Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex.

Daniel Aravena,Diego Venegas-Yazigi,Eliseo Ruiz

doi:10.1038/srep23847

Daniel Aravena, Diego Venegas-Yazigi + Show 1 more

Open Access

https://doi.org/10.1038/srep23847

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Abstract

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin FeIII ferromagnetically coupled and 24 diamagnetic low-spin FeII ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic FeII cations. Calculations were performed using either small Fe4 or Fe3 models or the whole Fe42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic FeIII centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties.

Highlights

IntroductionThis Mn19 system prevailed during years as the highest-spin reported molecule until the publication in 2015 by Kang and coworkers of an Fe42 complex with twenty-four diamagnetic FeII cations and eighteen FeIII centres ferromagnetically coupled, resulting in a S value of 45 (90/2)[18]
The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism
The Fe42 complex, [{Fe(Tp)(CN)3}24{Fe(H2O)2}6{Fe(dpp)(H2O)}12·6CF3SO3]·18H2O (where dpp = 1,3-di (4-pyridyl)propane, and Tp = hydrotris(pyrazolyl)borate), with the reported value of S = 45 has a singular structure[18], where the cyanide bridging ligands have FeII-CN-FeIII coordination and all the FeII cations coordinated to the bridging ligand through the C atom, the nitrogen atom is always attached to the FeIII centres

Summary

Introduction

This Mn19 system prevailed during years as the highest-spin reported molecule until the publication in 2015 by Kang and coworkers of an Fe42 complex with twenty-four diamagnetic FeII cations and eighteen FeIII centres ferromagnetically coupled, resulting in a S value of 45 (90/2)[18] Our findings indicated that the two-types of exchange interactions present in the system are ferromagnetic and such values theoretically corroborate the S = 45 total spin experimentally reported This agreement is relevant because of the difficult task of correctly asses magnetic characterizations of high spin molecules with theoretical methods have been a crucial tool to support experimental results

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