Abstract
Manganese clathrochelate complexes are rare, and the ones successfully isolated in the solid state are not stable in water and organic solvents. The manganese ion in these cage compounds typically attains the oxidation state +2 and high-spin state, which contributes to complex instability. Herein, we present the first report of a mononuclear manganese clathrochelate, in which the encapsulated metal exists in the oxidation state +4. The complex is formed spontaneously starting from Mn2+, formaldehyde and oxalodihydrazide in alkaline aqueous media in the presence of atmospheric oxygen. It was crystallized and characterized in the form of ionic (Ph4As)2[MnIV(L-6H)]∙13.5H2O (1) and coordination polymer {[Na2MnIV(L-6H)(H2O)3]∙4H2O}n (2) solvates, where L-6H is the biscapped macrobicyclic ligand bearing six deprotonated hydrazide groups. Solid-state cryomagnetochemical, EPR and DFT studies of 1 are indicative of a high spin Mn4+ d3 ion with a quartet electronic ground state. Both compounds are extremely stable in the crystalline state and in solutions. They show rich redox chemistry thus showcasing the potential of their application in redox catalysis.
