Structural Chemistry最新文献

A cyclopentane-5-spirohydantoin bearing a benzoyl group in position N1 was synthesized and its crystal structure was determined. The intermolecular interactions in the crystal packing were firstly investigated by Hirshfeld surface analysis. A detailed quantitative description is further provided through an analysis of dimeric motifs representing various recognition modes in the solid state. Non-covalent interactions (NCI) were analyzed using the NCI descriptor based on the reduced density gradient (RDG) to visualize non-covalent attractive and repulsive interactions within selected dimeric motifs. The crystal packing is dominated by chains running along the a axis, where the molecules are linked together by N3–H3⋯O3 hydrogen bonds. The molecular electrostatic potential (MEP) surface map revealed that the N3–H3 group is an electrophilic center. When compared to a structurally-related spirohydantoin bearing the benzoyl group in position N3, the title molecule exhibits a greater number of maxima on the MEP surface of the hydantoin ring. The global reactivity descriptors indicate that the position of the aromatic substituent directly affects the kinetic stability of the molecule. Introduction of the benzoyl group at the N3 position, between two carbonyl groups of the hydantoin ring, leads to higher chemical reactivity, while introduction on the N1 atom, adjacent to only one carbonyl group, enhances the kinetic stability of the compound.

This paper describes my interactions with Professor John A. Pople.

The paper systematizes and discusses the structures of uranyl tetrachloride complexes with inorganic and protonated organic cations, which were investigated by single-crystal X-ray structure analysis. The crystallochemical structural features of the analyzed compounds were determined. In the studied crystal structures of the UO₂²⁺ tetrachloride complexes, the coordination polyhedron of the hexavalent uranium atom has a tetragonal-bipyramidal (flattened octahedral) structure with the oxygen atoms of the uranyl group located at the apical vertices of the tetragonal-bipyramidal polyhedron. In the presence of free Cl⁻ ions and/or free neutral molecules containing acceptor atoms in the structures of the uranyl tetrachloride complexes that are not bound to the U atom, the cations do not interact with the donor Cl atoms of the anion, but form hydrogen bonds with free chlorine ions and acceptor atoms of free molecules.

The electronic and magnetic properties of diluted magnetic semiconductor (DMS) materials of the general formula NaY_1-xCe_xSe₂ (0.00 ≤ x ≤ 1.00) are studied using density functional theory (DFT) calculations. Alloys with fractional composition of the two rare earth elements (Y and Ce), which have not yet been synthesized, are predicted to exhibit magnetic transition and potential quantum spin liquid properties. As Ce concentration increases, these alloys transition from non-magnetic (NaYSe₂) to antiferromagnetic (AFM), with NaCeSe₂ forming magnetic layers of Ce³⁺ ions in a 2D triangular lattice. This structure suggests the potential for quantum spin liquid behavior. The Néel temperature (T_N) of these compounds increases with Ce concentration, reaching 114 K at 100% Ce doping. The direct bandgap of NaCeSe₂ (approximately 0.5 eV (PBE-GGA) and 1.3 eV (HSE06)) calculated for both spin-up and spin-down directions suggests that these alloys are suitable for magneto-optical applications, such as spin-polarized light-emitting diodes and spin transistors. The magnetic moment (~ 1 μ_B) primarily arises from Ce atoms and exhibits robustness with respect to changes in crystallographic parameters. These findings position NaY_1-xCe_xSe₂ alloys as promising candidates for both quantum spin liquid exploration and magneto-optical devices.

A new iron(III) sulfato complex [Fe₂(bpy)₂(H₂O)₂(µ-O)(µ-SO₄)₂]·3H₂O has been prepared from iron(II) chloride by using potassium peroxydisulfate being the oxidation agent and the source of sulfato ligands as well. The compound has been characterized by infrared, Raman and Mössbauer spectroscopies. X-ray structure analysis confirmed the presence of the Fe(III)–O–Fe(III) core in the complex. Both sulfato groups are bonded in the form of bridged bis(monodentate) ligands. The coordination polyhedra about the central atoms are completed by 2,2′-bipyridine and water molecules, forming thus distorted octahedra. A thorough comparison of bonding parameters of all dinuclear oxido-bridged sulfato complexes of iron(III) that have been solved by X-ray structure analysis revealed several strong correlations between these parameters and bonding mode of sulfato ligands. The characteristic vibrational bands of the FeOFe group has been observed at 770 cm⁻¹ (IR) for ν_as(FeOFe) and at 513 cm⁻¹ (IR) and 520 cm⁻¹ (Raman) for ν_s(FeOFe). The assignment of characteristic bands was corroborated by DFT calculation. The isomer shift values obtained in Mössbauer spectra indicate high-spin Fe³⁺, while the large quadrupole splitting is characteristic of oxygen bridged Fe³⁺ ions.

Dioxinodehydroeckol (DOO) is a natural phlorotannin with remarkable potential antioxidant activity. In this study, for the first time, the mechanism and kinetics of its radical scavenging activity specifically targeting hydroperoxyl radicals under physiological conditions (both aqueous and lipid environments) were elucidated. This compound was initially evaluated through its intrinsic thermochemical properties based on mechanisms such as formal hydrogen atom transfer (fHAT), sequential electron proton transfer (SETPT), and sequential proton loss electron transfer (SPLET). The kinetic calculations revealed that the reaction rates (k_overall) of DOO with HOO• radicals in aqueous and less polar phases (pentyl ethanoate) were 3.76 × 10² M⁻¹ s⁻¹ (when considering the influence of the molar fraction of HOO• for the water environment) and 1.54 × 10⁵ M⁻¹ s⁻¹, respectively, with the rate in the pentyl ethanoate phase particularly surpassing that of the reference antioxidant, Trolox. Furthermore, it was demonstrated that in aqueous conditions, the fHAT mechanism dominated over SPLET, as indicated by k_fHAT-total > k_SET-total. These findings highlight DOO as a promising antioxidant with potency to scavenge HOO• radicals in lipid environments.

Two new crystalline salts of l-cystine, [l-cystinium(2+) bis-iodide monohydrate (l-CsnH₂)(I)₂·H₂O (I) and l-cystinium(2+) bis-triiodide (l-CsnH₂)(I₃)₂ (II)], were obtained and characterized structurally, by vibrational spectroscopy and their electronic structure by quantum chemical calculations (CASTEP Package) in the framework of density functional theory (DFT). The bandgap of (II) was also determined experimentally by diffuse reflectance spectroscopy. Both salts crystallize in the orthorhombic space group P2₁2₁2₁. The composition and structure of (I) differ from those previously known chloride and bromide salts. A specific supramolecular anionic substructure was found in the structure of (II).

Exposure to benzaldehyde and benzoic acid poses risks to the environment and human health. The phosphoborane nanotube (PB-NT) has been identified as the primary material for research to detect these toxic and volatile substances. Besides, PB-NT material exhibits geometric stability, underpinned by a negative formation energy. After the adsorption of the benzaldehyde and benzoic acid onto the PB-NT, a reduction in the energy gap at all sites are noticed. Moreover, Density Functional Theory (DFT) calculations substantiate the geometric stability of PB-NT, which exhibits a band gap of 1.282 eV. Upon the adsorption, the band gap reduces significantly, decreasing by up to 60.76% for benzaldehyde and 34.63% for benzoic acid, thereby enhancing conductivity. The computed adsorption energy values, - 0.926 eV for benzaldehyde and - 1.196 eV for benzoic acid indicate that these interactions are characterized as physisorption. This property facilitates rapid desorption and contributes to the reusability of the sensor. Notably, the estimated recovery time for benzaldehyde is in the millisecond range, positioning PB-NT as a promising candidate for real-time monitoring applications. Furthermore, ab initio molecular dynamics (AIMD) simulations conducted at 300 K confirm the thermal stability of PB-NT. The future outcome of the proposed work with these results will lay inroads to the practical applicability of PB-NT in air quality sensors and biosensors warranting assessment for commercial viability, and enhancing its feasibility for practical use in various industries.

3-benzoyl-1,1-dimethyl-thiourea (3BDMT) is an important derivative of thiourea that has potential applications in different fields like medical, coordination and organic chemistry, pharmaceuticals, material science, and agriculture. This potential remains underexplored, leading to a lack of biological activity, electronic properties, or detailed structural characteristics of 3BDMT in the literature. This study discovered a new polymorph of 3BDMT and focuses on providing detailed information of the crystal structure, packing, molecular geometry, chemical stability, electronic properties, Hirshfeld surface (HS), and the interactions unique to both existing Form I and new Form II of 3BDMT. We used both experimental and computational approaches to establish this structural-property relationship. Form I and the new Form II were formed by concomitant crystallization and were characterized and confirmed by X-ray diffraction, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy techniques. The existing Form I and new Form II of 3BDMT have different morphologies and crystal packing, resulting in different energy of interaction, stability, and structural properties. The geometry of the experimental structures was in excellent agreement with the calculated geometry of the molecules at the B3LYP-D3/def2-TZVP level of theory. The presence of π⋅⋅⋅π stacking energies in the new Form II contributes to its energy of interaction and making the structure more stable than the existing Form I. This correlates with the higher enthalpy of melting observed in the DSC analysis for the new Form II 3BDMT structure. This finding suggests that both structures are chemically stable, but the new Form II is more stable than the existing Form I. The compounds’ chemical stability is essential in the synthesis and formulation of the molecules for applications and the exploration of the compounds’ biological and catalytic activities. The large theoretical energy gap of 3.98 eV in both existing Form I and new Form II of 3BDMT indicates that the molecules are stable and might be chemically reactive, making them useful in organic synthesis, coordination, and chemistry. Since the synthesis of various thiourea groups has shown that there is potential for the thiourea derivatives, the discoveries from this study have shed insight and could help in harnessing the potential applications of 3BDMT.

This study presents the synthesis and characterization of a new dithiocarbazate ligand (2-acetyl-pyridine-S-p-clorobenzyl-dithiocarbazate – HL) and its Cu(II) and Zn(II) complexes, [Cu(L)(Cl)] (1), [Cu(L)(Br)] (2), [Zn(L)(μ-CH₃COO)]₂ (3), and [Zn(L)₂] (4)_. The single-crystal X-ray diffraction analyses revealed that the ligand coordinates through its thiol tautomer by the NNS donor atom system to the metal center. The Cu(II) complexes are monomers with a square geometry. In contrast, complex (3) is presented as an asymmetric dimer with acetate bridges linking two Zn(II) atoms and shows a square base pyramid geometry. Complex (4) is a mononuclear compound with an octahedral geometry. UV–Vis spectra show ligand–metal charge transfer bands in all complexes and the IR spectra confirm the absence of the υ(N–H) and υ(C = S) stretching modes. The mass spectrometry shows the compounds [M + H]⁺ molecular ions, their isotopic distribution, and characteristic fragmentations. The ¹H NMR spectra of the ligand and zinc complex confirmed the thione tautomer of the dithiocarbazate. Hirshfeld surface analysis confirmed the intermolecular interactions in the crystal structures through the d_norm function and shape index functions, and the analysis of the fingerprint plots that quantified all the existing contacts. To explore the details of the electronic and vibrational structure of the synthesized complexes, a theoretical study was carried out using density functional theory (DFT) and its time-dependent variant TD-DFT to elucidate the nature of the main electronic transitions.

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