Large Hexadecametallic {MnIII-LnIII} Wheels: Synthesis, Structural, Magnetic, and Theoretical Characterization

The synthesis, gas sorption studies, magnetic properties, and theoretical studies of new molecular wheels of core type {Mn(8)(III)Ln(8)(III)} (Ln=Dy, Ho, Er, Y and Yb), using the ligand mdeaH(2), in the presence of ortho-toluic or benzoic acid are reported. From the seven wheels studied the {Mn8Dy8} and {Mn8Y8} analogues exhibit SMM behavior as determined from ac susceptibility experiments in a zero static magnetic field. From DFT calculations a S=16 ground state was determined for the {Mn8Y8} complex due to weak ferromagnetic Mn-III-Mn-III interactions. Ab initio CASSCF+RASSI-SO calculations on the {Mn8Dy8} wheel estimated the Mn-III-Dy-III exchange interaction as -0.1cm(-1). This weak exchange along with unfavorable single-ion anisotropy of Dy-III/Mn-III ions, however, led to the observation of SMM behavior with fast magnetic relaxation. The orientation of the g-anisotropy of the Dy-III ions is found to be perpendicular to the plane of the wheel and this suggests the possibility of toroidal magnetic moments in the cluster. The {Mn(8)Ln(8)} clusters reported here are the largest heterometallic Mn(III)Ln(III) wheels and the largest {3d-4f} wheels to exhibit SMM behavior reported to date.