Sb@Ni₁₂@Sb₂₀^-/+ and Sb@Pd₁₂@Sb₂₀ⁿ Cluster Anions, Where n = +1, -1, -3, -4: Multi-Oxidation-State Clusters of...

K₅Sb₄ and K₃Sb₇ Zintl ion precursors react with Pd(PPh₃)₄ in ethylenediamine/toluene/PBu₄⁺ solutions to give crystals of Sb@Pd₁₂@Sb₂₀^n-/PBu₄⁺ salts, where n = 3, 4. The clusters are structurally identical in the two charge states, with nearly perfect I_h point symmetry, and can be viewed as an Sb@Pd₁₂ icosahedron centered inside of an Sb₂₀ dodecahedron. The metric parameters suggest very weak Sb-Sb and Pd-Pd interactions with strong radial Sb-Pd bonds between the Sb₂₀ and Pd₁₂ shells. All-electron DFT analysis shows the 3- ion to be diamagnetic with I_h symmetry and a 1.33 eV HOMO-LUMO gap, whereas the 4- ion undergoes a Jahn-Teller distortion to an S = 1/2 D_3d structure with a small 0.1 eV gap. The distortion is predicted to be small and is not discernible by crystallography. Laser desorption-ionization time-of-flight mass spectrometry (LDI-TOF MS) studies of the crystalline samples show intense parent Sb@Pd₁₂@Sb₂₀^- ions (negative ion mode) and Sb@Pd₁₂@Sb₂₀⁺ (positive ion mode) along with series of Sb@Pd_12-y@Sb_20-x^-/+ ions. Ni(cyclooctadiene)₂ reacts with K₃Sb₇ in en/tol/Bu₄PBr solvent mixtures to give black precipitates of Sb@Ni₁₂@Sb₂₀^n- salts that give similar Sb@Ni₁₂@Sb₂₀^-/+ parent ions and Sb@Ni_12-y@Sb_20-x^-/+ degradation series in the respective LDI-TOF MS studies. The solid-state and gas-phase studies of the icosahedral Sb@M₁₂@Sb₂₀^n-/n+ ions show that the clusters can exist in the -4, -3, -1, +1 (M = Pd) and +1, -1 (M = Ni) oxidation states. These multiple-charge-state clusters are reminiscent of redox-active fullerenes (e.g., C₆₀ⁿ, where n = +1, 0, -1, -2, -3, -4, -5, -6).