[Pd16Ni4(CO)(22)(PPh3)(4)](2-) (1) and [Pd33Ni9(CO)(41)(PPh3)(6)](4-) (2) were obtained as the two major products from the reduction of PdCl2(PPh3)(2) with [Ni-6(CO)(12)](2-). Their crystal structures as [PPh4](+) salts were unambiguously determined from CCD X-ray crystallographic analyses, the resulting stoichiomotries were ascertained from elemental analyses. Infrared, multinuclear H-1, P-31{H-1} NMR, UV-vis, CV, variable-temperature magnetic susceptibility, and ESI FT/ICR mass spectrometric measurements were performed. The Pd16Ni4 core Of 1 ideally conforms to a ccp nu (3) tetrahedron of pseudo-T-d (43m) symmetry. Its geometry normal to each tetrahedral Pd7Ni3 face (i.e., along each of the four 3-fold axes) may be viewed as a four-layer stacking of 20 metal atoms in a ccp [a(Ni-1) b(Pd-3) c(Pd-6) a(Pd7Ni3)] sequence. A comparative analysis of the different ligand connectivities about the analogous metal-core geometries in 1 and the previously reported [Os-20(CO)(40)](2-) has stereochemical implications pertaining to the different possible modes of carbon monoxide attachment to ccp metal(III) surfaces. The unique geometry of the Pd33Ni9 core of 2, which has pseudo-Dsi, (62m) symmetry, consists of five equilateral triangular layers that are stacked in a hcp [a(Pd7Ni3) b(Pd-6) a(Pd7Ni3) b(Pd-6) a(Pd7Ni3)] sequence. Variable-temperature magnetic susceptibility measurements indicated both 1 and 2 to be diamagnetic over the entire temperature range from 5.0 to 300 K. Neutral Pd-12(CO)(12)(PPh3)(6) (3) and [Pd-29(CO)(28)(PPh3)(7)](2-) (4) as the [PPh4](+) salt were obtained as minor decomposition products from protonation reactions of 1 and 2, respectively, with acetic acid. Compound 3 of pseudo-D-3d (32/m) symmetry represents the second highly deformed hexacapped octahedral member of the previously established homopalladium family of clusters containing uncapped. monocapped. bicapped, and tetracapped Pds octahedra. The unprecedented centered 28-atom polyhedron for the Pd-29 core of 4 of pseudo-C-3 nu, (3m) symmetry may be described as a four-layer stacking of 29 metal atoms in a mixed hcp/ccp [a(Pd-1) b(Pd-3) a(Pd-10) c(Pd-15)] sequence.