Magnetocaloric Properties of Heterometallic 3d-Gd Complexes Based on the [Gd(oda)3]3− Metalloligand.

A series of heterometallic 3d-Gd³⁺ complexes based on a lanthanide metalloligand, [M(H₂O)₆][Gd(oda)₃] ⋅3 H₂O [M=Cr³⁺ ( 1-Cr)] (H₂oda=2,2′-oxydiacetic acid), [M(H₂O)₆][MGd(oda)₃]₂ ⋅3 H₂O [M=Mn²⁺ ( 2-Mn), Fe²⁺ ( 2-Fe) and Co²⁺ ( 2-Co)], and [M₃Gd₂(oda)₆(H₂O)₆] ⋅12 H₂O [M=Ni²⁺ ( 3-Ni), Cu²⁺ ( 3-Cu), and Zn²⁺ ( 3-Zn)], are reported. Magnetic and heat-capacity studies revealed a significant impact on the magnetocaloric effect depending on the anisotropy of the 3d transition metal ions, as confirmed by comparison of the observed maximum values of −Δ S_m between complexes 2-Co and 1-Cr. In these two complexes, the 3d metal ions have the same spin ( S=3/2 for Co²⁺ and Cr³⁺ ions), and the theoretical calculation suggested a larger −Δ S_m value for 2-Co (47.8 J K⁻¹ kg⁻¹) than 1-Cr (37.5 J K⁻¹ kg⁻¹); however, the significant anisotropy of Co²⁺ ions in 2-Co, which can result in smaller effective spins, gives a smaller value of −Δ S_m for 2-Co (32.2 J K⁻¹ kg⁻¹) than for 1-Cr (35.4 J K⁻¹ kg⁻¹) at Δ H=9 T. [ABSTRACT FROM AUTHOR]