Synthesis, structure and magnetocaloric properties of a new two-dimensional gadolinium(III) coordination polymer based on azo­benzene-2,2′,3,3′-tetra­carb­oxy­lic acid

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[Image: see text]) 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.