Manganese(II)-Containing MRI Contrast Agent Employing a Neutral and Non-Macrocyclic Ligand

The ligand N,N′-bis(2-pyridylmethyl)-bis(ethylacetate)-1,2-ethanediamine (debpn) coordinates divalent transition metal ions in either a pentadentate or hexadentate fashion. The coordination number correlates with the ionic radius of the metal ion, with larger cations being heptacoordinate as assessed by solid-state analysis. With Mn(II), the debpn ligand is hexadentate and remains bound to the oxophilic metal ion, even when dissolved in water. The ligand’s incomplete coordination of the manganous ion allows water molecules to coordinate to the metal center. These two properties, coupled with the high paramagnetism associated with the S = 5/2 metal center, enable [Mn(debpn)(H2O)](ClO4)2 to serve as a stable and effective magnetic resonance imaging contrast agent despite the ligand’s lack of both a macrocyclic component and an anionic charge.