Two strontium-based dicarboxylate systems [Sr(oBDC-F4)(H2O)2] (1) and [{Sr(oBDC)(H2O)2}·H2O] (2) were synthesized mechanochemically via milling of Sr(OH)2·8H2O with tetrafluorophthalic acid (H2oBDC-F4) or phthalic acid (H2oBDC), respectively. The new structures were determined ab initio from the powder X-ray diffraction (PXRD) data. Both compounds 1 and 2 crystallize in the monoclinic space group P21/c as two-dimensional coordination polymers (2D-CPs). The determined structures were validated by extended X-ray absorption (EXAFS) data. Compounds 1 and 2 show different thermal stabilities. The fluorinated CP 1 is decomposed at 300 °C while the nonfluorinated CP 2 transforms into a new phase after thermal treatment at 400 °C. The two hydrated CPs exhibit small surface areas which increase after the thermal post-treatment for 1 but remains unchanged for the dehydrated sample of 2. Dynamic vapor sorption (DVS) experiments indicate that both the dehydrated and hydrated samples of 2 depict no significant differences in their adsorption isotherms. The DVS of water indicates that the phase transition after thermal post-treatment of 2 is irreversible.

New fluorinated coordination polymers were prepared mechanochemically by milling the alkaline earth metal hydroxides MII(OH)2·xH2O (MII: Ca, Sr) with tetrafluoroisophthalic acid (H2mBDC-F4). The structures of [{Ca(mBDC-F4)(H2O)2}·H2O] (1) and [{Sr(mBDC-F4)(H2O)2}·H2O] (2) were determined based on ab initio calculations and their powder X-ray diffraction (PXRD) data. The compounds are isomorphous and crystallize in the orthorhombic space group P212121. The determined structures were validated by using extended X-ray absorption (EXAFS) data. The new materials were thoroughly characterized using elemental analysis, thermal analysis, magic angle spinning NMR, and attenuated total reflection-infrared spectroscopy. Further characterization methods such as BET, dynamic vapor sorption, and scanning electron microscopy imaging were also used. Our investigations indicate that mechanochemistry is an efficient method for preparing such materials.

New fluorinated alkaline earth metal–organic frameworks were successfully synthesized by milling of metal hydroxides M(OH)2 with tetrafluoroterephthalic acid H2pBDC-F4. Both calcium- and strontium-tetrafluoroterephthalates are tetrahydrated, while the barium tetrafluoroterephthalate is free of coordinating water molecules. The two isomorphic structures Ca(pBDC-F4)·4H2O and Sr(pBDC-F4)·4H2O were solved from the powder diffraction data by ab initio structure determination and subsequent Rietveld refinement. The products were thoroughly characterized by elemental analysis, thermal analysis, magic-angle spinning NMR, Fourier transform infrared spectroscopy, scanning electron microscopy imaging, and Brunauer–Emmett–Teller measurements. Our findings suggest that the mechanochemical synthesis route is a promising approach for the preparation of new fluorinated alkaline earth metal–organic frameworks.

•Low F-doped Al-hydroxide fluorides can be successfully prepared by mechanosynthesis.•Both F-doping and mechanochemical synthesis introduce a high number of defects in the structure.•The fluorination degree affects the amount of 4- and 5-fold coordinated Al sites as well as the transition temperature to corundum.Different aluminum hydroxide fluorides with varying Al/F molar ratios from 1:1.5 up to 1:0.05 were successfully synthesized by mechanochemical reactions. The characterization of the products by XRD, 27Al and 19F MAS NMR, thermal analysis, nitrogen adsorption and zeta potential techniques allows a detailed understanding of the structure and surface properties of the products. Using γ-Al(OH)3 and β-AlF3·3H2O as OH- and F-sources, respectively, strongly disordered products were obtained with an Al: F molar ratio higher than 1:0.25. The fluorination degree has affected the amount of 4- and 5-fold coordinated Al sites, not present in the reactants. An evolution of the sub-coordinated Al-species has been detected also as a consequence of annealing processes. Obviously, these species affect the phase transition to alumina, by decreasing the transition temperature of the formation of α-Al2O3. Synthesis conditions (milling time, fluorination degree) play a crucial role for the product composition.The impact of the combined action of the milling and the different fluorine doping on the structure of new aluminum hydroxide fluorides was followed by 27Al and 19F NMR and by other complementary techniques.

Nanocrystalline Sr1–xYxF2+x samples (0 ≤ x ≤ 0.50) were prepared by fluorolytic sol–gel and mechanochemical syntheses using anhydrous HF or NH4F as fluorinating agents. This way, we compare the generated nanoparticular nonstoichiometric phases synthesized by two different routes. The obtained nonstoichiometric fluorite-type phases were studied using 19F magic-angle spinning (MAS) and 19F–89Y CP MAS NMR techniques and applying the superposition model. The 19F spectra of these phases can be fully explained by the distribution of Sr2+ and Y3+ cations around fluoride ions. These samples can serve as model compounds for a better structural understanding of fluorescent up- and down-converting systems.

A modified approach of the fluorolytic sol–gel synthesis was used to synthesize pure, amorphous aluminum hydroxide fluorides with very low and easily adjustable fluorination degrees, as well as controllable surface areas. The careful investigation of their thermal behavior revealed that these aluminum hydroxide fluorides undergo dehydroxylation reactions already at very low temperatures (i.e., below 80 °C), which is in contrast to all crystalline aluminum hydroxide (fluoride) phases. 27Al and 19F MAS NMR experiments unambiguously demonstrated that this dehydroxylation is clearly linked to a drastic reorganization of local structures and leads to a remarkable evolution of subcoordinated Al-species. A maximum intensity of about 45% for 5-fold (AlV) and 54% for 4-fold (AlIV) coordinated Al-sites was found for sample AlF0.25(OH)2.75, calcined at elevated temperatures. The investigations also revealed that the relative intensity of AlIV- and AlV-species essentially depends on the fluorination degree.

Nanoscopic yttrium acetate fluorides Y(CH3COO)3−zFz and yttrium oxide fluorides YO(3−z)/2Fz were prepared with tunable Y/F molar ratios via the fluorolytic sol–gel route. All samples were characterized by X-ray diffraction, elemental analysis and thermal analysis. In addition, local structures of all samples were studied by 19F MAS, 19F–89Y CP MAS and 1H–89Y CP MAS NMR spectroscopy and the respective chemical shifts are given. For both classes of compounds, only the fluorination using one equivalent of F (z = 1) leads to defined, well crystalline matrices: yttrium acetate fluoride Y(CH3COO)2F and r-YOF.

High energy ball milling as fast, direct and solvent free method allows an easy access to nanocrystalline alkaline earth metal fluorides MF2 (M: Mg, Ca, Sr, Ba). Comparable metal sources (acetates, carbonates, hydroxides, alkoxides) were used for the reaction with NH4F as fluorinating agent. Even very simple manual shaking experiments between NH4F and the corresponding hydroxides in the stoichiometric ratio (M:F = 1:2, M: Ca, Sr, Ba) give phase pure fluorides. Moreover, comparable classical thermal reactions in closed crucibles at higher temperatures provide phase pure crystalline fluorides in nearly all cases as well.Highlights► Easy access to nanocrystalline alkaline earth metal fluorides MF2 (M: Mg, Ca, Sr, Ba). ► High energy ball milling of different metal sources with ammonium fluoride. ► Phase pure fluorides by simply shaking hydroxides with NH4F.

This study presents for the first time an NMR spectroscopic characterization of the room and high temperature phases of (NH4)3InF6 using 19F and 115In as probe nuclei. The reversible phase transition to the cubic phase at 353 K was followed by MAS NMR in situ. Static NMR experiments of the room temperature phase and MAS NMR experiments of the high temperature phase allowed the determination of the NMR parameters of both nuclei. Finally, the scalar In–F coupling, rarely observed in solid state NMR, is evidenced in both room and high temperature phases of (NH4)3InF6, and measured in the high temperature phase.Graphical abstractThe room and high temperature phases of (NH4)3InF6 are characterized using 19F and 115In as probe nuclei.Research highlights► Solid state NMR was applied to study the room and high temperature phases of (NH4)3InF6 using 19F and 115In as probe nuclei. ► For the first time static 115In spectra of (NH4)3InF6 were taken at three different fields at room temperature. ► The occurrence of two different In sites agrees with the occurrence of the different phases, namely the tetragonal and the monoclinic ones. ► The scalar In–F coupling, rarely observed in solid state NMR, is evidenced in both room and high temperature phases of (NH4)3InF6, and measured in the high temperature phase.

A successful mechanochemical synthesis of nanocrystalline aluminium hydroxide fluoride samples AlFx(OH)3-x·nH2O with pyrochlore structure is described for the first time. Optimal conditions for the synthesis can be adjusted using γ-Al(OH)3 and β-AlF3·3H2O as educts applying an Al:F ratio of 1:1.5. Under these circumstances, the reaction proceeds almost stoichiometrically. On the other hand a classical solid state chemical reaction at elevated temperature is not successful with the same educts. Strongly disordered or amorphous products are obtained with differing Al:F molar ratios at the beginning. It was found that structure and water content of the educts are playing a crucial role for the product composition.

Followed by X-ray diffraction, MAS NMR and elemental analysis the mechanochemical reaction between Al(OiPr)3, γ-AlOOH and Al(ac)2OH as possible aluminium sources on the one side, and NH4F as fluorinating agent on the other side was studied. Encouraged by the successful mechanochemical synthesis of CaF2 using the same fluorinating agent, the formation of AlF3 was expected. However, it can be established that as long as NH4F is supplied the formation of crystalline (NH4)3AlF6 is observed instead.

α-AlF3, the thermodynamically stable rhombohedral phase of aluminum fluoride, was used as starting material to produce nanostructured powders by high-energy ball milling. Both the polycrystalline and the nanostructured powders were studied by XRD, TEM, and 27Al and 19F MAS NMR. Thermally programmed desorption of NH3 and IR spectroscopy of adsorbed CO probe molecules unambiguously demonstrate the formation of Lewis acid and Brønsted acid sites as a consequence of the mechanical impact. Catalytic test reactions using milled α-AlF3 as solid catalyst proved experimentally the theoretically suggested catalytic activity of nanosized AlF3 particles as a result of high structural distortion brought into the solid by milling.

Mixtures of powders of crystalline sodium fluoride together with crystalline or amorphous aluminium fluoride were mechanically treated at ambient temperature by high-energy ball milling using a planetary mill. The application of X-ray powder diffraction together with 19F and 27Al MAS NMR spectroscopy gave unambiguous evidence that solid state chemical reactions between NaF and AlF3 take place at mechanical milling. Dependent on the molar ratio of the educts cryolite (Na3AlF6) and/or chiolite (Na5Al3F14) are obtained as reaction products. Moreover, the state of order of the educts, here crystalline or amorphous aluminium fluoride, has a strong influence on the reaction products formed.

Nanoscopic yttrium acetate fluorides Y(CH3COO)3−zFz and yttrium oxide fluorides YO(3−z)/2Fz were prepared with tunable Y/F molar ratios via the fluorolytic sol–gel route. All samples were characterized by X-ray diffraction, elemental analysis and thermal analysis. In addition, local structures of all samples were studied by 19F MAS, 19F–89Y CP MAS and 1H–89Y CP MAS NMR spectroscopy and the respective chemical shifts are given. For both classes of compounds, only the fluorination using one equivalent of F (z = 1) leads to defined, well crystalline matrices: yttrium acetate fluoride Y(CH3COO)2F and r-YOF.

New fluorinated coordination polymers were prepared mechanochemically by milling the alkaline earth metal hydroxides MII(OH)2·xH2O (MII: Ca, Sr) with tetrafluoroisophthalic acid (H2mBDC-F4). The structures of [{Ca(mBDC-F4)(H2O)2}·H2O] (1) and [{Sr(mBDC-F4)(H2O)2}·H2O] (2) were determined based on ab initio calculations and their powder X-ray diffraction (PXRD) data. The compounds are isomorphous and crystallize in the orthorhombic space group P212121. The determined structures were validated by using extended X-ray absorption (EXAFS) data. The new materials were thoroughly characterized using elemental analysis, thermal analysis, magic angle spinning NMR, and attenuated total reflection-infrared spectroscopy. Further characterization methods such as BET, dynamic vapor sorption, and scanning electron microscopy imaging were also used. Our investigations indicate that mechanochemistry is an efficient method for preparing such materials.