Reduction of Mn₁₉ Coordination Clusters on a Gold Surface

The magnetic properties of a Mn₁₉ coordination cluster equipped with methylmercapto substituents on the organic ligands, [Mn^III₁₂Mn^II₇(μ₄-O)₈(μ₃-Cl)_7.7(μ3-OMe)_0.3(HL^SMe)₁₂(MeOH)₆]Cl₂ 27MeCN(Mn₁₉(SMe))(H₃L^SMe = 2,6-bis(hydroxymethyl)-4-mercaptomethylphenol) deposited on Au(111) surfaces from solution, have been investigated by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The data reveal that in the submonolayer regime the molecules contain only divalent Mn^II in contrast to the presence of Mn^II and Mn^III ions in the powder sample. Brillouin function fits to the field-dependent magnetization suggest that the total spin ground state in the submonolayer is much lower than S_TOT = 83/2 of the pristine molecules. These findings suggest that significant changes of the electronic structure, molecular geometry, and intramolecular exchange coupling take place upon surface deposition. A sample with coverage of 2-3 monolayers shows the presence of Mn^III, suggesting that a decoupling layer could stabilize the Mn₁₉ core on a metallic surface.

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