Two Polymorphic Polyoxometalate-Based Metal-Organic Frameworks for the Efficient Synthesis of Functionalized Sulfoxides and Detoxification of Mustard Gas Simulants

The development of high-efficient catalysts for the oxidation reaction of sulfides received much attention in recent years due to the extensive applications of such reactions from the utility in pharmaceutical chemistry and biology to the detoxification of chemical warfare agents in war. Herein, we report two innovative polyoxometalate-based metal-organic frameworks (POMOFs) {[epsilon-(PMo8Mo4O37)-Mo-V-O-VI(OH)(3)][Zn-2(C10N2H8)(H2O)(2)](2)}(2)center dot 8H(2)O (1-alpha and 1-beta), which were characterized by elemental analysis, UV-vis diffuse reflectance spectroscopy, X-ray single-crystal and powder diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy techniques in detail. Single-crystal X-ray diffraction analysis indicates that 1-alpha and 1-beta are polymorphic with the identical compositions and analogical structures. Compounds 1-alpha and 1-beta are both connected by Zn-4-epsilon-Keggin polyoxoanions and 4,4'-bipyridine (bpy) ligands to form twofold interpenetrated three-dimensional POMOF structures. 1-beta can be seen as a rotational polymorph of 1-alpha, that is, 1-alpha takes the b axis as the rotation axis and rotates similar to 39 degrees clockwise to obtain 1-beta. Both compounds 1-alpha and 1-beta can be used as heterogeneous catalysts to catalyze the selective oxidation of multitudinous sulfides with H2O2 as an oxidant. When the oxidation of methyl phenyl sulfide was used as the template reaction, the yield of methyl phenyl sulfoxide is close to 100% within 30 min by 1-alpha and 1-beta and the oxidant utilization efficiency is more than 93%. Gratifying catalytic effects have also been achieved in the selective oxidation of phenyl and aliphatic sulfide derivatives. Simultaneously, both 1-alpha and 1-beta showed an extraordinary degradation efficiency of 2-chloroethyl ethyl sulfide and have a half lifetime (t(1/2)) approximately 2.5 or 3 min, respectively, with 100% selectivity toward the nontoxic product 2-chloroethyl ethyl sulfoxide and an abnormally high oxidant utilization efficiency (94.5% for 1-alpha and 94.3% for 1-beta) at room temperature. In addition, after seven cycles and continuous cycle catalytic experiments, their structures remained and catalytic activities did not decrease obviously, revealing their outstanding recyclability and structural stability.

Automated summary

In this study, two innovative polyoxometalate-based metal-organic frameworks (POMOFs) were reported as efficient catalysts for the selective oxidation of sulfides. These catalysts exhibited high catalytic activity, exceptional oxidant utilization efficiency, and remarkable structural stability, showing great potential for practical applications in oxidation reactions.