Decanuclear Ln(10) Wheels and Vertex-Shared Spirocyclic Ln(5) Cores: Synthesis, Structure, SMM Behavior, and MCE Properties.

The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln(10) (Ln=Dy(1), Tb(2), and Gd (3)) and pentanuclear Ln(5) complexes (Ln=Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln(10) and Ln(5) complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1-6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (U-eff)=16.12(8)K and relaxation time (iota(o))= 3.3 x 10(-5) s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out-of-phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: -Delta S-m=26.6 J kg(-1)K(-1) at T = 2.2 K for 3 and -Delta S-m= 27.1 J kg(-1)K(-1) at T=2.4 K for 4, both for an applied field change of 7 T.