On the analogy of B-BO and B-Au chemical bonding in B11O- and B10Au- clusters

During photoelectron spectroscopy experiments, the spectra of B(11)O(-) and B(10)Au(-) clusters are found to exhibit similar patterns except for a systematic spectral shift of ～0.5 eV, hinting that they possess similar geometric structures. The electron affinities are measured to be 4.02 ± 0.04 eV for B(11)O and 3.55 ± 0.02 eV for B(10)Au. DFT calculations at the B3LYP level show that B(11)O(-) and B(10)Au(-) adopt similar C(1) ((1)A) ground states, which are based on the quasiplanar B(10) cluster interacting with a BO unit and Au, respectively. The B(11)O(-) and B(10)Au(-) clusters are thus valent isoelectronic because both BO and Au can be viewed as monovalent units, forming highly covalent B-BO and B-Au bonds analogous to the B-H bond in B(10)H(-). For B(10)Au(-), we also find a highly symmetric D(10h) ((1)A(1g)) planar molecular wheel as a minimum on the potential energy surface. However, it is 45 kcal/mol above the ground state at the B3LYP level and not viable for experimental observation. Natural bond orbital analyses reveal interesting covalent versus ionic B-Au bonding in the C(1) B(10)Au(-) and D(10h) B(10)Au(-) structures, respectively, providing insight for the design of D(nh) MB(n) molecular wheels.