Single crystal structure features of a new tri-hetero metallic polymer, a catalyst for mild homogeneous peroxidative oxidation of cyclohexane

Abstract

This work reports the synthesis of a new water-soluble tri-hetero metallic polymer formulated as [Cu0.152 Mn0.848 (μ-dipic)2{Na2 (μ-H2O)4}]n·nH2O (1) where dipic2− ​= ​pyridine 2,6-dicarboxylato. Elemental analysis, fourier transformed-infrared (FT-IR) spectroscopy, thermogravimetric analyses (TGA), differential thermal analysis (DTA), vibration sample magnetometer (VSM), and single-crystal X-ray diffraction (SC-XRD) analysis were used for characterization of polymer 1. According to crystal structure analysis, polymer 1 belongs to a monoclinic system with space group C2/m, while cations of Cu2+ and Mn2+ occupy 15.2% and 84.8% of octahedral sites, respectively. The divalent ions of Mn2+ and Cu2+ show coordination number six, which have significantly distorted octahedral geometry. The as-synthesized polymer presents a 3D network extended by monomeric [Mn/Cu(dipic)2]2– units and polymeric{[Na2(μ-H2O)4]2+}n chains with extensive hydrogen bonding between crystal water molecules and adjacent layers. Polymer 1 was used as homogeneous catalyst for the mild oxidation of cyclohexane to the corresponding products (alcohol and ketone) in the presence of hydrogen peroxide as an environmentally friendly oxidant. To obtain the highest catalytic performance, various reaction parameters such as temperature, reaction time, the molar ratio of nitric acid to the catalyst, and the molar ratio of oxidant to the catalyst, were optimized. As a result, polymer 1 exhibited the maximum catalytic performance with a total product yield of 39.2% under optimized conditions. The mechanism of cyclohexane oxidation catalyzed by polymer 1 was also discussed.