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

A series of heterometallic 3d–Gd 3+ complexes based on a lanthanide metalloligand, [M(H 2 O) 6 ][Gd(oda) 3 ] ⋅ 3 H 2 O [M=Cr 3+ ( 1‐Cr )] (H 2 oda=2,2′‐oxydiacetic acid), [M(H 2 O) 6 ][MGd(oda) 3 ] 2 ⋅ 3 H 2 O [M=Mn 2+ ( 2‐Mn ), Fe 2+ ( 2‐Fe ) and Co 2+ ( 2‐Co )], and [M 3 Gd 2 (oda) 6 (H 2 O) 6 ] ⋅ 12 H 2 O [M=Ni 2+ ( 3‐Ni ), Cu 2+ ( 3‐Cu ), and Zn 2+ ( 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 Co 2+ and Cr 3+ 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 Co 2+ 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.