Redox‐Induced Spin‐State Switching and Mixed Valency in Quinonoid‐Bridged Dicobalt Complexes |
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| Authors: | David Schweinfurth Yvonne Rechkemmer Stephan Hohloch Naina Deibel Irina Peremykin Jan Fiedler Raphael Marx Dr. Petr Neugebauer Prof. Dr. Joris van Slageren Prof. Dr. Biprajit Sarkar |
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| Affiliation: | 1. Institut für Chemie und Biochemie, Anorganische Chemie, Fabeckstrasse 34–36, 14195 Berlin (Germany);2. Institut für Physikalische Chemie, Universit?t Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany);3. Institut für Anorganische Chemie, Universit?t Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany);4. J. Heyrovsky Institute of Physical Chemistry, v.v.i. Academy of Sciences of the Czech Republic, Dolej?kova 3, 18223 Prague (Czech Republic) |
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| Abstract: | The complexes [{(tmpa)CoII}2(μ‐L1)2?]2+ ( 12+ ) and [{(tmpa)CoII}2(μ‐L2)2?]2+ ( 22+ ), with tmpa=tris(2‐pyridylmethyl)amine, H2L1=2,5‐di‐[2‐(methoxy)‐anilino]‐1,4‐benzoquinone, and H2L2=2,5‐di‐[2‐(trifluoromethyl)‐anilino]‐1,4‐benzoquinone, were synthesized and characterized. Structural analysis of 22+ revealed a distorted octahedral coordination around the cobalt centers, and cobalt–ligand bond lengths that match with high‐spin CoII centers. Superconducting quantum interference device (SQUID) magnetometric studies on 12+ and 22+ are consistent with the presence of two weakly exchange‐coupled high‐spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 12+ and ferromagnetic for 22+ . Both complexes exhibit several one‐electron redox steps, and these were investigated with cyclic voltammetry and UV/Vis/near‐IR spectroelectrochemistry. For 12+ , it was possible to chemically isolate the pure forms of both the one‐electron oxidized mixed‐valent 13+ and the two‐electron oxidized isovalent 14+ forms, and characterize them structurally as well as magnetically. This series thus provided an opportunity to investigate the effect of reversible electron transfers on the total spin‐state of the molecule. In contrast to 22+ , for 14+ the metal–ligand distances and the distances within the quinonoid ligand point to the existence of two low‐spin CoIII centers, thus showing the innocence of the quintessential non‐innocent ligands L. Magnetic data corroborate these observations by showing the decrease of the magnetic moment by roughly half (neglecting spin exchange effects) on oxidizing the molecules with one electron, and the disappearance of a paramagnetic response upon two‐electron oxidation, which confirms the change in spin state associated with the electron‐transfer steps. |
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| Keywords: | bridging ligands mixed‐valent compounds non‐innocent ligands quinones spectroelectrochemistry |
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