Synthesis and Structural Characterization of Dinuclear Manganese(III) Complexes with Cyclam-Based Macrocyclic Ligands Having Schiff-Base Pendant Arms as Chelating Agents

Abstract

Abstract Reaction of a series of dodecadentate ligands (H4L), 1,4,8,11-tetrakis(salicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane and its substituted derivatives, with manganese(II) salts afforded ten dinuclear manganese(III) complexes, [Mn2X2L] (X = O2CCH3, O2CC6H5, and N3), which were characterized by analyzing infrared and electronic spectra and determining the temperature dependence of magnetic susceptibilities (4.5–300 K). Single-crystal X-ray crystallography of [Mn2(O2CCH3)2(tbsaec)]·2CHCl3 (3·2CHCl3) (H4tbsaec = 1,4,8,11-tetrakis(5-bromosalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane), [Mn2(O2CC6H5)2(tbsaec)] (4), [Mn2(O2CC6H5)2(tcsaec)] (6) (H4tcsaec = 1,4,8,11-tetrakis(5-chlorosalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane), [Mn2(N3)2(tnaec)]·2CHCl3 (7·2CHCl3) (H4tnaec = 1,4,8,11-tetrakis(2-hydroxy-1-naphthylmethylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane), [Mn2(O2CCH3)2(tmsaec)] (8) (H4tmsaec = 1,4,8,11-tetrakis(3-methoxysalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane) showed that each manganese(III) ion is chelated by two Schiff-base pendant arms outside the central tetraazacyclotetradecane ring, forming an axially compressed octahedron (for 3, 4, 6, and 8) or trigonal bipyramid (for 7) with an intramolecular Mn–Mn distance of 9.676(4)–10.096(2) Å. In accordance with the crystal structures, the magnetic interaction between the two manganese ions was very weak with a rather significant zero-field splitting of the manganese(III) ions.