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Abstract: 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. [Copyright &y& Elsevier]

Abstract: To get some insight by conclusions of analogy into the drying process of alcoholic aluminium fluoride sol–gels [AlF3/(ROH) x ], the structures of α- and β-AlF3⋅3H2O as well as of the nonahydrate AlF3⋅9H2O are reinvestigated and discussed based on X-ray single crystal structural data. In addition, neutron diffraction experiments of the latter allowed the refinement of proton positions. In accordance with crystal structures, low-temperature solid state 27Al-, 1H- and 19F-MAS NMR spectra convincingly confirm the structural similarity between α-AlF3⋅3H2O and AlF3⋅9H2O, while the β-phase material is structurally different forming chain structures. Thermal analysis of AlF3/(ROH) x gave evidence for discrete AlF3:ROH ratios of only 1:0.45 and 1:0.1, and solution NMR showed some similarities between aqueous and alcoholic systems. [Copyright &y& Elsevier]

Abstract: Several procedures for the calibration of MS signals such as m/z =19 (F+) representing hydrogen fluoride, HF, have been tested in order to achieve a reliable quantitative description of the thermal behaviour of fluorides and/or fluoride hydrates by applying the recent PulseTA ® technique (PTA). Instead of desirable indirect calibration methods without the use of the corrosive HF, only the direct injection of 40% aqueous HF gave satisfying results. A differential calibration procedure, recently reported in literature, has been successfully applied. It will be demonstrated that both the calibration of m/z =18 for water and m/z =19 for hydrogen fluroride can be performed in a correct way for each mass number. But their joint application to the quantitaive description of a given compound revealed to be difficult if not impossible. This is interpreted in terms of the extreme properties of fluorides simultaneously liberating H2O and HF. [Copyright &y& Elsevier]

Lead(II)-fluoride was successfully prepared by high energy ball milling and for comparison by classical thermal solid state chemical reaction. The influence of different starting materials, fluorinating agents and synthesis methods on the formation of the orthorhombic α -phase and the cubic β -phase was investigated. XRD analysis provided insight of which phase was formed under varying synthesis conditions. 19 F and 207 Pb MAS NMR measurements delivered an even further insight into the local structures. Additional simulations of the 19 F spectra were performed to identify the 19 F- 207 Pb coupling constants of the four-fold coordinated fluorine sites in both phases. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Followed by 19F and 27Al MAS NMR and XRD measurements the present study unambiguously addresses the distinct influence of humidity on the product composition in the mechanochemical reaction of NaF with AlF3. The water content, either delivered from the educts or controlled by the gaseous atmosphere, plays a crucial role for the reactions investigated here. Generally, the mechanically induced chemical reactions are favoured under wet conditions. They do not proceed stoichiometrically yielding mixtures of at least two components: Na5Al3F14 and AlF3, or Na5Al3F14 and Na3AlF6. However, applying the molar ratio Na:Al=1:1 and using NaF and β-AlF3·3H2O as educts, several hours of milling surprisingly forms the thermodynamically unstable phase NaAlF4·H2O. [Copyright &y& Elsevier]

Eu3+ doped metal fluorides in fluorite structure were prepared on a solvent-free mechanochemical synthesis route. Beside structural characterization by XRD and 19F MAS NMR, their luminescence behavior was followed in dependence on the Eu3+ content and in comparison with other synthesis strategies. High luminescence life times were measured for as-prepared nanoparticles. Additionally, pure EuF 3 was mechanochemically prepared and characterized for comparison. Image 1 • Mechanochemical synthesis of M 1- x Eu x F 2+ x (M: Ca, Sr, Ba, Pb) with different precursors. • Structural information was obtained by 19F MAS NMR spectroscopy and XRD measurements. • Emission spectra and luminescent decay times were recorded. • Strong influence of synthesis parameters and precursors on luminescent lifetimes. [ABSTRACT FROM AUTHOR]

The paper deals with the mechanochemical synthesis of lead containing alkaline earth metal fluoride solid solutions M x Pb 1 -x F 2 (M = Ca, Sr, Ba) by high-energy ball milling. Several metal precursors and fluorinating agents were tested for synthesizing M 0.5 Pb 0.5 F 2 . Metal acetates and ammonium fluoride as precursors show the most promising results and were therefore used for the formation of M x Pb 1 -x F 2 with different metal cationic ratios. The characterization of the local fluorine coordination and the crystal structure was performed by 19 F MAS NMR spectroscopy and X-ray diffraction. Additional calculations of 19 F chemical shifts using the superposition model allow a deeper insight into the local structure of the compounds. The fluoride ion conductivity was followed by temperature dependent DC conductivity measurements. Significantly higher conductivities were found in comparison with those of the corresponding binary fluorides. The highest values were observed for samples with high lead content M 0.25 Pb 0.75 F 2 , bearing in mind the much higher conductivity of PbF 2 compared to MF 2 . [ABSTRACT FROM AUTHOR]

The capability of mechanochemical synthesis for the formation of solid solutions of alkaline earth metal fluorides M a 1− x M b x F 2 (M: Ca, Sr, Ba) was tested by fluorination of metal acetates and metal hydroxides with ammonium fluoride directly at milling. Evidence was found for a mutual substitution of cations on their lattice positions in Ca 1− x Sr x F 2 and Ba 1− x Sr x F 2 samples. For the Ba/Ca-system this synthesis route is only partially successful. X-ray diffraction and 19 F MAS NMR spectroscopy were used to characterize all samples concerning their crystal structure and local fluorine coordination. Calculations of 19 F chemical shifts with the superposition model along with probability calculations for the intensity of the individual 19 F lines, performed in dependence on the molar composition of the samples, perfectly agree with the experimental findings. The fluoride ion conductivity of as-prepared samples, determined by temperature dependent DC conductivity measurements, is significantly higher than those of crystalline binary fluorides. Moreover, a higher F − ion conductivity is observed for samples with higher mixing grade in the Ca/Sr-and the Ba/Sr-systems. [ABSTRACT FROM AUTHOR]

The capability of mechanochemical synthesis for the formation of MgF 2 –MF 2 (M: Ca, Sr, Ba) composites, solid solutions or well-defined compounds was tested applying a fluorination of different fluorine-free metal sources with NH 4 F directly at milling. No evidence was found for a substitution of Mg 2+ with Ca 2+ (Sr 2+ , Ba 2+ ) ions, or vice versa, in rutile or fluorite structure. However, an equimolar ratio of Mg 2+ to the second cation allows the mechanochemical synthesis of tetrafluoromagnesates, MMgF 4 , which is more and more hampered the smaller the radius of the cation M 2+ is. BaMgF 4 is formed even phase pure from the acetates, SrMgF 4 can only be observed in a mixture accompanied by the binary fluorides. In addition, 19 F MAS NMR spectra along with calculations of 19 F isotropic chemical shift values according to the superposition model point to the formation of a metastable phase of CaMgF 4 , which disappears at thermal treatment and decomposes into the binary fluorides CaF 2 and MgF 2 . [ABSTRACT FROM AUTHOR]

Abstract: 19F MAS NMR signals of a variety of X-ray amorphous magnesium hydroxide (oxide) fluorides (MgF x (OH(R))2−x (0< x ≤2)) prepared using different synthesis routes are compared and assigned. Relations between their 19F signal positions and local coordinations are elaborated on the basis of the chemical behaviour and data available for the few crystalline reference compounds known so far. Supported by the superposition model, 19F signals appearing between −150ppm and −200ppm were subdivided into three groups due to local [FMg6], [FMg5] and [FMg4], and [FMg3] environments, respectively. [Copyright &y& Elsevier]