A Tale of Two Stabilities: How One Boron Atom Affects a Switch in Bonding Motifs in CeO₂B_<i>x</i>^– (<i>x</i> = 2, 3) Complexes

Boronyl (BO) ligands have garnered much attention as isoelectronic and isolobal analogues of CO and CN–, yet successful efforts in synthesizing metal boronyl complexes remain scarce. Anion photoelectron (PE) spectroscopy and density functional theory calculations were employed to investigate two small CeO2Bx– (x = 2, 3) complexes generated from laser ablation of a mixed Ce/B pressed powder target. The spectra reveal markedly different bonding upon incorporation of an additional B atom. Most interestingly, CeO2B2– was found to have a Ce­(I) center coordinated to two monoanionic boronyl ligands in a bent geometry. This result was unexpected as previous studies suggest electron-rich metals are most suitable for stabilizing such ligands; furthermore, it is one of the first examples of an experimental metal–polyboronyl complex. Introducing another boron atom, however, favors a much different geometry in which Ce­(II) coordinates an O2B33– unit through both the O and B atoms, which was evident in the markedly different PE spectra