Solution-phase and DFT studies revealed that 1− could accommodate an additional H 2O capping ligand. Density functional theory (DFT) and 45Sc nuclear magnetic resonance (NMR) spectroscopy showed Sc 3+ encapsulation was retained when the crystals were dissolved. We confirmed that our procedure forced Sc 3+ into the NOTA 3− binding pocket by using single crystal X-ray diffraction to determine the Na structure.
Herein, we developed a synthetic approach that contradicted those assumptions. A common assumption is that metalation does not fully encapsulate Sc 3+ within the NOTA 3− macrocycle, leaving Sc 3+ on the periphery of the chelate and susceptible to demetalation. This H 3NOTA chelator is often regarded as an underperformer for complexing Sc 3+. Within this context, we interrogated the complexation chemistry of the scandium( III) (Sc 3+) trication with the hexadentate 1,4,7-triazacyclononane-1,4,7-triacetic acid (H 3NOTA) chelator. Solving these challenges is becoming more important because of increasing use of rare-earth elements in numerous technologies, ranging from paramagnets to luminescent materials. Developing chelators that strongly and selectively bind rare-earth elements (Sc, Y, La, and lanthanides) represents a longstanding fundamental challenge in inorganic chemistry.
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