Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 141, Issue 29, Pages 11686-11693Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.9b04937
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Funding
- ACCEL program of the Japan Science and Technology Agency (JST) [JPMJAC1501]
- JSPS KAKENHI [13J07305]
- Japan Synchrotron Radiation Research Institute (JASRI) [2017A1468]
- Grants-in-Aid for Scientific Research [13J07305] Funding Source: KAKEN
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We first demonstrate the influence of d-elements on the electronic-state alternation of molecules coupled with proton transfer in d-pi hybridized electron systems. Compact and planar metal complexes with protonated 2,3-pyrazinedithiolates (L), M(HL)(2) (M = Ni, Pd, and Pt), were synthesized and subsequently determined to be assembled by hydrogen bond (H-bond) interactions between pyrazine moieties. Structural and theoretical investigations revealed that these complexes are regarded as d-pi hybridized electron systems based on a M(S2C2)(2) core, especially, significant d-pi hybridization in the Pt(S2C2)(2) core was indicated. The pH-dependent optical and electrochemical measurements revealed that the Ni complex has a higher proton-accepting character and a stronger pH dependence for redox potential compared with the Pt complex. This indicates that the Ni complex has a larger amount of pi-electron density on ligands than the Pt complex because the significant d-pi hybridization in the Pt complex could reduce the amount of pi-electron reconstructed by attaching/detaching proton. Cyclic voltammetry of Ni and Pt complexes that form an H-bonded multimer showed a potential splitting at the first redox wave (Delta E-1/2 = 0.28 V for M = Ni and 0.17 V for M = Pt) corresponding to a mixed-valence state coupled with proton transfer. The Delta E-1/2 values indicate that the change in electronic states by proton transfer is remarkable in the Ni complex, but moderate in the Pt complex. These experimental results lead that the d-element substitution plays a role in controlling the degree of proton-electron coupling in d-pi hybridized electron systems.
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