A Zig‐Zag [Mn II 4 ] Cluster from a Novel Bis(β‐diketonate) Ligand

A new ligand, H 5 L3, has been synthesized featuring seven linearly arranged oxygen donors in form of two 1,3‐diketone and three phenol groups. The X‐ray structure of H 5 L3 unveils a rare case where one of the diketones is in the enolic form and the other one in the bis(carbonyl) form. This structure is shown by 1 H NMR to persist in solution. Reaction of H 5 L3 with Mn(AcO) 2 in pyridine leads to the novel tetranuclear cluster [Mn 4 (H 2 L3) 2 (OAc) 2 (py) 5 ] ( 1 ), which displays an unusual core in form of a zig‐zag chain. Bulk magnetic measurements revealed the existence of weak antiferromagnetic coupling within the molecule. Numerical fits to a model described by the Hamiltonian H = –2 J 1 ( S 1 S 2 + S 3 S 4 ) – 2 J 2 ( S 2 S 3 ) yield coupling constants of J 1 = –2.23 cm –1 , J 2 = –0.85 cm –1 and g = 2.08. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)