Syntheses, structures, and magnetic properties of a series of Mn-M-Mn trinuclear complexes with different spin configurations.

A series of trinuclear complexes, [MnII2Y ^III (L) ₂ (HL) ₂ (NO ₃ ) ₃ ][Y ^III (NO ₃ ) ₅ ]·7H ₂ O (1'), [MnII2Gd ^III (HL) ₄ (NO ₃ ) ₄ ] ₂ [MnII2Gd ^III (L)(HL) ₃ (NO ₃ ) ₄ ][Gd ^III (NO ₃ ) ₅ ] ₄ ·2( o -Xy)·12H ₂ O (2') and [MnII3(L)(HL) ₂ (NO ₃ ) ₄ ](NO ₃ )·1.25( p -Xy) (3'), were synthesized using a β-diketone ligand HL (HL = 1,3-bis(pyridin-2-yl)propane-1,3-dione). X-ray structural analyses revealed that each complex has a trinuclear core with an Mn(II)-M-Mn(II) arrangement (M = Y ^III (1), Gd ^III (2), and Mn ^II (3)). In 1' with a diamagnetic Y(III) ion, negligible antiferromagnetic interactions between terminal Mn(II) ions are operative. On the other hand, 2' shows ferromagnetic interactions between Mn(II) and Gd(III) ions, affording a spin ground state of S _T = 17/2. The homometallic Mn(II) ₃ complex of 3' has an S _T = 5/2 spin ground state resulting from the antiferromagnetic interactions between neighboring Mn(II) ions. The maximum magnetic entropy change (-Δ S _m ) of 1'-3' was estimated to be 12.3, 24.8, and 8.0 J kg ^-1 K ^-1 , respectively.