Room-Temperature Spin Crossover in a Solution of Iron(II) Complexes with N, N'-Disubstituted Bis(pyrazol-3-yl)pyridines

Dmitry Yu Aleshin; Igor Nikovskiy; Valentin V Novikov; Alexander V Polezhaev; Elizaveta K Melnikova; Yulia V Nelyubina

doi:10.1021/acsomega.1c05463

Room-Temperature Spin Crossover in a Solution of Iron(II) Complexes with N, N'-Disubstituted Bis(pyrazol-3-yl)pyridines

ACS Omega. 2021 Nov 22;6(48):33111-33121. doi: 10.1021/acsomega.1c05463. eCollection 2021 Dec 7.

Authors

Dmitry Yu Aleshin¹, Igor Nikovskiy^{1

2}, Valentin V Novikov^{1

3}, Alexander V Polezhaev^{1

2}, Elizaveta K Melnikova^{1

4}, Yulia V Nelyubina^{1

2

3}

Affiliations

¹ A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova Str., 28, 119991 Moscow, Russia.
² Bauman Moscow State Technical University, 2nd Baumanskaya Str., 5, 105005 Moscow, Russia.
³ Moscow Institute of Physics and Technology, Institutskiy per., 9, 141700 Dolgoprudny, Russia.
⁴ Lomonosov Moscow State University, Leninskiye Gory, 1-3, 119991 Moscow, Russia.

Abstract

Here, we report a combined study of the effects of two chemical modifications to an N,N'-disubstituted bis(pyrazol-3-yl)pyridine (3-bpp) and of different solvents on the spin-crossover (SCO) behavior in otherwise high-spin iron(II) complexes by solution NMR spectroscopy. The observed stabilization of the low-spin state by electron-withdrawing substituents in the two positions of the ligand that induce opposite electronic effects in SCO-active iron(II) complexes of isomeric bis(pyrazol-1-yl)pyridines (1-bpp) was previously hidden by NH functionalities in 3-bpp precluding the molecular design of SCO compounds with this family of ligands. With the recent SCO-assisting substituent design, the uncovered trends converged toward the first iron(II) complex of N,N'-disubstituted 3-bpp to undergo an almost complete SCO centered at room temperature in a less polar solvent of a high hydrogen-bond acceptor ability.