Family of Quasi-Isotropic Mn^II and Mn₂^II Complexes Exhibiting Slow Relaxation of the Magnetization

Slow relaxation of magnetization has been studied for a family of mononuclear Mn^II complexes and one ferromagnetic dinuclear system, all of them presenting very weak anisotropy. Complexes with formula [{NiL1Mn(H₂O)₂(MeOH)}{NiL1}₂](ClO₄)₂ (<b>1</b>), [Mn{NiL1}₂](ClO₄)₂ (<b>2</b>), [Mn{NiL2}₂](ClO₄)₂ (RR-L2^2-, <b>3</b>RR, SS-L2^2-, <b>3</b>SS), [Mn{NiL3}₂](ClO₄)₂ (RR-L3^2-, <b>4</b>RR, SS-L3^2-, <b>4</b>SS) and (μ_1,1-N₃)₂[Ni₂Mn₂(L1)₂(N₃)₂] (<b>5</b>) are derived from compartmental Schiff bases, in which the Ni^II environment is square planar and thus diamagnetic. All of the systems have been structurally and magnetically characterized. Zero field splitting (<i>D</i>) values for the Mn^II cations have been obtained from EPR spectroscopy and NEVPT2 calculations. The slow relaxation of the magnetization for <b>1</b>-<b>5</b> has been studied by means of ac magnetometry and rationalized on the basis of their low, but not zero, anisotropy, providing the first example of a polynuclear Mn^II complex, with <i>S</i> = 5 ground state, exhibiting slow relaxation.