Turning on Single-Molecule Magnet Behavior in a Linear {Mn3} Compound
Résumé
The synthesis, structure, and magnetic properties are reported for a new manganese compound with a mixed-valent {Mn3} core arranged in a linear fashion. The previously reported complex 1, [MnIV3(dpo)6]*2MeCN, where H2dpo is (E)-1-hydroxy-1,1-diphenylpropan-2-one oxime, served as a starting point for the isolation of a {Mn3} compound with an analogous core arrangement through the reaction of Mn-(OAc)2*4H2O, H3oxol ((E)-2,5-dihydroxy-2,5-dimethylhexan-3-one oxime), and NaOH in MeOH and MeCN. By using these reaction conditions, compound 2, Na[MnIV 2MnIII(Hoxol)6]n*MeOH*H2O, was successfully isolated revealing a central MnIII ion thereby introducing structural and magnetic anisotropy to the system. The structure of 2 reveals linear trinuclear MnIV−MnIII−MnIV units connected through Na+ ions forming a linear one-dimensional coordination polymer. The Jahn−Teller axes of each trinuclear unit are aligned parallel within the same chain and form a 75° angle between the two symmetry related chains. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9−300 K reveal that only the reduced compound, 2, is a single-molecule magnet (SMM) largely due to the anisotropy introduced by the Jahn−Teller distortions on the MnIII ions, which effectively induce this magnet behavior. Weak antiferromagnetic interactions along the chains through the Na+ cations lead to a modulation of the intrinsic properties of the MnIV−MnIII−MnIV SMMs.