New chromotropic behavior of manganese complexes with 1,4,7-triazacyclononane-N,N′,N″-tricarboxylates

Synthesis and characterization of a manganese(III) complex containing 1,4,7-triazacyclononane-N,N′,N″-tripropionate (tacntp) are reported. The complex [Mn(acntp)](II) (1) crystallizes in a hexagonal environment of a facial N3O3 donor set with space group P3c1, apparently violating the Jahn–Teller effect. Complex 1 is more stable for reduction than the corresponding complex [Mn(tacnta)] (2) where, tacnta is a triacetate homologue of tacntp. Both complexes showed reversible electrochromism in aqueous solutions. In addition, complex 1 was reversibly reduced in a methanol solution too. They also showed solvatochromism in a variety of solvents. The UV–Vis absorption maxima of the complexes were correlated to the acceptor number of the solvent.