Structural Consequences of Electron Hyperdeficiency

Alternative Title

Synthesis and crystal structure of an iron-cobalt metallocarborane having two closed polyhedra fused along an edge


A metallocarborane of novel structure, (CH3)4C4B8H 8FeCo(η5-C5H5), has been synthesized and structurally characterized from 11B and 1H FT NMR, mass spectroscopic, infrared, and single-crystal x-ray diffraction data. The dark green crystals are monoclinic, space group P21, with two molecules per unit cell and a = 7.203 (4) Å, b = 14.77 (2) Å, c = 8.830 (2) Å, and β = 99.7 (1)° (ρcalcd = 1.38, ρobsd = 1.38 g cm-3). The structure was solved by the heavy-atom method and refined by full-matrix least-squares procedures to a final R value of 0.069 and Rw = 0.081 for the 1657 reflections for which Fo2 > 3σ(Fo)2. The molecule contains a direct iron-cobalt bond and consists of two pentagonal bipyramidal units fused at a common iron atom with an additional BH group capping triangular faces on both polyhedra simultaneously. The structure is explained in terms of a shortage of two electrons in the cage framework, relative to the normal requirement for polyhedral clusters, which causes one BH group to adopt a capping location. These results are discussed in relation to the known structures of two osmium carbonyls and a diiron metallocarborane.



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