Density functional theoretical investigation on structure, optical response and hydrogen adsorption properties of Bg/metal-Bg clusters

摘要

DFT calculations have been carried out to shed light on the electronic structure, optical properties and hydrogen adsorption capability of neutral MB9 (where M = Li3, Na3, K3, Al, Ga, In, Rh and Co) dusters. Electronic structural studies on the parent B9~(3-) clusters reveal that a less aromatic hypervalent B-centred B8 ring geometry is energetically more favoured. However, GM~(3+) (Al, Ga and In) in GM@B9 prefers a highly aromatic metal-centred 9-membered molecular wheel structure. In addition, the larger size of indium breaks the D_(9h) symmetry of the molecular wheel by coming slightly out of the ring plane unlike AI@B9 and Ga@B9. B9~(n-) (n = 1-3) is also neutralized with 'n' number of Li, Na and K which revealed that AM2B9 and AM2Bg~- result in pyramidal geometries while AM3B9 results in an irregular shape by retaining the B9 framework similar to the most stable conformer of B9~(3-). Metal@B9 molecular wheels show optical absorption in a broad range of the spectrum (from UV to NIR: 260-1000 nm), which is attributed to the metal's ability to perturb the ring centred excited state. Ga@B9 and Co@B9 bind with hydrogen molecules in a dissociative manner, forming two covalent bonds with peripheral B atoms of the B9 ring.