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5 years ago in Analytical Chemistry , EDTA By Rohini Singh

How do lanthanides interact with EDTA?

In my separation chemistry project, I'm using EDTA to selectively complex certain lanthanides. The textbooks state they form strong complexes, but I'm struggling with the practical details like how the stability changes across the series, and what the actual coordination geometry looks like given their large ionic radii and high coordination number preferences.

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By Sonam Bhatia Answered 5 years ago

This is a classic case where theory meets practical nuance. While all lanthanides form 1:1 complexes with EDTA's hexadentate grasp, the stability constants increase markedly across the series due to the lanthanide contraction the decreasing ionic radius makes for a tighter, more electrostatic fit. In practice, I've seen that the early, larger lanthanides often achieve full coordination by also binding water molecules, leading to different kinetics. For separation, I would recommend paying close attention to the subtle differences in these stability constants and the solution pH, which controls the protonation state of EDTA and thus its effective chelating power.

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