# Exploratory Synthetic Studies of the Praseodymium/Di-2-Pyridyl Ketoxime System Leads to Unusual Reactivity and Interesting New Molecules

## TL;DR

This study explores new chemical reactions involving praseodymium and a specific ligand, leading to the formation of unusual and complex molecules.

## Contribution

The paper reports the discovery of a novel PrIII-assisted ligand transformation and the synthesis of unique lanthanide complexes.

## Key findings

- The reaction system yielded complexes with unique structures, including dinuclear and tetranuclear species.
- A PrIV center was identified in a highly symmetrical cluster with specific bridging ligands and magnetic properties.
- EPR spectroscopy confirmed the presence of a half-integer spin in the PrIV center of the cluster.

## Abstract

Reactions of lanthanoid­(III) ions with di-2-pyridyl ketoxime,
dpkoxH,
have been studied. Full synthetic investigation of the Pr­(NO3)3·6H2O/dpkoxH reaction system has provided
access to complexes [Pr2
III(NO3)4(L)2] (isolated as MeCN and MeNO2 solvates; 1 and 2), [Pr4
III(OH)2(NO3)4(dpkox)6(EtOH)2] (3) and [Pr8
IIIPrIVO4(OH)4(NO3)4(dpkox)12(H2O)4] (4). A novel PrIII-assisted/promoted ligand transformation
has occurred in the dinuclear complexes, where L– is the anion of di­(pyridin-2-yl)­methanone O-(1-hydroxy-1,1-di­(pyridin-2-yl))
methyl oxime (HL). Mechanistic schemes have been proposed. In 1 and 2, the two PrIII centers are
bridged by two deprotonated oxygen atoms of two “head-to-head”
2.2011110 (Harris notation) L– ligands. The tetranuclear
molecule 3 is held together by two μ3-hydroxido groups, two 2.2110, two 2.1110 and two 3.2110 dpkox– ligands. The {Pr4
III(μ3–OH)2}10+ unit of the {Pr4
III(μ3–OH)2(μ2-oximato)4}6+ core comprises four coplanar
PrIII ions in a “butterfly”-type disposition.
In the highly symmetrical cluster 4, the nine Pr ions
are held together by four μ3-O2– and four μ3–OH– groups,
as well as four 2.1110, four 3.2111 and four 2.2110 dpkox– ligands. The inorganic {Pr8
IIIPrIV(μ3-O)4(μ3–OH)4}16+ unit of the core can be described as four
fused “butterflies”, the PrIV center being
the common site at one of their “body” positions. The
X-band (∼9.5 GHz) EPR spectrum of 4 at 4.2 K shows
a sharp peak at 630 G, a derivative feature at 1340 G, and a multitude
of weaker signals; the data are compatible with the presence of the
half-integer spin expected for the 4f1 PrIV center.