title: Modulating Magnetic Refrigeration through Structural Variation in CoII/III-GdIIIClusters.
abstract: 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 CoIIcenters in compound 1, mixed valent Co centers (CoII/CoIII) in compound 2, and only CoIIIcenters 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 (-ΔSmvalues of 28.14, 25.06, and 29.19 J kg-1K-1for 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 GdIIIin the molecule.
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843-3255, United States.
authors.forename: Javeed Ahmad
authors.initials: JA
authors.lastname: Sheikh
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843-3255, United States.
authors.forename: Abraham
authors.identifier: http://orcid.org/0000-0001-8318-8122
authors.initials: A
authors.lastname: Clearfield