Push and Pull Effect of Methoxy and Nitro Groups Modifies the Spin-State Switching Temperature in Fe(III) Complexes

Bijoy Dey; Sakshi Mehta; Abhishake Mondal; Jordi Cirera; Enrique Colacio; Vadapalli Chandrasekhar

doi:10.1021/acsomega.2c05380

Push and Pull Effect of Methoxy and Nitro Groups Modifies the Spin-State Switching Temperature in Fe(III) Complexes

ACS Omega. 2022 Oct 17;7(43):39268-39279. doi: 10.1021/acsomega.2c05380. eCollection 2022 Nov 1.

Authors

Bijoy Dey¹, Sakshi Mehta², Abhishake Mondal², Jordi Cirera³, Enrique Colacio⁴, Vadapalli Chandrasekhar^{1

5}

Affiliations

¹ Tata Institute of Fundamental Research Hyderabad, Gopanpally, Hyderabad500107, India.
² Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore, Karnataka560012, India.
³ Departament de Química Inorgànica i Orgànica and Institut de Recerca de Química Teòrica i Computacional, Universitat de Barcelona, Diagonal 645, 08028Barcelona, Spain.
⁴ Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, 18071Granada, Spain.
⁵ Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh208016, India.

Abstract

We have explored the impact of electron-donating (methoxy) and electron-withdrawing (nitro) substituents on SalEen ligand based spin crossover (SCO) behavior of Fe(III) complexes. Thus, 3-X-substituted SalEen ligands were employed to prepare [Fe(3-X-SalEen)₂]·NCSe, where X = OMe (1), H (2), and NO₂ (3) (3-X-SalEen is the condensation product of 3-substituted salicylaldehyde and N-ethylethylenediamine). The characteristic spin transition temperature (T _1/2) is shown to shift to a lower temperature when an electron-donating substituent (OMe) is used and to a higher temperature when an electron-withdrawing substituent (NO₂) is used. We used experimental and theoretical methods to determine the reasons for this behavior. The solid-state magnetic data revealed the transition temperatures for complexes 1, 2, and 3 to be 219, 251, and 366 K, respectively. The solution-state magnetic data also support this trend in T _1/2 values. UV-vis spectra analysis indicates that there is greater delocalization in the π-manifold of the ligand when the nitro group is the substituent. Theoretical studies through density functional theory methods suggest the methoxy substituent decreases the energy gap between the t_2g and e_g orbitals (explaining the lower T _1/2 value), while the nitro substituent increases the energy gap between the t_2g and e_g orbitals and thus increases the T _1/2 value.