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Dalton Trans. 2019 Jul 21;48(27):10089-10103. doi: 10.1039/c9dt01776c. Epub 2019 Jun 10.

Stepwise oxidations of a nickel(ii)-iron(iii) heterobimetallic porphyrin dimer: structure, spectroscopic and theoretical investigation.

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Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.


We have reported here the synthesis, structure and spectroscopic properties of the NiII-FeIII heterobimetallic ethene-bridged porphyrin dimer and investigate the effect upon step-wise one- and two-electron oxidations to produce a mixed-valence π-cation radical dimer and a dication diradical complex, respectively. We then investigate their electronic structure and spin coupling model and compare them with the corresponding homobimetallic analog. Detailed UV-vis-NIR, IR, and variable temperature magnetic studies and EPR and NMR spectroscopic investigations along with X-ray structure determination of the 2e-oxidized complex have demonstrated strong electronic communications through the bridge between two porphyrin π-cation radicals. The structure and geometrical parameters revealed the stabilization of the high-spin state of iron and the low-spin state of nickel in the 2e-oxidized complex. The extensive conjugation between the two porphyrin π-cation radicals has also altered the bridge from an ethylene to an exo-methylene moiety. Variable temperature magnetic studies of the 2e-oxidized complex revealed stronger antiferromagnetic coupling between two π-cation radical spins (Jr1-r2) of the NiII-FeIII heterodimer which is in sharp contrast to its diiron(iii) analog where the porphyrin π-cation radical undergoes stronger antiferromagnetic coupling predominantly with the corresponding Fe(iii) unpaired spin (JFe-r). The experimental observations are also strongly supported by DFT calculations.


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