Revealing the electronic properties of the B-B bond: the bis-catecholato diboron molecule.

The electronic properties of a diboron molecule, namely the Bis(cathecolato)diboron (2-(1,3,2-benzodioxaborol-2-yl)-1,3,2-benzodioxaborole), (B2Cat2) have been studied by comparing photoemission (XPS) and Near Edge absorption spectroscopy (NEXAFS) experiments with the outcome of DFT calculations. The B1s, C1s and O1s K-edges have been investigated for both the isolated gas phase molecule and the adsorbed one on the Au(111) surface . The main features of the polarized NEXAFS spectra at each of the three edges considered are not significantly affected by the presence of the substrate, with respect to the isolated molecule, indicating that the molecule-gold interaction is weak. Moreover, the comparison between the observed dichroism in the NEXAFS spectra of the adsorbed B2Cat2 and the NEXAFS spectra of the isolated molecule has confirmed the orbital symmetry assigned in the gas phase absorption spectra. The transitions to π (B-B) bonding and the π* (B-B) anti-bonding final states represent the most relevant probe of the chemistry of the B2Cat2 molecule. We show that their theoretical description requires the treatment of the relaxation changes among different excited state configurations, which we successfully implemented by using ΔSCF-DFT (ΔSCF) calculations.