Modulating Magnetic Refrigeration through Structural Variation in Co<sup>II/III</sup>–Gd<sup>III</sup> Clusters
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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.
成功通过调控反应物计量比或更换溶剂，由前驱体[Co₂(μ-H₂O)(O₂CtBu)₄]·(HO₂CtBu)₄、六水合硝酸钆（Gd(NO₃)₃·6H₂O）、叔丁基膦酸（tBu-PO₃H₂）与二乙醇胺（deaH₃）的反应，分离得到三种异金属聚集体：[(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]·甲醇（MeOH）（3）。 最终产物的结构受反应物计量比的微小变化或溶剂改变的影响极为显著。 上述配合物的金属氧簇核呈现半立方烷或缺陷双立方烷的结构构型。 键价和计算与键长数据表明，化合物1中仅存在二价钴（CoII）中心，化合物2中存在混合价态钴中心（CoII/CoIII），化合物3中仅存在三价钴（CoIII）中心，该结果符合电荷平衡要求，且得到磁学测试结果的佐证。 磁学研究显示，配合物1~3均表现出显著的磁熵变性能：在3 K、7 T的外磁场条件下，其磁熵变绝对值（−ΔSₘ）分别为28.14、25.06和29.19 J·kg⁻¹·K⁻¹。 本研究揭示了各向异性、磁相互作用（铁磁或反铁磁相互作用）、金属与配体比例以及分子中三价钆（GdIII）含量对磁制冷性能的影响机制。
