From Operando Raman Mechanochemistry to “NMR Crystallography”: Understanding the Structures and Interconversion of Zn-Terephthalate Networks Using Selective ¹⁷O-Labeling

Abstract

The description of the formation, structure, and reactivity of coordination networks and metal−organic frameworks (MOFs) remains a real challenge in a number of cases. This is notably true for compounds composed of Zn 2+ ions and terephthalate ligands (benzene-1,4-dicarboxylate, BDC) because of the difficulties in isolating them as pure phases and/or because of the presence of structural defects. Here, using mechanochemistry in combination with operando Raman spectroscopy, the observation of the formation of various zinc terephthalate compounds was rendered possible, allowing the distinction and isolation of three intermediates during the ball-milling synthesis of Zn 3 (OH) 4 (BDC). An "NMR crystallography" approach was then used, combining solid-state NMR ( 1 H, 13 C, and 17 O) and density functional theory (DFT) calculations to refine the poorly described crystallographic structures of these phases. Particularly noteworthy are the high-resolution 17 O NMR analyses, which were made possible in a highly efficient and cost-effective way, thanks to the selective 17 O-enrichment of either hydroxyl or terephthalate groups by ball-milling. This allowed the presence of defect sites to be identified for the first time in one of the phases, and the nature of the H-bonding network of the hydroxyls to be established in another. Lastly, the possibility of using deuterated precursors (e.g., D 2 O and d 4 -BDC) during ball-milling is also introduced as a means for observing specific transformations during operando Raman spectroscopy studies, which would not have been possible with hydrogenated equivalents. Overall, the synthetic and spectroscopic approaches developed herein are expected to push forward the understanding of the structure and reactivity of other complex coordination networks and MOFs.

Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Li-Ion Batteries: Beneficial Impact on Mechanical Properties and Electrochemical Performance

“…For each composition, all of the signals characteristic of the CA and CMC were detected as expected. The signals centered at approximately 170–180 ppm are of particular interest as they correspond to the carboxylic/ate groups and thus are a priori sensitive to the formation of coordination bonds . As a matter of fact, for all electrodes, a broad and unresolved signal centered at 180 ppm was detected which showed variations in peak maximum position and line width depending on the binder composition.…”

17O solid state NMR as a valuable tool for deciphering reaction mechanisms in mechanochemistry: the case study on the 17O-enrichment of hydrated Ca-pyrophosphate biominerals

“…5 Subsequently, Leroy et al demonstrated that 17 O ssNMR analyses could provide valuable insight into the structure of Zn-terephthalate phases, isolated in pure form using ball-milling and operando analyses of the reaction medium. 6 Lastly, in a recent investigation by Goldberga et al , it was shown that the water molecules within calcium oxalate hydrates could be enriched in 17 O, further enabling to investigate the dynamics of the water molecules within these crystalline phases. 7 Moreover, the isotopic labelling of the water molecules in 2 H and 18 O was also performed as part of the same work.…”

Induction-heated ball-milling: a promising asset for mechanochemical reactions

“…11 While most ball-milling reactions are performed in absence of external heating, the movements of the beads are accompanied by impacts and frictional forces, which cause an increase in temperature within the reactor. 12,13 The extent of heat generated depends on both the milling conditions and the reagents involved. 12,14,15 For example, a temperature rise of ≈7-10 °C has been measured during the simple ball-milling of pure quartz or terephthalic acid for 15 minutes.…”

“…12,13 The extent of heat generated depends on both the milling conditions and the reagents involved. 12,14,15 For example, a temperature rise of ≈7-10 °C has been measured during the simple ball-milling of pure quartz or terephthalic acid for 15 minutes. 12,14 Such an increase in temperature, in conjunction with the highly efficient mixing of the reagents, has been shown to be beneficial to help overcome the activation energy for some chemical reactions, and/or help accelerate their kinetics.…”

“…12,14,15 For example, a temperature rise of ≈7-10 °C has been measured during the simple ball-milling of pure quartz or terephthalic acid for 15 minutes. 12,14 Such an increase in temperature, in conjunction with the highly efficient mixing of the reagents, has been shown to be beneficial to help overcome the activation energy for some chemical reactions, and/or help accelerate their kinetics. 16,17 Moreover, it was shown that by pre-heating the milling jars prior to the milling, it is also possible to change the kinetics and selectivity of mechanochemical reactions.…”