Monovalent lanthanide(I) in borozene complexes

Lanthanide (Ln) elements are generally found in the oxidation state +II or +III, and a few examples of +IV and +V compounds have also been reported. In contrast, monovalent Ln(+I) complexes remain scarce. Here we combine photoelectron spectroscopy and theoretical calculations to study Ln-doped octa-boron clusters (LnB 8 − , Ln = La, Pr, Tb, Tm, Yb) with the rare +I oxidation state. The global minimum of the LnB 8 − species changes from C s to C 7v symmetry accompanied by an oxidation-state change from +III to +I from the early to late lanthanides. All the C 7v -LnB 8 − clusters can be viewed as a monovalent Ln(I) coordinated by a η 8 -B 8 2− doubly aromatic ligand. The B 7 3− , B 8 2− , and B 9 − series of aromatic boron clusters are analogous to the classical aromatic hydrocarbon molecules, C 5 H 5 − , C 6 H 6 , and C 7 H 7 + , respectively, with similar trends of size and charge state and they are named collectively as “borozenes”. Lanthanides with variable oxidation states and magnetic properties may be formed with different borozenes. The most common oxidation state for lanthanides is +3. Here the authors use photoelectron spectroscopy and theoretical calculations to study half-sandwich complexes where a lanthanide center in the oxidation state +1 is bound to an aromatic wheel-like B 8 2- ligand.