Magnetic Properties of a Family of [MnIII4LnIII4] Wheel Complexes: An Experimental and Theoretical Study

The chelating ligand 1,3-bis(tris(hydroxymethyl)methylamino)propane (H₆L) has been used to synthesize a family of octanuclear heterometallic complexes with the formula (NMe₄)₃[Mn₄Ln₄(H₂L)₃(H₃L)(NO₃)₁₂] (Ln = La (1), Ce (2), Pr (3), Nd (4)). Encapsulation by the ligand causes the Mn(III) centers to lie in an unusually distorted (∼C_2v) environment, which is shown by density functional theory and complete active space self-consistent field calculations to impact on the magnetic anisotropy of the Mn(III) ion. The theoretical study also supports the experimental observation of a ferromagnetic superexchange interaction between the Mn(III) ions in 1, despite the ions being separated by the diamagnetic La(III) ion. The optical properties of the compounds show that the distortion of the Mn(III) ions leads to three broad absorption bands originating from the transition metal ion, while the Nd(III) containing complex also displays some weak sharp features arising from the lanthanide f-f transitions.