Synthesis, structure and magnetocaloric properties of a new two‐dimensional gadolinium(III) coordination polymer based on azobenzene‐2, 2′, 3, 3′‐tetracarboxylic acid. Issue 10 (10th September 2021) - Wei, Wen-Wen
Abstract : A novel coordination polymer (CP) has been successfully constructed under hydrothermal conditions via the combination of Gd 3+ ions and the azobenzene‐2, 2′, 3, 3′‐tetracarboxylic acid linker. The underlying structural principles comprise a 1D [Gd2 (COO)4 ] n chain and the linking of neighbouring chains via the organic ligand into a 2D structure with point symbol (4 4 ·6 2 ). Further crosslinking into a 3D framework occurs via very short hydrogen bonds. The new CP offers potential for application; magnetic studies reveal that it displays intrachain antiferromagnetic Gd…Gd coupling and a cryogenic magnetocaloric effect. Abstract : A new Gd 3+ coordination polymer (CP), namely, poly[diaqua[μ4 ‐1′‐carboxy‐3, 3′‐(diazene‐1, 2‐diyl)dibenzene‐1, 2, 2′‐tricarboxylato]gadolinium(III)], [Gd(C16 H7 N2 O8 )(H2 O)2 ] n, (I), has been synthesized hydrothermally from Gd(NO3 )3 ·6H2 O and azobenzene‐2, 2′, 3, 3′‐tetracarboxylic acid (H4 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 C 2/ 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 ) 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 −Δ S m of 27.26 J kg −1 K −1 for Δ H = 7 T at 3.0 K. As the MCE in (I) exceeds that of the commercial magnetic refrigerant GGG (Gd3 Ga5 O12, −Δ S m = 24 J kg −1 K −1, Δ H = 30 kG), CP (I) can be regarded as a potential cryogenic material for low‐temperature magnetic refrigeration.