University of Oulu

Phys. Chem. Chem. Phys., 2023,25, 3121-3135,

Computational NMR of the iron pyrazolylborate complexes [Tp₂Fe]⁺ and Tp₂Fe including solvation and spin-crossover effects

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Author: Pyykkönen, Ari1; Vaara, Juha1
Organizations: 1NMR Research Unit, University of Oulu, P.O. Box 3000, Oulu FIN-90014, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.2 MB)
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Language: English
Published: Royal Society of Chemistry, 2022
Publish Date: 2023-08-17


Transition metal complexes have important roles in many biological processes as well as applications in fields such as pharmacy, chemistry and materials science. Paramagnetic nuclear magnetic resonance (pNMR) is a valuable tool in understanding such molecules, and theoretical computations are often advantageous or even necessary in the assignment of experimental pNMR signals. We have employed density functional theory (DFT) and the domain-based local pair natural orbital coupled-cluster method with single and double excitations (DLPNO-CCSD), as well as a number of model improvements, to determine the critical hyperfine part of the chemical shifts of the iron pyrazolylborate complexes [Tp₂Fe]⁺ and Tp₂Fe using a modern version of the Kurland–McGarvey theory, which is based on parameterising the hyperfine, electronic Zeeman and zero-field splitting interactions via the parameters of the electron paramagnetic resonance Hamiltonian. In the doublet [Tp₂Fe]⁺ system, the calculations suggest a re-assignment of the ¹³C signal shifts. Consideration of solvent via the conductor-like polarisable continuum model (C-PCM) versus explicit solvent molecules reveals C-PCM alone to be insufficient in capturing the most important solvation effects. Tp₂Fe exhibits a spin-crossover effect between a high-spin quintet (S = 2) and a low-spin singlet (S = 0) state, and its recorded temperature dependence can only be reproduced theoretically by accounting for the thermal Boltzmann distribution of the open-shell excited state and the closed-shell ground-state occupations. In these two cases, DLPNO-CCSD is found, in calculating the hyperfine couplings, to be a viable alternative to DFT, the demonstrated shortcomings of which have been a significant issue in the development of computational pNMR.

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Series: PCCP. Physical chemistry chemical physics
ISSN: 1463-9076
ISSN-E: 1463-9084
ISSN-L: 1463-9076
Volume: 25
Issue: 4
Pages: 3121 - 3135
DOI: 10.1039/d2cp03721a
Type of Publication: A1 Journal article – refereed
Field of Science: 114 Physical sciences
Funding: This work was funded by the Academy of Finland (project no. 331008), the University of Oulu (Kvantum Institute) and the Finnish Cultural Foundation. Computational resources were provided by the CSC – IT Center for Science (Espoo, Finland) and the Finnish Grid and Cloud Infrastructure project (persistent identifier urn:nbn:fi:research-infras-2016072533).
Academy of Finland Grant Number: 331008
Detailed Information: 331008 (Academy of Finland Funding decision)
Copyright information: This journal is © the Owner Societies 2023. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.