Thermal decomposition of inclusion compounds and metal–organic frameworks on the basis of heterometallic complex [Li2Zn2(bpdc)3

Abstract

Metal–organic frameworks (MOFs) have promising practical applications in gas storage, separation and purification and catalysis. The standard process for MOF production begins with the synthesis of the inclusion compound. The molecules of the organic solvent used are caught in the channels and caves of the MOF structure. These primary inclusion guest molecules are excluded further by the weak heating or by the evacuation. The thermal stability of the primary inclusion compounds (i.e., the ease of removal of the guest molecules) must be connected both with the structure of the empty (guest free) frameworks and with the size of the guest molecules. We investigate a series of inclusion compounds: [Li2Zn2(bpdc)3(dabco)]·9DMF·4H2O, [{LiZn}2(bpdc)3(dma)4]·3DMA·H2O and [{LiZn}2(bpdc)3(nmp)4]·4NMP (bpdc2− = C14H8O42− anion, dma = C4H9NO, nmp = C5H9NO, dmf = C3H7NO and dabco = C6H12N2) for the study of the correlation between their kinetic stability and the framework and guest molecule properties. Thermodynamic properties were studied using differential scanning calorimeter Netzsch DSC 204 F1 Phoenix. Thermogravimetric measurements were carried out on a Netzsch thermal analyzer TG 209 F1. Thermogravimetric curves are used for the kinetic studies. Kinetic parameters of decomposition are estimated within the approaches of non-isothermal kinetics (“model-free” kinetics and nonlinear regression methods), with the computer program Netzsch Thermokinetics 2. All guest-free frameworks turned out to be the unstable phases; the peculiarities of the thermal decomposition of the inclusion compounds under these circumstances are considered.