Miroslav Pospíšil

Metal-organic frameworks (MOFs) are attracting increasing attention as adsorbents of contaminants of emerging concern which are difficult to remove by conventional processes. However, common carboxylate-based MOFs suffer from low stability in water environment, which limits their environmental applications. In this study, we use phosphinate-based MOFs with higher hydrolytic stability and we focus on the influence of functional groups covering the pore walls on the adsorption of pharmaceutical pollutants present in water – diclofenac, cephalexin and sulfamethoxazole. We present a synthesis of new structures isoreticular to the phosphinate MOF ICR-7. The presented MOFs contain phenyl rings facing the pore walls modified with dimethylamino groups (ICR-8) and ethyl carboxylate groups (ICR-14). These functionalized MOFs were obtained from two newly synthetized phospinate linkers containing the respective functional groups. Generally, the presence of additional functional groups resulted in higher affinity to the tested pollutants in comparison with ICR-7 or activated carbon, however, it also decreased the sorption capacity.

Classical molecular simulation methods were used for a description of an arrangement of intercalated molecules N-(pyridin-4-yl)pyridin-4-amine (AH) and its derivatives, 3-methyl-N-(pyridin-4-yl)pyridin-4-amine (AMe), and 3-nitro-N-(pyridin-4-yl)pyridin-4-amine (ANO2) within a layered structure of zirconium 4-sulfophenylphosphonate. The intercalated molecules were placed between SO₃H groups of the host layers. Their mutual positions and orientations were solved by molecular simulation methods and compared with the presented experimental results. Final calculated data showed differences of partially disordered arrangement of the intercalated molecules between zirconium 4-sulfophenylphosphonate layers. The calculation results revealed a dense net of hydrogen bonds connecting water molecules and the guests in the interlayer space and the sulfo groups of the host layers. We calculated the dipole moments of the AH, AMe and ANO2 guests in the final models in order to illustrate potential use of these materials in non-linear optics.

The intercalation chemistry of layered alkaline-earth metal phenylphosphonates with the general formula MeC₆H₅PO₃·2H₂O (Ca, Sr, Ba) is reviewed. The preparation of the host materials is described and their behavior in dependence on the relative humidity and pH of the reaction medium is discussed. Mutual relationships between MeC₆H₅PO₃·2H₂O and Me(C₆H₅PO₃H)₂ were investigated using a method of computer-controlled addition of reagents. The MeC₆H₅PO₃·2H₂O compounds are able to intercalate species having a free electron pair through the so-called coordination intercalation. In this way, 1-alkylamines, 1-alkanols, 1,n-diols and 1,2-diols were intercalated. In the case of the ethanol and methanol intercalates of strontium phenylphosphonate we were able to determine the structure of the host part by single-crystal X-ray diffraction. By combination of the data obtained from the diffraction with molecular modeling we suggested the arrangement of the host molecules in the interlayer space of the host. The arrangement of the shorter diols in the interlayer space of strontium phenylphosphonate was also proposed on the basis of molecular modeling calculations. These models help us to understand the structure of the prepared intercalates.

Classical molecular simulation methods were used for a detailed structural description of zirconium 4-sulfophenylphosphonate and zirconium phenylphosphonate 4-sulfophenylphosphonates with general formula Zr(HO₃SC₆H₄PO₃) _x (C₆H₅PO₃)_2-x ·yH₂O (x = 0.7–2; y = 0 or 2). First, models describing the structure of zirconium 4-sulfophenylphosphonate (x = 2) were calculated for the hydrated (y = 2) and dehydrated (y = 0) compounds. Subsequently, models for two mixed zirconium phenylphosphonate 4-sulfophenylphosphonates (x = 1.3 and 0.7) were calculated. Optimized models suggest that the presence of water molecules between sulfo groups creates a water-sulfonate layer with a system of hydrogen bonds. We suppose that this arrangement is the reason for a higher proton conductivity of the hydrated samples compared to dehydrated samples. When the water molecules are removed, a small decrease in the basal spacing (around 0.06 Å) is observed. This behavior is confirmed by the simulated models, where no significant changes in the structure on dehydration were observed except the absence of the water molecules and a lower number of hydrogen bonds between two adjacent sulfonate sheets. Due to the good crystallinity of the samples and the presence of sharp non-basal peaks in their X-ray diffraction patterns, Miller indices of the non-basal peaks in the diffraction patterns calculated from the models can be compared with those found in the experimental data. This allowed us to precisely describe for example (15 5–2) planes, from which mutual distances of the phenyl rings were determined to be 2.62 Å.