Figure 2.

(A) ¹H NMR spectra in D₂O of [Re-1a]²⁻ at pH 4 (top) and a mixture of [Re-1a]³⁻ and [Re-1b]³⁻ at pH 7 (bottom). (B) ¹³C NMR (B) spectra in D₂O of [Re-1a]²⁻ at pH 4 (top) and a mixture of [Re-1a]³⁻ and [Re-1b]³⁻ at pH 7 (bottom). Selected signals from the symmetrical isomer [Re-1a]²⁻ (blue) and the unsymmetrical isomer [Re-1b]³⁻ (red) are labeled to highlight significant differences for both ¹H NMR and ¹³C NMR spectra.