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Metal-Stabilized [B8H8]2− Derivatives with Dodecahedral Structure in the Solid and Solution States: [(Cp2MBH3)2B8H6] (Cp=η5-C5H5; M=Zr (1-Zr) and Hf (1-Hf)).
Authors:Sourav Kar  Subhash Bairagi  Gaurav Joshi  Prof Dr Eluvathingal D Jemmis  Prof Dr Sundargopal Ghosh
Institution:1. Department of Chemistry, Indian Institute of Technology Madras, Chennai, 600036 India;2. Department of Chemistry, Indian Institute of Technology Madras, Chennai, 600036 India

These authors contributed equally to this work.;3. Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, 560012 India

Abstract:Despite the synthesis and structural characterization of closo-hydroborate dianions, BnHn]2− (n=6–12) more than 50 years ago, some ambiguity remains about the structure of B8H8]2−. Although the solid-state structure of B8H8]2− was established by single-crystal X-ray studies in 1969, fast rearrangements in solution at accessible temperatures prevented its detailed characterization. We therefore stabilized a derivative of B8H8]2− by using Cp2MBH3 and structurally characterized two new octaborane analogues, (Cp2MBH3)2B8H6] (Cp=η5-C5H5; M=Zr ( 1-Zr ) and Hf ( 1-Hf )), so that the dynamics of the B8 skeleton were arrested. The solid-state structures of both 1-Zr and 1-Hf comprise a dodecahedron core protected by {Cp2MBH3} moieties on both sides of the cluster. Spectroscopic characterization (11B NMR) validates the intactness of the B8 dodecahedron core in solution as well. Theoretical calculations establish that the two exo-{Cp2MBH3} fragments provide structural and electronic structural stability to the B8 core and its intact dodecahedral dianionic nature. Furthermore, we propose isodesmic equations for the formation of higher analogues of the Bn core (n>8) guarded by different group 4 transition metals. Our analysis suggests that, as we move to higher polyhedra (n>10), the formation becomes unfavourable irrespective of metal.
Keywords:borane  dodecahedra  hafnium  octaborane  zirconium
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