Polyoxopalladates Encapsulating\n8‑Coordinated Metal Ions, [MO₈Pd^II₁₂L₈]^<i>n</i>− (M =\nSc³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Lu³⁺; L = PhAsO₃^2–, PhPO₃^2–, SeO₃^2–)

Abstract

A total of 16 discrete polyoxopalladates­(II) [MO₈Pd^II₁₂L₈]^<i>n</i>−, with a metal ion <b>M</b> encapsulated in a\ncuboid-shaped {Pd₁₂O₈L₈} cage, have\nbeen synthesized: the phenylarsonate-capped series (1) <b>L</b> = PhAsO₃^2–, <b>M</b> = Sc³⁺ (<b>ScPhAs</b>), Mn²⁺ (<b>MnPhAs</b>), Fe³⁺ (<b>FePhAs</b>), Co²⁺ (<b>CoPhAs</b>), Ni²⁺ (<b>NiPhAs</b>), Cu²⁺ (<b>CuPhAs</b>), Zn²⁺ (<b>ZnPhAs</b>); the\nphenylphosphonate-capped series: (2) <b>L</b> = PhPO₃^2–, <b>M</b> = Cu²⁺ (<b>CuPhP</b>), Zn²⁺ (<b>ZnPhP</b>); and the selenite-capped\nseries (3) <b>L</b> = SeO₃^2–, <b>M</b> = Mn²⁺ (<b>MnSe</b>), Fe³⁺ (<b>FeSe</b>), Co²⁺ (<b>CoSe</b>), Ni²⁺ (<b>NiSe</b>), Cu²⁺, (<b>CuSe</b>), Zn²⁺ (<b>ZnSe</b>), Lu³⁺ (<b>LuSe</b>)).\nThe polyanions were prepared in one-pot reactions in aqueous solution\nof [Pd₃(CH₃COO)₆] with an appropriate\nsalt of the metal ion <b>M</b>, as well as PhAsO₃H₂, PhPO₃H₂, and SeO₂, respectively, and then isolated as hydrated sodium salts Na_<i>n</i>[MO₈Pd^II₁₂L₈]·<i>y</i>H₂O (<i>y</i> = 10–37). The compounds were characterized in the solid state\nby IR spectroscopy, single-crystal XRD, elemental and thermogravimetric\nanalyses. The solution stability of the diamagnetic polyanions <b>ScPhAs</b>, <b>ZnPhAs</b>, <b>ZnPhP</b>, <b>ZnSe</b>, and <b>LuSe</b> was confirmed by multinuclear (⁷⁷Se, ³¹P, ¹³C, and ¹H) NMR spectroscopy.\nThe polyoxopalladates <b>ScPhAs</b>, <b>MnPhAs</b>, <b>CoPhAs</b>, and <b>CuPhAs</b> were investigated by electrospray\nionization mass spectrometry (ESI-MS) and tandem mass spectrometry\n(MS/MS). Electrochemical studies on the manganese- and iron-containing\nderivatives demonstrated that the redox properties of the Mn²⁺, Fe³⁺, and Pd²⁺ centers in the polyanions\nare strikingly influenced by the nature of the capping group. These\nresults have subsequently been verified by density functional theory\n(DFT) calculations. Interestingly, electron paramagnetic resonance\n(EPR) measurements suggest that the coordination geometry around Mn²⁺ is dynamically distorted on the EPR time scale (∼10^–11 s), whereas it appears as a static ensemble with\ncubic symmetry on the X-ray diffraction (XRD) time-scale (10^–15 s). The octacoordinated Cu²⁺ cuboid is similarly distorted,\nin good agreement with DFT calculations. Interestingly, <i>g</i>_∥ is smaller than <i>g</i>_⊥, which is quite unusual, needing further theoretical development.