Thermal (kinetic) stability of inclusion compounds on the basis of porous metal–organic frameworks

Abstract

Metal–organic frameworks (MOFs) have promising practical applications in gas storage, in separation and purification of substances, and in catalysis. The standard process of the MOF production begins from the synthesis of the inclusion compound; the molecules of the used organic solvent are caught in the channels and caves of the MOF structure. These primary included guest molecules are excluded further by the evacuation or by the heating. We studied the correlation between the thermal (kinetic) stability of the inclusion compounds and the framework and guest molecules properties. The thermogravimetric curves were used for the kinetic studies; kinetic parameters of decomposition were estimated within the approaches of the non-isothermal kinetics (“model-free” kinetics and nonlinear regression methods). Studied compounds series: [Zn2(bdc)2(dabco)]·4DMF and [Zn4(DMF)(ur)2(ndc)4]·5DMF, [Zn4(DMF)(ur)2(ndc)4]·6benzene and [Zn4(DMF)(ur)2(ndc)4]·5toluene (bdc = bdc2− = terephthalate, dabco = 1,4-diazabicyclo[2.2.2]octane, DMF = dimethylformamide; ur = hexamethylenetetramine, ndc2− = 2,6-naphthalenedicarboxylate); [Mn(HCOO)2]·0.33dioxane and [Li2(H2btc)]·dioxane (H4btc = 1,2,4,5-benzenetetracarboxylic acid). The values of commonly used molecular kinetic diameters do not take into consideration the real molecular form and the size (e.g. benzene and toluene molecules have the same kinetic diameters 5.85 A). Therefore, the ease of removal of guest molecules does not correlate with them directly.