Issue 26, 2022

Synthesis, solid-state, solution, and theoretical characterization of an “in-cage” scandium-NOTA complex

Abstract

Developing chelators that strongly and selectively bind rare-earth elements (Sc, Y, La, and lanthanides) represents a longstanding fundamental challenge in inorganic chemistry. Solving these challenges is becoming more important because of increasing use of rare-earth elements in numerous technologies, ranging from paramagnets to luminescent materials. Within this context, we interrogated the complexation chemistry of the scandium(III) (Sc3+) trication with the hexadentate 1,4,7-triazacyclononane-1,4,7-triacetic acid (H3NOTA) chelator. This H3NOTA chelator is often regarded as an underperformer for complexing Sc3+. A common assumption is that metalation does not fully encapsulate Sc3+ within the NOTA3− macrocycle, leaving Sc3+ on the periphery of the chelate and susceptible to demetalation. Herein, we developed a synthetic approach that contradicted those assumptions. We confirmed that our procedure forced Sc3+ into the NOTA3− binding pocket by using single crystal X-ray diffraction to determine the Na[Sc(NOTA)(OOCCH3)] structure. Density functional theory (DFT) and 45Sc nuclear magnetic resonance (NMR) spectroscopy showed Sc3+ encapsulation was retained when the crystals were dissolved. Solution-phase and DFT studies revealed that [Sc(NOTA)(OOCCH3)]1− could accommodate an additional H2O capping ligand. Thermodynamic properties associated with the Sc-OOCCH3 and Sc-H2O capping ligand interactions demonstrated that these capping ligands occupied critical roles in stabilizing the [Sc(NOTA)] chelation complex.

Graphical abstract: Synthesis, solid-state, solution, and theoretical characterization of an “in-cage” scandium-NOTA complex

Supplementary files

Article information

Article type
Paper
Submitted
16 Nov 2021
Accepted
19 May 2022
First published
24 Jun 2022
This article is Open Access
Creative Commons BY license

Dalton Trans., 2022,51, 9994-10005

Synthesis, solid-state, solution, and theoretical characterization of an “in-cage” scandium-NOTA complex

K. E. Aldrich, I. A. Popov, H. D. Root, E. R. Batista, S. M. Greer, S. A. Kozimor, L. M. Lilley, M. Y. Livshits, V. Mocko, M. T. Janicke, B. L. Scott, B. W. Stein and P. Yang, Dalton Trans., 2022, 51, 9994 DOI: 10.1039/D1DT03887G

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