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Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
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Light-Induced Spin Crossover in an Intermediate-Spin Penta-Coordinated Iron(III) Complex.

Sabyasachi Roy Chowdhury1, Sabyashachi Mishra1

  • 1Department of Chemistry , Indian Institute of Technology Kharagpur , Kharagpur , West Bengal 721302 , India.

The Journal of Physical Chemistry. A
|October 31, 2019
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This study investigates spin crossover in an Fe(III) complex, revealing thermal pathways at high temperatures and two light-induced mechanisms. These findings are crucial for understanding spin crossover dynamics in coordination compounds.

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Area of Science:

  • Inorganic Chemistry
  • Computational Chemistry
  • Materials Science

Background:

  • The iron(III) complex (PMe3)2FeCl3 exhibits an intermediate-spin ground state.
  • A nearby high-spin electronic state positions it as a potential spin crossover material.
  • Spin crossover (SCO) materials can switch between low-spin and high-spin states.

Purpose of the Study:

  • To elucidate the mechanisms of spin crossover in (PMe3)2FeCl3.
  • To explore both thermal and light-induced pathways for spin state transitions.
  • To investigate the potential for high-temperature thermal SCO and light-triggered SCO.

Main Methods:

  • Utilized complete active space self-consistent field (CASSCF) calculations.
  • Incorporated dynamic correlation and spin-orbit coupling.
  • Analyzed minimum energy pathways along electronic states for spin crossover dynamics.

Main Results:

  • A significant energy barrier suggests thermal spin crossover may occur at elevated temperatures.
  • Two distinct light-induced spin crossover pathways were identified.
  • Photoexcitation leads to the Q4 state, which can return to the ground state or access the S1 state via intersystem crossings and internal conversions.

Conclusions:

  • The Fe(III) complex (PMe3)2FeCl3 demonstrates potential for both thermal and light-induced spin crossover.
  • Light-induced spin crossover can proceed through distinct pathways involving excited states and intersystem crossings.
  • Understanding these mechanisms is key for designing SCO materials with tunable properties.