The solution properties of Mn-III-hydroxo and Mn-III-methoxy complexes featuring N-5 amide-containing ligands were investigated using H-1 NMR spectroscopy. The H-1 NMR spectrum for one of these complexes, the previously reported [Mn-III(OH)(dpaq)] (OTf (dpaq = 2-[bis(pyridin-2-ylmethyl)] amino-N-quinolin-8-yl-acetamidate) shows hyperfine-shifted signals, as expected for this S = 2 Mn-III-hydroxo adduct. However, the H-1 NMR spectrum of [Mn-III(OH)(dpaq)](OTf also shows a large number of proton resonances in the diamagnetic region, suggesting the presence of multiple species in CD3CN solution. The majority of the signals in the diamagnetic region disappear when a small amount of water is added to a CH3CN solution of [Mn-III(OH)(dpaq)](OTf). Electronic absorption and Mn K-edge X-ray absorption experiments support the formulation of this diamagnetic species as the mu-oxodimanganese(III,III) complex [Mn-2(III)(mu-O)(dpaq)(2))](2+). On the basis of these observations, we propose that the dissolution of [Mn-III(OH)(dpaq)](OTf) in CD3CN results in the formation of mononuclear Mn-III-hydroxo and dinuclear mu-oxodimanganese(III,III) species that are in equilibrium. The addition of a small amount of water is sufficient to shift this equilibrium in favor of the Mn-III-hydroxo adduct. Surprisingly, electronic absorption experiments show that the conversion of [Mn-2(III)(mu-O)(dpaq)(2))](2+) to [Mn-III(OH)(dpaq)](+) by added water is relatively slow. Because this dimer to monomer conversion is slower than TEMPOH oxidation by [Mn-III(OH)(dpagy)](+), the previously observed TEMPOH oxidation rates for [Mn-III(OH)(dpaq)](+) reflected both processes. Here, we report the bona fide TEMPOH oxidation rate for [Mn-III(OH)(dpaq)](+), which is significantly faster than previously reported. H-1 NMR spectra are also reported for the related [Mn-III(OMe)(dpaq)](+) and [Mn-III(OH)(dpaq(2Me))](+) complexes. These spectra only show hyperfine-shifted signals, suggesting the presence of only mononuclear Mn-III-methoxy and Mn-III-hydroxo species in solution. Measurements of T-1 relaxation times and proton peak integrations for [Mn-III(OMe)(dpaq)](+) provide preliminary assignments for H-1 NMR resonances.