High valent manganese-oxo complexes typically involve N-chelating ligands and have low-spin ground states. Recently, we synthesized and characterized high-spin oxomanganese complexes in four oxidation states stabilized within quasi-Wells-Dawson polyfluorooxometalate structures. Experimentally, O=MnV-PFOM is a poor oxygen transfer agent but acts as an outer-sphere electron acceptor, while O=MnIV-PFOM is generally more reactive.We present an extensive DFT study of the geometric and electronic structures of these complexes, their composition in solution and reactivity. The Mn atom in the quasi-Wells-Dawson complexes [Mn(OHn)W17NaH2F6O55] (n=0,1,2) can replace tungsten in any of 12 'belt' or six �cap� positions. PBE-DF/PC1/PCM(H2O) optimizations suggest that only belt-substituted complexes are stable, whereas no Mn-oxo bond is formed in the cap-substituted complexes (Figure 1). Comparison of calculated and experimental Raman spectra reveals, that decrease in the Mn oxidation state favors protonation of the oxo-ligand moving from strong MnV=O to weak MnII�OH2bond. Accurate all-electron DKH calculations showed linear dependence of the Mn 2p level on the Mn oxidation state, fitting well with XPS experiments (Figure 1).The observed properties of the oxomanganese complexes can be qualitatively explained by p-repulsion, while s- and p-donating properties of bridging O-atoms are responsible for significant Mn valence orbital populations even in high oxidation states. This prevents formation of cap-substituted complexes with an oxomanganese moiety trans to O-atom, while the highly electronegative fluoride in transposition enables formation of belt-substituted complexes.

DFT study of the quasi Wells-Dawson compound [Mn(L)W17NaH2F6O55] (L=O, OH, H2O)

248th National Meeting (2014)

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