No abstract

The hybrid frameworks M 2 dobdc (dobdc 4-= 2,5-dioxidoterephthalate, M 2+ = Mg 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ ), commonly known as CPO-27 or MOF-74, are shown to be active catalysts in base-catalyzed reactions such as Knoevenagel condensations or Michael additions. Rather than utilizing Nfunctionalized linkers as a source of basicity, the intrinsic basicity of these materials arises from the presence of the phenolate oxygen atoms coordinated to the metal ions. The overall activity is due a complex interplay of the basic properties of these structural phenolates and the reactant binding characteristics of the coordinatively unsaturated sites. The nature of the active site and the order of activity among the different M 2 dobdc materials were rationalized via computational efforts; the most active material, both in theory and experiment, is the Ni-containing variant. The basicity of Ni 2 dobdc was experimentally proven by chemisorption of pyrrole and observation by IR spectroscopy.

The synthesis of titanium-carboxylate metal-organic frameworks (MOFs) is hampered by the high reactivity of the commonly employed alkoxide precursors. Herein, we present an innovative approach to titanium-based MOFs by the use of titanocene dichloride to synthesize COK-69, the first breathing Ti MOF, which is built up from trans-1,4-cyclohexanedicarboxylate linkers and an unprecedented [Ti(IV)3(μ3-O)(O)2(COO)6] cluster. The photoactive properties of COK-69 were investigated in depth by proton-coupled electron-transfer experiments, which revealed that up to one Ti(IV) center per cluster can be photoreduced to Ti(III) while preserving the structural integrity of the framework. The electronic structure of COK-69 was determined by molecular modeling, and a band gap of 3.77 eV was found.

A new method has been developed for generating highly dispersed base sites on metal-organic framework (MOF) lattices. The base catalytic activity of two alkaline earth MOFs, M-2(BTC)(NO3)(DMF) (M = Ba or Sr, H3BTC = 1,3,5-benzenetricarboxylic acid, DMF = N,N-dimethylformamide) was studied as a function of their activation procedures. The catalytic activity in Knoevenagel condensation and Michael addition reactions was found to increase strongly with activation temperature. Physicochemical characterization using FTIR, C-13 CP MAS NMR, PXRD, XPS, TGA-MS, SEM, EPR, N-2 physisorption and nitrate content analysis shows that during activation, up to 85% of the nitrate anions are selectively removed from the structure and replaced with other charge compensating anions such as O-2(-). The defect sites generated via this activation act as new strong basic sites within the catalyst structure. A fluorescence microscopic visualization of the activity convincingly proves that it is exclusively associated with the hexagonal crystals, and that reaction proceeds inside the crystal's interior. Theoretical analysis of the Ba-material shows that the basicity of the proposed Ba2+-O2--Ba2+ motifs is close to that of the edge sites in BaO