[Sn9Pt2(PPh3)](2-) (2) was prepared from Pt(PPh3)(4), K4Sn9, and 2,2,2-cryptand in en/toluene solvent mixtures. The [K(2,2,2-cryptand)]1 salt is very air and moisture sensitive and has been characterized by ESI-MS, variable-temperature Sn-119, P-31, and Pt-195 NMR and single-crystal X-ray diffraction studies. The structure of 2 comprises an elongated tricapped Sn-9 trigonal prism with a capping PtPPh3, an interstitial Pt atom, a hypercloso electron count (10 vertex, 20 electron) and C-3v point symmetry. Hydrogenation trapping experiments and deuterium labeling studies showed that the formation of 2 involves a double C-H activation of solvent molecules (en or DMSO) with the elimination of H-2 gas. The ESI-MS analysis of 2 showed the K[Sn9Pt2(PPh3)](1-) parent ion, an oxidized [Sn9Pt2(PPh3)](1-) ion, and the protonated binary cluster anion [HSn9Pt2](1-). 2 is highly fluxional in solution giving rise to a single time-averaged Sn-119 NMR signal for all nine Sn atoms but the Pt atoms remain distinct. The exchange is intramolecular and is consistent with a rigid, linear Pt-Pt-PPh3 rod embedded in a liquidlike Sn-9 matrix. [Sn9Ni2(CO)](3-) (3) was prepared from Ni(CO)(2)(PPh3)(2), K4Sn9, and 2,2,2-cryptand in en/toluene solvent mixtures. The [K(2,2,2-cryptand)](+) salt is very air and moisture sensitive, is paramagnetic, and has been characterized by ESI-MS, EPR, and single-crystal X-ray diffraction. Complex 3 is a 10-vertex 21-electron polyhedron, a slightly distorted closo-Sn9Ni cluster with an additional interstitial Ni atom and overall C-4v point symmetry. The EPR spectrum showed a five-line pattern due to 4.8-G hyperfine interactions involving all nine tin atoms. The ESI-MS analysis showed weak signals for the potassium complex [K2Sn9Ni2(CO)](1-) and the ligand-free binary ions [K2Sn9Ni2](1-), [KSn9Ni2](1-), and [HSn9Ni2](1-).