Masakazu HIROTSU,* Masaaki KOJIMA* and Yuzo YOSHIKAWA (*Okayama Univ.)
[Bull. Chem. Soc. Jpn. 70, 649 (1997)]
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'-dimethyl-ethylenediamine, 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.