Lattice solvent- and substituent-dependent spin-crossover in isomeric iron(ii) complexes
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Date
2024-07-02
Authors
Senthil Kumar, Kuppusamy
Mizuno, Asato
Kämmerer, Lea
Salamon, Soma
Heinrich, Benoît
Bailly, Corinne
Šalitroš, Ivan
Wende, Heiko
Ruben, Mario
ORCID
0000-0003-3856-0399Advisor
Referee
Mark
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Volume Title
Publisher
Royal Society of Chemistry
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Abstract
Spin-state switching in iron(ii) complexes composed of ligands featuring moderate ligand-field strength-for example, 2,6-bi(1H-pyrazol-1-yl)pyridine (BPP)-is dependent on many factors. Herein, we show that spin-state switching in isomeric iron(ii) complexes composed of BPP-based ligands-ethyl 2,6-bis(1H-pyrazol-1-yl)isonicotinate (BPP-COOEt, L1) and (2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)methylacetate (BPP-CH2OCOMe, L2)-is dependent on the nature of the substituent at the BPP skeleton. Bi-stable spin-state switching-with a thermal hysteresis width (Delta T-1/2) of 44 K and switching temperature (T-1/2) = 298 K in the first cycle-is observed for complex 1<middle dot>CH3CN composed of L1 and BF4- counter anions. Conversely, the solvent-free isomeric counterpart of 1<middle dot>CH3CN-complex 2a, composed of L2 and BF4- counter anions-was trapped in the high-spin (HS) state. For one of the polymorphs of complex 2b<middle dot>CH3CN-2b<middle dot>CH3CN-Y, Y denotes yellow colour of the crystals-composed of L2 and ClO4- counter anions, a gradual and non-hysteretic SCO is observed with T-1/2 = 234 K. Complexes 1<middle dot>CH3CN and 2b<middle dot>CH3CN-Y also underwent light-induced spin-state switching at 5 K due to the light-induced excited spin-state trapping (LIESST) effect. Structures of the low-spin (LS) and HS forms of complex 1<middle dot>CH3CN revealed that spin-state switching goes hand-in-hand with pronounced distortion of the trans-N{pyridyl}-Fe-N{pyridyl} angle (phi), whereas such distortion is not observed for 2b<middle dot>CH3CN-Y. This observation points that distortion is one of the factors making the spin-state switching of 1<middle dot>CH3CN hysteretic in the solid state. The observation of bi-stable spin-state switching with T-1/2 centred at room temperature for 1<middle dot>CH3CN indicates that technologically relevant spin-state switching profiles based on mononuclear iron(ii) complexes can be obtained.
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Citation
Dalton Transactions. 2024, vol. 53, issue 26, p. 1-16.
https://pubs.rsc.org/en/content/articlelanding/2024/dt/d4dt00429a
https://pubs.rsc.org/en/content/articlelanding/2024/dt/d4dt00429a
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Peer-reviewed
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en