Structures, stabilities and spectral properties of borospherene B44− and metalloborospherenes MB440/− (M = Li, Na, and K)

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations are carried out to study the stabilities, photoelectron, infrared, Raman and electronic absorption spectra of borospherene B44- and metalloborospherenes MB440/- (M = Li, Na, and K). It is found that all atoms can form stable exohedral metalloborospherenes M&B440/-, whereas only Na and K atoms can be stably encapsulated inside B440/- cage. In addition, relative energies of these metalloborospherenes suggest that Na and K atoms favor exohedral configuration. Importantly, doping of metal atom can modify the stabilities of B44 with different structures, which provides a possible route to produce stable boron clusters or metalloborospherenes. The calculated results suggest that B44 tends to get electrons from the doped metal. Metalloborospherenes MB44- are characterized as charge-transfer complexes (M2+B442-), where B44 tends to get two electrons from the extra electron and the doped metal, resulting in similar features with anionic B442-. In addition, doping of metal atom can change the spectral features, such as blueshift or redshift and weakening or strengthening of characteristic peaks, since the extra metal atom can modify the electronic structure. The calculated spectra are readily compared with future spectroscopy measurements and can be used as fingerprints to identify B44- and metalloborospherenes.