Heterometallic Ce^IV/ V^V Oxo Clusters with Adjustable Catalytic Reactivities

Abstract

Heterometallic Ce^IV/M oxo clusters are underexplored yet and can benefit from synergistic properties from combining cerium and other metal cations to produce efficient redox catalysts. Herein, we designed and synthesized a series of new Ce₁₂V₆ oxo clusters with different capping ligands: <b>Ce</b>_<b>12</b><b>V</b>_<b>6</b><b>-SO</b>_<b>4</b>, <b>Ce</b>_<b>12</b><b>V</b>_<b>6</b><b>-OTs</b> (OTs: toluenesulfonic acid), and <b>Ce</b>_<b>12</b><b>V</b>_<b>6</b><b>-NBSA</b> (NBSA: nitrobenzenesulfonic acid). Single crystal X-ray diffraction (SCXRD) for all three structures reveals a Ce₁₂V₆ cubane core formulated [Ce₁₂(VO)₆O₂₄]¹⁸⁺ with cerium on the edges of the cube, vanadyl capping the faces, and sulfate on the corners. While infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV-vis), electrospray ionization mass spectrometry (ESI-MS), and proton nuclear magnetic resonance (¹H NMR) proved the successful coordination of the organic ligands to the Ce₁₂V₆ core, liquid phase ⁵¹V NMR and small-angle X-ray scattering (SAXS) confirmed the integrity of the clusters in the organic solutions. Furthermore, functionalization of the Ce₁₂V₆ core with organic ligands both provides increased solubility in term of homogeneous application and introduces porosity to the assemblies of <b>Ce</b>_<b>12</b><b>V</b>_<b>6</b><b>-OTs</b> and <b>Ce</b>_<b>12</b><b>V</b>_<b>6</b><b>-NBSA</b> in term of heterogeneous application, thus allowing more catalytic sites to be accessible and improving reactivity as compared to the nonporous and less soluble <b>Ce</b>_<b>12</b><b>V</b>_<b>6</b><b>-SO</b>_<b>4</b>. Meanwhile, the coordinated ligands also influenced the electronic environment of the catalytic sites, in turn affecting the reactivity of the cluster, which we probed by the selective oxidation of 2-chloroethyl ethyl sulfide (CEES). This work provides a strategy to make full use of the catalytic sites within a class of inorganic sulfate capped clusters <i>via</i> organic ligand introduction.