Decanuclear Ln10 Wheels and Vertex-Shared Spirocyclic Ln5 Cores: Synthesis, Structure, SMM Behavior, and MCE Properties

The reaction of a Schiff base ligand (LH) 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 (Ln=Dy(1), Tb(2), and Gd (3)) and pentanuclear Ln complexes (Ln=Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln and Ln 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)=16.12(8) K and relaxation time (?)=3.3×10 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: -?S=26.6 J kg K at T=2.2 K for 3 and -?S=27.1 J kg K at T=2.4 K for 4, both for an applied field change of 7 T. Homometallic complexes: The reaction of a multidentate flexible Schiff base ligand (LH; see figure) with [LnCl]6 HO affords homometallic decanuclear complexes, [Ln(LH)(?-Piv)] (Ln=Dy, Tb, and Gd), and homometallic pentanuclear complexes, [Ln(LH)(?-??Piv)(?Piv)(S)] (Ln=Dy, Tb, and Gd). The Dy analogues exhibit single-molecule magnet (SMM) behavior, whereas the Gd complexes show a significant magnetocaloric effect (MCE).