Sn-9(4-) reacts with Pd(PPh3)(4) in ethylenediamine/toluene solvent mixtures in the presence of 2,2,2-cryptand to give the Pd-2@Sn-18(4-) cluster as the K(2,2,2,-crypt)(+) salt. The cluster is isostructural with Pd-2@Ge-18(4-) and has a nuclearity different from that of the Pt and Ni analogues, Ni-2@Sn-17(4-) and Pt-2@Sn-17(4-). The Pd-2@Sn(18)(4-)ion has a deltahedral capsulelike structure with 40 cluster bonding electrons and is the largest free-standing polystannide characterized to date. Like Pt-2@Sn-17(4-), the Pd-2@Sn-18(4-) Complex is highly dynamic in solution, showing a single Sn-119 NMR resonance indicative of an intramolecular liquidlike dynamic exchange. LDI-MS studies of the crystalline sample show extensive fragmentation and the formation of five gas-phase cluster series: Sn-x(-) (1 < x < 12), PdSnx-1- (4 < x < 18), Pd2Snx-2- (6 < x < 21), Pd3Snx-3- (8 < x < 21), and Pd4Snx-4- (13 < x < 21). The most abundant ion in the gas phase is the PdSn10- cluster, which presumably has an Sn-10 bicapped-square-antiprismatic structure with an endohedral Pd (e.g., Ni@Pb-10(2-)).