High-valent bis(oxo)-bridged dinuclear manganese oxamates: Synthesis, crystal structures, magnetic properties, and electronic structure calculations of bis(n-oxo)dimanganese(IV) complexes with a binucleating o-phenylenedioxamate ligand

Abstract

[EN] Two novel bis(oxo)-bridged dinuclear manganese(IV) complexes with the binucleating ligand o-phenylenebis(oxamate) (opba), formulated as (Me4N)(4)[Mn2O2(opba)(2)] (1a) and (Me4N)(2)(Ph4P)(2)[Mn2O2(opba)(2)] (.) 8H(2)O (1b), have been synthesized and characterized structurally and magnetically. Like the parent complex (Ph4P)(4)[Mn2O2(opba)(2)] (.) 4H(2)O (1c), they possess unique Mn-2(mu-O)(2) bridging cores with two additional o-phenylenediamidate bridges which lead to exceptionally short Mn-Mn distances (2.63-2.67 angstrom) and fairly bent Mn-O-Mn angles (93.8-95.5 degrees). Complexes 1a-c show a moderate to strong antiferromagnetic coupling between the two high-spin Mn-IV ions through the bis(oxo)bis(o-phenylenediamidate) quadruple bridge (-J = 70-164 cm(-1); H = -JS(1) (.) S-2) Along this series, the -J values increase with the shortening of the Mn-Mn distance and/or the lessening of the Mn-O-Mn angle. Electronic structure calculations on model complexes reproduce the observed dependence of -J with the Mn-O-Mn angle at short intermetallic distances, and reveal that the magnetic coupling is dominated by the in-plane 3d(x2-y2) type superexchange pathway via the oxo bridges with a small but nonnegligible contribution from direct 3d(x2-y2) type Mn-Mn sigma-bond.