Synthesis and Characterization of a [Mn₁₂O₁₂(O ₂CR)₁₆(H₂O)₄] Complex Bearing Paramagnetic Carboxylate Ligands. Use of a Modified Acid Replacement Synthetic Approach

A new modified approach for the synthesis of Mn₁₂ clusters, based on the use of complex [Mn₁₂O₁₂(O₂C ^tBu)₁₆(H₂O)₄] (2) as starting material to promote the acidic ligand replacement, is presented here. This new synthetic approach allowed us to obtain complex [Mn₁₂O ₁₂(O₂CC₆H₄N(O^•) ^tBu)₁₆(H₂O)₄] (3), whose preparation remained elusive by direct replacement of the acetate groups of Mn₁₂Ac (1). Complex 3 bearing open-shell radical units, was prepared to increase the total spin number of its ground state, and consequently, to increase T_B, with the expectation that the radical ligands may couple ferromagnetically with the Mn₁₂ core. Unfortunately, magnetic measurements of complex 3 revealed that the sixteen radical carboxylate ligands interact antiferromagnetically with the Mn₁₂ core to yield a S = 2 magnetic ground state.