Complexation of lanthanides with nitrate at variable temperatures: thermodynamics and coordination modes

Area of Science:

• Inorganic Chemistry
• Solution Chemistry
• Thermodynamics

Background:

• Understanding metal-ion complexation is crucial in various chemical and environmental processes.
• Neodymium(III) and other lanthanides are important in nuclear waste management and catalysis.
• Nitrate is a common ligand in aqueous solutions, influencing metal ion speciation.

Purpose of the Study:

• To investigate the complexation of neodymium(III) with nitrate ions.
• To determine the thermodynamic parameters of this complexation reaction.
• To explore the structural aspects of lanthanide-nitrate complexes in aqueous solutions.

Main Methods:

• Spectrophotometry was employed to study complex formation.
• Microcalorimetry was used to measure the enthalpy of complexation.
• Luminescence spectroscopy of Europium(III) provided insights into complex structure.
• A specific ion interaction model was applied to determine stability constants.

Main Results:

• The neodymium(III)-nitrate complex (NdNO3(2+)) is weak and its stability increases with temperature.
• The enthalpy of complexation at 25°C is small and positive (1.5 ± 0.2 kJ·mol⁻¹).
• Evidence suggests the formation of inner-sphere, bidentate complexes for neodymium(III) and europium(III) with nitrate.

Conclusions:

• The thermodynamic data aligns with the observed trend of increasing stability constants with temperature.
• The findings indicate specific coordination modes for trivalent lanthanides with nitrate in aqueous media.
• This research contributes to the understanding of lanthanide speciation in nitrate-containing solutions.