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 e...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.展开更多
基金supported by the“973 Project”(2012CB821704 and 2014CB845602)project NSFC(Grant no.91122032,21371183,21121061 and 21201137)+1 种基金the NSF of Guangdong(S2013020013002)Program for Changjiang Scholars and Innovative Research Team in University of China(IRT1298).
文摘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.
