Modulating Magnetic Refrigeration through Structural Variation in CoII/III–GdIII Clusters

Three heterometallic aggregates, [(CoII)2(GdIII)2­(tBuPO3)2­(O2CtBu)2­(HO2CtBu)2­(NO3)4]·NEt3 (1), [(CoII)2(CoIII)2­(GdIII)3­(μ3-OH)2­(tBuPO3)2­(O2CtBu)9­(deaH)2­(H2O)2] (2), and (CoIII)2(GdIII)5­(μ2-OH)­(μ3-OH)2­(tBuPO3)2­(O2CtBu)10­(HO2CtBu)­(deaH)2]·MeOH (3), were successfully isolated in reactions of [Co2(μ-OH2)­(O2CtBu)4]·(HO2CtBu)4, Gd­(NO3)3·6H2O, tBu-PO3H2, and diethanolamine (deaH3) by varying the stoichiometry of the reactants and/or changing the solvent. The structures of the final products were profoundly affected by these minor changes in stoichiometry or a change in solvent. The metal–oxo core of these complexes displays a hemicubane or a defective dicubane-like view. Bond valence sum calculations and bond lengths indicate the presence of CoII centers in compound 1, mixed valent Co centers (CoII/CoIII) in compound 2, and only CoIII centers in compound 3 as required for the charge balances and supported by the magnetic measurements. Magnetic studies reveal significant magnetic entropy changes for complexes 1–3 (−ΔS m values of 28.14, 25.06, and 29.19 J kg–1 K–1 for 3 K and 7 T, respectively). This study shows how magnetic refrigeration can be affected by anisotropy, magnetic interactions (ferro- or antiferromagnetic), the metal/ligand ratio, and the content of GdIII in the molecule.