La6Pd13Cd4 and Ce6Pd13Cd4 with palladium-centred rare earth octahedra: synthesis, structure, and chemical bonding

Abstract  

The palladium-rich cadmium compounds La₆Pd₁₃Cd₄ and Ce₆Pd₁₃Cd₄ were synthesized by induction melting the elements in sealed tantalum ampoules and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: Na₁₆Ba₆N type, Im[`3] mIm\overline{3} m, a = 988.12(9) pm, wR2 = 0.0463, 225 F ² values, and 12 variables for La₆Pd₁₃Cd₄, and a = 982.1(2) pm, wR2 = 0.0521, 215 F ² values, and 12 variables for Ce₆Pd₁₃Cd₄. The striking structural motifs are palladium-centred La₆ and Ce₆ octahedra, which are packed in a bcc fashion. Further palladium and cadmium atoms built up three-dimensional [Pd₃Cd] networks in which the La₆Pd and Ce₆Pd octahedra are embedded. Chemical bonding analyses show that the dominant interaction occurs within the palladium-centred RE ₆ octahedra, while weaker bonding exists between them.     

FeNH4(SO4)2·12H2O (alum)-catalyzed preparation of 1,4-dihydropyridines: improved conditions for the Hantzsch reaction

Abstract  

FeNH₄(SO₄)₂·12H₂O (alum) efficiently catalyzes the one-pot three-component reaction of dimedone, aldehydes, and 3-aminocrotonate to afford 1,4-dihydropyridines. The work-up is easy, and the products are obtained in good to excellent yields and high purity.     

Stability constants of the Li+, Na+, H3O+, NH4+, Ag+, and K+ complexes of the cone conformer of tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate in nitrobenzene saturated with water

Abstract  

From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constants of the tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate (cone)·M⁺ complexes (M⁺ = Li⁺, H₃O⁺, NH₄ ⁺, Ag⁺, or K⁺) were determined in water-saturated nitrobenzene. It was found that these constants increase in the cation order NH₄ ⁺ < K⁺ < H₃O⁺ < Ag⁺ < Li⁺ < Na⁺.     

Novel and chemoselective one-pot synthesis of 4-arylidene-2-phenyl-5(4H)-oxazolones starting from benzyl alcohols promoted by [(C14H24N4)2W10O32]-[bmim]NO3

Abstract  

A new and practical promoter system for one-pot, efficient, chemoselective synthesis of 4-arylidene-2-phenyl-5(4H)-oxazolones using [(C₁₄H₂₄N₄)₂W₁₀O₃₂]-[bmim]NO₃ under solvent-free conditions is described. The present work opens up a new and ecofriendly synthetic route to Erlenmeyer–Pl?chl adducts from primary benzyl alcohols in a one-pot operation.     

Synthesis of arylaminotetrazoles by ZnCl2/AlCl3/silica as an efficient heterogeneous catalyst

Abstract  

Arylaminotetrazoles were efficiently synthesized from secondary arylcyanamides by application of ZnCl₂/AlCl₃/silica as a reusable heterogeneous Lewis acid catalyst. 5-Arylamino-1H-tetrazoles can be obtained from arylcyanamides carrying electron-withdrawing substituents on the aryl ring, while with electron-releasing groups 1-aryl-5-amino-1H-tetrazoles will be produced. The former isomer is also produced within longer reaction times (~20 h) even with electron-releasing groups.     

La3Pd4Zn4 and La3Pt4Zn4 with a different coloring of the Gd3Cu4Ge4-type structure

Abstract  

The intermetallic zinc compounds La₃Pd₄Zn₄ and La₃Pt₄Zn₄ were synthesized by induction melting of the elements in sealed tantalum tubes. The structures were refined from X-ray single-crystal diffractometer data: Gd₃Cu₄Ge₄ type, Immm, a = 1,440.7(5), b = 743.6(2), c = 419.5(2) pm, wR ₂ = 0.0511, 353 F ² for La₃Pd₄Zn₄; and a = 1,439.9(2), b = 748.1(1), c = 415.66(6) pm, wR ₂ = 0.0558, 471 F ² for La₃Pt₄Zn₄ with 23 variables per refinement. The palladium (platinum) and zinc atoms build up a three-dimensional polyanionic [Pd₄Zn₄] (260–281 pm Pd–Zn) and [Pt₄Zn₄] (260–279 pm Pt–Zn) network in which the lanthanum atoms fill cavities of CN 14 (6 Pd/Pt + 8 Zn for La1) and CN 12 (6 Pd/Pt + 6 Zn for La2), respectively. The copper position of the Gd₃Cu₄Ge₄ type is occupied by zinc and the two crystallographically independent germanium sites by palladium (platinum), a new coloring pattern for this structure type. Within the [Pd₄Zn₄] and [Pt₄Zn₄] the Pd2 and Pt2 atoms form Pd2–Pd2 (291 pm) and Pt2–Pt2 (296 pm) dumbbells. The structures of La₃Pd₄Zn₄ and La₃Pt₄Zn₄ are discussed with respect to the prototype Gd₃Cu₄Ge₄ and the Zintl phase Sr₃Li₄Sb₄. Temperature-dependent magnetic susceptibility measurements indicate diamagnetism for La₃Pt₄Zn₄ and Pauli paramagnetism for La₃Pd₄Zn₄.     

Synthesis, structural characterization, and magnetic properties of the metallamacrocycle [Fe6(C11H11N2O3)6(C4H9NO)6]

Abstract  

The 18-metallacrown-6 metallamacrocycle [Fe₆(pmshz)₆(C₄H₉NO)₆] has been synthesized by the self-assembly reaction of iron ions with N-substituted salicylhydrazide ligands. Six Fe(III) ions and six deprotonated N-propanoyl-4-methylsalicylhydrazide (H₃ pmshz) ligands construct a planar 18-membered ring based on Fe–N–N–Fe linkage. Because of the coordination, the ligand enforces the stereochemistry of the Fe(III) ions as a propeller shape with alternating …ΔΛΔΛ… configurations. There is a strong antiferromagnetic exchange interaction between the paramagnetic iron centers.     

KF/Al2O3: an efficient solid heterogeneous base catalyst in one-pot synthesis of benzimidazoles and bis-benzimidazoles at room temperature

Abstract  

KF/Al₂O₃ is an efficient solid heterogeneous base catalyst in the one-pot synthesis of 2-substituted benzimidazoles and 2,2′-disubstituted bis-benzimidazoles from 1,2-phenylenediamines or 3,3′-diaminobenzidines and acid chlorides, anhydrides, and esters at room temperature.     

Br?nsted-acidic ionic liquid [HO3S(CH2)4MIM][HSO4] as efficient and reusable catalyst for one-pot synthesis of β-acetamido ketones

Abstract  

Efficient and convenient synthesis of β-acetamido ketones has been achieved by one-pot reaction of acetophenone, aryl aldehydes, acetyl chloride, and acetonitrile in the presence of 3-methyl-1-(4-sulfonylbutyl)imidazolium hydrogensulfate [HO₃S(CH₂)₄MIM][HSO₄], a Br?nsted-acidic ionic liquid, as a green and reusable catalyst in solvent-free media at room temperature. The catalyst could be recycled and reused without noticeable decrease in catalytic activity.     

A facile and efficient method for synthesis of xanthone derivatives catalyzed by HBF4/SiO2 under solvent-free conditions

Abstract  

HBF₄/SiO₂ was used as an efficient, green, and inexpensive catalytic system for synthesis of 12-aryl or 12-alkyl-8,9,10,12-tetrahydro-11H-benzo[a]xanthen-11-one derivatives via a one-pot three-component reaction of aldehydes, 2-naphthol, and cyclic 1,3-dicarbonyl compounds. The reactions proceeded rapidly at 80 °C under solvent-free conditions and the desired products were obtained in good to excellent yields.     

A combined extraction and DFT study on the complexation of H3O+ with a hexaarylbenzene-based receptor

Abstract  

By means of theoretical calculations at density functional level, the complex structure of a hexaarylbenzene-based receptor with Na⁺ was derived. In the resulting complex having C ₃ symmetry, the sodium cation synergistically interacts with the hydrophilic polar ethereal oxygen fence and with the central hydrophobic benzene bottom of the parent receptor via cation–π interaction.     

Hydroxy- and boronic-acid-functionalized carbosilanes: Synthesis and solid state structure of Si(C6H4-4-SiMe2((CH2)3OH))4

Consecutive synthesis methodologies for the preparation of carbosilanes (Ph)(Me)Si((CH₂)₃B(OH)₂)₂ (2), Si(C₆H₄-4-SiMe₂((CH₂)₃B(OH)₂))₄ (5), (Ph)(Me)Si((CH₂)₃OH)₂ (3), and Si(C₆H₄-4-SiMe_3−n((CH₂)₃OH)_n)₄ (6a, n = 1; 6b, n = 2; 6c, n = 3) are reported. Boronic acids 2 and 5 are accessible by treatment of (Ph)(Me)Si(CH₂CHCH₂)₂ (1) or Si(C₆H₄-4-SiMe₂(CH₂CHCH₂))₄ (4a) with HBBr₂·SMe₂ followed by addition of water, while 3 and 6 are available by the hydroboration of 1 or Si(C₆H₄-4-SiMe_3−n(CH₂CHCH₂)_n)₄ (4a, n = 1; 4b, n = 2; 4c, n = 3) with H₃B·SMe₂ and subsequent oxidation with H₂O₂.The single molecular structure of 6a in the solid state is reported. Representative is that 6a crystallized in the chiral non-centrosymmetric space group P2₁2₁2₁ forming 2D layers due to intermolecular hydrogen bond formation of the HO functionalities along the crystallographic a and c axes.     

Formation of [Cp2TiSbMe2]2, [Cp2TiSb(SiMe3)2]2 and [Cp2TiCl]2·2Mes4Sb2

Reactions of [Cp₂Ti(btmsa)] (btmsa = bis(trimethylsilyl)acetylene) with R₄Sb₂ (R = Me, Me₃Si) give [Cp₂TiSbMe₂]₂ (1) or [Cp₂TiSb(SiMe₃)₂]₂ (2) respectively. [Cp₂TiCl]₂·2Mes₄Sb₂ (3) is serendipitously formed from [Cp₂Ti(btmsa)] and Mes₂SbH containing NH₄Cl traces.     

Determination of heat capacities of PbCrO4(s), Pb2CrO5(s), and Pb5CrO8(s)

Abstract  

Heat capacities of PbCrO₄(s), Pb₂CrO₅(s), and Pb₅CrO₈(s) were measured by differential scanning calorimetry. The measured heat capacities as a function of temperature are expressed as C _p <PbCrO₄> J K⁻¹ mol⁻¹ = 150.37 + 27.74 × 10⁻³ T − 2.80 × 10⁶ T ⁻² (T = 300–750 K), C _p <Pb₂CrO₅> J K⁻¹ mol⁻¹ = 194.55 + 76.09 × 10⁻³ T − 4.64 × 10⁶ T ⁻² (T = 300–700 K), and C _p  <Pb₅CrO₈> J K⁻¹ mol⁻¹ = 323.35 + 184.80 × 10⁻³ T − 5.48 × 10⁶ T ⁻² (T = 300–600 K). From the measured heat capacity data, thermodynamic functions such as enthalpy increments, entropies, and Gibbs energy functions were derived.     

The influence of tetramethylthiourea on a two-step Zn2+ ion electroreduction in concentrated NaClO4 solutions

Abstract  

A two-step Zn²⁺ ion reduction was estimated at the dropping mercury electrode in 2, 3, and 4 mol dm⁻³ NaClO₄ with the addition of tetramethylthiourea using an impedance method at wide potential and frequency ranges. With increasing tetramethylthiourea and NaClO₄ concentrations the k_{\texts 1} ^t k_{{{\text{s}}_{ 1} }}^{t} and k_{\texts 2} ^t k_{{{\text{s}}_{ 2} }}^{t} values increased, achieving their maximum values at the highest concentrations of tetramethylthiourea in 3 and 4 mol dm⁻³ NaClO₄ solutions. The catalytic effect of tetramethylthiourea at its lowest employed concentration increased with increasing NaClO₄ concentration.     

B24N24 nanocages: a GIAO density functional theory study of 14N and 11B nuclear magnetic shielding and electric field gradient tensors

Abstract  

Density functional theory (DFT) calculations were performed to determine boron-11 and nitrogen-14 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spectroscopy parameters in the three most stable B₂₄N₂₄ fullerenes for the first time. The considered samples were first allowed to relax entirely, and then the NMR and NQR calculations were performed on the geometrically optimized models. The calculations of the ¹¹B and ¹⁴N nuclear magnetic shielding tensors and electric field gradient tensors employed the Gaussian 98 software implementation of the gauge-including atomic orbital (GIAO) method using the Becke3, Lee-Yang-Parr (B3LYP) DFT level and 6-311G** and 6-311++G** standard basis sets in each of the three optimized forms, and converted the results to experimentally measurable NMR parameters.The calculated NMR chemical shieldings of the three cages show significant differences, providing a way to identify these clusters. The evaluated NQR parameters of the ¹¹B and ¹⁴N nuclei in the clusters are also reported and discussed.     

Extraction and DFT study on the complexation of H3O+ ion with tetrakis(2-ethoxyethoxy)-tetra-p-tert-butylcalix[4]arene

Abstract  

Extraction experiments in the two-phase water/nitrobenzene system and γ-activity measurements were used to determine the stability constant of protonated tetrakis(2-ethoxyethoxy)-tetra-p-tert-butylcalix[4]arene in nitrobenzene saturated with water. Density functional theory (DFT) calculations were applied to derive the most probable structure of the tetrakis(2-ethoxyethoxy)-tetra-p-tert-butylcalix[4]arene·H₃O⁺ complex species.     

Kinetics of Ag/TiO2-photocatalyzed iodide ion oxidation

Abstract  

Ag-doped TiO₂ (anatase) samples (mass fraction w _Ag = 0.01 and w _Ag = 0.02) of 15.9 and 14.5 nm mean particle size and 11.46 and 10.14 m² g⁻¹ BET surface area were prepared by photodeposition. Doping results in surface plasmon resonance of the metallic silver nanoclusters at around 500 nm, but the absorption edge remains unaltered at 365 nm. Ag-doping remarkably enhances the photooxidation of iodide ion under UV light; iodine formation with Ag/TiO₂ with w _Ag = 0.01 is 16 times greater than with bare TiO₂. The reaction conforms to Langmuir–Hinshelwood kinetics with regard to both I⁻ and O₂. Increase of pH slows down iodine formation and sacrificial electron donors arrest the reaction. Pre-sonication of the catalyst slurry hinders the photocatalysis. Generation of iodine is much greater in acetonitrile than in water. Under the experimental conditions, Ag/TiO₂ with w _Ag = 0.01 is more efficient than Ag/TiO₂ with w _Ag = 0.02, and the enhanced photocatalysis is likely to be because of suppression of electron–hole pair recombination. Kinetic analysis reveals that increasing the Ag mass fraction from 0.01 to 0.02 enhances the surface pseudo-first-order rate constant but inhibits the adsorption of iodide ion and the oxygen molecule on the illuminated oxide surface.     

CO_2/H_2O混合绿色介质中的有机催化反应

绿色化学是化学发展的必然趋势。有效利用绿色溶剂是绿色化学的重要内容。CO2和H2O混合体系是具有很多特点的绿色反应介质,可以用于不同化学反应,特别是弱酸催化的反应,从而替代传统的有机酸和无机酸。本文讨论了CO2/H2O体系的酸性随温度和压力的变化,综述了在CO2/H2O混合绿色介质中有机化学反应研究进展,这些反应包括脱水反应、烷基化反应、香茅醛环化反应、重氮化反应、多元醇转化成环醚的反应、溴氧化反应、芳硝基化合物选择性还原、多糖水解反应、生物质转化反应、环氧丙烷水解反应、脱羧反应、醇氧化反应、对映选择氧化反应以及酮不对称还原;最后对CO2/H2O体系在化学反应中应用的发展趋势进行了探讨。