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Homochiral Mn3+ Spin-Crossover Complexes: A Structural and Spectroscopic Study.
Irina A Kühne1,2, Andrew Ozarowski3, Aizuddin Sultan1
1School of Chemistry, University College Dublin (UCD), Belfield, Dublin 4, Ireland.
Inorganic Chemistry
|February 17, 2022
Summary
This study reports on a manganese spin-crossover complex with a Schiff base ligand, showing varied spin states and crossovers depending on the counteranion. The ligand appears to direct homochiral crystallization.
Area of Science:
- Coordination Chemistry
- Materials Science
- Spectroscopy
Background:
- Manganese complexes with Schiff base ligands are of interest for their magnetic properties.
- Spin-crossover phenomena in metal complexes can be influenced by crystal lattice environments and counterions.
Purpose of the Study:
- To investigate the structural, magnetic, and spectroscopic properties of a Mn(III) spin-crossover complex with a Schiff base ligand (4-OMe-Sal2323).
- To explore the effect of different counteranions on the spin state and crystallization behavior of the complex.
Main Methods:
- X-ray crystallography to determine structural and crystallographic properties.
- Variable-temperature magnetic susceptibility measurements to assess spin state transitions.
- High-field electron paramagnetic resonance (EPR) spectroscopy to determine zero-field splitting parameters.
- UV-Vis absorption and circular dichroism (CD) spectroscopy for electronic and chiral analysis.
Main Results:
- Five isotypic Mn(III) complexes with varying counteranions (ClO4-, BF4-, NO3-, Br-, I-) were synthesized and characterized.
- Complexes exhibited diverse spin state behaviors, including high-spin states, gradual spin crossover, and stepped spin crossovers.
- Zero-field splitting parameters for spin triplet and quintet states were determined using high-field EPR.
- Solid-state CD spectra revealed a 2:1 ratio of enantiomers in a chiral conglomerate, indicating ligand-directed homochiral crystallization.
Conclusions:
- The counteranion significantly influences the spin state preferences and crossover behavior of the [Mn(4-OMe-Sal2323)]+ complex.
- The Schiff base ligand (4-OMe-Sal2323) appears to play a crucial role in directing homochiral crystallization, even with achiral counterions.
- The observed properties highlight the tunability of spin-crossover complexes through counteranion and ligand design.
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