Tetrazine bridging ligand in spin-only magnetic coupling in complex dimers

Abstract

This study focuses on examining the unconventional magnetic coupling between two metal centers in dimers bridged by a tetrazine ring. Computational analysis was conducted to understand the impact of radical perturbation in the bridging ligand on the magnetic properties of previously synthesized three compound of nickel (Ni) dimers. To achieve this, broken-symmetry density functional theory (BS-DFT) functionals were applied to explore the magnetic interactions in greater depth. This approach provided an accurate quantitative representation of the coupling nature between the metal centers. To investigate the effect of the radical, the dimers were analyzed in two different oxidation states of the bridging tetrazine: the neutral state and the radical state were selected to explore the effectiveness of incorporating radical bridges into the architecture of single-molecule magnets. Initially, these complexes were studied in their neutral forms, prior to one-electron reduction. Magnetic coupling between the two nickel centers revealed antiferromagnetic interactions across all three models (Noodleman, Bencini, and Yamaguchi), as determined using broken-symmetry density functional theory (BS-DFT) calculations. However, the addition of one electron to the bridging ligands induced a notable shift in the magnetic behavior. The magnetic moment curves indicated a preference for ferromagnetic coupling upon cooling, consistent with experimental observations. A series of DFT calculations was conducted to further investigate the influence of Hartree–Fock exchange (HF%) in hybrid functionals. The study highlights the critical importance of functional dependency in interpreting magnetic coupling and emphasizes the need for careful selection of functionals before drawing definitive conclusions.