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Metal stabilized [B8H8]2- derivatives with dodecahedral structure in solid- and solution-state: [(Cp2MBH3)2B8H6], (Cp = ƞ5-C5H5; M = Zr (1-Zr) and Hf (1-Hf)).

Despite the synthesis and structural characterization of closo-hydroborate dianions, [BnHn2-(n = 6-12) more than 50 years ago, some ambiguity remains about the structure of B8H82-. Although solid state structure of B8H82- was established by single crystal X-ray studies in 1969, fast rearrangements in solution at accessible temperatures prevented its detailed characterization. We have therefore stabilized a derivative of B8H8(2-)  using Cp2MBH3 and structurally characterized two new octaborane analogues, [(Cp2MBH3)2B8H6)] (Cp = ƞ5-C5H5; M = Zr (1-Zr) and Hf (1-Hf)). The solid-state structures of both 1-Zr and 1-Hf comprise of a dodecahedron core, protected by Cp2MBH3 moieties on both sides of the cluster. The spectroscopic characterizations (11B NMR) validate the intactness of 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 have proposed isodesmic equations for the formation of higher analogue of Bn core  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.