Mechanochemical Metathesis between AgNO₃ and NaX (X = Cl, Br, I) and Ag₂XNO₃ Double-Salt Formation

Abstract

Here we describe real-time, in situ monitoring of mechanochemical solid-state metathesis between silver nitrate and the entire series of sodium halides, on the basis of tandem powder X-ray diffraction and Raman spectroscopy monitoring. The mechanistic monitoring reveals that reactions of AgNO 3 with NaX (X = Cl, Br, I) differ in reaction paths, with only the reaction with NaBr providing the NaNO 3 and AgX products directly. The reaction with NaI revealed the presence of a novel, short-lived intermediate phase, while the reaction with NaCl progressed the slowest through the well-defined Ag 2 ClNO 3 intermediate double salt. While the corresponding iodide and bromide double salts were not observed as intermediates, all three are readily prepared as pure compounds by milling equimolar mixtures of AgX and AgNO 3 . The in situ observation of reactive intermediates in these simple metathesis reactions reveals a surprising resemblance of reactions involving purely ionic components to those of molecular organic solids and cocrystals. This study demonstrates the potential of in situ reaction monitoring for mechanochemical reactions of ionic compounds as well as completes the application of these techniques to all major compound classes.

Toward Mechanistic Understanding of Mechanochemical Reactions Using Real-Time In Situ Monitoring

“…Simple visual analysis of two-dimensional background-corrected diffractograms (Figure a) can reveal a plethora of information, such as the number of transformations occurring during milling and even preliminary identification of participating phases. If crystal structures of all participating phases are known, quantitative analysis of reaction profiles is accessible through a Rietveld refinement . Otherwise, qualitative reaction profiles can be extracted by a Pawley refinement or single-peak fitting .…”

“…If crystal structures of all participating phases are known, quantitative analysis of reaction profiles is accessible through a Rietveld refinement. 38 Otherwise, qualitative reaction profiles can be extracted by a Pawley refinement 39 or single-peak fitting. 1 The inclusion of an X-ray scattering standard, such as crystalline silicon, permits estimating homogeneity of the reaction mixture, quantification of the amorphous content, as well as determination of the instrument contribution to peak width and shape and therefore also to information such as average particle strain and size (Figure 3).…”

Shaking Things from the Ground-Up: A Systematic Overview of the Mechanochemistry of Hard and High-Melting Inorganic Materials

“…More recently, Lukin and coworkers explored the ball-milling metathesis reaction between AgNO 3 and NaX (X = Cl, Br, I) to form AgX and NaNO 3 [ 113 ]. The reaction rates for milling reactions involving NaI and NaBr were similar and were significantly faster than those with NaCl, potentially due to the observed of the formation of the intermediate Ag 2 ClNO 3 , while the corresponding intermediates did not form with NaBr and NaI.…”

Direct thermodynamic characterization of solid-state reactions by isothermal calorimetry

“…23,24 This was achieved through in situ monitoring of reaction mixtures using spectroscopic techniques (Raman, NMR and IR spectroscopies) and diffraction methods. 23–29…”

“…23,24 This was achieved through in situ monitoring of reaction mixtures using spectroscopic techniques (Raman, NMR and IR spectroscopies) and diffraction methods. [23][24][25][26][27][28][29] On the other hand, thermodynamic studies within the field of mechanochemistry have not yet received appropriate attention. Several reports focusing on solid-state thermodynamics clearly demonstrated that such an approach is fundamental for the systematic advancement of the field.…”