Synthesis and Characterization of a [Mn_(12)O_(12)(O_2CR)_(16)(H_2O)_4] Complex Bearing Paramagnetic Carboxylate Ligands. Use of a Modified Acid Replacement Synthetic Approach

摘要

A new modified approach for the synthesis of Mn_(12) clusters, based on the use of complex [Mn_(12)O_(12)(O_2CR)_(16)(H_2O)_4] (2) as starting material to promote the acidic ligand replacement, is presented here. This new synthetic approach allowed us to obtain complex [Mn_(12)O_(12)(O_2CC_6H_4N(O)~tBu)_(16)(H_2O)_4] (3), whose preparation remained elusive by direct replacement of the acetate groups of Mn_(12)Ac (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 Mn_(12) core. Unfortunately, magnetic measurements of complex 3 revealed that the sixteen radical carboxylate ligands interact antiferromagnetically with the Mn_(12) core to yield a S = 2 magnetic ground state.