Intrinsic Semiconducting Behavior in a Large Mixed-Valent Uranium(V/VI) Cluster

We disclose the intrinsic semiconducting properties of one of the largest mixed-valent uranium clusters, [H3O+][U-V((UO2)-O-VI)(8)(mu(3)-O)(6)(PhCOO)(2)(Py(CH2O)(2))(4)(DMF)(4)] (Ph=phenyl, Py=pyridyl, DMF=N,N-dimethylformamide) (1). Single-crystal X-ray crystallography demonstrates that U-V center is stabilized within a tetraoxo core surrounded by eight uranyl(VI) pentagonal bipyramidal centers. The oxidation states of uranium are substantiated by spectroscopic data and magnetic susceptibility measurement. Electronic spectroscopy and theory corroborate that U-V species serve as electron donors and thus facilitate 1 being a n-type semiconductor. With the largest effective atomic number among all reported radiation-detection semiconductor materials, charge transport properties and photoconductivity were investigated under X-ray excitation for 1: a large on-off ratio of 500 and considerable charge mobility lifetime product of 2.3x10(-4) cm(2) V-1, as well as a high detection sensitivity of 23.4 mu C Gy(air)(-1) cm(-2).