Accurate Prediction of Mössbauer Hyperfine Parameters in Bis-Axially Coordinated Iron(II) Phthalocyanines Using Density Functional Theory Calculations: A Story of a Single Orbital Revealed by Natural Bond Orbital Analysis

Victor N Nemykin; Dustin E Nevonen; Laura S Ferch; Michael Shepit; David E Herbert; Johan van Lierop

doi:10.1021/acs.inorgchem.0c03373

Accurate Prediction of Mössbauer Hyperfine Parameters in Bis-Axially Coordinated Iron(II) Phthalocyanines Using Density Functional Theory Calculations: A Story of a Single Orbital Revealed by Natural Bond Orbital Analysis

Inorg Chem. 2021 Mar 15;60(6):3690-3706. doi: 10.1021/acs.inorgchem.0c03373. Epub 2021 Mar 2.

Authors

Victor N Nemykin^{1

2}, Dustin E Nevonen¹, Laura S Ferch¹, Michael Shepit³, David E Herbert¹, Johan van Lierop³

Affiliations

¹ Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
² Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
³ Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.

PMID: 33651595
DOI: 10.1021/acs.inorgchem.0c03373

Abstract

Density Functional Theory (DFT) calculations coupled with several exchange-correlation functionals were used for the prediction of Mössbauer hyperfine parameters of 36 bis-axially coordinated iron(II) phthalocyanine complexes with the general formulas PcFeL₂, PcFeL'L″, and [PcFeX₂]^2-, including four new compounds. Both gas-phase and PCM calculations using BPW91 and MN12L exchange-correlation functionals were found to accurately predict both Mössbauer quadrupole splittings and the correct trends in experimentally observed isomer shifts. In comparison, hybrid exchange-correlation functionals underestimated quadrupole splittings, while still accurately predicted isomer shifts. Out of ∼40 exchange-correlation functionals tested, only MN12L was found to correctly reproduce quadrupole splitting trends in the PcFeL₂ complexes coordinated with phosphorus-donor axial ligands (i.e., P(OnBu)₃ ≈ P(OEt)₃ < PMe₃ < P[(CH₂O)₂CH₂]-p-C₆H₄NO₂ < PEt₃ ≈ PnBu₃). Natural Bond Orbital (NBO) analysis was successfully used to explain the general trends in the observed quadrupole splitting for all compounds of interest. In particular, the general trends in the quadrupole splitting correlate well with the axial ligand dependent, NBO-predicted population of the 3d_z2 orbital of the Fe ion and are reflective of the hypothesis proposed by Ohya and co-workers ( Inorg. Chem., 1984, 23, 1303) on the adaptability of the phthalocyanine's π-system toward Fe-L_ax interactions. The first X-ray crystal structure of a PcFeL₂ complex with axial phosphine ligands is also reported.