A new family of hybrid inorganic-organic materials has been synthesized using a combination of flexible bis-pyridyl ligands in conjunction with a perfluorinated or nonfluorinated benzenedicarboxylate ligand. A significant difference between the carboxylate torsion angles of the fluorinated and nonfluorinated ligands leads to the formation of markedly different structures for the two groups of materials. No isostructural phases were found, and the use of perfluorinated ligands tends to increase the dimensionality of the resulting frameworks.Metal-organic frameworks containing fluorinated ligands are receiving increasing attention due to reports of interesting H 2 adsorption in these materials. 1-4 However, few have been synthesized to date and little is known of the structural chemistry of perfluorinated ligands in hybrid framework materials as compared to their nonfluorinated analogues. 5-13 Our current work involves developing a better understanding of the manner in which perfluorinated benzenedicarboxylates incorporate into hybrid structures and examining structural trends of the resulting materials. We have previously reported structures containing perfluorinated carboxylates in combination with nonfluorinated coligands such as imidazole, 14 triazole, 3 and both 2,2 0 -and 4,4 0 -bipyridine. 15,16 Here we extend this work to include the similar but longer and more flexible 1,2-bis(4-pyridyl)ethane (bpe) and 1,3-bis(4-pyridyl)propane (bpp) ligands in conjunction with tetrafluoroterephthalate (tftpa) and tetrafluoroisophthalate (tfipa). In contrast to our previous work, there are few reports of materials containing bpe or bpp and the nonfluorinated analogues of these dicarboxylates (tpa and ipa) for comparison. We have therefore undertaken a synthetic study of these materials as well.There are two important differences in the chemistry of perfluorinated benzenedicarboxylates as compared to their nonfluorinated analogues. First is their significantly enhanced acidity, which may contribute to the inability of compounds containing only transition metals and perfluorinated benzenedicarboxylates to crystallize, as hybrid frameworks are typically not obtained under strongly acidic conditions. This could explain the relative ease with which perfluorinated benzenedicarboxylates incorporate into hybrid materials when other basic ligands such as triazole and bipyridines are present in the reaction. The second difference involves the effect that the fluorine atoms have on the torsion angle by which the carboxylate groups are twisted out of the plane of the benzene ring. In structures containing tpa and ipa, the carboxylate group typically remains roughly in plane with the benzene ring to which it is attached (i.e., torsion angle near 0°). However, in structures containing tftpa and tfipa, the carboxylate groups are typically rotated between 45°and 60°with respect to the benzene ring. 12 This can be attributed both to an electrostatic repulsion between the highly electronegative fluorine atoms on the ring and the lone-pair ...
We report the application of nanoindentation and atomic force microscopy to establish the fundamental relationships between mechanical properties and chemical bonding in a dense inorganic-organic framework material: Ce(C(2)O(4))(HCO(2)), 1. Compound 1 is a mixed-ligand 3-D hybrid which crystallizes in an orthorhombic space group, in which its three basic building blocks, i.e. the inorganic metal-oxygen-metal (M-O-M) chains and the two organic bridging ligands, (oxalate and formate) are all oriented perpendicular to one another. This unique architecture enabled us to decouple the elastic and plastic mechanical responses along the three primary axes of a single crystal to understand the contribution associated with stiff vs compliant basic building blocks. The (001)-oriented facet that features rigid oxalate ligands down the c-axis exhibits the highest stiffness and hardness (E approximately 78 GPa and H approximately 4.6 GPa). In contrast, the (010)-oriented facet was found to be the most compliant and soft (E approximately 43 GPa and H approximately 3.9 GPa), since the formate ligand, which is the more compliant building block within this framework, constitutes the primary linkages down the b-axis. Notably, intermediate stiffness and hardness (E approximately 52 GPa and H approximately 4.1 GPa) were measured on the (100)-oriented planes. This can be attributed to the Ce-O-Ce chains that zigzag down the a-axis (Ce...Ce metal centers form an angle of approximately 132 degrees) and also the fact that the 9-coordinated CeO(9) polyhedra are expected to be geometrically more compliant. Our results present the first conclusive evidence that the crystal orientation dominated by inorganic chains is not necessarily more robust from the mechanical properties standpoint. Rigid organic bridging ligands (such as oxalate), on the other hand, can be used to produce greater stiffness and hardness properties in a chosen crystallographic orientation. This study demonstrates that there exists a vast opportunity to design the mechanical properties of dense hybrid framework materials through the incorporation of organic multifunctional ligands of varying rigidity.
The systematic and controlled reduction of vanadium oxide nanoscrolls results in routes to the largescale preparation of nanostructures of the interesting and useful materials rutile VO 2 and corundum V 2 O 3 . Vanadium oxide (V 2 O 5-δ ) nanoscrolls, prepared by the hydrothermal treatment of aged suspensions of V 2 O 5 and dodecylamine, were reduced in a furnace in an atmosphere of 5% H 2 :95% N 2 under different time and temperature conditions to monitor systematic trends in the structure and morphology of the resulting oxides. The products were characterized by X-ray diffraction (XRD), electron microscopy, N 2 sorption measurements, and electrical transport studies. We find that the reduction conditions (time and temperature) play a significant role in determining the crystal structure and morphology of the products. At short times and low temperatures, the reduction products are rutile VO 2 . These convert to corundum V 2 O 3 when temperatures are increased. In all cases, the appearance of crystalline Bragg peaks in XRD is associated with the breaking up of the starting high-aspect nanostructures into small, dense crystallites. Under certain reduction conditions, porous materials with ill-defined X-ray structures are obtained as intermediates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.