Linear-shaped LnIII4 and LnIII6 clusters constructed by a polydentate Schiff base ligand and a β-diketone co-ligand: structures, fluorescence properties, magnetic refrigeration and single-molecule magnet behavior

Herein, ten new linear-shaped LnIII4 and LnIII6 clusters, with the formula [Ln(4)(acac)(6)L-2(CH3O)(2)(CH3OH)(4)]center dot xCH(3)OH (Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), and Tm (8), Hacac = acetylacetone), [Ln(6)(acac)(4)L-4(CH3O)(6)]center dot xCH(3)OH (Er (7) and Yb (9)), and [Lu-4(acac)(6)L-2(OH)(2)]center dot 2CH(2)Cl(2) (10), based on a polydentate Schiff base ligand, H2L, and a beta-diketone co-ligand were successfully synthesized and structurally characterized. Single crystal X-ray diffraction measurements reveal that the structures of the clusters 1-6, 8 and 10 are very similar and their central Ln(iii) ions are linearly arranged Ln(4); however, the clusters 7 and 9 possess a rare linearly arranged Ln(6). The investigations on the solid-state fluorescence properties show that the clusters 2, 3, 5 and 6 display the characteristic lanthanum luminescence at room temperature. Magnetic studies reveal that weak antiferromagnetic interactions exist between adjacent Gd(iii) ions in cluster 4. More importantly, the cluster 4 exhibits significant MCE with the maximum -Delta S-m value of 27.96 J kg(-1) K-1 at 2.0 K and 7.0 T, whereas the cluster 6 displays a slow magnetic relaxation behavior under a zero dc field with the effective energy barrier Delta E/k(B) = 8.64 K and tau(0) = 6.98 x 10(-6) s.