Tripodal Trimanganese(III) Complexes of New Unsymmetrical Pentadentate Ligands Derived from 2‐(Salicylideneamino)phenol: Syntheses, Crystal Structures and Properties

Trinuclear manganese(III) complexes of new unsymmetrical pentadentate ligands, 6‐hydroxy‐2‐(2‐hydroxyphenyl)‐5‐(salicylideneamino)benzoxazole (H 3 L 1 ) and 5‐(5,6‐benzosalicylideneamino)‐6‐hydroxy‐2‐(2‐hydroxynaphthyl)benzoxazole (H 3 L 2 ), [Mn 3 (L 1 ) 3 (CH 3 OH) 3 ] ( 1 ) and [Mn 3 (L 2 ) 3 (dmf)(CH 3 OH)(H 2 O)] ( 2 ) (dmf = N , N ‐dimethylformamide), have been prepared. The structures of the ligands H 3 L 1 , H 3 L 2 and complex 1 were determined by X‐ray crystallography, which revealed that the ligands have two distant chelating sites. The molecular structure of 1 is regarded as a tripodal pyramid with a cavity of about 3 Å diameter. Each Mn III ion is coordinated by ONO atoms from a tridentate Schiff base site and ON atoms from a benzoxazole site of two respective H 3 L 1 ligands. The intramolecular Mn ··· Mn distances for 1 are in the range 8.0683–8.1791 Å, and the nearest intermolecular Mn ··· Mn distance, 5.7824(15) Å, is shorter than theintramolecular values. Magnetic measurements of 1 indicate that weak antiferromagnetic interactions ( J = –0.2 cm –1 , g = 2.0) are dominant in the trinuclear manganese(III) core. Cyclic voltammogram of 1 in dmf showed obscure redox couples assigned to two single‐electron transfer processes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)