Photoelectron spectroscopy of aromatic compound clusters of the B12 all-boron benzene: B12Au- and B12(BO)-.

We report a photoelectron spectroscopy and density-functional theory study of the B12Au(-) and B13O(-) clusters and their neutrals, which are shown to be six π electron aromatic compounds between the quasi-planar all-boron B12 benzene-analogue and a monovalent Au or BO ligand. Electron affinities of B12Au and B13O are measured to be 3.48 ± 0.04 and 3.90 ± 0.04 eV, respectively. Structural searches are performed for B12Au(-) and B13O(-), which are compared with the isovalent B12H(-) cluster. The global minima of B12Au(-) and B13O(-) both feature an almost intact B12 cluster with the Au and BO ligands bonded to its periphery, respectively. For B12Au(-), a low-lying isomer is also identified, which is only 0.4 kcal mol(-1) above the global minimum, in agreement with the experimental observation of a weakly populated isomer in the cluster beam of B12Au(-). These aromatic compound clusters provide new examples for the Au/H isolobal analogy and the boronyl (BO) chemistry.