Nanoscale {LnIII24ZnII6} Triangular Metalloring with Magnetic Refrigerant, Slow Magnetic Relaxation, and Fluorescent Properties.

The self-assembly of Ln(ClO4)3·6H2O and Zn(OAc)2·2H2O with pyrazine-2-carboxylic acid (HL) results in the formation of three novel nanosized {LnIII24ZnII6} triangular metallorings, [Gd24Zn6L24(OAc)22(µ3-OH)30(H2O)14](ClO4)7(OAc)·2CH3OH·26H2O (1), [Tb24Zn6L24(OAc)22(μ3-OH)30(CH3O)2(CH3OH)2(H2O)10](ClO4)5(OH)·6CH3OH·12H2O (2), and (H3O)[Dy24Zn6L24(OAc)22(μ3-OH)30(H2O)14](ClO4)7(OAc)2·4CH3OH·22H2O (3), having the largest nuclearity among any known Ln/Zn clusters. Magnetic and luminescent studies reveal the special prowess for each lanthanide complex. Magnetic studies reveal that 1 exhibits a significant cryogenic magnetocaloric effect with a maximum -ΔSm (isothermal magnetic entropy change) value of 30.0 J kg-1 K-1 at 2.5 K and 7 T and that a slow magnetization relaxation is observed for the dysprosium analogue. In addition, the solid-state photophysical properties of 2 display strong characteristic TbIII photoluminescent emission in the visible region, suggesting that TbIII-based luminescence is sensitized by the effective energy transfer from the ligand HL to the metal centers. [ABSTRACT FROM AUTHOR]