified: | 04 Jun 2011 06:00 |
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