Electron Localization of Polyoxomolybdates with ε‑Keggin Structure Studied by Solid-State ⁹⁵Mo NMR and DFT Calculation

We report electron localization of polyoxomolybdates with ε-Keggin structure investigated by solid-state ⁹⁵Mo NMR and DFT calculation. The polyoxomolybdates studied are the basic ε-Keggin crystals of [Me₃NH]₆[H₂Mo₁₂O₂₈(OH)₁₂{MoO₃}₄]·2H₂O (<b>1</b>), the crystals suggested to have a disordered {ε-Mo₁₂} core of [PMo₁₂O₃₆(OH)₄{La­(H₂O)_2.75Cl_1.25}₄]·27H₂O (<b>2</b>), and the paramagnetic Keggin crystals of [H₂Mo₁₂O₃₀(OH)₁₀{Ni­(H₂O)₃}₄]·14H₂O (<b>3</b>). The spectra of ⁹⁵Mo static NMR of these samples were measured under moderate (9.4 and 11.7 T) and ultrahigh magnetic fields (21.8 T). From spectral simulation and quantum chemical calculation, the NMR parameters of the chemical shift and quadrupole interactions for ⁹⁵Mo were estimated. By the analysis based on the result for <b>1</b>, it was found for <b>2</b> that although the {ε-Mo₁₂} core is disordered, the eight d¹ electrons in it are not completely localized on four Mo–Mo bonds. Furthermore, it was shown for <b>3</b> that the d¹ electrons are localized to make the Mo–Mo bonds, while the unpaired electrons are also almost localized on the paramagnetic Ni^II ions