The effect of magnetic coupling on magnetocaloric behaviour in two 3D Gd(III)-glycolate coordination polymers

Two different 3D coordination polymers, [Gd(glc)(Hglc)(H2O)](n)center dot nH2O (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 alpha-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 -Delta S-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 -Delta S-m than 2 at various fields (e.g. -Delta S-m,S-max = 24.8 J kg(-1) K-1 and 41.1 J kg(-1) K-1 for 1 and 2 respectively at Delta H = 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.