Mononuclear and Mixed-Valence Trinuclear Manganese Complexes Containing Tripodal Tetradentate Ligands. Phenolato, Carboxylato, and Alkoxo Bridges

Abstract

Abstract Manganese complexes containing tripodal tetradentate ligands with an N2O2 donor set (H2L1: N,N-bis(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine, H2L2: N-(3,5-di-t-butyl-2-hydroxybenzyl)-N-(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine, H2L3: N,N-bis(3,5-di-t-butyl-2-hydroxybenzyl)-N′,N′-dimethylethylenediamine) have been prepared. The mononuclear and trinuclear complexes with the additional carboxylate ligand were isolated. The steric effect of the 3-positioned t-butyl groups on the aromatic rings of the tripodal ligand controls the type of the complex structure. The L3 ligand gave a mononuclear complex, [Mn(L3)(mcba)(CH3OH)], where mcba is a m-chlorobenzoate anion; the structure has been determined by X-ray analysis. The trinuclear complexes are formulated as [Mn3(Ln)2(carboxylato)2(OCH3)2] (n = 1, 2). For the L4 and L5 ligands (H2L4: N,N-bis(5-methoxy-2-hydroxybenzyl)-N′,N′-dimethylethylenediamine, H2L5: N,N-bis(5-chloro-2-hydroxybenzyl)-N′,N′-dimethylethylenediamine), trinuclear complexes were also obtained. Three trinuclear complexes were also structurally characterized by X-ray analysis. The three manganese cores are arranged linearly, and the structural parameters indicate that the oxidation states are MnIII–MnII–MnIII. The MnIII and MnII cores are bridged by phenolate, carboxylate, and alkoxide groups, and the manganese cores are separated in the range of 3.14 and 3.17 Å. The variable-temperature magnetic susceptibility measurements of the mixed-valence trinuclear complexes revealed that the spin exchange coupling constants (J) between MnIII and MnII ions range from −0.25 to 1.9 cm−1. The exchange interactions are weak, and both antiferromagnetic and ferromagnetic interactions were observed.