'Metal Complexes as Ligands' for the Synthesis of Coordination Polymers: A Mn Monomer as a Building Block for the Preparation of an Unprecedented 1-D {MnMn} Linear Chain.

A relatively unexplored synthetic route in redox-active Mn(II/III) coordination chemistry has been employed toward the preparation of a new mixed-valence Mn 1-D linear chain from the reaction of [Mn(sacb)] precursor with a Mn source, where sacbH is the Schiff base ligand -salicylidene-2-amino-5-chlorobenzoic acid. The mononuclear (PrNH)[Mn(sacb)] () compound was obtained in excellent yields (>85%) from the 1:2:3 reaction of Mn(OCMe)∙4HO, sacbH and PrNH, respectively. In , the two doubly deprotonated sacb ligands act as O,N,O-tridentate chelates, while the second carboxylate O atom of sacb is dangling and H-bonded to the PrNH countercation. Complex was subsequently used as a 'ligand' to react stoichiometrically with the 'metal' Mn(NO)∙4HO, thus leading to the 1-D coordination polymer {MnMn(sacb)(HO)(MeOH)} () in good yields (~50%). The removal of PrNH from the vicinity of the [Mn(sacb)] metalloligand has rendered possible (vide infra) the coordination of the second O of sacb to neighboring {Mn(HO)(MeOH)} units, and consequently the formation of the 1-D polymer . Direct-current (dc) magnetic susceptibility studies revealed the presence of very weak antiferromagnetic exchange interactions between alternating Mn and Mn atoms with a coupling constant of = -0.08 cm for = 2.00. The combined results demonstrate the potential of the 'metal complexes as ligands' approach to yield new mixed-valence Mn(II/III) coordination polymers with interesting structural motifs and physicochemical properties.