Structural Chemistry最新文献

In a series of three chiral thioureas bearing a tetrahydronaphthyl fragment, none of the homochiral samples forms “true chiral” hydrogen-bonded motifs in the crystal. In all three cases, the addition of a second independent molecule to the cell is observed. In one case, a pseudosymmetric dimer was found in the crystal, and in the other two cases, a chain motif with alternation of independent molecules was found. The conformational transformations of the thiourea fragment are considered.

Zeolites are valued and extensively used industrially silicate materials with microporous framework structures containing uniform channels typically below 1 nm in diameter. The efforts to synthesize new frameworks and crystal forms revealed another exceptional trait of zeolites, namely, that for the same topology, 2 forms are possible: the standard extended 3D crystals and 2D materials composed of nanosheets with uniform thickness below approximately 3 nm. The latter can be converted to 3D frameworks by topotactic condensation, e.g., upon thermal treatment. They are named formally as layered zeolite precursors. So far, approximately 20 such precursors have been identified out of over 250 recognized 3D frameworks, but the number is gradually increasing (of both). Herein we analyze 2 recently reported structures designated ITQ-8 and PKU-22. ITQ-8 was described as related to zeolite levyne (LEV; zeolite structures are denoted with three letter codes) but its parent framework remained unrecognized. By analyzing structures in the online zeolite database, we identified SAS as the parent framework of ITQ-8, its formal precursor. The mentioned LEV topology is produced by joining the sas layers with additional single atoms, making it formally the so-called interlayer expanded zeolite form (IEZ). The layers of ITQ-8 and PKU-22 (parent structure stilbite, STI) are lacking in-plane mirror plane and produce different topologies by translation and mirror reflection operations. In addition to detailed presentation of the structures, we provide suggestions for experimental transformation of ITQ-8 and PKU-22 to the corresponding 3D frameworks.

Interaction of A(HSeO₃) [A = K, Rb, Cs, (NH₄)] and CdX₂ (X = Cl, Br) in aqueous solutions results in crystallization of multinary hydroselenite halides. The overwhelming majority of the products correspond to the ACd(HSeO₃)X₂ composition and crystallize in triclinic symmetry similarly to the recently reported ACu(HSeO₃)X₂. Yet, the only exception is KCd(HSeO₃)₂Br, which expands the chemistry of the “layered hydroselenite” A_n(H₂O)_m[M(HSeO₃)₂X_n] family (M = Cu, Co, Zn; n = 1, 2). Formation of the two possible stoichiometries of the metal hydroselenite halide frameworks, [M(HSeO₃)X₂]^– vs. [M(HSeO₃)₂X]^–, (M = Cu, Cd; X = Cl, Br) is likely to depend on both the synthesis conditions and the r(A⁺)/r(X^–) ratio. The potassium-free substructure of the triclinic ACd(HSeO₃)X₂ is represented by a planar net comprised of trans-CdO₂X₄ octahedra and hydroselenite anions. If the dimer of anions instead of the monomer is considered a secondary building unit (SBU), the net acquires a kagome net-like topology. The potassium-free substructure of monoclinic KCd(HSeO₃)₂Br is represented by planar nets, and upon considering SBU = (HSeO₃)₂ instead of (HSeO₃), one obtains a simple square net.

A self-consistent approach is proposed for the basis set extrapolation of Hartree–Fock (HF) energies. Similar to existing extrapolation techniques, our scheme is based on convergent basis set hierarchies such as correlation-consistent basis sets. However, unlike the former, which utilize two or more HF energies obtained in separate HF calculations, the present method approximates the complete basis set limit HF energy in a single self-consistent field calculation minimizing a simple energy functional. Our benchmark results demonstrate that the performance of the self-consistent extrapolation approach is very similar to that of the conventional ones. The major advantage of the self-consistent technique is that the variational nature of the extrapolated energy facilitates the evaluation of analytic derivatives.

Contemporary quantum chemistry methods are the legacy of pioneers like John A. Pople, a Nobel Prize winner in 1998. Using such methods, we investigate the open-cage hydrocarbon derived from cubane upon removal of one of its CH moieties located at the vertex of the carbon skeleton. This hydrocarbon has C_3v symmetry and, following a geometric analogy, is termed vertexane (VA). The halogen derivatives of VA, obtained by replacing the apical hydrogen atom with a halogen, and their organotin congeners with a tin-halogen bond are polar molecules which represent novel building blocks in the design of tomorrow’s materials. The covalently-bonded dimers of VA are also explored, one is dumbbell-shaped while the other is a caged hydrocarbon of intermediate composition between those of cubane and dodecahedrane. 

Density functional theoretical calculations are used to investigate the nature of the metal–ligand bonding in the η³-propargyl complexes of Pt(II) and related species. Of particular interest are the interactions between the central propargyl C atom and the Pt centre. Experimental data has shown that the distance between Pt and the central C atom is the shortest Pt-C bond in the η³-propargyl complex [(η³-PhCCCH₂)Pt(PPh₃)₂]⁺, suggesting a strong bonding interaction. However, approximate molecular orbital calculations have suggested that bonding between Pt and the propargyl ligand occurs primarily through the terminal propargyl C atoms. In this contribution, Pt-C interactions are analysed using molecular orbital theory, natural bonding orbital analysis, and the quantum theory of atoms in molecules (QTAIM). Calculated bond orders and delocalization indices suggest that there is a significant bonding interaction between the Pt centre and central carbon atom, but that this interaction is much weaker than the short bond distance would suggest. Energy decomposition using the interacting quantum atoms (IQA) approach further supports this conclusion. A comparison is made to the bonding in related model metallacyclobutene and η³-allyl complexes.

Ephedrine is an ancient Chinese medicine drug used on patients with asthma, bronchitis and hay fever. In more recent times, it is used to prevent low blood pressure during anesthesia and to treat narcolepsy and obesity. It seemed important to understand the interaction of this drug with as large a variety of substrates as possible to get hints as to its modus operandi. It was, therefore, of interest that it appeared to crystallize as a Racemic Mimic in the form of its 4-nitrobenzoate derivative as determined by the cell parameters of that salt when it crystallized in both racemic and Sohncke space groups. Below, we describe the procedure used to prove that ephedrine belongs in that class and to illustrate the nature of the intra- and inter-molecular interactions between the constituent moieties in that monoclinic (P2₁ and P2₁/c) pair. Both crystal structures, obtained from the literature, were determined at 123 K and refined, respectively, to R-factors of 3.73 and 5.51%.

Two N′-(adamantan-2-ylidene)-substituted benzohydrazide derivatives, namely, N′-(adamantan-2-ylidene)-2,4-dichlorobenzohydrazide (1) and N′-(adamantan-2-ylidene)-3,4,5-trimethoxybenzohydrazide (2), were successfully synthesized and thoroughly characterized. Single-crystal X-ray diffraction analysis revealed that both compounds form robust molecular dimers stabilized by multiple hydrogen bonds, including N–H···O/N and C–H···O/N/Cl/π interactions. In the dichloro-substituted compound, numerous C–H···Cl interactions contribute to the stabilization of various molecular dimers in the solid state. Conversely, the trimethoxy-substituted derivative features numerous C–H···O interactions, which stabilize distinct molecular dimeric arrangements. Furthermore, the dichloro compound exhibits a Cl···Cl halogen bond, while the trimethoxy derivative demonstrates a tetrel bond involving methoxy groups. The energetics of the molecular dimers observed in these structures were analyzed, and the intermolecular interactions were further explored using atoms in molecules theory. Furthermore, in vitro antiproliferative activity, molecular docking, and molecular dynamic simulations were conducted to gain deeper insights into their bioactivity.

This study explores the impact of functionalization strategies on single-walled carbon nanotubes (SWCNTs) for drug delivery applications. It focuses on polyethylene glycol (PEG) and PEG-poly (maleic anhydride-alt-1-octadecene) (PEG-PMHC18) functionalized systems, comparing covalent and non-covalent approaches. The choice of functionalization method significantly influences molecular interactions and drug encapsulation behavior. Molecular dynamic (MD) simulations were conducted to evaluate the stability, drug encapsulation efficiency, and molecular mobility of functionalized SWCNTs. Covalent and non-covalent functionalization strategies using PEG and PEG-PMHC18 were analyzed to assess their effects on drug binding. Covalent functionalization provided strong and stable drug binding, ensuring controlled release, but limited molecular flexibility. PEG-PMHC18 covalent functionalization demonstrated enhanced stability due to increased steric interactions. In contrast, non-covalent functionalization offered greater flexibility, facilitating higher drug mobility and faster release. However, it exhibited weaker initial binding, leading to potential instability. The results also revealed that the type of functionalization and PEG chain length influence drug mobility, with non-covalent systems enabling more movement along the nanotube axis, while covalent systems restricted mobility for sustained release. The findings highlight that covalent functionalization is ideal for prolonged drug release, while non-covalent systems are better suited for rapid delivery. Optimizing these approaches can enhance drug carrier performance, balancing stability, mobility, and release characteristics for various therapeutic needs.