Nanoscale {Ln(24)(III)Zn(6)(II)} Triangular Metalloring with Magnetic Refrigerant, Slow Magnetic Relaxation, and Fluorescent Properties

The self-assembly of Ln(ClO4)(3)center dot 6H(2)O and Zn(OAc)(2)center dot 2H(2)O with pyrazine-2-carboxylic acid (HL) results in the formation of three novel nanosized {Ln(24)(III)Zn(6)(II)} triangular metallorings, [Gd24Zn6L24 (OAc)(22)(mu(3)-OH)(30)(H2O)(14)](ClO4)(7)(OAc)center dot 2CH(3)OH center dot 26H(2)O (1), [Tb24Zn6L24(OAc)(22)(mu(3)-OH)(30)(CH3O)(2)(CH3OH)(2)-(H2O)(10)](ClO4)(5)(OH)center dot 6CH(3)OH center dot 12H(2)O (2), and (H3O)[Dy24Zn6L24-(OAc)(22)(mu(3)-OH)(30)(H2O)(14)](ClO4)(7)(OAC)(2)center dot 4CH(3)OH center dot 22H(2)O (3), having the largest nudearity 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 -Delta S-m (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 Tb-III photoluminescent emission in the visible region, suggesting that Tb-III-based luminescence is sensitized by the effective energy transfer from the ligand HL to the metal centers