Multinuclear Paramagnetic NMR Spectra and Solid State X-ray Crystallographic Characterization of Manganese(III) Schiff-Base Complexes

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Abstract

The 1H NMR spectra of symmetrically substituted paramagnetic [(R,R‘-SALOPHEN)MnIII]+ and [(R,R‘-SALOPHEN)MnIII]2(μ-O) complexes (SALOPHEN is 1,3-bis(salicylideneamino)benzene) were obtained. All of the monomers and dimers yielded well-resolved but isotropically shifted 1H NMR spectra. A diamagnetic suppression routine was applied to the 1H NMR spectra that allowed observation of all rapidly relaxing resonances. The binding of axial ligands, acetate, methanol, water, and pyridine was also observable by 1H NMR. Two X-ray crystal structures were obtained: [(3,3‘-17-crown-6-SALOPHEN)MnIII]·(CH3C(O)O)·BaTf2·2H2O, [9b]OAc·BaTf2·2H2O, crystallized in the triclinic space group P1̄; with a = 10.747(2) Å, b = 12.271(8) Å, c = 16.206(6) Å, α = 106.10(4)°, β = 103.07(2)°, γ = 106.06(3), and Z = 2, while [(3,3‘,6,6‘-(CH3)4-SALOPHEN)MnIII]PF6·H2O, [6b]PF6·H2O, crystallized in the monoclinic space group P21/n, with a = 12.465(1) Å, b = 13.366(2) Å, c = 15.240(1) Å, β = 103.051(7)°, and Z = 2. [9b]OAc·BaTf2·2H2O has the Mn(III) center ligated in the axial positions by one oxygen of the acetate group and an oxygen from one SO3CF3-. The second oxygen of the acetate is bound to the Ba2+ residing in the crown ether. The water molecule in [6b]PF6·H2O is O-bound to the Mn(III) center and also hydrogen bonded to one of the fluorine atoms of the PF6 counterion, O−F 3.01 Å. 1H and 19F NMR spectra revealed that the hydrogen bond in [6b]PF6·H2O was preserved in CD3OD.

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