Antiferromagnetic porous metal–organic framework containing mixed-valence [Mn^II₄Mn^III₂(μ₄-O)₂]¹⁰⁺ units with catecholase activity and selective gas adsorption

Abstract

A multifunctional porous metal organic framework based on mixed-valence hexa-nuclear [Mn^III₂Mn^II₄O₂(pyz) ₂(C₆H₅CH₂COO)₁₀] (pyz = pyrazine) units has been synthesized. The complex has been characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis, and variable-temperature magnetic measurements. The structural analysis reveals that the bidentate pyz molecules connect each [Mn₆] unit to its four [Mn₆] neighbors through the peripheral Mn(II) centers, giving rise to a three-dimensional (3D) distorted diamond-like porous framework. Variable-temperature (2–300 K) magnetic susceptibility measurements show the presence of dominant antiferromagnetic interactions within the discrete [Mn₆] cluster that have been fitted with a model containing three exchange constants developed for the complex (J₁ = −8.6 cm^–1, J₂ = −3.9 cm^–1 and J₃ = −100.0 cm^–1). Using 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, catecholase activity of the complex has been studied; the turn over number is determined to be of 2547 h^–1 in acetonitrile. This porous compound shows remarkable selectivity for adsorption of CO₂ over N₂ that may be correlated with the effect of window flexibility of the pore to the corresponding adsorbate molecules.