Linear Pentanuclear 3d–4f M‐Gd‐M‐Gd‐M Complexes Prepared From a One‐Pot Reaction Show Intramolecular Ferromagnetic Interactions (M  =  Cu, Ni, and Co)

Three novel 3d–4f pentanuclear complexes, [Cu ^II ₃ Gd ^III ₂ (L) ₄ (NO ₃ ) ₄ (H ₂ O) ₈ ] ( [Cu ₃ Gd ₂ ] ), [Ni ^II ₃ Gd ^III ₂ (L) ₄ (NO ₃ ) ₄ (H ₂ O) ₈ ] ( [Ni ₃ Gd ₂ ] ), and [Co ^II ₃ Gd ^III ₂ (L) ₄ (NO ₃ ) ₄ (H ₂ O) ₈ ] ( [Co ₃ Gd ₂ ] ), were synthesized via one‐pot reactions using a new multidentate ligand H ₂ L (= 6‐(3‐oxoheptanoyl)picolinate) and corresponding metal salts. The ligand H ₂ L possesses bi‐ and tridentate chelating sites, along with a peripheral bridging carboxylate group. Single‐crystal X‐ray structural analyses revealed selective formation of the heterometallic pentanuclear core with a linear arrangement of metal ions (M‐Gd‐M‐Gd‐M). The M‐Gd‐M‐Gd‐M core is composed of two M‐Gd dinuclear units bridged by a central M ion (M = Cu, Ni, and Co). Temperature‐dependent magnetic susceptibility measurements for the three complexes indicate that ferromagnetic interactions are operative in the M‐Gd‐M‐Gd‐M core. The maximum magnetic entropy changes were estimated to be 18.2 J kg ⁻¹  K ⁻¹ (2.4 K) for [Cu ₃ Gd ₂ ] , 17.6 J kg ⁻¹  K ⁻¹ (2.4 K) for [Ni ₃ Gd ₂ ] , and 18.2 J kg ⁻¹  K ⁻¹ (2.8 K) for [Co ₃ Gd ₂ ] (under 5 T).