A total of 16 discrete polyoxopalladates(II) [MO(8)Pd(II)(12)L(8)](n-), with a metal ion M encapsulated in a cuboid-shaped {Pd(12)O(8)L(8)} cage, have been synthesized: the phenylarsonate-capped series (1) L = PhAsO(3)(2-), M = Sc(3+) (ScPhAs), Mn(2+) (MnPhAs), Fe(3+) (FePhAs), Co(2+) (CoPhAs), Ni(2+) (NiPhAs), Cu(2+) (CuPhAs), Zn(2+) (ZnPhAs); the phenylphosphonate-capped series: (2) L = PhPO(3)(2-), M = Cu(2+) (CuPhP), Zn(2+) (ZnPhP); and the selenite-capped series (3) L = SeO(3)(2-), M = Mn(2+) (MnSe), Fe(3+) (FeSe), Co(2+) (CoSe), Ni(2+) (NiSe), Cu(2+), (CuSe), Zn(2+) (ZnSe), Lu(3+) (LuSe)). The polyanions were prepared in one-pot reactions in aqueous solution of [Pd(3)(CH(3)COO)(6)] with an appropriate salt of the metal ion M, as well as PhAsO(3)H(2), PhPO(3)H(2), and SeO(2), respectively, and then isolated as hydrated sodium salts Na(n)[MO(8)Pd(II)(12)L(8)]·yH(2)O (y = 10-37). The compounds were characterized in the solid state by IR spectroscopy, single-crystal XRD, elemental and thermogravimetric analyses. The solution stability of the diamagnetic polyanions ScPhAs, ZnPhAs, ZnPhP, ZnSe, and LuSe was confirmed by multinuclear ((77)Se, (31)P, (13)C, and (1)H) NMR spectroscopy. The polyoxopalladates ScPhAs, MnPhAs, CoPhAs, and CuPhAs were investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). Electrochemical studies on the manganese- and iron-containing derivatives demonstrated that the redox properties of the Mn(2+), Fe(3+), and Pd(2+) centers in the polyanions are strikingly influenced by the nature of the capping group. These results have subsequently been verified by density functional theory (DFT) calculations. Interestingly, electron paramagnetic resonance (EPR) measurements suggest that the coordination geometry around Mn(2+) is dynamically distorted on the EPR time scale (∼10(-11) s), whereas it appears as a static ensemble with cubic symmetry on the X-ray diffraction (XRD) time-scale (10(-15) s). The octacoordinated Cu(2+) cuboid is similarly distorted, in good agreement with DFT calculations. Interestingly, g(∥) is smaller than g(⊥), which is quite unusual, needing further theoretical development.