The dense, anhydrous zeolitic imidazolate frameworks (ZIFs), Zn(Im)(2) (1) and LiB(Im)(4) (2), adopt the same zni topology and differ only in terms of the inorganic species present in their structures. Their mechanical properties (specifically the Young's and bulk moduli, along with the hardness) have been elucidated by using high pressure, synchrotron X-ray diffraction, density functional calculations and nanoindentation studies. Under hydrostatic pressure, framework 2 undergoes a phase transition at 1.69 GPa, which is somewhat higher than the transition previously reported in 1. The Young's modulus (E) and hardness (H) of 1 (E≈8.5, H≈1 GPa) is substantially higher than that of 2 (E≈3, H≈0.1 GPa), whilst its bulk modulus is relatively lower (≈14 GPa cf. ≈16.6 GPa). The heavier, zinc-containing material was also found to be significantly harder than its light analogue. The differential behaviour of the two materials is discussed in terms of the smaller pore volume of 2 and the greater flexibility of the LiN(4) tetrathedron compared with the ZnN(4) and BN(4) units.
A national survey of inorganic chemists explored the self-reported topics covered in foundation-level courses in inorganic chemistry at the postsecondary level; the American Chemical Society's Committee on Professional Training defines a foundation course as one at the conclusion of which, "a student should have mastered the vocabulary, concepts, and skills required to pursue in-depth study in that area." Anecdotal evidence suggested that more than one type of Inorganic Chemistry Foundation course was offered in the undergraduate chemistry curriculum. Cluster analysis confirmed this evidence, revealing four distinct foundation courses, each with unique profiles of topics covered. Faculty reported changes in content coverage over the past five years that mirror the evolving foci of inorganic chemistry research. These results potentially complicate how graduate programs evaluate incoming students' understanding of inorganic chemistry and the design of national assessments of undergraduate inorganic chemistry courses.
Silver is known to strongly affect the adsorptive properties of some zeolites. It is also
known that thermal vacuum dehydration of some argentiferous zeolites leads to the formation
of charged silver clusters within the zeolite. In this work we have synthesized silver zeolites
of the types Y, X, and low-silica X. The zeolites were treated in such a way as to promote
the formation of intracrystalline charged silver clusters. Equilibrium room-temperature
isotherms were measured for adsorption of nitrogen for each of the zeolites after various
heat treatments and dehydration. These materials were structurally characterized via
Rietveld refinement using neutron powder diffraction data. Color changes upon heat
treatment and subsequent X-ray photoemission spectroscopy confirmed some reduction of
Ag+ → Ag0. The effects of various dehydration conditions, including the time, temperature,
and atmosphere, on the room-temperature adsorption of nitrogen are discussed. Structural
characterization, along with valence bond calculations, revealed the presence of cations in
site II*, which are more active in Ag−LSX samples that were vacuum dehydrated at 450 °C
as compared to those that were vacuum dehydrated at 350 °C.
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