Mononuclear and mixed-valence trinuclear manganese complexes containing tripodal tetradentate ligands. Phenolate, carboxylato, and alkoxo bridges

Manganese complexes containing tripodal tetradentate ligands with an N2O2 donor set (H(2)L(1): N,N-bis(2-hydroxybenzyl)-N',N'-dimethylethylenediamine, H(2)L(2): N-(3,5-di-t-butyl-2-hydroxybenzyl)-N-(2-hydroxybenzyl)-N',N'-dimethylethylenediamine, H(2)L(3): 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 L(3) ligand gave a mononuclear complex, [Mn(L(3))(mcba)(CH3OH)], where mcba is a m-chlorobenzoate anion; the structure has been determined by X-ray analysis. The trinuclear complexes are formulated as [Mn-3(L '')(2)(carboxylato)(2)(OCH3)(2)] (n=1,2). For the L(4) and L(5) ligands (H(2)L(4): N,N-bis(5-methoxy-2-hydroxybenzyl)-N',N'-dimethylethylenediamine, H(2)L(5): 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 Mn-III-Mn-II-Mn-III. The Mn-III and Mn-II cores are bridged by phenolate, carboxylate, and alkoxide groups, and the manganese cores are separated in the range of 3.14 and 3.17 Angstrom. The variable-temperature magnetic susceptibility measurements of the mixed-valence trinuclear complexes revealed that the spin exchange coupling constants (J) between Mn-III and Mn-II ions range from -0.25 to 1.9 cm(-1). The exchange interactions are weak, and both antiferromagnetic and ferromagnetic interactions were observed.