Heterospin MnIII complex as a reaction product of the redox-induced change in the ligand coordination mode

Abstract

The reaction of MnII chloride with imino nitroxide radical, 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (HL2), affords the MnIII complex [MnL22L3]·Me2CO, a distinctive feature of which is the simultaneous presence in the ligand shell of both the initial imino nitroxide and the product of its reduction 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide (HL3). The reaction involves the oxidation of MnII to MnIII and the reduction of the imino nitroxide radical to the corresponding amidine oxide along with a change in the coordination mode of the heterocyclic ligand on going from L2 to L3. The MnIII ion forms with L2 six-membered metallocycles typical of Schiff bases, whereas with L3 MnIII forms a seven-membered metallocycle due to the coordination of L3 by oxygen atoms of the phenol and N-oxide It was found in a similar reaction of NiII chloride with imino nitroxide HL2 that no oxidation of the metal occurred and bis(chelate) [NiL22(H2O)2]·2Me2CO was formed in the solid phase. The molecular and crystal structures of the compounds were determined, and their magnetic properties were studied.