Mixed-valence trinuclear manganese(II/III) complexes of flexible tetradentate N2O2 ligands: Ferromagnetic versus antiferromagnetic coupling

Four linear trinuclear manganese complexes containing ligands with an N2O2 donor set have been prepared and characterized structurally and magnetically. The complexes have the general formula [Mn3(Ln)2(OAc)2(OCH3)2] (n = 1, 2, 3, 4. H2L1 = N,N′-dimethyl-N,N′-(2-hydroxy-4,5-dimethylbenzyl)ethylenediamine, H2L2 = N,N-bis(3,4-dimethyl-2-hydroxybenzyl)-N-(2-pyridylmethyl)amine, H2L3 = N,N-bis(3,4-dimethyl-2-hydroxybenzyl)-N,N′-dimethylethylenediamine, H2L4 = N,N-bis(3,4-dimethyl-2-hydroxybenzyl)-2-aminoethanol). X-ray single-crystal structure analyzes of the complexes show that the linear MnIII–MnII–MnIII cores are triply bridged by phenolate, acetate (syn–syn), and MeO− groups with the MnIII and MnII distances in the range 3.123(3)–3.167(4) Å. Magnetic studies show that the spin exchange coupling constants (J) between MnIII and MnII ions range from −1.58(1) to 1.15(3) cm−1 (Hˆ=-2J(Sˆ1·Sˆ2+Sˆ1·Sˆ3)). The antiferromagnetic and ferromagnetic interactions were analyzed based on the structural features, and the MnIII–O–MnII bond angles have been found to be the dominant factor affecting the intermetallic magnetic coupling.

Four mixed-valence trinuclear Mn(II/III) complexes that have similar structural motif display intramolecular intermetallic antiferromagnetic or ferromagnetic coupling. The results verify that bridging MnII–Oalkoxide–MnIII bond angles are crucial to the magnetic coupling of the linear manganese complexes: the interaction becomes less antiferromagnetic with larger Mn–Oalkoxide–Mn bond angles.Figure optionsDownload as PowerPoint slideHighlights
► Four mixed-valence trinuclear Mn(II/III) complexes are derived from tetradentate tripodal ligands.
► The analogous complexes display intramolecular antiferromagnetic or ferromagnetic coupling.
► The results verify that the MnII–Oalkoxide–MnIII bond angles are crucial to the magnetic coupling.