Single-Molecule-Magnet Fe4II Fe2III and Antiferromagnetic Fe4III Coordination Clusters

Supported by endogenous (part of the ligand, in-built) phenoxo bridges provided by the ligand 2,6-bis[{{(5-bromo-2-hydroxybenzyl)}{(2-(pyridylethyl)}amino}methyl]-4-methylphenol) (H3L), in its deprotonated form, exogenous (not part of the ligand, externally added or generated) oxo-/hydroxo- and acetato-bridged [Fe-4(II) Fe-2(III) (O)(2) (O2CMe)(4) (L)(2)]center dot 4Et(2)O(1) and [Fe-4(III) (OH)(2) (O2CMe)(3)(L)(2)](ClO4)center dot 3MeCN center dot 2H(2)O (2) coordination clusters have been synthesized and structurally characterized. Complexes 1 and 2 have mu(4)-O and mu(3)-OH bridges, respectively. Magnetic studies on 1 reveal slow magnetic relaxation below 2 K. Both in-phase (chi'(M)) and out-of-phase (chi ''(M)) magnetic susceptibility were found to be frequency dependent. This is typical of a single-molecule magnet (SMM) with tau(0) = 1.9(2) X 10(-7) s(-1) and E-a = 5.1(3) cm(-1) . Assuming that E-a corresponds to the energy splitting of the ground spin state (S = 2) by the zero-filed-splitting (zfs), E-a = 4 vertical bar D vertical bar (D is the axial zfs parameter), D approximate to -1.3 cm(-1) could be estimated. For 2, three types of magnetic interactions are observed: J(A) = - 56.5(3), J(B) = - 71.6(4), and J(C) = +4.5(2) cm(-1). Considering the observed structural parameters, the magnetic behavior for both of the coordination clusters 1 and 2 has been rationalized.