Unusual Chemical Ratio, Z″ Values, and Polymorphism in Three New <i>N-</i>Methyl Aminopyridine–4-Nitrophenol Adducts

Cocrystallization of 4-nitrophenol (<b>I</b>) with <i>N</i>-methyl substituted aminopyridines, 4-<i>N</i>-methylaminopyridine <b>1</b>, 2-<i>N</i>-methylaminopyridine <b>2</b>, and 2-<i><i>N,N</i></i>-dimethylaminopyridine <b>3</b>, resulted in three novel adducts <b>1</b>·2­(<b>I</b>), <b>2</b>·3­(<b>I</b>), and <b>3</b>·3­(<b>I</b>), one of which, <b>2</b>·3­(<b>I</b>), was found in three polymorphic forms, <b>A</b>, <b>B</b>, and <b>C</b>. The single crystals were grown by slow evaporation from ethanol. The proton transfer from the phenoxy to the pyridine moieties was registered in all compounds. The adducts comprise pyridinium cations, 4-nitrophenolate anions, and varying in number neutral 4-nitrophenol molecules. Though the asymmetric hydrogen-bonded network involving the −N⁺H groups of pyridinium cations and the −C–O^– and −C–OH groups of 4-nitrophenol moieties is registered in the adducts, the delicate balance of noncovalent interactions that include CH···O hydrogen bonds and face-to-face stacking interactions between the extended antiparallel arrays of components controls the centrosymmetric packing. Although three polymorphs of <b>2</b>·3­(<b>I</b>) share several structural common features, they reveal significant differences in the conformation of the pyridinium cation, and the hydrogen-bonding patterns

Interconversion between Discrete and a Chain of Nanocages: Self-Assembly via a Solvent-Driven, Dimension-Augmentation Strategy

Using a ligand bearing a bulky hydrophobic group, a “shish kabob” of nanocages, has been assembled through either a one-fell-swoop or a step-by-step procedure by varying the dielectric constant of the assembly mixture. A hydrophobic solvent breaks down the chain to discrete nanocages, while a hydrophilic solvent reverses the procedure. Although the shish kabob of nanocages has exactly the same chemical composition and even the same Archimedean-solid structure as those of its discrete analogue, its gas-adsorption capacity is remarkably improved because assembly of a chain exposes the internal surface of an individual cage. This dimension-augmentation strategy may have general implications in the preparation of porous materials

Structural Diversity in the Complexes of Trimeric Perfluoro‑<i>o</i>‑phenylene Mercury with Tetrathia- and Tetramethyltetraselenafulvalene

Five potential charge transfer complexes of trimeric perfluoro-<i>o</i>-phenylene mercury (<b>I</b>) with tetrathiafulvalene (TTF) and tetramethyltetraselenefulvalene (TMTSF) were grown from different solvent mixtures. The adducts (<b>I</b>)₂·TTF (<b>1</b>) and <b>I</b>·TTF (<b>2</b>) were grown by slow evaporation from the 1:1 mixture of dichloromethane (CH₂Cl₂, DCM) and carbon disulfide (CS₂). Use of the different 1:1 solvent mixtures of dichloromethane (CH₂Cl₂, DCM) and dichloroethane (C₂H₄Cl₂, DCE) has led to the crystalline adducts <b>I</b>·TTF (<b>3</b>) and <b>I</b>·TTF·DCE (<b>4</b>). Adduct <b>I</b>.TMTSF (<b>5</b>) was grown by the interface crystallization on the border of two immiscible layers, ethyl acetate, and carbon disulfide. The cocrystals differ by the donor–acceptor ratio, molecular packing, and the solvent inclusion. The components in <b>1</b>–<b>5</b> form mixed donor–acceptor stacks. The stacks are stabilized by Hg···S and Hg···C short contacts, while the lateral interactions between stacks include F···F, CH···F, and S/Se···F short contacts

Structural Diversity in the Complexes of Trimeric Perfluoro‑<i>o</i>‑phenylene Mercury with Tetrathia- and Tetramethyltetraselenafulvalene

Five potential charge transfer complexes of trimeric perfluoro-<i>o</i>-phenylene mercury (<b>I</b>) with tetrathiafulvalene (TTF) and tetramethyltetraselenefulvalene (TMTSF) were grown from different solvent mixtures. The adducts (<b>I</b>)₂·TTF (<b>1</b>) and <b>I</b>·TTF (<b>2</b>) were grown by slow evaporation from the 1:1 mixture of dichloromethane (CH₂Cl₂, DCM) and carbon disulfide (CS₂). Use of the different 1:1 solvent mixtures of dichloromethane (CH₂Cl₂, DCM) and dichloroethane (C₂H₄Cl₂, DCE) has led to the crystalline adducts <b>I</b>·TTF (<b>3</b>) and <b>I</b>·TTF·DCE (<b>4</b>). Adduct <b>I</b>.TMTSF (<b>5</b>) was grown by the interface crystallization on the border of two immiscible layers, ethyl acetate, and carbon disulfide. The cocrystals differ by the donor–acceptor ratio, molecular packing, and the solvent inclusion. The components in <b>1</b>–<b>5</b> form mixed donor–acceptor stacks. The stacks are stabilized by Hg···S and Hg···C short contacts, while the lateral interactions between stacks include F···F, CH···F, and S/Se···F short contacts

Zero Thermal Expansion and Abrupt Amorphization on Compression in Anion Excess ReO₃‑Type Cubic YbZrF₇

Heat treatment of cubic YbZrF₇, after quenching from 1000 °C, leads to a material displaying precisely zero thermal expansion at ∼300 K and negative thermal expansion at lower temperatures. The zero thermal expansion is associated with a minimum in the lattice constant at ∼300 K. X-ray total scattering measurements are consistent with a previously proposed model in which the incorporation of interstitial fluoride into the ReO₃-related structure leads to both edge and corner sharing coordination polyhedra. The temperature dependence of the experimental pair correlation functions suggests that the expansions of edge and corner sharing links partly compensate for one another, supporting the hypothesis that the deliberate incorporation of excess fluoride into ReO₃ structure materials can be used as a design strategy for controlling thermal expansion. Cubic YbZrF₇ has a bulk modulus, <i>K</i>₀, of 55.4(7) GPa and displays pronounced pressure-induced softening [<i>K</i>₀′ = −27.7(6)] prior to an abrupt amorphization on compression above 0.95 GPa. The resulting glass shows a single sharp scattering maximum at <i>Q</i> ∼ 1.6 Å^–1

Study of Guest Molecules in Metal–Organic Frameworks by Powder X‑ray Diffraction: Analysis of Difference Envelope Density

The structural characterization of metal–organic frameworks (MOFs) by powder X-ray diffraction can be challenging. Even more difficult are studies of guest solvent or gas molecules inside the MOF pores. Hence, recently we successfully designed several new approaches for structural investigations of porous MOFs. These methods use structure envelopes, which can be easily generated from the structure factors of a few (1–10) of the most intense low index reflections. However, the most interesting results have been found by using difference envelope density (DED) analysis. DED can be produced by taking the difference between observed and calculated structure envelope densities. The generation and analysis of DED maps are straightforward but allow studying guest molecules in the pores of MOFs by using routine powder X-ray diffraction data. Examples of DED used for studies of solvent molecule location, porosity activation, and gas loading are presented herein. We show that DED analysis is an important technique in the study of host–guest properties in MOFs by providing position, shape, and approximate occupancy of molecules in the MOF pores

Study of Guest Molecules in Metal–Organic Frameworks by Powder X‑ray Diffraction: Analysis of Difference Envelope Density

The structural characterization of metal–organic frameworks (MOFs) by powder X-ray diffraction can be challenging. Even more difficult are studies of guest solvent or gas molecules inside the MOF pores. Hence, recently we successfully designed several new approaches for structural investigations of porous MOFs. These methods use structure envelopes, which can be easily generated from the structure factors of a few (1–10) of the most intense low index reflections. However, the most interesting results have been found by using difference envelope density (DED) analysis. DED can be produced by taking the difference between observed and calculated structure envelope densities. The generation and analysis of DED maps are straightforward but allow studying guest molecules in the pores of MOFs by using routine powder X-ray diffraction data. Examples of DED used for studies of solvent molecule location, porosity activation, and gas loading are presented herein. We show that DED analysis is an important technique in the study of host–guest properties in MOFs by providing position, shape, and approximate occupancy of molecules in the MOF pores

Rigidifying Fluorescent Linkers by Metal–Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal–organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 ± 0.5%) under Ar, representing ca. 3600 cm^–1 blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity

Regioselective Atomic Layer Deposition in Metal–Organic Frameworks Directed by Dispersion Interactions

The application of atomic layer deposition (ALD) to metal–organic frameworks (MOFs) offers a promising new approach to synthesize designer functional materials with atomic precision. While ALD on flat substrates is well established, the complexity of the pore architecture and surface chemistry in MOFs present new challenges. Through <i>in situ</i> synchrotron X-ray powder diffraction, we visualize how the deposited atoms are localized and redistribute within the MOF during ALD. We demonstrate that the ALD is regioselective, with preferential deposition of oxy-Zn­(II) species within the small pores of NU-1000. Complementary density functional calculations indicate that this startling regioselectivity is driven by dispersion interactions associated with the preferential adsorption sites for the organometallic precursors prior to reaction

Regioselective Atomic Layer Deposition in Metal–Organic Frameworks Directed by Dispersion Interactions

The application of atomic layer deposition (ALD) to metal–organic frameworks (MOFs) offers a promising new approach to synthesize designer functional materials with atomic precision. While ALD on flat substrates is well established, the complexity of the pore architecture and surface chemistry in MOFs present new challenges. Through <i>in situ</i> synchrotron X-ray powder diffraction, we visualize how the deposited atoms are localized and redistribute within the MOF during ALD. We demonstrate that the ALD is regioselective, with preferential deposition of oxy-Zn­(II) species within the small pores of NU-1000. Complementary density functional calculations indicate that this startling regioselectivity is driven by dispersion interactions associated with the preferential adsorption sites for the organometallic precursors prior to reaction