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

Abstract

Two novel bis(oxo)-bridged dinuclear manganese(IV) complexes with the binucleating ligand o-phenylenebis(oxamate) (opba), formulated as (Me 4N) 4[Mn 2O 2(opba) 2] ( 1a) and (Me 4N) 2(Ph 4P) 2[Mn 2O 2(opba) 2] · 8H 2O ( 1b), have been synthesized and characterized structurally and magnetically. Like the parent complex (Ph 4P) 4[Mn 2O 2(opba) 2] · 4H 2O ( 1c), they possess unique Mn 2(μ-O) 2 bridging cores with two additional o-phenylenediamidate bridges which lead to exceptionally short Mn–Mn distances (2.63–2.67 Å) and fairly bent Mn–O–Mn angles (93.8–95.5°). 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 3 d x 2 - y 2 type superexchange pathway via the oxo bridges with a small but nonnegligible contribution from direct 3 d x 2 - y 2 type Mn–Mn σ-bond.