Spectroscopy as a tool to detect multinuclear Cu(ii)-triethanolamine complexes in aqueous solution

Area of Science:

• Materials Science
• Inorganic Chemistry
• Solution Chemistry

Background:

• Copper(II)-triethanolamine (TEA) complexes are vital in aqueous precursor solutions for copper-based catalysts and metal oxides.
• The multinuclear nature of these complexes in solution remains an unresolved question.

Purpose of the Study:

• To definitively prove the existence of multinuclear copper(II)-TEA complexes in aqueous solutions.
• To investigate the influence of pH on complex formation and structure.
• To provide insights for designing stable copper triethanolamine-based precursor solutions.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy combined with the Evans method to detect and monitor multimer formation.
• Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to probe Cu-Cu interactions.
• Nuclear Magnetic Resonance Dispersion (NMRD) measurements for additional structural insights.

Main Results:

• Multimer formation of Cu(II)-TEA complexes was confirmed in aqueous solutions at pH 4 and above.
• NMR spectroscopy allowed precise monitoring of complex formation as pH increased.
• EXAFS spectroscopy revealed a Cu-Cu interaction at pH 9.5, absent in acidic conditions (pH 2).
• NMRD measurements provided further structural details on the multinuclear complexes.

Conclusions:

• The study unequivocally demonstrates the existence of multinuclear Cu(II)-TEA complexes in solution.
• pH is a critical factor influencing the speciation and structure of these complexes.
• Understanding these complexes is essential for developing accurate speciation models and improving precursor solution stability.