No abstract

Various isoreticular mono-(Co 2+ , Ni 2+ , Cu 2+ and Zn 2+) and bimetallic (Co-Ni, Co-Zn, Mn-Ni) trimesate MOFs have been prepared by a fast (10 minutes) and green synthesis method from aqueous solutions, at room temperature and ambient pressure. A combined XRD and SEM/EDX analysis clearly revealed that bimetallic compounds for true solid solutions rather than a simple physical mixture of pure phase monometallic compounds. Moreover, a detailed evaluation of the evolution of cell parameters with the composition provides strong evidences indicating a preferential occupation of one crystallographic position (bidentate terminal sites) by Co 2+ (or Mn 2+) ions. This leads to a precise and predictable array of metal ions in the framework, which can be finely tuned by changing the overall composition of the bimetallic MOF. Implications are envisaged in the design and catalytic properties of well-defined single-site catalysts.

Co-Ni and Mn-Ni bimetallic trimesate MOFs prepared by a fast aqueous synthesis method are excellent and reusable catalysts for the selective oxidation of cumene to cumene hydroperoxide. Isolation of Co 2+ (or Mn 2+ ) in an inert Ni-BTC framework is a good strategy to optimize CHP selectivity above 90%: since only Co 2+ sites catalyze CHP decomposition, a drop of the CHP selectivity is observed as the cobalt content increases.The statistical probability of having isolated Co 2+ sites is calculated as a function of the total cobalt content of the bimetallic compound, assuming homogeneous distribution of Co 2+ ions in the Ni-BTC framework and preferential occupation of terminal sites. Thus, in our best sample, with a Co:Ni ratio of 5:95, 73% of the total Co 2+ ions are isolated so that CHP decomposition/over-oxidation processes at the surface of the catalyst are not likely to occur before CHP desorption. This can explain the excellent CHP selectivity (91%) attained over this material. This "site isolation" effect is further supported by similar findings on Mn-Ni bimetallic compounds.