Will an η3-Si3H3 Ligand Form Sandwich Compounds with Main Group Elements? [J. Am. Chem. Soc. 2000, 122, 1725−1728].

Srinivas, G.; Hamilton, Tracy P.; Jemmis, Eluvathingal D.; McKee, and Michael L.; Lammertsma, Koop

doi:10.1021/ja004645a

Cited by 5 publications

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“…The B-B bond lengths in the optimized geometry are within the reasonable range for the closo-borane family. 31 In addition, there exists good correspondence between the X-ray-determined values of the B 57 skeleton of the β-rhombohedral boron and the bond lengths calculated for B 57 H 36 3+ (variation within 0.006 Å). 23 The longest bond length (1.991 Å) is found between the boron atoms forming the triangle that connects the central boron atom, which is very close to the X-ray value of 1.98 Å.…”

Section: Bonding In the B 57 Unitmentioning

confidence: 59%

“…Only four stabilized molecular orbitals result from these, so that eight electrons can be accommodated. 31 However, there are nine electrons available, six from the two B 28 H 18 + species and three from the central boron atom. It is therefore necessary to have an additional positive charge for B 57 H 36 , making a total charge of +3.…”

Section: Bonding In the B 57 Unitmentioning

confidence: 99%

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Polyhedral Boranes and Elemental Boron: Direct Structural Relations and Diverse Electronic Requirements

Jemmis

Balakrishnarajan

2001

J. Am. Chem. Soc.

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Details of the electronic and structural connections between macropolyhedral boranes and elemental boron are reported. The nature of electron deficiency in the beta-rhombohedral polymorph of boron is analyzed by using a molecular fragments approach with boranes as model systems. The B57H36 molecule constructed from such an approach has three more electrons than mandated by the electron-counting rules (Balakrishnarajan, M. M.; Jemmis, E. D. J. Am. Chem. Soc. 2000, 122, 456. Jemmis, E. D.; Balakrishnarajan, M. M.; Pancharatna, P. D. J. Am Chem. Soc. 2001, 123, 4313-4323.) devised for macropolyhedral boranes. This is also confirmed by electronic structure calculations at the extended Hückel and B3LYP/6-31G levels. The aromaticity of this B57H36(3+) molecule is on par with the most stable B12H12(2-) itself, as revealed by nuclear independent chemical shift calculations. The B57 skeleton can be made electron precise by adopting a nido arrangement by eliminating an atom from the closo skeleton, so that three valence electrons will be removed. The exact site of elimination, governed by thermodynamic factors, necessitates the removal of a boron atom from any of the six symmetrically equivalent B[13] sites in the unit cell. This leads to partial occupancies, which causes disorder in packing, as revealed by X-ray structure studies. The rest of the boron atoms are distributed in icosahedral B12 fragments, whose two-electron deficiency is satisfied by the capping of extra atoms, distributed statistically in the interstitial sites. These results show that the three-dimensional network of the idealized beta-rhombohedral unit cell is not stable, unlike the electron-precise carbon polymorphs such as diamond and graphite. Thus, disorder in the form of partial occupancies, interstitial atoms, alien atoms, etc., is necessary for electron sufficiency and hence for the stability of this polymorphic form. Through these ingenious steps, all components of the unit cell attain electron sufficiency, which explains the high thermodynamic stability of the polymorph. The connection established between boranes and elemental boron in terms of their structure and distribution of electrons has important implications in understanding the structure of boron-rich solids and new strategies to utilize their diverse and technologically important properties.

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Section: Bonding In the B 57 Unitmentioning

confidence: 59%

Section: Bonding In the B 57 Unitmentioning

confidence: 99%

Polyhedral Boranes and Elemental Boron: Direct Structural Relations and Diverse Electronic Requirements

Jemmis

Balakrishnarajan

2001

J. Am. Chem. Soc.

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“…Even with a four-membered ring, the interactions are significant enough to cause deviations, as has been observed in octahedral aluminum clusters. 28,31 No isolated molecule is experimentally characterized with this framework, though this pattern is observed in the solid state for aluminum clusters of the type AeM 2 Al 9 (Ae ) Ba, M ) Fe, Co, Ni; Ae ) Sr, M ) Co; Ae ) Ca, M ) Co) and CaNiAl 9 . [28][29][30] With heavier elements in the ring, such a possibility has been suggested.…”

Section: Application Of the Rulementioning

confidence: 99%

“…[28][29][30] With heavier elements in the ring, such a possibility has been suggested. 31 The only known structure with sandwich-type bonding to boron is found as part of the B 10 -B-B 10 unit of the β-rhombohedral boron unit cell (see the following paper in this issue). 2e The mismatch between a bridged atom and the ring size is seen in simple multidecker sandwiches, where a single fivemembered ring bridges two metals.…”

Section: Application Of the Rulementioning

confidence: 99%

A Unifying Electron-Counting Rule for Macropolyhedral Boranes, Metallaboranes, and Metallocenes

2001

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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.

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“…The validity of this expectation has been recently demonstrated by the B3LYP/6-311++G * * calculations [27] of a silicon analogue, C[(SiH) 3 ] 2+ 2 , of the carbocene 4 (n = 3). It is also possible to explore another way to match the requirements of the 8e rule in the carborane sandwich systems 5, in which carbons in the basal rings of 4 are substituted by more electropositive boron atoms and the electron-deficient (BH) n rings leave more vacancies for electrons of the central carbon.…”

Section: Introductionmentioning

confidence: 81%

Sandwich compounds with central hypercoordinate carbon, nitrogen, and oxygen: A quantum‐chemical study

Minyaev

Gribanova

Starikov

2006

Heteroatom Chemistry

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Will an η³-Si₃H₃ Ligand Form Sandwich Compounds with Main Group Elements? [J. Am. Chem. Soc. 2000, 122, 1725−1728].

Cited by 5 publications

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Polyhedral Boranes and Elemental Boron: Direct Structural Relations and Diverse Electronic Requirements

Polyhedral Boranes and Elemental Boron: Direct Structural Relations and Diverse Electronic Requirements

A Unifying Electron-Counting Rule for Macropolyhedral Boranes, Metallaboranes, and Metallocenes

Sandwich compounds with central hypercoordinate carbon, nitrogen, and oxygen: A quantum‐chemical study

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