# Polynuclear Complexes of Nd and Dy with N2O3 Donor Ligands: Solution Speciation and Selective Precipitation Studies

## TL;DR

This study investigates how neodymium and dysprosium form different complex structures with specific ligands, enabling partial separation of these metals in solution.

## Contribution

The research introduces new insights into the structural and solubility differences of polynuclear neodymium and dysprosium complexes for selective separation.

## Key findings

- Dy³+ complexes show varied architectures from dinuclear to hexanuclear with distinct solubility.
- H3LH achieves a high separation factor of 12.0 for neodymium over dysprosium.
- H3Lo-tBu favors dysprosium precipitation with a separation factor of 20.0.

## Abstract

This study explores the formation and selective separation
of polynuclear
neodymium and dysprosium complexes with N2O3 donor ligands derived from N,N-bis­(salicylidene)-1,3-diamino-2-propanol (H3LH). The research focuses on the structural characterization and solution
speciation of Nd3+ and Dy3+ complexes by using
ligands with different peripheral substituents: H3LH, H3Lp‑OMe, and H3Lo‑tBu. These substituents significantly influence
the nuclearity of the resulting complexes. For Dy3+, single-crystal
X-ray diffraction (SC-XRD) revealed a range of molecular architectures,
from dinuclear to hexanuclear species, each with distinct solubility
profiles, whereas for Nd3+ an heptanuclear molecular structure
with H3Lo‑tBu was obtained. Separation
experiments with Nd:Dy ratios of 1:1 and 4:1 demonstrated the ability
of the ligands to give a partial selective precipitation of Nd3+ and Dy3+ complexes, depending on both metal identity
and ligand structure. In particular, H3LH achieved
a separation factor (S
Nd/Dy) of 12.0 (±2.0),
concentrating Nd3+ in the solid phase. In contrast, H3Lo‑tBu favored Dy precipitation, yielding
a separation factor of 20.0 (±4) after just 10 min. In various
instances, the low separation factor values were ascribed to the formation
of mixed-metal polynuclear species, which was confirmed through Electrospray
Ionization Mass Spectrometry (ESI-MS) and by the structural characterization
of a heteronuclear complex with H3Lo‑tBu.