Thermal analysis of solvatomorphic decakis (dimethylammonium) dihydrogendodecatungstate hydrates

Abstract

This study aims to describe the thermal decomposition of two solvatomorphs of decakis(dimethylammonium) dihydrogendodecatungstate ((Me2NH2)10H2W12O42·10H2O and 11 H2O) under inert and oxidizing atmospheres. Thermal studies have been done by TG-MS, TG-DSC-MS, XRD and IR methods in both synthetic air and helium atmospheres. The general characteristics of thermal decomposition are similar for both solvatomorphs. Minor differences could be observed in the resolution and shifting of the decomposition peak temperatures depending on the heating rate or atmosphere used. The first step of decomposition is endothermic in both atmospheres and involves 2 and 5 water molecule elimination with ~ 150 and ~ 120 °C peak temperatures for the decahydrate and undecahydrate, respectively. The elimination of further water and dimethylamine was observed with increasing the temperature, as well as the disruption of the lattice of compounds. Until 300 °C, these processes are endothermic in both atmospheres, and the further decomposition processes at higher temperatures are left endothermic in helium, but become exothermic in synthetic air atmosphere. In helium atmosphere, above 350 °C, a solid-phase quasi-intramolecular redox reaction takes place when the dimethylamine degradation products react with the W=O bonds with formation of oxidative coupling products of the organic fragments and reduced tungsten oxide with WO~2.93 composition. In synthetic air, above 350 °C, burning of organic fragments takes place, there are no oxidative coupling products and reduced tungsten oxide formation, and the end product of decomposition is monoclinic WO3.

Structure and Thermal Transformations of Methylammonium Tungstate

“…The multi‐step decompositions indicate that water and methylamine release in several steps from the compound. The results are in agreement with the TG‐DTA of dimethylammonium dihydrogendodecatungstate hydrates that decomposition processes were found to be endothermic below 300 °C and exothermic above 300 °C [48] . The first weight loss can be ascribed to the release of H 2 O.…”

“…The formation of the degradation and oxidized products indicates a redox reaction between methylammonium and W=O has occurred. Similar degradation and oxidation of dimethylamine in dimethylammonium dihydrogendodecatungstate hydrates has been reported by Kótai group [48] …”

Solid-Phase “Self-Hydrolysis” of [Zn(NH3)4MoO4@2H2O] Involving Enclathrated Water—An Easy Route to a Layered Basic Ammonium Zinc Molybdate Coordination Polymer

“…The ammonia content was determined by boiling it off with 0.1 M aq. NaOH and acidimetric titration and checked with gravimetry using H 2 PtCl 6 as the precipitating agent [ 28 , 29 ].…”

“…DSC tests were performed with a Perkin Elmer DSC 7 instrument (Perkin-Elmer, Waltham, MA, USA). The details of the measurements are given in [ 22 , 29 ].…”

Butyl-Methyl-Pyridinium Tetrafluoroborate Confined in Mesoporous Silica Xerogels: Thermal Behaviour and Matrix-Template Interaction

“…The power of thermal analysis of composite materials can be substantially enhanced by using analysis of the evolved gases during heating and decomposition [ 16 , 17 ]. Thermogravimetric analysis coupled with mass spectrometry (TA-MS) has been successfully applied for analysis of decomposition products upon heating ionic liquids [ 18 , 19 , 20 ].…”