Two new dialkoxy‐substituted nido‐platinaundecaboranes: [(PPh3)2PtB10H10‐8,10–2(OCH2CH3)] ± CH2Cl2(I), { (PPh3)2‐PtB10H10‐8,10–2[OCH(CH3)2]} (II)

Two title nido‐11‐vertex platinaundecaboranes, 7,7‐bis‐(triphenylphosphine‐P)‐8, 10‐diethoxy‐8, 9:10, 11‐bis‐μ‐H‐7‐platina‐nido‐undecaborane‐dichloromethane (I) and 7,7‐bis‐(triphenylphosphine‐P) ‐8, 10‐di(i‐propoxy) ‐8,9:10,11‐bis‐μ‐H‐7‐platina‐nido‐undecaborane (II), were prepared and their structures were determined by single crystal X‐ray diffraction method. Each of them has an 11‐vertex nido‐polyhedral skeleton. {PtB₁₀} cage is substituted by two ethoxy or i‐propoxy groups at 8 and 10 positions, respectively.     

核-壳和中空多面体二氧化钛制备、表征及光催化

本文采用水热法控制制备了具有特殊纳米结构的核-壳和中空多面体二氧化钛, 以进一步提高具有特定暴露面多面体二氧化钛的比表面积, 达到更优异的光催化效果。用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等技术对所制备特殊结构二氧化钛的物相和微/纳结构进行表征分析, 结果表明所得核-壳和中空结构多面体二氧化钛具有一个类似隧道结构的(001)/(001)洞开的截顶双金字塔型壳层。这两种特殊结构的形成可能是源于配位/弱酸性腐蚀原理的共同作用。用核-壳和中空结构二氧化钛对亚甲基蓝进行光降解实验, 结果表明:所得两种新颖结构二氧化钛的光催化效率得到明显提高, 尤其是在添加过氧化氢条件下。可能原因是:两种特殊结构二氧化钛大比表面积正面作用抵消了(001)晶面消失或减少所产生的副作用, 以及过氧化氢在光催化反应中提供的活性氢氧根自由基使得光辐照二氧化钛产生的电子-空穴对在催化剂表面得到有效分离。     

Rubidium gadolinium bis­(tungstate)

The structure of rubidium gadolinium bis­(tungstate), RbGd(WO₄)₂, has been determined. The crystal is built up from corner‐ and edge‐sharing WO₆ octa­hedral and GdO₈ polyhedral groups, giving rise to a Gd–WO₄ polyhedral backbone surrounding structural cavities filled with Rb⁺ cations. The Gd and Rb atoms lie on twofold axes.     

A new approach to predict the formation of 3D hybrid organic-inorganic perovskites

Recently, hybrid organic-inorganic perovskite (HOIPs) materials are used to enhance the power conversion efficiency of the solar cells. The tolerance factor (TF) and octahedral factor (μ) are widely used to predict the formation of three-dimensional (3D) HOIPs structures. However, in some of the cases (e.g. CH₃NH₃GeI₃ (MAGeI₃) [TF = 1.06, μ = 0.33] NH₂CHNH₂GeI₃ (FAGeI₃) [TF = 1.14, μ = 0.33] and CH₃C(NH₂)₂GeI₃ (ACGeI₃) [TF = 1.17, μ = 0.33]), these factors could not predict the formation of HOIPs structures. Thus, we have introduced a new factor based on the HOMO-LUMO energy gap of the organic cations, metal cations, anions, and volume of the organic cations. We have tested and utilized the HOMO-LUMO energy gap factor (β) on 403 ABX₃ combinations. The factor β successfully predicts and differentiate the perovskite and non-perovskite materials. Further, we also observed that for the formation of HOIPs structure, volume of the organic cation should also be in the range of 20 to 46 cm³/mol. Based on the newly reported factor, we have also designed some new organic cations which may form a 3D HOIPs structure.     

Molecular dynamics study of perovskite structures with modified interatomic interaction potentials

The structure of compounds with the perovskite structure ABX₃ (A and B are cations, X are anions O^2—, F^—, Cl^—, Br^—, and I^—), which are widely used in engineering due to unique electrical, optical, and photovoltaic properties, has been considered. Hybrid organic—inorganic halide perovskites important for photovoltaics of a new generation are worth mentioning; they contain cations of organic nitrogen bases as monovalent cations. A molecular dynamics (MD) study of the CaTiO₃ base structure (Ca²⁺, Ti⁴⁺, and O^2—) has been performed in order to develop the methodology of computer simulation and optimization of the shape and parameters of atomic potentials for perovskite systems.     

Ab initio calculations on the isomerization of alkene radical cations

Ab initio calculations on the isomerization of butene and pentene radical cations indicate that, for all classical ion structures, the lowest barrier for a rearrangement to the most stable ion structure is below the dissociation limit. Isomerizations of linear butene radical cations to the isobutene structure take place via the CH₃CC₂H₅^·+ structure, whereas in the pentene case the connection between linear and branched ion structures proceeds via the 1,2-dimethylcyclopropane radical cation. From the results a qualitative model is derived which suggests that for larger alkene radical cations an isomerization to structures with four alkyl substituents on the double bond may be in close competition with dissociation.     

Self-Assembly of Polyoxometalate-Based Sub-1 nm Polyhedral Building Blocks into Rhombic Dodecahedral Superstructures

Self-assembly of subnanometer (sub-1 nm) scale polyhedral building blocks can yield some superstructures with novel and interesting morphology as well as potential functionalities. However, achieving the self-assembly of sub-1 nm polyhedral building blocks is still a great challenge. Herein, through encapsulating the titanium-substituted polyoxometalate (POM, K₇PTi₂W₁₀O₄₀) with tetrabutylammonium cations (TBA⁺), we first synthesized a sub-1 nm rhombic dodecahedral building block by further tailoring the spatial distribution of TBA⁺ on the POM. Molecular dynamics (MD) simulations demonstrated the eight TBA⁺ cations interacted with the POM cluster and formed the sub-1 nm rhombic dodecahedron. As a result of anisotropy, the sub-1 nm building blocks have self-assembled into rhombic dodecahedral POM (RD-POM) assemblies at the microscale. Benefiting from the regular structure, Br⁻ ions, and abundant active sites, the obtained RD-POM assemblies exhibit excellent catalytic performance in the cycloaddition of CO₂ with epoxides without co-catalysts. This work provides a promising approach to tailor the symmetry and structure of sub-1 nm building blocks by tuning the spatial distribution of ligands, which may shed light on the fabrication of superstructures with novel properties by self-assembly.     

KNi3(AsO4)(As2O7)

The structure of the title compound, potassium trinickel arsenate diarsenate, is built up from corner‐ and edge‐sharing NiO₆ octahedra, AsO₄ tetrahedra and As₂O₇ groups, giving rise to a polyhedral connectivity which produces large tunnels running along the crystallographic [010] direction. The K⁺ cations are located within these tunnels.     

Synthesis of polyoxovanadates via “chimie douce”

A large variety of new polyoxovanadates have been synthesized during the past few years by sol–gel chemistry or hydrothermal methods. These wet chemistry methods offer many advantages compared to the usual solid state syntheses. New open structures have been obtained from aqueous precursors. They result from the self-assembling of ionic species in the solution.Vanadium oxide gels and sols, V₂O₅·nH₂O, are formed around the point of zero charge (pH≈2). They have a ribbon-like structure and exhibit a liquid crystal behavior. These mesophases are similar to those currently observed with nematic polymers. Xerogel layers deposited from V₂O₅·nH₂O gels exhibit some preferred orientation and behave as versatile host structures for intercalation giving new hybrid organic–inorganic nanocomposites.Layered structures are formed around pH≈7 in the presence of large organic cations. They are built of mixed valence polyoxovanadate planes made of [VO₅] pyramids and [VO₄] tetrahedra. Organic cations lie between the oxide layers where they interact with the negative oxygen of the VO double bonds.Anions can behave as templating agents. Hollow cluster shells are formed around anions that remain encapsulated within the negatively charged polyvanadate cage. Large cations only behave as counter ions for the formation of a neutral crystalline network.It appears that the molecular structure of V^V precursors depends mainly on pH, but the way they self-assemble may be governed by other ionic species in the solution.     

Conversion from a π to a σ structure on replacing oxygen by sulphur: an ESR study

The radical cations of 1,3-dioxacylohexane and 1,3-dioxacyclopentane have π-structures involving delocalisation within the [-OCH₂O-]⁺ unit with high spin-density on the CH₂ group, whilst, in complete contrast, the corresponding sulphur derivatives have a weak σ bond between the two sulphur atoms, the unpaired electron being in the σ^* orbital with negligible spin-density on the CH₂ group.     

Distribution of Valence Electron Density in C n H m and BnHm Framework and Polyhedral Molecules and Orbital-Reduntant Bonds

In framework molecular cations and radical cations of adamantane C₁₀H _m ^q+ and also in polyhedral molecules and molecular ions C₅H₅ ⁺, C₆H₆ ^{2 +}, B₅H₉, and B₁₀H₁₀ ^{2 -}, the charge density of valence electrons in the central areas of C _n and B _n cavities and faces is significant. In the molecule of adamantane C₁₀H₁₆, the valence electron density in central areas of the cavity and faces of the C₁₀ framework is small as compared to the electron density along its edges C-C. These distinctions are due to the fact that, in the electronic structure of C _n H ^q _m cations and radical cations and also of B _n H _m molecules and molecular ions, there is an additional orbital interaction involving vacant valence orbitals of C⁺ or B (orbital-reduntant bonds); the absence of vacant valence orbitals of C atoms in neutral adamantane molecule excludes additional orbital interactions in excess of C-H and C-C.     

Hydrogen‐bonded sheets in 2‐(2‐aminophenyl)‐1H‐benzimidazol‐3‐ium dihydrogen phosphate

The title salt, C₁₃H₁₂N₃⁺·H₂PO₄⁻, contains a nonplanar 2‐(2‐aminophenyl)‐1H‐benzimidazol‐3‐ium cation and two different dihydrogen phosphate anions, both situated on twofold rotation axes in the space group C2. The anions are linked by O—H...O hydrogen bonds into chains of R₂²(8) rings. The anion chains are linked by the cations, via hydrogen‐bonding complementarities and electrostatic interactions, giving rise to a sheet structure with alternating rows of organic cations and inorganic anions. Comparison of this structure with that of the pure amine reveals that the two compounds generate characteristically different sheet structures. The anion–anion chain serves as a template for the assembly of the cations, suggesting a possible application in the design of solid‐state materials.     

Infrared Spectrum of the Adamantane+–Water Cation: Hydration‐Induced C−H Bond Activation and Free Internal Water Rotation

Diamondoid cations are reactive intermediates in their functionalization reactions in polar solution. Hydration is predicted to strongly activate their C?H bonds in initial proton abstraction reactions. To study the effects of microhydration on the properties of diamondoid cations, we characterize herein the prototypical monohydrated adamantane cation (C₁₀H₁₆⁺–H₂O, Ad⁺–W) in its ground electronic state by infrared photodissociation spectroscopy in the CH and OH stretch ranges and dispersion‐corrected density functional theory (DFT) calculations. The water (W) ligand binds to the acidic CH group of Jahn–Teller distorted Ad⁺ via a strong CH???O ionic H‐bond supported by charge–dipole forces. Although W further enhances the acidity of this CH group along with a proton shift toward the solvent, the proton remains with Ad⁺ in the monohydrate. We infer essentially free internal W rotation from rotational fine structure of the ν₃ band of W, resulting from weak angular anisotropy of the Ad⁺–W potential.     

Infrared Spectrum of the Adamantane+–Water Cation: Hydration-Induced C−H Bond Activation and Free Internal Water Rotation

Diamondoid cations are reactive intermediates in their functionalization reactions in polar solution. Hydration is predicted to strongly activate their C−H bonds in initial proton abstraction reactions. To study the effects of microhydration on the properties of diamondoid cations, we characterize herein the prototypical monohydrated adamantane cation (C₁₀H₁₆⁺–H₂O, Ad⁺–W) in its ground electronic state by infrared photodissociation spectroscopy in the CH and OH stretch ranges and dispersion-corrected density functional theory (DFT) calculations. The water (W) ligand binds to the acidic CH group of Jahn–Teller distorted Ad⁺ via a strong CH⋅⋅⋅O ionic H-bond supported by charge–dipole forces. Although W further enhances the acidity of this CH group along with a proton shift toward the solvent, the proton remains with Ad⁺ in the monohydrate. We infer essentially free internal W rotation from rotational fine structure of the ν₃ band of W, resulting from weak angular anisotropy of the Ad⁺–W potential.     

Photochemistry of trimethylene oxide and trimethylene sulfide radical cations in freonic matrices at 77 K

It was shown that trimethylene oxide (oxetane) radical cations were converted at 77 K into either distonic radical cations ·CH₂CH₂CH=OH⁺ or 2-oxetanyl radicals, depending on the freonic matrix used, by the action of light at λ = 546 nm and trimethylene sulfide radical cations transformed into distonic radical cations CH₂CHSH⁺CH ₂ ^· under 436-nm irradiation. The quantum yields of the photochemical reactions were determined. Quantum-chemical calculations on the structure and HFC constants of the radical cations and possible paramagnetic products of their transformation were performed. The reasons behind the observed difference in reactivity between the radical cations under the action of light are discussed.     

Tetrachloroferrate(III) Complexes Containing Some Heteroaromatic Organic Cations: Structures and Magnetic Properties

The crystal structures of tetrachloroferrate(III) complexes having stoichiometry (BH)⁺ [FeCl₄]^? (where B = isoquinoline and 4‐aminopyridine) were determined at 100 K. While weak interactions, particularly N–H···Cl hydrogen bonds, are evident in the structures, distances between the Fe(III) centers are quite long in both cases. The structure of the compound with B = quinoline was compared with that previously established at room temperature, and showed that neither solid‐solid nor magnetic phase transitions occurred in this temperature range. Magnetic measurements on the paramagnetic powders indicate weak antiferromagnetic interactions transmitted through the crystal lattice, giving rise to Néel temperatures that are significantly below 10 K. Comparisons are made with other characterized [FeCl₄]^? compounds having similar organic base cations, enabling clarification of the superexchange mechanism.     

[Cp3Ba]−: The First Structurally Characterized Barate Complex

A [Cp ₃ Ba] _∞ coordination polymer with a chain structure is present in the compound [Cp₃Ba]⁻[Bu₄P]⁺. The barium center is tetrahedrally coordinated by four η⁵-Cp rings (a section of the chain is shown on the right). The Bu₄P cations bridge neighboring [Cp₃Ba]_∞ chains through short hydrogen bonds, and the cocrystallized THF molecules do not coordinate to the barium centers but are instead involved in short CH⋅⋅⋅O hydrogen bonds with the Bu₄P cations.     

ESR studies on the structure of C6F−6 anions

Rigid solution spectra for C₆F^?₆ and C₄F^?₈ are compared, and it is concluded that C₆F^]t-₆ cannot have the planar, σ^* structure previously postulated. Instead, a puckered-ring structure with σ and pseudo π delocalisation is postulated.     

Application of molecular orbital calculations to the bicyclo[3.2.2]nonatrienyl anion and some related ions

The stabilities and the electronic structures of (CH)₉^? and (CH)₉⁺ systems were investigated using INDO MO calculation. The total overlap populations of the C-C bonds of bicyclo[3.2.2]nonatrienyl anion indicated its high degree of conjugation, in contrast to less conjugated bicyclo[3.2.2]nonatrienyl cation. On the other hand, the (CH)₉^? intermediate of the D_3h symmetrical structure was shown to be much less conjugated than the D_3h symmetrical (CH)₉⁺ ion. It was suggested from the calculated results that the sum of the total overlap populations of all C-C bonds involved in a (CH)_n molecule could be a quantitative measure of aromaticity for the (CH)_n systems in the three-dimensional structures.     

Phototransformations of azetidine radical cations stabilized in freonic matrices

It has been established that transformations of azetidine radical cations observed in freonic matrices under the action of light with λ = 436 nm (T = 77 K) are associated with C-N bond cleavage which corresponds to the cyclic form yielding a mixture of open distonic C-centered radical cations of the following structure: ·CH₂CH₂CH=NH ₂ ⁺