Electrochemical studies of the salts [cat](4)[Pt-2(mu-pop)(4)] (cat(+) = Bu4N+ or PPN+ [Ph3P=N=PPh3](+); pop = pyrophosphite, [P2O5H2](2-)) have been carried out in dichloromethane. In agreement with published studies of K-4[Pt-2(mu-pop)(4)] in water and [Ph4As](4)[Pt-2(mu-pop)(4)] in acetonitrile, the [Pt-2(mu-pop)(4)](4) anion is found to undergo an initial one-electron oxidation under conditions of cyclic voltammetry to a short-lived trianion, [Pt-2(mu-pop)(4)](3-). However, in the more weakly coordinating solvent dichloromethane, [Pt-2(mu-pop)(4)](3-) appears to undergo oligomerization instead of solvent-induced disproportionation; thus the overall process remains a one-electron reaction rather than an overall two-electron oxidative addition process, even under long time-scale, bulk electrolysis conditions, Chemical oxidation of [cat](4)[Pt-2(mu-pop)(4)] with [NO][BF4] or AgBF4 gives mainly a dark, insoluble, ill-defined solid that appears to contain Pt(III) according to X-ray photoelectron spectroscopy (XPS). In the case of [NO][BF4], a second reaction product, an orange solid, has been identified as a nitrosyl complex, [cat](3)[Pt-2(mu-pop)(4)(NO)]. The X-ray structure of the PPN+ salt shows the anion to consist of the usual lantern-shaped Pt2(U-POP)4 framework with an unusually large Pt-Pt separation [2.8375(6) angstrom]; one of the platinum atoms carries a bent nitrosyl group [r(N-O) = 1.111 (15) angstrom; angle(Pt-N-0) = 118.1(12)degrees] occupying an axial position. The nitrosyl group migrates rapidly on the P-31 NMR time-scale between the metal atoms at room temperature but the motion is slow enough at 183 K that the expected two pairs of inequivalent phosphorus nuclei can be observed. The X-ray photoelectron (XP) spectrum of the nitrosyl-containing anion confirms the presence of two inequivalent platinum atoms whose 4f(7/2) binding energies are in the ranges expected for Pt(II) and Pt(III); an alternative interpretation is that the second platinum atom has a formal oxidation number of +4 and that its binding energy is modified by the strongly a-donating NO- ligand. Reduction of [Pt-2(mu-pop)(4)X-2](4-) (X = Cl, Br, I) in dichloromethane corresponds to a chemically reversible, electrochemically irreversible two-electron process involving loss of halide and formation of [Pt-2(mu-pop)(4)](4-), as is the case in more strongly coordinating solvents.