Pressure-driven symmetry breaking and electron disproportionation of the trigonal Nb_(3)cluster in Nb_(3)Cl_(8)

Symmetry breaking of metal cluster-based strongly correlated systems can give rise to collective phenomena.Here,the twodimensional Nb_(3) cluster compound Nb_(3)Cl_(8) 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 Nb_(3) clusters from delocalized Nb^(8/3+)Nb^(8/3+)Nb^(8/3+)to localized Nb^(3+)Nb^(3+)Nb^(2+),which results in a subtle bandgap discontinuity,as evidenced by electrical transport and UV-Vis absorption measurements.