Large Magnetocaloric Effect in a Ferromagnetically Coupled [Mn3Gd] Complex With a Spin Ground State of S = 11.

A series of 3d-4f heterometallic tetranuclear complexes, (TEA)[Mn3Gd(L)3(NO3)4(CH3CN)2] ([Mn3Gd]), (TEA)[Mn3La(L)3(NO3)4(CH3CN)2] ([Mn3La]), and (TEA)2[Zn3Gd(L)3(NO3)5] ([Zn3Gd]) (TEA = triethylammonium), were synthesized by using a bis-diketonato ligand H2L ((3Z,5Z)-4,5-dihydroxy-3,5-octadiene-2,7-dione), and their cryomagnetic properties were investigated. [Mn3La] complex, having a diamagnetic La(III) ion, shows negligibly small antiferromagnetic interactions between terminal Mn(II) ions. On the other hand, [Mn3Gd] 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 [Mn3Gd] complex showed large -ΔSm 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.