Incorporation of cubane-type Mo3S4 molybdenum cluster sulfides in the framework of mesoporous silica

Abstract

A new molybdenum siloxo cluster of formula [Mo3S4(dmpe)3(MPTES)3]PF6 (dmpe = 1,2-(bis)dimethylphosphinoethane; MPTES = (3-mercaptopropyl)triethoxysilane) has been synthesized with the ultimate goal of incorporating it into ordered mesoporous silica via covalent attachment. For this purpose, two different approaches, in situ and grafting, are employed. The first one is based in the co-condensation of the Mo3S4 siloxo cluster and tetraethylorthosilicate (TEOS) as mixed silicon sources in the presence of a surfactant (CTAB). The use of this approach allows for the incorporation of the Mo3S4 siloxo cluster into the structure of the mesoporous silica. For comparison purposes, the same Mo3S4 siloxo cluster has been immobilized on the surface of conventional mesoporous silica MCM-41, using more traditional grafting techniques. The physical and structural properties of both series of materials, containing different Mo3S4 cluster loadings, have been thoroughly investigated by means of powder X-ray diffraction (XRD), N2 adsorption/desorption isotherms, transmission electron microscopy (TEM), magic-angle spinning (MAS) 31P and CP/MAS 29Si NMR, Fourier transform infrared (FT-IR) and UV–Vis diffuse reflectance (DRUV–Vis) spectroscopies. The chemical and structural integrity of the diphosphino Mo3S4 siloxo cluster is preserved in both the in situ and grafted mesoporous silica based materials. Depending on the incorporation approach, immobilization of the trinuclear sulfido cluster occurs into the silica matrix structure for the in situ materials or on the surface for the grafted ones. With these results, we show that it is possible to extend the incorporation of chemical functionalities into the structure of mesoporous materials to Mo3S4 siloxo clusters.