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 (−ΔSm 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.

三种异金属聚集体，分别为[(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)以及(CoIII)2(GdIII)5(μ2-OH)(μ3-OH)2(tBuPO3)2(O2CtBu)10(HO2CtBu)(deaH)2]·MeOH (3)，通过调节反应物的化学计量比和/或改变溶剂，在[Co2(μ-OH2)(O2CtBu)4]·(HO2CtBu)4、Gd(NO3)3·6H2O、tBu-PO3H2和二乙醇胺(deaH3)的反应中成功分离。这些最终产物的结构受到化学计量比微小的变化或溶剂改变的显著影响。这些配合物的金属-氧配位核心呈现出半立方烷或缺陷二立方烷状的构象。键价和键长计算表明，化合物1中存在CoII中心，化合物2中存在混合价态的Co中心(CoII/CoIII)，而化合物3中仅存在CoIII中心，以满足电荷平衡并得到磁性测量的支持。磁性研究表明，复合物1-3显示出显著的磁性熵变（在3 K和7 T下，分别为-ΔSm值为28.14、25.06和29.19 J kg–1 K–1）。本研究揭示了磁致冷在单轴各向异性、磁性相互作用（铁磁或反铁磁）、金属/配体比例以及分子中GdIII含量等方面的影响。