Magnetocaloric effect in 1D-polymers bearing 15-metallacrown-5 {GdCu 5 } 3+ units and anionic oxalate complexes

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 53; no. 37; pp. 15713 - 15724
• Main Authors: Pavlishchuk, Anna V, Kolotilov, Sergey V, Zeller, Matthias, Pavlishchuk, Vitaly V, Pointillart, Fabrice, Addison, Anthony W
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 24.09.2024
• Subjects: Antiferromagnetism; Atomic structure; Chains (polymeric); Chemical Sciences; Chromium; Coordination polymers; Copper; Crosslinking; Ferromagnetism; Gadolinium; Oxalates; Structural analysis
• ISSN: 1477-9226; 1477-9234; 1477-9234
• DOI: 10.1039/d4dt02413c

Two complexes {[GdCu (GlyHA) (H O) Cr(C O ) ]·11.02H O} (1) and {{[GdCu (GlyHA) (H O) ]μ -[Cu(C O ) (H O)]} μ -[Cu(C O ) ]·15.8H O} (2), were obtained as outcomes of the reactions between the cationic hexanuclear {GdCu (GlyHA) } 15-metallacrown-5 complex (where GlyHA = glycinehydroxamate) and the anionic oxalate complexes K [Cr(C O ) ] or K [Cu(C O ) ]. Both 1 and 2 possess polymeric 1D-chain structures according to X-ray structural analysis. As a consequence of the geometric orientations of the donor atoms in the oxalates from [Cr(C O ) ] , the Cu mean planes of neighboring 15-metallacrown-5 units {GdCu (GlyHA) } are angled at 75.5° to each other, which leads to formation of a zig-zag motif in the 1D-chains of complex 1. The centrosymmetric complex 2 contains two structurally different bis(oxalato)cuprate anions μ -[Cu(C O ) (H O)] , for one of which, coordination to two adjacent {GdCu (GlyHA) } units leads to formation of linear 1D-chains in 2, while the second type, μ -[Cu(C O ) ] , is coordinated to four {GdCu (GlyHA) } units, causing the cross-linking of single 1D-chains into a double-chain 1D coordination polymer. Studies of data for 1 and 2 in a 2-300 K temperature range revealed the presence of both ferromagnetic and antiferromagnetic interactions amongst paramagnetic centres. The experimental data for 1 were fitted using a model which takes into account exchange interactions between adjacent copper(II) ions, the Gd-Cu exchange interactions within {GdCu (GlyHA) } units and additionally Gd-Cr exchange interactions. Fitting of the data for 2 was not possible, since coordination of μ -[Cu(C O ) ] to {GdCu (GlyHA) } led to the non-equivalence of several Cu-Cu exchange interactions within the metallacrown units and hence a superfluity of fittable parameters. Complexes 1 and 2 are the first examples of 15-metallacrown-5 complexes demonstrating a magnetocaloric effect (-Δ at 13 T reaches 24.26 J K kg at 5 K and 19.14 J K kg at 4 K for 1 and 2, respectively).