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

• Published in: Acta crystallographica. Section C, Crystal structure communications Vol. 77; no. 10; pp. 591 - 598
• Main Authors: Wei, Wen-Wen, Lu, Li-Ping, Feng, Si-Si, Zhu, Miao-Li, Englert, Ulli
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.10.2021; Wiley Subscription Services, Inc
• Subjects: Antiferromagnetism; Azo compounds; azobenzenetetracarboxylic acid; bridging carboxylate; Coordination polymers; Cryogenic temperature; crystal structure; Gadolinium; Gadolinium-gallium garnet; Gd3+ coordination polymer; Hydrogen bonds; Infrared analysis; Infrared spectroscopy; Magnetic properties; magnetic refrigeration; magnetocaloric effect; Polymers; Refrigeration; Topology
• DOI: 10.1107/S2053229621008871
• ISSN: 2053-2296; 0108-2701

A new Gd3+ coordination polymer (CP), namely, poly[diaqua[μ4‐1′‐carboxy‐3,3′‐(diazene‐1,2‐diyl)dibenzene‐1,2,2′‐tricarboxylato]gadolinium(III)], [Gd(C16H7N2O8)(H2O)2]n, (I), has been synthesized hydrothermally from Gd(NO3)3·6H2O and azobenzene‐2,2′,3,3′‐tetracarboxylic acid (H4abtc). 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 Gd3+ ions are connected by carboxylate groups into a linear chain along the monoclinic symmetry direction. Adjacent one‐dimensional aggregates are bridged by Habtc3− 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 −ΔSm 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 (Gd3Ga5O12, −ΔSm = 24 J kg−1 K−1, ΔH = 30 kG), CP (I) can be regarded as a potential cryogenic material for low‐temperature magnetic refrigeration. A novel coordination polymer (CP) has been successfully constructed under hydrothermal conditions via the combination of Gd3+ 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 (44·62). 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.