Observation of a promethium complex in solution.

Area of Science:

• Inorganic Chemistry
• Radiochemistry
• Physical Chemistry

Background:

• Lanthanide rare-earth elements are crucial in technology, yet promethium (Pm) chemistry remains largely unknown due to its radioactivity and inaccessibility.
• Understanding Pm is vital for comprehending the lanthanide contraction, a fundamental periodic table trend.
• Previous experimental studies of lanthanides have lacked Pm, hindering a complete picture.

Purpose of the Study:

• To synthesize a stable complex of the radioactive 147Pm radionuclide in aqueous solution.
• To elucidate the coordination structure and bonding of promethium within this complex.
• To enable a comprehensive experimental investigation of the lanthanide contraction phenomenon.

Main Methods:

• Synthesis of a novel organic diglycolamide ligand for stable chelation.
• Characterization of the homoleptic Pm(III) complex using synchrotron X-ray absorption spectroscopy.
• Utilizing quantum chemical calculations to determine coordination structure and bond distances.

Main Results:

• Successful stable chelation of 147Pm (half-life 2.62 years) in aqueous solution was achieved.
• The coordination structure and bond distance of promethium were established.
• Experimental data allowed for the capture of the lanthanide contraction in solution for a full set of isostructural lanthanide complexes.
• Accelerated bond shortening was observed at the beginning of the lanthanide series.

Conclusions:

• The study provides fundamental insights into the chemistry of radioactive promethium.
• It enables a complete experimental understanding of the lanthanide contraction phenomenon.
• The findings enhance knowledge of intra-lanthanide behavior and f-block element chemistry and separation.