Three polynuclear transition metal carbonyl cluster anions, Ru3Co(CO)13−, Ru6C(CO)162−, and Ru6(CO)182− have been studied using energy-dependent electrospray ionization mass spectrometry (EDESI–MS) and photodetachment photoelectron spectroscopy (PES). EDESI–MS maps show a simple collision-induced dissociation (CID) process for Ru3Co(CO)n− by stripping CO down to the metal core. For the doubly charged species, two competing CID channels were observed, viz. loss of neutral CO and loss of CO+e−. It was found that the parent dianions first lose neutral CO down to n = 9, producing a series of dianions, Ru6C(CO)n2− (n = 9–16) and Ru6(CO)n2− (n = 9–18). For n<9, the dianions become electronically unstable against autodetachment, and singly charged anions, Ru6C(CO)n− and Ru6(CO)n− (n = 0–9), were observed. The PES spectra of the dianions show the electron binding energies decrease monotonically as n decreases and become ∼0.0 eV for n = 9, in exact agreement with the CID patterns that reflect the electronic instability of the doubly charged metal complexes with n<9. All of the PES spectra show congested features, indicating very high density of low-lying electronic states for the transition metal carbonyl clusters. The electron binding energies of Ru3Co(CO)n− are similar for n = 4–13, but decrease sharply from n = 4 to 0. The intramolecular Coulomb repulsion in the dianions was observed to increase with loss of CO, ranging from ∼1.8 eV for Ru6C(CO)162− to ∼2.4 eV for Ru6C(CO)92−. © 2002 American Institute of Physics.