Tuning Packing, Structural Flexibility, and Porosity in 2D Metal–Organic Frameworks by Metal Node Choice

2019 ◽  
Vol 72 (10) ◽  
pp. 797 ◽  
Author(s):  
Witold M. Bloch ◽  
Christian J. Doonan ◽  
Christopher J. Sumby
Keyword(s):  
Structural Changes ◽  
Metal Organic Frameworks ◽  
Chemical Properties ◽  
Complete Removal ◽  
Structural Flexibility ◽  
X Ray Diffraction ◽  
Metal Centre ◽  
Metal Organic ◽  
Physical And Chemical ◽  
And Chemical Properties

Understanding the key features that determine structural flexibility in metal–organic frameworks (MOFs) is key to exploiting their dynamic physical and chemical properties. We have previously reported a 2D MOF material, CuL1, comprising five-coordinate metal nodes that displays exceptional CO2/N2 selectively (L1=bis(4-(4-carboxyphenyl)-1H-pyrazolyl)methane). Here we examine the effect of utilising six-coordinate metal centres (CoII and NiII) in the synthesis of isostructural MOFs from L1, namely CoL1 and NiL1. The octahedral geometry of the metal centre within the MOF analogues precludes an ideal eclipse of the 2D layers, resulting in an offset stacking, and in certain cases, the formation of 2-fold interpenetrated analogues β-CoL1 and β-NiL1. We used a combination of thermogravimetric analysis (TGA), and powder and single crystal X-ray diffraction (PXRD and SCXRD) to show that desolvation is accompanied by a structural change for NiL1, and complete removal of the coordinated H2O ligands results in a reduction in long-range order. The offset nature of the 2D layers in combination with the structural changes impedes the adsorption of meaningful quantities of gases (N2, CO2), highlighting the importance of a five-coordinate metal centre in achieving optimal pore accessibility for this family of flexible materials.

scholarly journals Fluorinated Organic Porous Materials

2019 ◽  
Vol 01 (01) ◽  
pp. 019-029 ◽  
Author(s):  
Zhenglin Zhang ◽  
Ognjen Š. Miljanić
Keyword(s):  
Porous Materials ◽  
Organic Molecules ◽  
Metal Organic Frameworks ◽  
Molecular Crystals ◽  
Chemical Properties ◽  
Physical And Chemical Properties ◽  
Metal Organic ◽  
Physical And Chemical ◽  
And Chemical Properties

Fluorine is in many aspects unique among the elements, and its incorporation into organic molecules can dramatically change their physical and chemical properties. This minireview will survey the existing classes of fluorinated porous materials, with a particular focus on all-organic porous materials. We will highlight our work on the preparation and study of metal–organic frameworks and porous molecular crystals derived from extensively fluorinated rigid aromatic pyrazoles and tetrazoles. Where possible, comparisons between fluorinated and nonfluorinated materials will be made.

Engineering Isoreticular 2D Metal–Organic Frameworks with Inherent Structural Flexibility

2017 ◽  
Vol 70 (5) ◽  
pp. 566 ◽  
Author(s):  
Alexandre Burgun ◽  
Witold M. Bloch ◽  
Christian J. Doonan ◽  
Christopher J. Sumby
Keyword(s):  
Metal Organic Frameworks ◽  
Mixed Valence ◽  
Chemical Properties ◽  
Fine Tuning ◽  
Gate Opening ◽  
Sterically Demanding ◽  
Metal Organic ◽  
Structure Metrics ◽  
Physical And Chemical ◽  
And Chemical Properties

The chemical mutability of metal–organic frameworks (MOFs) is an advantageous feature that allows fine-tuning of their physical and chemical properties. Herein, we report the successful isoreticulation of a MOF with an outstanding gas selectivity for CO2 versus N2: [Cu(L1)(H2O)]·xS (CuL1), where H2L1 = bis(4-(4-carboxyphenyl)-1H-pyrazolyl)methane) and S = solvate. By modifying the steric bulk and length of the original ligand, we synthesised three new MOFs with 2D networks isoreticular to CuL1, namely [Cu(L1Me)(H2O)]·xS (CuL1Me), [Cu(L2)(H2O)]·xS (CuL2), and [Cu(L2Me)(H2O)]·xS (CuL2Me) (where H2L1Me = bis(4-(4-carboxyphenyl)-3,5-dimethyl-1H-pyrazolyl)methane, H2L2 = bis(4-(4-carboxyphenyl)-(ethyne-2,1-yl)-1H-pyrazolyl)methane, and H2L2Me = bis(4-(4-carboxyphenyl)-(ethyne-2,1-yl)-3,5-dimethyl-1H-pyrazolyl)methane). Depending on the steric hindrance and structure metrics of the organic links, staggered and eclipsed arrangements of 2D 44 net layers were obtained. The anisotropy of the pore dimensions is proportional to the linker length (L2 and L2Me), which when increased, renders these materials non-porous. However, the more sterically demanding ligand L1Me gives a material that shows gate-opening behaviour in response to a CO2 absorbate. The synthesis and structure of an unexpected mixed-valence CuII/CuI 3D MOF, Cu3[Cu(L2Me)2]2(H2O)4]·xS (Cu5(L2Me)4), containing an unusual trimeric CuII node are also reported.

scholarly journals Metal–organic frameworks (MOFs) based nanofiber architectures for the removal of heavy metal ions

RSC Advances ◽  
2022 ◽  
Vol 12 (3) ◽  
pp. 1433-1450
Author(s):  
Heja Ibrahim Adil ◽  
Mohammad R. Thalji ◽  
Suhad A. Yasin ◽  
Ibtisam A. Saeed ◽  
Mohammed A. Assiri ◽  
...  
Keyword(s):  
Heavy Metal ◽  
Metal Ions ◽  
Heavy Metal Ions ◽  
Metal Organic Frameworks ◽  
Chemical Properties ◽  
High Specific Surface Area ◽  
High Porosity ◽  
Metal Organic ◽  
Physical And Chemical ◽  
And Chemical Properties

Metal–organic frameworks (MOFs) are promising and effective materials for removing heavy metal ions from contaminated water owing to their high porosity, remarkable physical and chemical properties, and high specific surface area.

scholarly journals Thermochemical and Structural Analysis of Tautomers of Sulfur and Selenium Modified RNA Nucleobases

2019 ◽  
Vol 2 (2) ◽  
pp. 47-48
Author(s):  
Megan Joy ◽  
Alex Brown ◽  
Arturo Mora Gomez ◽  
Maria Rossano-Tapia ◽  
Shyam Parshotam
Keyword(s):  
Ir Spectra ◽  
Structural Changes ◽  
Chemical Properties ◽  
Hydrogen Atoms ◽  
Relative Population ◽  
Geometry Analysis ◽  
Physical And Chemical ◽  
Modified Nucleobases ◽  
Relative Gibbs Free Energy ◽  
And Chemical Properties

Nucleobases (adenine, cytosine, guanine, and uracil), the four molecules that forms RNA, have been found to be useful in probing in the human body when modified because they can emit light. Non-modified nucleobases do not exhibit emissive properties and cannot be used as probes. Some of the modifications include the substitution of nitrogen atoms with sulfur and selenium, and the resulting modified nucleobases give place to the so-called tz- and ts- RNA alphabets, respectively. Therefore, the aim of this project was to provide insights about the viability, from a computational perspective, of using the modified nucleobases as probes, evaluating the differences in thermochemical, structural and emissive properties of the modified nucleobases with respect to the non-modified ones. Nucleobases can coexist with other modified nucleobases or tautomers, molecules that differ due to the change in position of hydrogen atoms in a molecule’s structure and as a result have different physical and chemical properties. The thermochemical properties evaluation mainly consisted in the computation of the relative Gibbs Free Energy (G), which is related to the fraction F, an index of the relative population among tautomers. This was done using Gaussian 09 software by performing geometry analysis and frequency computations on each one of the tautomers. By comparing the equilibrium fractions, it was determined that in both cases, tz- and ts- guanine and cytosine exist principally in the form of one of their tautomers (Cytosine 2 and Guanine 2) as in the case of the non-modified cases. After confirming which tz- and ts- tautomers were the ones with the largest probable population, infrared (IR) and ultraviolet-visible (UV-vis) spectra were obtained. The IR spectra of selenium and sulfur tautomers of guanine and cytosine indicated that the tautomers had peaks at similar frequencies with respect to each other, however, the intensities varied, implying slight structural changes between the tautomers. On the other hand, the UV-vis spectra showed a change in peak positions between the tautomers with sulfur and selenium, suggesting that the change between sulfur and selenium has an effect on the spectra by shifting the peaks from the original molecules’ λmax values. Their relative population fractions show that only the canonical forms of the modified nucleobases exist in a larger extent than the rest of their tautomer forms. In addition, the features in their UV-vis and IR spectra allow these tautomers to be differentiated from each other.

Monitoring of Fluctuations in the Physical and Chemical Properties of a High-Calcium Fly Ash

1987 ◽  
Vol 113 ◽  
Author(s):  
Scott Schlorholtz ◽  
Ken Bergeson ◽  
Turgut Demirel
Keyword(s):  
Fly Ash ◽  
Chemical Properties ◽  
Operating Conditions ◽  
Physical And Chemical Properties ◽  
X Ray Diffraction ◽  
X Ray ◽  
Morphological Studies ◽  
High Calcium ◽  
Physical And Chemical ◽  
And Chemical Properties

ABSTRACTThe physical and chemical properties of fly ash produced at Ottumwa Generating Station have been monitored since April, 1985. The fly ash is produced from burning a low sulfur, sub-bituminous coal obtained from the Powder River Basin near Gillette, Wyoming. One-hundred and sixty samples of fly ash were obtained during the two year period. All of the samples were subjected to physical testing as specified by ASTM C 311. About one-hundred of the samples were also subjected to a series of tests designed to monitor the self-cementing properties of the fly ash. Many of the fly ash samples were subjected to x-ray diffraction and fluorescence analysis to define the mineralogical and chemical composition of the bulk fly ash as a function of sampling date. Hydration products in selected hardened fly ash pastes, were studied by x-ray diffraction and scanning electron microscopy. The studies indicated that power plant operating conditions influenced the compressive strength of the fly ash paste specimens. Mineralogical and morphological studies of the fly ash pastes indicated that stratlingite formation occurred in the highstrength specimens, while ettringite was the major hydration product evident in the low-strength specimens.

Experimental Investigation on Grinding Temperature of Titanium Alloy

2014 ◽  
Vol 1027 ◽  
pp. 127-130 ◽  
Author(s):  
Bing Jun Hao ◽  
Zhi Gang Dong ◽  
Ren Ke Kang ◽  
Huan Wang ◽  
Ke Cao
Keyword(s):  
Titanium Alloy ◽  
Structural Changes ◽  
Thermal Damage ◽  
Elevated Temperatures ◽  
Chemical Properties ◽  
Grinding Temperature ◽  
Physical And Chemical Properties ◽  
Machine Material ◽  
Physical And Chemical ◽  
And Chemical Properties

Titanium alloy has been widely used in aeronautics and astronautics industry owing to its unique combinations of properties. The unique physical and chemical properties of titanium alloy make it a typical difficult-to-machine material. The elevated temperatures at the machining zones may cause thermal damage, residual stress and micro-structural changes in the surface layer of titanium alloy during grinding. In this study, grinding experiments were performed on the titanium alloy, and the grinding temperature was experimentally tested with the grindable thermocouples. The effects of the grinding parameters on the grinding temperature were analyzed. The grinding temperature rises with the increase of grinding speed and grinding depth.

Preparation and Melting of Zr-1.0Nb Alloy

2016 ◽  
Vol 869 ◽  
pp. 578-584 ◽  
Author(s):  
Armando Cirilo Souza ◽  
J.L. Rossi ◽  
P. Tsakiropoulos ◽  
L.G. Martinez ◽  
Carlos Roberto Grandini ◽  
...  
Keyword(s):  
Nuclear Reactor ◽  
Chemical Properties ◽  
Zirconium Alloys ◽  
Processing Parameters ◽  
X Ray Diffraction ◽  
High Permeability ◽  
Physical And Chemical ◽  
Good Homogeneity ◽  
Consumable Electrodes ◽  
And Chemical Properties

Zirconium alloys have many applications in industry in services too harsh for stainless steels, nickel alloys or where a noteworthy improvement in service life may be achieved, by choosing zirconium alloys instead of other metals, such as high permeability to thermal neutrons and excellent corrosion resistance in nuclear reactor environments. Mixing alloying elements, such as niobium, molybdenum, tin, titanium and tantalum, with zirconium changes its physical and chemical properties, especially its resistance to corrosion. In this study, specimens of Zr-1.0Nb alloy were obtained by melting in a furnace with non-consumable electrodes in argon atmosphere. Different samples were prepared to ensure good homogeneity of the specimens. The melting procedure was tested several times to determine the parameters that ensure proper alloy handling. These parameters include the melting point of the alloys under pressure and the current in the furnace. Using the derived melting parameters and processing parameters, it has been obtained Zr-1.0Nb alloy specimens with appropriate homogeneity, as confirmed by auxiliary characterization techniques, such as optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. For these methods, the requirements for physicochemical properties in the nuclear sector were incorporated into the analyses.

Characterization of Shivirtui Zeolite Modified with Aluminum Oxyhydroxide Nanofibers

2019 ◽  
Vol 942 ◽  
pp. 40-49
Author(s):  
Yulia Murashkina ◽  
Olga B. Nazarenko
Keyword(s):  
Chemical Properties ◽  
Nitrogen Adsorption ◽  
X Ray Diffraction ◽  
Scanning Electronic Microscopy ◽  
Electronic Microscopy ◽  
X Ray ◽  
Physical And Chemical ◽  
And Chemical Properties ◽  
Aluminum Oxyhydroxide

Natural zeolite of Shivirtui deposit (Russia) was modified with nanofibers of aluminum oxyhydroxide AlOOH. Aluminum oxyhydroxide nanofibers were produced at the heating and oxidation of aluminum powder with water. The properties of modified zeolite were investigated by means of X-ray diffraction, transmission electronic microscopy, scanning electronic microscopy, low-temperature nitrogen adsorption, thermal analysis, and Fourier transform infrared spectroscopy. It was found that water content in the modified sample of zeolite was about 15 %. Based on the study of the physical and chemical properties, shivirtui zeolite modified with nanofibers of aluminum oxyhydroxide can be proposed for use as a flame-retardant additive to polymers.

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