An Experimental and Theoretical Investigation on Pentacoordinated Cobalt(III) Complexes with an Intermediate S=1 Spin State: How Halide Ligands Affect their Magnetic Anisotropy

Abstract

What is the most significant result of this study? We report on the experimental and theoretical investigation of the magnetic behavior for as eries of Co III complexes displaying an intermediate S = 1s pin state. The magnetic anisotropy of these complexes , the zero-field splitting parameter (D), shows ad ependence on the nature of the halide:t he largest D value was obtained for the chloride compound and the smallest for the iodide one. Examples of such reported behavior are still very limited and in most of studies, it was observed that the D value increases from the chloride to the iodide metal complexes. By using quantum chemical methods (DFT and CASSCF calculations), we were able to predict and rationalize both the sign and magnitude of D for the three complexes. The DFT method appears as the most appropriate method if one wants to obtain structure-property relationships. No general rule can be extrapolated from the present study and magneto-structural correlations can only be defined though benchmark studies using ac ombination of experimental and theoretical approaches.

Experimental and Theoretical Identification of the Origin of Magnetic Anisotropy in Intermediate Spin Iron(III) Complexes

“…The origin of the magnetic anisotropy, and even the trend in values, differs from our earlier studies on the same ligand system with Co III ( S= 1),10e and different complexes with S= 3/2 (Mn IV ),13c which is a clear indication that any change induces different magnetic behavior depending on the spin system and analogies cannot be drawn a priori with systems that are yet to be investigated. Understanding of these effects and the potential for DFT methods to predict them, opens new opportunities in the rational design of magnetic materials with desired properties.…”

“…In summary, the present combined experimental and theoretical approach enables the rationalization of experimental data leading to a more complete understanding of the electronic structure of such systems and of the factors that govern the contribution of the different excited spin states in the magnetic anisotropy of intermediate spin state Fe III complexes. The origin of the magnetic anisotropy, and even the trend in values, differs from our earlier studies on the same ligand system with Co III ( S= 1), and different complexes with S= 3/2 (Mn IV ), which is a clear indication that any change induces different magnetic behavior depending on the spin system and analogies cannot be drawn a priori with systems that are yet to be investigated. Understanding of these effects and the potential for DFT methods to predict them, opens new opportunities in the rational design of magnetic materials with desired properties.…”

Tuning electronic structure through halide modulation of mesoionic carbene cobalt complexes

“…The two components contributing to ZFS are the minor direct spin-spin interactions and the dominant second-order spin-orbit coupling (SOC) introduced by mixing of ground and excited states. 37 Computational 31,38 and experimental [39][40][41][42][43] works have shown how anisotropy can be influenced via heavy atom coordination with further corroboration for ligand influence on ZFS in tetrahedral Co halide complexes emerging over the past five years. 14,[40][41][42][43][44][45] Complexes 1-3 show a clear trend in their |D| values consistent with the expected electronic-structure effect.…”

“…37 Computational 31,38 and experimental [39][40][41][42][43] works have shown how anisotropy can be influenced via heavy atom coordination with further corroboration for ligand influence on ZFS in tetrahedral Co halide complexes emerging over the past five years. 14,[40][41][42][43][44][45] Complexes 1-3 show a clear trend in their |D| values consistent with the expected electronic-structure effect. Specifically, we can attribute this trend to three effects: (1) Ligand-field strength correlates inversely with halide size, bringing the Co excited-states lower in energy for larger halides (Figure 4).…”

Magnetic Anisotropy in Pentacoordinate NiII and CoII Complexes: Unraveling Electronic and Geometrical Contributions

“…The fundamental understanding of the influence of both the electronic configuration of metal ions and the geometrical structure imposed by organic ligands on the magnetic anisotropy of mononuclear complexes is an active field of research . Magnetic anisotropy stems from the simultaneous effects of spin–orbit coupling (SOC) and symmetry lower than cubic.…”