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Compressed and Expanded Lattices - Barriers to Spin-State Switching in Mn3+ Complexes
Michelle M Harris1, Irina A Kühne1,2, Conor T Kelly1
1School of Chemistry, University College Dublin, Belfield, Dublin, D04 V1W8, Ireland.
Crystal Growth & Design
|June 12, 2023
Summary
We explored how chemical modifications to manganese complexes affect their spin states. Different substituents on ligands influenced whether the manganese ions remained in a low-spin or high-spin state, impacting their magnetic properties.
Area of Science:
- Coordination Chemistry
- Materials Science
- Magnetism
Background:
- Spin crossover (SCO) complexes exhibit distinct magnetic properties based on their spin state (e.g., spin triplet, spin quintet).
- The [Mn(R-sal2323)]+ series provides a platform for studying SCO phenomena in manganese complexes.
- Tuning ligand substituents is a key strategy to control the spin state and SCO behavior of metal complexes.
Purpose of the Study:
- To synthesize and characterize new Mn3+ complex cations within the [Mn(R-sal2323)]+ family.
- To investigate the impact of electron-donating and electron-withdrawing groups on the phenolate donors of the ligand on the Mn3+ spin state.
- To correlate structural and magnetic properties with ligand substitution patterns and their effect on spin crossover behavior.
Main Methods:
- Synthesis of two new hexadentate Schiff base ligands (L1 and L2) with varied phenolate substituents (3-nitro-5-methoxy and 3-methoxy-5-nitro).
- Complexation of Mn3+ with these ligands to form [MnL1]+ and [MnL2]+ complex cations.
- Structural characterization (e.g., X-ray diffraction) and magnetic property measurements (e.g., temperature-dependent magnetic susceptibility) of the resulting 14 new compounds with different counterions.
Main Results:
- Complexes with 3-nitro-5-methoxy-phenolate donors ([MnL1]+, compounds 1a-7a) predominantly adopted the spin triplet (low-spin) state at room temperature.
- Complexes with the 3-methoxy-5-nitro-phenolate ligand isomer ([MnL2]+, compounds 1b-7b) exhibited spin triplet, spin quintet (high-spin), and thermal spin crossover behavior.
- Structural data revealed trends related to bond lengths and angular distortion, suggesting a potential barrier to switching for high-spin states in certain complexes.
Conclusions:
- Ligand design, specifically the electronic nature and isomeric arrangement of phenolate substituents, significantly influences the spin state and SCO behavior of Mn3+ complexes.
- Geometric and steric factors play a crucial role in determining the observed magnetic properties.
- The study provides insights into the factors governing spin state transitions in Mn3+ SCO systems, with potential implications for designing new magnetic materials.
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