Photoelectron Spectroscopy and Theoretical Study of Di-Copper-Boron Clusters: Cu 2 B 3 - and Cu 2 B 4 .

Copper has been found to be able to mediate the formation of bilayer borophenes. Copper-boron binary clusters are ideal model systems to probe the copper-boron interactions, which are essential to understand the growth mechanisms of borophenes on copper substrates. Here, we report a joint photoelectron spectroscopy and theoretical study on two di-copper-doped boron clusters: Cu 2 B 3 - and Cu 2 B 4 - . Well-resolved photoelectron spectra are obtained, revealing the presence of a low-lying isomer in both cases. Theoretical calculations show that the global minimum of Cu 2 B 3 - ( C 2 v , 1 A 1 ) contains a doubly aromatic B 3 - unit weakly interacting with a Cu 2 dimer, while the low-lying isomer ( C 2 v , 1 A 1 ) consists of a B 3 triangle with the two Cu atoms covalently bonded to two B atoms at two vertexes. The global minimum of Cu 2 B 4 - ( D 2 h , 2 A g ) is found to consist of a rhombus B 4 unit covalently bonded to the two Cu atoms at 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.