Tracking Structural and Electron Spin Density Changes in a Cooperative Mn³⁺ Spin Crossover Complex at Atomic Scale...

Area of Science:

• Solid-state NMR spectroscopy
• Quantum chemistry
• Materials science

Background:

• Electron spin-state changes in transition-metal complexes are crucial for biochemistry and molecular spin-control.
• Paramagnetic NMR provides atomic-scale insights but faces limitations in solution-state measurements.
• These limitations include solvent effects, lattice cooperativity, and inaccessibility at cryogenic temperatures.

Purpose of the Study:

• To overcome the limitations of traditional solution-state NMR for studying spin-crossover (SCO) phenomena.
• To develop and apply a high-resolution cryogenic magic-angle spinning (MAS) NMR approach for SCO complexes.
• To probe SCO transitions at the atomic level in solids at low temperatures.

Main Methods:

• High-resolution 13C and 1H magic-angle spinning (MAS) NMR spectroscopy at cryogenic temperatures (130 K).
• Advanced quantum chemical calculations to determine NMR and EPR parameters.
• Monitoring selected 1H resonances across the SCO transition to determine the order parameter.

Main Results:

• Successful acquisition of high-resolution cryogenic MAS NMR spectra for a mononuclear spin-crossover (SCO) Mn(III) complex.
• Assignment and rationalization of paramagnetic shifts using quantum chemical calculations.
• Observation of hysteresis behavior in the order parameter, consistent with magnetic susceptibility measurements.

Conclusions:

• Cryogenic magic-angle spinning NMR is a powerful technique for studying SCO in solids at low temperatures.
• The combination of NMR and quantum chemical calculations provides atomic-level understanding of SCO mechanisms.
• This approach overcomes previous limitations, enabling detailed investigation of spin-state dynamics.