PrB7- : A Praseodymium-Doped Boron Cluster with a PrII Center Coordinated by a Doubly Aromatic Planar η7 -B73- Ligand

Abstract

The structure and bonding of a Pr-doped boron cluster (PrB₇^- ) are investigated using photoelectron spectroscopy and quantum chemistry. The adiabatic electron detachment energy of PrB₇^- is found to be low [1.47(8) eV]. A large energy gap is observed between the first and second detachment features, indicating a highly stable neutral PrB₇ . Global minimum searches and comparison between experiment and theory show that PrB₇^- has a half-sandwich structure with C_6v symmetry. Chemical bonding analyses show that PrB₇^- can be viewed as a Pr^II [η⁷ -B₇^3- ] complex with three unpaired electrons, corresponding to a Pr (4f² 6s¹ ) open-shell configuration. Upon detachment of the 6s electron, the neutral PrB₇ cluster is a highly stable Pr^III [η⁷ -B₇^3- ] complex with Pr in its favorite +3 oxidation state. The B₇^3- ligand is found to be highly stable and doubly aromatic with six delocalized π and six delocalized σ electrons and should exist for a series of lanthanide M^III [η⁷ -B₇^3- ] complexes.

Keywords: ab initio calculation; aromaticity; boron clusters; metal-boron cluster complex; photoelectron spectroscopy.