Polycrystalline octa-nuclear copper(I) O, O′-di- i-propyl- and O, O′-di- i-amyldithiophosphate cluster compounds, {Cu 8[S 2P(OR) 2] 6(μ 8-S)} where R = i Pr and i Am, were synthesized and characterized by 31P CP/MAS NMR at 8.46 T and static 65Cu NMR at multiple magnetic field strengths (7.05, 9.4 and 14.1 T). The symmetries of the electronic environments around the P sites were estimated from the 31P chemical shift anisotropy (CSA) parameters, δ aniso and η. Analyses of the 65Cu chemical shift and quadrupolar splitting parameters for these compounds are presented with the data being compared to those for the analogous octa-nuclear cluster compounds with R = n Bu and i Bu. The 65Cu transverse relaxation for the copper sites in {Cu 8[S 2P(O i Pr) 2] 6(μ 8-S)} and {Cu 8[S 2P(O i Am) 2] 6(μ 8-S)} was found to be very different, with a relaxation time, T 2, of 590 μs (Gaussian) and 90 μs (exponential), respectively. The structures of {Cu 4[S 2P(O i Pr) 2] 4} and {Cu 8[S 2P(O i Pr) 2] 6(μ 8-S)} cluster compounds in the liquid- and the solid-state were studied by Cu K-edge EXAFS. The disulfide, [S 2P(O i Am) 2] 2, was obtained and characterized by 31P{ 1H} NMR. The interactions of the disulfide and of the potassium O, O′-di- i-amyldithiophosphate salt with the surfaces of synthetic chalcocite (Cu 2S) were probed using solid-state 31P NMR spectroscopy and only the presence of copper(I) dithiophosphate species with the {Cu 8[S 2P(O i Am) 2] 6(μ 8-S)} structure was observed.