Mechanochemically-induced glass formation from two-dimensional hybrid organic-inorganic perovskites.

Hybrid organic-inorganic perovskites (HOIPs) occupy a prominent position in the field of materials chemistry due to their attractive optoelectronic properties. While extensive work has been done on the crystalline materials over the past decades, the newly reported glasses formed from HOIPs open up a new avenue for perovskite research with their unique structures and functionalities. Melt-quenching is the predominant route to glass formation; however, the absence of a stable liquid state prior to thermal decomposition precludes this method for most HOIPs. In this work, we describe the first mechanochemically-induced crystal-glass transformation of HOIPs as a rapid, green and efficient approach for producing glasses. The amorphous phase was formed from the crystalline phase within 10 minutes of ball-milling, and exhibited glass transition behaviour as evidenced by thermal analysis techniques. Time-resolved in situ ball-milling with synchrotron powder diffraction was employed to study the microstructural evolution of amorphisation, which showed that the crystallite size reaches a comminution limit before the amorphisation process is complete, indicating that energy may be further accumulated as crystal defects. Total scattering experiments revealed the limited short-range order of amorphous HOIPs, and their optical properties were studied by ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy.

Hirshfeld atom refinement of metal-organic frameworks for accurate positioning of hydrogen atoms and disorder analysis.

The application of Hirshfeld atom refinement (HAR) fragmentation is demonstrated for the refinement of metal-organic framework (MOF) crystal structures. The presented method enables anisotropic refinement of imidazolate hydrogen atoms, as well as complex analysis of solvent disorder within MOF pores. The data used were derived from standard resolution in-house single crystal X-ray diffraction measurements, demonstrating that high quality structural analysis of MOFs no longer requires access to neutron or synchrotron facilities.

Advancing mechanochemical synthesis by combining milling with different energy sources.

Owing to its efficiency and unique reactivity, mechanochemical processing of bulk solids has developed into a powerful tool for the synthesis and transformation of various classes of materials. Nevertheless, mechanochemistry is primarily based on simple techniques, such as milling in comminution devices. Recently, mechanochemical reactivity has started being combined with other energy sources commonly used in solution-based chemistry. Milling under controlled temperature, light irradiation, sound agitation or electrical impulses in newly developed experimental setups has led to reactions not achievable by conventional mechanochemical processing. This Perspective describes these unique reactivities and the advances in equipment tailored to synthetic mechanochemistry. These techniques - thermo-mechanochemistry, sono-mechanochemistry, electro-mechanochemistry and photo-mechanochemistry - represent a notable advance in modern mechanochemistry and herald a new level of solid-state reactivity: mechanochemistry 2.0.

Low-Dimensional Magnetism in Multivariate Copper/Zinc MOF-74 Materials Formed via Different Mechanochemical Methods.

MOF-74 is an archetypal magnetic metal-organic framework (MOF) family, with metal nodes bridged by 2,5-dioxido-1,4-benzenedicarboxylic acid (H4dobdc) and arranged into one of the simplest representations of the 1D Ising magnetic model. Recently, a novel mechano-synthetic approach opened a pathway toward a series of bimetallic multivariate (1:1) M1M2-MOF-74 materials, with the uniform distribution of metal cations in the oxometallic chains, offering a unique opportunity to investigate low-dimensional magnetism in these heterometallic MOFs. We explore here how different mechanochemical procedures affect the interaction between the metal nodes of the model system of three multivariate copper(II)/zinc(II)-MOF-74 materials, two of which were obtained through a template-controlled procedure, and the third one was obtained by recently developed mechanical MOF-alloying combined with subsequent accelerated aging. While the three Cu/Zn-MOF-74 products have almost identical powder X-ray diffraction (PXRD) diffractograms and Fourier transform infrared spectra, they differ significantly in their magnetic properties, as revealed through detailed magnetization and X-band and multifrequency high-field electron spin resonance measurements. The magnetic results of the three multivariate Cu/Zn-MOF-74s were compared to the properties of the monometallic Cu-MOF-74, which shows antiferromagnetic intrachain and weaker ferromagnetic interchain interactions. Energy-dispersive X-ray spectroscopy/scanning electron microscopy and solid-state nuclear magnetic resonance spectroscopy helped rationalize the observed differences in magnetization, and in situ synchrotron PXRD monitoring of template-controlled MOF formation revealed different reaction pathways when using the zinc or copper intermediates, involving even the fleeting occurrence of a rare MOF-74 polymorph.

Exploring the Halogen-Bonded Cocrystallization Potential of a Metal-Organic Unit Derived from Copper(ii) Chloride and 4-Aminoacetophenone.

In this work, we describe a novel halogen-bonded metal-organic cocrystal involving a square-planar Cu(ii) complex and 1,4-diiodotetrafluorobenzene (14tfib) by utilizing an amine ligand whose pendant acetyl group enables halogen bonding. The cocrystal was prepared by both mechanochemical synthesis (liquid-assisted grinding) and the conventional solution-based method. Crystal structure determination by single crystal X-ray diffraction revealed that the dominant supramolecular interactions are the I···O halogen bond between 14tfib and CuCl2(aap)2 building blocks, and the N-H···Cl hydrogen bonds between CuCl2(aap)2 molecules. The combination of halogen and hydrogen bonding leads to the formation of a 2D network. Overall, this work showcases an example of the possibility for extending the complexity of metal-organic crystal structures by using halogen bonding in a way that does not affect other hydrogen bonding synthons.

Exploring the Scope of Macrocyclic "Shoe-last" Templates in the Mechanochemical Synthesis of RHO Topology Zeolitic Imidazolate Frameworks (ZIFs).

The macrocyclic cavitand MeMeCH2 is used as a template for the mechanochemical synthesis of 0.2MeMeCH2@RHO-Zn16(Cl2Im)32 (0.2MeMeCH2@ZIF-71) and RHO-ZnBIm2 (ZIF-11) zeolitic imidazolate frameworks (ZIFs). It is shown that MeMeCH2 significantly accelerates the mechanochemical synthesis, providing high porosity products (BET surface areas of 1140 m2/g and 869 m2/g, respectively). Templation of RHO-topology ZIF frameworks constructed of linkers larger than benzimidazole (HBIm) was unsuccessful. It is also shown that cavitands other than MeMeCH2-namely MeHCH2, MeiBuCH2, HPhCH2, MePhCH2, BrPhCH2, BrC5CH2-can serve as effective templates for the synthesis of x(cavitand)@RHO-ZnIm2 products. The limitations on cavitand size and shape are explored in terms of their effectiveness as templates.

Manometric real-time studies of the mechanochemical synthesis of zeolitic imidazolate frameworks.

We demonstrate a simple method for real-time monitoring of mechanochemical synthesis of metal-organic frameworks, by measuring changes in pressure of gas produced in the reaction. Using this manometric method to monitor the mechanosynthesis of the zeolitic imidazolate framework ZIF-8 from basic zinc carbonate reveals an intriguing feedback mechanism in which the initially formed ZIF-8 reacts with the CO2 byproduct to produce a complex metal carbonate phase, the structure of which is determined directly from powder X-ray diffraction data. We also show that the formation of the carbonate phase may be prevented by addition of excess ligand. The excess ligand can subsequently be removed by sublimation, and reused. This enables not only the synthesis but also the purification, as well as the activation of the MOF to be performed entirely without solvent.

Microporosity of a Guanidinium Organodisulfonate Hydrogen-Bonded Framework.

Guanidinium organosulfonates (GSs) are a large and well-explored archetypal family of hydrogen-bonded organic host frameworks that have, over the past 25 years, been regarded as nonporous. Reported here is the only example to date of a conventionally microporous GS host phase, namely guanidinium 1,4-benzenedisulfonate (p-G2 BDS). p-G2 BDS is obtained from its acetone solvate, AcMe@G2 BDS, by single-crystal-to-single-crystal (SC-SC) desolvation, and exhibits a Type I low-temperature/pressure N2 sorption isotherm (SABET =408.7(2) m2 g-1 , 77 K). SC-SC sorption of N2 , CO2 , Xe, and AcMe by p-G2 BDS is explored under various conditions and X-ray diffraction provides a measurement of the high-pressure, room temperature Xe and CO2 sorption isotherms. Though p-G2 BDS is formally metastable relative to the "collapsed", nonporous polymorph, np-G2 BDS, a sample of p-G2 BDS survived for almost two decades under ambient conditions. np-G2 BDS reverts to zCO2 @p-G2 BDS or yXe@p-G2 BDS (y,z=variable) when pressure of CO2 or Xe, respectively, is applied.

Use of a "Shoe-Last" Solid-State Template in the Mechanochemical Synthesis of High-Porosity RHO-Zinc Imidazolate.

We report the first use of a nonionic solid (NIS) as a template in mechanosynthesis of a metal-organic framework. Through eight intermolecular C-H···O hydrogen bonds, the macrocyclic MeMeCH2 template predictably functions as a "shoe-last" for the assembly of double-eight rings in the liquid-assisted reaction of ZnO and imidazole (ImH). The resulting new form of ZnIm2 (namely xMeMeCH2@RHO-Zn16Im32) is available in multigram amounts, highly porous, and thermally stable.

Effect of atmosphere on solid-state amine-aldehyde condensations: gas-phase catalysts for solid-state transformations.

The presence of water or organic solvent vapour accelerates the solid-state condensation of solid aromatic amines and aromatic aldehydes into Schiff bases; we show the important role of catalytic triethylamine in the vapour phase in such vapour digestion synthesis, as well as in the liquid phase in synthesis via liquid-assisted grinding.

Measurement of tooth extraction forces in upper incisors.

A new method, applied for the first time in this research, was used for measurement of tooth extraction forces. The research has been done in a group of 50 examinees to whom the tooth extraction has been done with lower premolar forceps - forceps "13" and in the control group of 54 examinees in whom the tooth extraction has been done with upper incisive forceps - forceps "1". The measurement instrument registered the extraction forces values in both types of forceps. There was no difference in any parameters in these two groups except in used pressure. While using the forceps "13", a significantly lower tooth extraction force was measured than the force measured while using the forceps "1" (p < 0.001). This means that in clinical work we can already apply noticeably less force using the lower premolar forceps for the extraction of the upper incisors (in the moments of rotation up to 70%). These results are meaningful, because they lead to better and improved instrument solutions and working techniques.

Detection of tumor necrosis factor alpha in normal and inflamed human dental pulps.

BACKGROUND: The aim of this study was to determine concentrations of tumor necrosis factor-alpha (TNF-alpha) in normal, painful, and asymptomatic human dental pulps. METHODS: Pulps were obtained from three groups of teeth, including healthy teeth, asymptomatic teeth with caries and/or large restoration, and symptomatic teeth with clinical diagnosis of irreversible pulpitis. Pulpal tissues were collected, prepared, and analyzed for TNF-alpha concentration by ELISA technique. RESULTS: Nonparametric Kruskal-Wallis test revealed significant differences between TNF-alpha concentration in normal samples (64.01 +/- 53.12 pg/g) and irreversible symptomatic pulpal tissue (1962.99 +/- 1288.75 pg/g), between irreversible symptomatic and asymptomatic (1120.09 +/- 649.72 pg/g), and between normal and irreversible asymptomatic pulpal tissue (p = 0.000). CONCLUSIONS: TNF-alpha may be an objective marker for determining extent of pulpal inflammation associated with irreversible pulpitis.