A series of tetrabutylammonium salts of transition-metal substituted Wells-Dawson polyoxometalates has been synthesized by phase-transfer techniques and characterized by infrared spectroscopy, elemental analysis, and variable-temperature magnetic measurements. X-ray-quality crystals were obtained with a diffusion method using different organic solvents. The X-ray crystal structure of [(n-C4H9)(4)N](11)H-5[Cu-4(P2W15O56)(2)] (1) (monoclinic, P2(1)/n, Z = 2, a = 19.7269(6) angstrom, b = 17.6602(5) angstrom, c = 44.2525(11) angstrom, beta = 91.182(2)degrees; R-1 = 8.35% based on 31 282 independent reflections) reveals the presence of two unusual coordinatively unsaturated Cu(II) centers. In the absence of cocatalysts, 1 does not catalyze the aerobic oxidation of organic substrates in organic solvents.