Endohedral C3 Ca@B39+ and C2 Ca@B39+: axially chiral metalloborospherenes based on B39−

Abstract

Using the newly discovered borospherenes C₃ B₃₉⁻ and C₂ B₃₉⁻ as molecular devices and based on extensive global-minimum searches and first-principles calculations, we present herein the possibility of the first axially chiral metalloborospherenes C₃ Ca@B₃₉⁺ (1, ¹A) and C₂ Ca@B₃₉⁺ (2, ¹A), which are the global minimum and the second lowest-lying isomer of CaB₃₉⁺, respectively. These metalloborospherene species turn out to be charge-transfer complexes Ca²⁺@B₃₉⁻ in nature, with the Ca centre on the C₃ or C₂ molecular axis donating one electron to the B₃₉ cage which behaves like a superhalogen. Molecular orbital analyses indicate that C₃/C₂ Ca²⁺@B₃₉⁻ possess the universal bonding pattern of σ plus π double delocalization, similar to their C₃/C₂ B₃₉⁻ parents. Molecular dynamics simulations show that both C₃ Ca@B₃₉⁺ (1) and C₂ Ca@B₃₉⁺ (2) are dynamically stable at 200 K, with the former starting to fluctuate structurally at 300 K and the latter at 400 K, again similar to C₃/C₂ B₃₉⁻. The infrared and Raman spectra of C₃/C₂ Ca@B₃₉⁺ (1/2) are simulated and compared with those of C₃/C₂ B₃₉⁻ to facilitate their forthcoming experimental characterization.