# Sc(III) Complexes of 1,4,7-Triazacyclononane-1,4,7-triacetic Acid and Its Monoamides

## TL;DR

This paper studies scandium complexes with specific ligands, revealing their stability and structural features in different states.

## Contribution

The study provides new insights into the coordination chemistry of Sc(III) with triazacyclononane derivatives and their monoamides.

## Key findings

- Sc(III) complexes with H3nota and its monoamides show high stability in solution.
- Ternary complexes with oxalate form isomers differing in oxalate position.
- Sc(III) ions are octacoordinated with a specific coordination mode in all complexes.

## Abstract

Scandium­(III) complexes with H3nota and its N-ethyl (H2
L
1) and N,N-diethyl (H2
L
2) monoamides
were studied in the solid state and solution. Potentiometric measurements
showed high stabilities of the binary ScIII complexes with
the ligands (log K
[Sc(L)] = 19.50, 16.64,
and 17.94 for H3nota, H2
L
1 and H2
L,2 respectively) and weak
coordination of the second ligand molecule under the ligand excess.
The chemical model was confirmed by 45Sc NMR. Multinuclear
NMR spectroscopy was used to study the ternary ScIII-ligand-oxalate
systems. The results showed the presence of species with 2:1 and 1:1
[Sc­(L)]-to-oxalate stoichiometry. Ternary complexes with the nota-monoamides
form two isomers differing in the position of oxalate versus amide
pendant arm. In the solid state, the [Sc­(L)] complexes form oligomers
interconnected through ligand carboxylate groups. Crystallization
from solutions containing H2O2 or oxalate anions
yielded ternary complexes. In all binary and ternary complexes, the
ScIII ion is octacoordinated with the N3O4O1 coordination mode. All of the carboxylate groups
of the ligands are coordinated in the O4-plane. The apical
position is occupied by an oxygen atom of water, peroxide, or carboxylate
anion. The apical Sc–O bonds are usually longer compared to
those of the oxygen atoms forming the O4-plane.