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

The ¹H NMR spectra of symmetrically substituted paramagnetic [(R,R'-SALOPHEN)Mn^III]⁺ and [(R,R'-SALOPHEN)Mn^III]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)Mn^III]·(CH ₃C(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)Mn ^III]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 SO₃CF^3-. 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.