The dimagnesium complex [Mg(Et2NCO2)(THF)(2)Br](2) (Et2NCO2- = diethylcarbamate, THF = tetrahydrofuran) contains two Mg2+ ions bridged by two diethylcarbamate ligands and exists as two related isomers, 1 and 2, in the solid state. Solution NMR data indicate that both complexes exist in equilibrium in solution as well. This novel intramolecular rearrangement, which is reminiscent of the carboxylate-shift paradigm, has implications for the dynamics of dinuclear metalloenzyme active sites bridged by carboxylate ligands.