Rh(III) hydroxocomplexes speciation using HPLC-ESI-MS

Area of Science:

• Inorganic Chemistry
• Analytical Chemistry
• Materials Science

Background:

• Rhodium(III) hydroxocomplexes are formed during polycondensation in alkaline media.
• Characterization of these complex mixtures is crucial for understanding their properties and applications.
• Previous studies may lack detailed speciation of these oligomeric species.

Purpose of the Study:

• To fully characterize a mixture of rhodium(III) hydroxocomplexes.
• To identify and quantify the specific oligomeric species present in the mixture.
• To elucidate the formation process of these complexes in alkaline media.

Main Methods:

• Utilized hyphenated High-Performance Liquid Chromatography with Electrospray Ionization Mass Spectrometry (HPLC-ESI-MS).
• Employed Reverse Phase Ion-Pair Chromatography (RP-IP-HPLC) with gradient elution for baseline separation.
• Considered the formation of SDS associates with acetonitrile and rhodium aquahydroxocomplex oligomers.

Main Results:

• Successfully separated and identified a mixture of rhodium(III) hydroxocomplexes.
• The characterized mixture consists of specific oligomeric species: [Rh(H2O)6]3+, [Rh2(μ-OH)2(H2O)8]4+, [Rh3(μ-OH)4(H2O)10]5+, and [Rh4(μ-OH)6(H2O)12]6+.
• Demonstrated the effectiveness of RP-IP-HPLC with SDS for analyzing complex inorganic mixtures.

Conclusions:

• The polycondensation of rhodium(III) in alkaline media yields a defined set of aquahydroxocomplex oligomers.
• HPLC-ESI-MS is a powerful technique for the speciation and characterization of inorganic complex mixtures.
• The findings provide fundamental insights into the solution chemistry of rhodium(III).