Pressure-driven symmetry breaking and electron disproportionation of the trigonal Nb3 cluster in Nb3Cl8.

Symmetry breaking of metal cluster-based strongly correlated systems can give rise to collective phenomena. Here, the two-dimensional Nb₃ cluster compound Nb₃Cl₈ is shown to suffer dramatic symmetry breaking and electron disproportionation under compression. A structural phase transition from trigonal P-3m1 to monoclinic C2/m is observed near 8 GPa with the three-fold symmetry breaking. Electron disproportionation occurs on Nb₃ clusters from delocalized Nb^8/3+Nb^8/3+Nb^8/3+ to localized Nb³⁺Nb³⁺Nb²⁺, which results in a subtle bandgap discontinuity, as evidenced by electrical transport and UV-Vis absorption measurements. [ABSTRACT FROM AUTHOR]