Solvent Exchange and Electron-Spin Relaxation on Homoleptic Acetonitrile Complexes of Trivalent Lanthanides

Homoleptic acetonitrile complexes [Nd(CH3CN)(9)]Al(OC(CF3)(3))(4), [Dy(CH3CN)(9)]Al(OC(CF3)(3))(4), and [Tm(CH3CN)(8)]Al(OC(CF3)(3))(4) have been studied in anhydrous acetonitrile by 14N and 1H NMR relaxation. Solvent-exchange rate constants increase from (22 +/- 6) x 106 s(1) (Nd3+) and (160 +/- 40) x 106 s(1) (Dy3+) for the nonasolvated ions to (360 +/- 40) x 106 s(1) (Tm3+) for the octasolvated ions. Electron-spin relaxation of the lanthanide ions studied is similar to that found in aqua ions. This dependence on the binding properties of the coordinating molecules is consistent with the model proposed by Fries et al. for fast electron-spin relaxation of lanthanide ions other than Gd3+.