Large Magnetocaloric Effect in a Ferromagnetically Coupled [Mn 3 Gd] Complex With a Spin Ground State of S = 11

A series of 3d‐4f heterometallic tetranuclear complexes, (TEA)[Mn 3 Gd(L) 3 (NO 3 ) 4 (CH 3 CN) 2 ] ( [Mn 3 Gd] ), (TEA)[Mn 3 La(L) 3 (NO 3 ) 4 (CH 3 CN) 2 ] ( [Mn 3 La] ), and (TEA) 2 [Zn 3 Gd(L) 3 (NO 3 ) 5 ] ( [Zn 3 Gd] ) (TEA = triethylammonium), were synthesized by using a bis‐diketonato ligand H 2 L ((3 Z ,5 Z )‐4,5‐dihydroxy‐3,5‐octadiene‐2,7‐dione), and their cryomagnetic properties were investigated. [Mn 3 La] complex, having a diamagnetic La(III) ion, shows negligibly small antiferromagnetic interactions between terminal Mn(II) ions. On the other hand, [Mn 3 Gd] complex shows relatively strong intramolecular ferromagnetic interactions leading to S = 11 spin ground state. Magnetic entropy changes of complexes were estimated from field dependences of magnetizations at various temperatures and the [Mn 3 Gd] complex showed large –Δ S m values of 4.08 J kg −1 K −1 at 25 K under 5 T, suggesting that ferromagnetically coupled 3d–4f clusters are promising candidates for magnetocaloric materials applicable to hydrogen liquefaction.