Photoelectron Spectroscopy and Theoretical Study of Di-Copper-Boron Clusters: Cu₂B₃ ^- and Cu₂B₄ ^-

Copper has been found to be able to mediate the formationof bilayerborophenes. Copper-boron binary clusters are ideal model systemsto probe the copper-boron interactions, which are essentialto understand the growth mechanisms of borophenes on copper substrates.Here, we report a joint photoelectron spectroscopy and theoreticalstudy on two di-copper-doped boron clusters: Cu2B3 (-) and Cu2B4 (-). Well-resolved photoelectron spectra are obtained, revealing thepresence of a low-lying isomer in both cases. Theoretical calculationsshow that the global minimum of Cu2B3 (-) (C (2v ), (1) A (1)) contains a doubly aromatic B-3 (-) unit weakly interacting with a Cu-2 dimer,while the low-lying isomer (C (2v ), (1) A (1)) consists of aB(3) triangle with the two Cu atoms covalently bonded totwo B atoms at two vertexes. The global minimum of Cu2B4 (-) (D (2h ), (2) A (g)) is found to consistof a rhombus B-4 unit covalently bonded to the two Cu atomsat two opposite vertexes, whereas in the low-lying isomer (C-s , (2) A '),one of the two Cu atoms is bonded to two B atoms.