摘要
Two different 3D coordination polymers,[Gd(glc)(Hglc)(H_(2)O)]_(n)·nH_(2)O(1)and[Gd(Hglc)_(3)]_(n)(2)(H_(2)glc=glycolic acid),have been prepared based on the reaction of Gd(Ⅲ)ions with H_(2)glc in different pH environments.Due to the deprotonation of the α-OH groups from half of the H_(2)glc ligands in 1,[Gd_(2)]units with a Gd–O–Gd bridging model are observed and suggest a stronger magnetic coupling than that in 2.Magnetic and heat capacity studies reveal the significant impact of the strength of magnetic coupling on the magneto-caloric effect(MCE)in systems.Although a theoretical calculation suggests the−ΔS_(m)(50.5 J kg^(-1) K^(-1))of 1 is larger than 2(45.2 J kg^(-1) K^(-1)),the stronger antiferromagnetic coupling in 1 decreases the number of low-lying excited spin states upon the lowering of temperature,thus giving a smaller value of −ΔS_(m) than 2 at various fields(e.g.−ΔS_(m,max)=24.8 J kg^(-1) K^(-1) and 41.1 J kg^(-1) K^(-1) for 1 and 2 respectively at ΔH=3 T).This case reveals that the effect of magnetic coupling on MCE plays a dominant role for designing low-temperature 3D Gd(Ⅲ)-based magnetic coolants.
基金
supported by the“973 Project”(2012CB821704 and 2014CB845602)
project NSFC(Grant no.91122032,21371183,21121061 and 21201137)
the NSF of Guangdong(S2013020013002)
Program for Changjiang Scholars and Innovative Research Team in University of China(IRT1298).
