Ultrafast Ligand Self-Exchanging Gadolinium Complexes In Ionic Liquids For Nmr Field Probes

Concurrent magnetic field monitoring in MRI with an array of NMR field probes allows for reducing image imperfections. High F-19 concentrations together with short relaxation times are basic probe properties. We present the NMR properties of [Gd(NTf2)(4)](-) dissolved in an ionic liquid consisting of an imidazolium cation and the [NTf2](-) anion. These solutions achieve fluorine concentrations as high as 26 M and rapid relaxation times in the sub-ms time range. The second order self-exchange rate of coordinated [NTf2](-) with [NTf2](-) as determined with [Y(NTf2)(4)](-) is 4.5 X 10(5).M-1.s(-1). X-ray structure analyses confirm the coordination number of eight around Gd(3+)and Y3+. These ionic-liquid solutions are thus excellent candidates for dynamically probing the NMR fields in MRI.