Structure, Magnetism and Theory of a Family of Nonanuclear Cu5IILn4III-Triethanolamine Clusters Displaying Single-Molecule Magnet Behaviour

Synthesis, crystal structures and magnetic studies are reported for four new heterometallic Cu-II-Ln(III) clusters. The reaction of Cu(NO3)(2)center dot 3H(2)O with triethanolamine (teaH3), pivalic acid, triethylamine and Ln(NO3)(3)center dot 6H(2)O (Ln=Gd, Tb, Dy and Ho) results in the formation of four isostructural nonanuclear complexes of general formula [Cu(5)(II)Ln(4)(III)O(2)(teaH)(4){O2CC(CH3)(3)}(2)(NO3)(4)(OMe)(4)]center dot 2MeOH center dot 2Et(2)O [Ln = Gd (1), Tb (2), Dy (3) and Ho (4)]. The metal core of each cluster is made up of four face- and vertex-sharing tetrahedral units. Solid-state DC magnetic susceptibility studies reveal competing anti-and ferromagnetic interactions within each cluster leading to large-spin ground states for 1-4. Solid-state AC magnetic susceptibility studies show frequency-dependent out-of-phase (chi(M)'') signals for 2-4 below 4 K, suggestive of single-molecule magnet behaviour. Ab initio calculations on one of the anisotropic examples (3) provided a rare set of J values for Dy-Cu and Cu-Cu exchange interactions (Dy-Dy zero), some ferro-and some antiferromagnetic in character, that explain its magnetic behaviour.