Abstract
A new Gd(3+) coordination polymer (CP), namely, poly[diaqua[μ(4)-1'-carboxy-3,3'-(diazene-1,2-diyl)dibenzene-1,2,2'-tricarboxylato]gadolinium(III)], [Gd(C(16)H(7)N(2)O(8))(H(2)O)(2)](n), (I), has been synthesized hydrothermally from Gd(NO(3))(3)·6H(2)O and azobenzene-2,2',3,3'-tetracarboxylic acid (H(4)abtc). The target solid has been characterized by single-crystal and powder X-ray diffraction, elemental analysis, IR spectroscopy and susceptibility measurements. CP (I) crystallizes in the monoclinic space group C2/c. The structure features a 4-connected topology in which Gd(3+) ions are connected by carboxylate groups into a linear chain along the monoclinic symmetry direction. Adjacent one-dimensional aggregates are bridged by Habtc(3-) ligands to form a two-dimensional CP in the (10-1) plane. A very short hydrogen bond [O...O = 2.4393 (4) Å] links neighbouring layers into a three-dimensional network. A magnetic study revealed antiferromagnetic Gd...Gd coupling within the chain direction. CP (I) displays a significant magnetocaloric effect (MCE), with a maximum -ΔS(m) of 27.26 J kg(-1) K(-1) for ΔH = 7 T at 3.0 K. As the MCE in (I) exceeds that of the commercial magnetic refrigerant GGG (Gd(3)Ga(5)O(12), -ΔS(m) = 24 J kg(-1) K(-1), ΔH = 30 kG), CP (I) can be regarded as a potential cryogenic material for low-temperature magnetic refrigeration.