Probing the Influence of Size and Composition on the Photoelectron Spectra of Cadmium Chalcogenide Cluster Dianions

We have synthesized a series of compounds comprising the halide-free cadmium chalcogenide cluster dianions [Cd₈Se­(SePh)₁₆]^2–, [Cd₁₇Se₄(SePh)₂₈]^2–, [Cd₁₇S₄(SPh)₂₈]^2–, and [Cd₁₇Se₄(SPh)₂₈]^2– to study their size- and composition-dependent electronic properties free of matrix effects. Toward this end, photoelectron spectra of the isolated dianions electrosprayed from solution were recorded at several detachment photon energies. Together with quantum chemical calculations, these data reveal a systematic correlation between electronic properties such as electron affinities or repulsive Coulomb barriers and the composition/size of these semiconducting cluster complexes. We infer that the excess negative charges are localized at the apical sites of these near-tetrahedral molecules