We have performed TD-DFT and CASSCF calculations to understand the spectroscopy and reactive photochemistry of the [Cr(tn)(3)](3+) complex. Our results show that, after population of a quartet ligand field excited state, the system relaxes by dissociation of a Cr-N bond to reach a quasi-trigonal bipyramid five-coordinate species that is a conical intersection connecting the excited and ground quartet manifolds. Nonadiabatic relaxation through these leads to square pyramidal structures that can coordinate water and account for the observed monoaquated photoproducts. Such features are also present on the potential energy surfaces of these photoproducts and account for the range of experimentally observed photostereoisomers of the photoaquation reactions.
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The Role of the Lowest Excited Triplet State in Defining the Rate of Photoaquation of Hexacyanometalates.
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Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany.
Photosolvation is a type of ligand substitution reaction started by irradiation of a solution with light, triggering the replacement of a ligand with a molecule from the solvent. The excited state is created through many possible pathways. For the class of hexacyanides of groups 8 and 9 of the periodic table, irradiation in the ligand field band is followed by intersystem crossing to the lowest excited triplet state, which we propose to mediate the photoaquation reaction in this class of complexes.
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Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Methods and Instrumentation for Synchrotron Radiation Research, 12489 Berlin, Germany.
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J Chem Phys
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Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA.
Ligand substitution reactions are common in solvated transition metal complexes, and harnessing them through initiation with light promises interesting practical applications, driving interest in new means of probing their mechanisms. Using a combination of time-resolved x-ray absorption spectroscopy and hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations and x-ray absorption near-edge spectroscopy calculations, we elucidate the mechanism of photoaquation in the model system iron(ii) hexacyanide, where UV excitation results in the exchange of a CN ligand with a water molecule from the solvent. We take advantage of the high flux and stability of synchrotron x-rays to capture high precision x-ray absorption spectra that allow us to overcome the usual limitation of the relatively long x-ray pulses and extract the spectrum of the short-lived intermediate pentacoordinated species.
View Article and Find Full Text PDFQuantum chemistry of OsCl photoaquation products and the reaction scheme.
Photochem Photobiol Sci
May 2019
Vologograd State University, 100 University Ave., 400062, Volgograd, Russian Federation.
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