Here we report a simple Mn coordination complex with utility as a redox-sensitive MR probe. The HBET ligand stabilizes both the Mn2+ and Mn3+ oxidation states. In the presence of glutathione (GSH), low relaxivity Mn-III-HBET is converted to high relaxivity Mn-II-HBET with a 3-fold increase in relaxivity, and concomitant increase in MR signal. Alternately, hydrogen peroxide can convert Mn-II-HBET to Mn-III-HBET with a reduction in MR signal.