Complexation of lanthanides with nitrate at variable temperatures: thermodynamics and coordination modes.
Complexation of neodymium(III) with nitrate was studied at variable temperatures (25, 40, 55, and 70 degrees C) by spectrophotometry and microcalorimetry. The NdNO(3)(2+) complex is weak and becomes slightly stronger as the temperature is increased. The enthalpy of complexation at 25 degrees C was determined by microcalorimetry to be small and positive, 1.5 +/- 0.2 kJ x mol(-1), in good agreement with the trend of the stability constant at variable temperatures. Luminescence emission spectra and the lifetime of Eu(III) in nitrate solutions suggest that inner-sphere and bidentate complexes form between trivalent lanthanides (Nd(3+) and Eu(3+)) and nitrate in aqueous solutions. A specific ion interaction approach was used to obtain the stability constants of NdNO(3)(2+) at infinite dilution and variable temperatures.
Rao
Linfeng
L
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. LRao@lbl.gov
Tian
Guoxin
G