Modulating Magnetic Refrigeration through Structural Variation in Co-Gd Clusters.

Three heterometallic aggregates, [(Co)(Gd)(BuPO)(OCBu)(HOCBu)(NO)]·NEt (1), [(Co)(Co)(Gd)(μ-OH)(BuPO)(OCBu)(deaH)(HO)] (2), and (Co)(Gd)(μ-OH)(μ-OH)(BuPO)(OCBu)(HOCBu)(deaH)]·MeOH (3), were successfully isolated in reactions of [Co(μ-OH)(OCBu)]·(HOCBu), Gd(NO)·6HO, Bu-POH, and diethanolamine (deaH) 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 Co centers in compound 1, mixed valent Co centers (Co/Co) in compound 2, and only Co 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 values of 28.14, 25.06, and 29.19 J kg K 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 Gd in the molecule.