Oxygen-17 NMR Study of the Uranyl Ion. IV. 17O Nuclear Magnetic Relaxation and Chemical Shifts of Uranyl Oxygen Atoms and Coordinated Water

Abstract 17O nuclear magnetic relaxation times and chemical shifts of uranyl oxygen atoms (hereafter uranyl oxygens) and solvent water have been measured with changing concentration of the uranyl ion in aqueous solution. The 17O resonance of the water molecule in the first-coordination sphere is determined to be at 90.1±1.2 ppm relative to free water at 25 °C. The effective correlation time for the 17O quadrupolar relaxation of the coordinated water, which corresponds to the reorientation time for the hydrated uranyl ion, is about 8.7 times that of free water. The 17O spin-lattice relaxation times (T1) of uranyl oxygens have been measured at 25 °C. From the 17O T1 values the 17O nuclear quadrupole coupling constant of uranyl oxygens has been estimated to be 0.44 MHz. This small value implies the high symmetry of electron distribution around uranyl oxygens.