## 2 Materials and Methods
Sample preparation was attained by drop-casting the suspension (1 mg/mL in ethanol) on a TEM grid (Cu; 400 mesh; carbon film) which was dried at 30 \({}^{\circ}\)C for 2 h.  
Fourier-Transform infrared (FT-IR) spectroscopy using a Nicolet 6700 spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) was used to explore the thermal stability of the prepared MOC 5-1-8 phase. Mid-infrared spectra were collected after 32 scans with wave numbers ranging from 7800 to 350 cm\({}^{-1}\) and with a spectral resolution of 4 cm\({}^{-1}\). Samples in powder form were preparedby homogenization in an agate grinding mortar and analyzed on diamond crystal using the ATR (attenuated total reflection) technique. In order to support the STA data and assign the observed decomposition processes to the macro and micro parameters of the hardened MOC 5-1-8 phase, measurements of bulk density, specific density, porosity, pore size distribution, water absorption, and compressive strength were conducted for samples heated for 2 h at 150 \({}^{\circ}\)C, 250 \({}^{\circ}\)C, and 350 \({}^{\circ}\)C. For each test, five samples of a particular material were used. Before the thermal exposure, the samples were matured for 96 h in an air-conditioned laboratory at a temperature of \(22\pm 2\)\({}^{\circ}\)C and relative humidity (RH) of 30% \(\pm\) 5%. The heating temperatures were chosen based on the results of STA. The only effect that was not considered in the testing of residual parameters of MOC 5-1-8 phase after heating was the release of hydrochloric acid at the peak temperature at 435 \({}^{\circ}\)C in order to avoid damage of the refractory lining of the testing furnace. For sample heating, an electric testing furnace Ht 60B Svoboda (Svetice, Czech Republic) was used. The samples were 40 mm \(\times\) 40 mm \(\times\) 160 mm prisms. The bulk density \(\rho_{b}\) (kg/m\({}^{3}\)) was determined from the sample mass and its dimensions were in accordance with the EN 1015-10 [27]. The expanded combined uncertainty of the bulk density test was 1.4%. The specific density \(\rho_{s}\) (kg/m\({}^{3}\)) was assessed using an automated temperature-controlled helium pycnometer Pycnomatic ATC (Thermo Scientific, Milan, Italy). The combined expanded uncertainty of this measurement was 1.2%. From the bulk density and specific density data, the porosity \(\psi\) was calculated as introduced, e.g., in Reference [28]. The expanded combined uncertainty of the total open porosity test was 1.8%. Water absorption \(W_{a}\) by the specimens at atmospheric pressure was measured according to the standard EN 13,755 [29]. The samples were 40-mm cubes cut from the originally casted prisms, and they were immersed in water for 24 h. The expanded combined uncertainty of the water absorption test was 1.2%. Following the European technical standard EN 1015-11 [30], the compressive strength test was performed. The loading area was 40 mm \(\times\) 40 mm. The relative expanded uncertainty of the compressive strength \(f_{c}\) (MPa) determination was 1.4%. Pore size distribution was measured using Thermo Scientific Pascal series mercury porosimeters Pascal 140 and Pascal 440 (Thermo Scientific, Milano, Italy). The mass of the specimens was typically 1.0-1.5 g. The following parameters were used in calculation of pore size distribution: Hg density = 13.5414 g/cm\({}^{3}\) at 22 \({}^{\circ}\)C, capillary radius = 1.5 mm, Hg contact angle = 130\({}^{\circ}\), Hg surface tension 480 dyne/cm. Two specimens were tested for each tested material. The propagation of cracks was well documented by an optical digital microscope Dino-Lite with a resolution of 5 Mpx (AnMo Electronics Corporation, Hsinch, Taiwan).