Abstract Carbon-13 longitudinal relaxation times T 1 of aqueous solutions of proline at pH=11 containing 10 −4–10 −5M manganese(II) perchlorate are measured at 62.86 MHz and 60°C. Under these conditions, the Mn 2+ cation is bound to three proline molecules in their dibasic form to form the complex [Mn(L-PRO −) 3] −. The relaxation of carbons α, β, γ, δ in this complex is shown to be dipolar. The relevant correlation time is rotational τ r=4.3×10 −11s (at 60°C). A method is given to compute the Mn 2+- 13C distances in the complex from the paramagnetic relaxation rates 1/T 1M of carbons α to δ and an assumed geometry of the proline molecule. The manganese (II) cation may be positioned with respect to each proline ligand, thus determining the structure of the hexacoordinated complex. The sites of coordination are the uncharged nitrogen and one carboxylic oxygen atom of the proline molecules, their distance to the Mn 2+ cation are respectively 2.22 and 1.97 å.