Precise modulation of spin-orbit coupling at a transition metal center would impact physical properties ranging from photoluminescence to its magnetic properties. One approach to increase spin-orbit coupling in paramagnetic complexes utilizes heavy diamagnetic main group elements as sources of magnetic anisotropy. Engendering metal-metal interactions between first row transition metals and main group elements enables the transfer of magnetic anisotropy to the paramagnetic transition metal center, providing a modular source of spin-orbit coupling. We sought to study the impact of covalency on magnetic anisotropy by probing the effect of halides as compared to electropositive main group elements. Towards this end, we synthesized a series of isostructural heterobimetallic complexes, with divalent germanium or tin covalently bound to an Fe(II) center. These complexes are ligated by a halide (Br− or I−) in the apical position to yield a series of four complexes with variation in the mass of both the main group element and halide. This series enables us to interrogate which electronic structure factors influence the heavy atom effect. Using a suite of approaches including magnetometry, computation, and Mössbauer spectroscopy we interrogated the electronic structure and the spin-orbit coupling, as parameterized by the axial zero-field splitting parameter (D) throughout the series of complexes. We find an increase in D from −11.8 cm−1 to −17.9 cm−1 by increasing the axial ligand mass. Through direct comparison between halides and group 14 elements, we observe a greater impact on magnetic anisotropy from the halide interaction relative to the main group element. We attribute this counterintuitive effect to a larger spin population on the halide elements, despite greater covalency in the group 14 interactions. These results recommend modification of the intuitive design principle of increasing covalency towards a deeper focus on the interactions of the spin bearing orbitals.

Magnetic anisotropy from main group elements: Halide versus group 14 elements

254th National Meeting (2017)

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