Al2Pt for Oxygen Evolution in Water Splitting: A Strategy for Creating Multifunctionality in Electrocatalysis

The production of hydrogen via water electrolysis is feasible only if effective and stable catalysts for the oxygen evolution reaction (OER) are available. Intermetallic compounds with well‐defined crystal and electronic structures as well as particular chemical bonding features are suggested here to act as precursors for new composite materials with attractive catalytic properties. Al₂Pt combines a characteristic inorganic crystal structure (anti‐fluorite type) and a strongly polar chemical bonding with the advantage of elemental platinum in terms of stability against dissolution under OER conditions. We describe here the unforeseen performance of a surface nanocomposite architecture resulting from the self‐organized transformation of the bulk intermetallic precursor Al₂Pt in OER.     

Preparation and application of poly(alkoxytitanate) as a TiO2 precursor with high storage stability

Titanium dioxide is a basic material of our daily life. Because of its favourable properties, such as harmlessness, chemical stability, photocatalytic activity, or whiteness it is increasingly applied in both micro and nano particles and thin films and coating. One of the available procedures for film forming is the sol–gel technology, an inexpensive low temperature process with wide possibilities to vary film properties by changing the composition of the precursor solution or other parameters. In the paper a new precursor polymer for TiO₂ film-preparation with high storage and processing stabilities is introduced and applied in thin film forming. The new precursor poly(alkoxytitanate) is prepared by a one step, water-free sol–gel method. A smooth TiO₂ film can be prepared using this precursor by spin-coating followed by H₂-plasma curing. Comparing to a common precursor such as Ti(O–iPr)₄, this precursor has a good solubility in different solvents and a much higher storage stability. The easy to modify precursor end groups enable the tailoring of properties regarding to hydrolysis to both TiO₂ particles and films.     

Assembly of 3D Coordination Polymers from 2D Sheets by [2+2] Cycloaddition Reaction

The synthesis of three 2D interdigitated Zn^II coordination polymers (CPs), by using three monotopic ligands containing C?C bonds, is reported. Among these, two CPs with 4spy (4‐styryl pyridine) and 2F‐4spy (a 2′‐fluoro derivative of 4spy) ligands showed quantitative formation of cyclobutane rings, thus demonstrating a unique synthetic procedure to synthesize metal–organic frameworks (MOFs) by using this photochemical reaction. Interestingly, these compounds can also be synthesized by mechanochemical grinding procedures by using Zn(OAc)₂. In contrast, Zn(NO₃)₂ did not yield the required product, unlike in the solution route. In addition, compounds with 4vpy (4‐vinylpyridine), 4spy and 2F‐4spy ligands created different units in the CPs; 4vpy and 2F‐4spy furnished paddle wheel units, whereas 4spy yielded tetrahedral Zn^II repeating units. Furthermore, the change in coordination geometry manifests in the photoluminescence properties, attributed to the difference in charge‐transfer and ligand‐centered fluorescent phenomenon.     

The design of molecules containing planar tetracoordinate carbon

A novel preference for planar tetracoordination was observed over the conventional tetrahedral arrangement in a new series of C₅H₂, C₅H₄, C₅H₄^1+/2+ and related compounds. The stability of these molecules is assessed with the ring-opening barriers, HOMO-LUMO gap, singlet-triplet energy differences and nucleus independent chemical shift values.     

Fluorinated surfactants in supercritical CO2

Liquid or supercritical carbon dioxide has important environmental and economic advantages over petrochemical solvents currently used for industrial processes. However, low solubility in CO₂, particularly of polar compounds, is a hurdle to its implementation as an acceptable alternative. These solubility problems have been overcome by employing specialised fluorinated surfactants to stabilise water nano-droplets as water-in-supercritical/liquid CO₂ microemulsions. Such novel microemulsions can now facilitate innovative ‘green-and-clean’ applications of carbon dioxide technology.     

Gas-phase base-catalyzed Claisen—Schmidt reactions of the acetone enolate anion with various para-substituted benzaldehydes

Substituent effects were determined for the gas-phase base-catalyzed Claisen-Schmidt reaction of the acetone enolate anion and various para-substituted benzaldehydes. Under chemical ionization conditions, the adduct for the reaction was detected and the fraction of adduct that is tetrahedral was determined. The Hammett constants for the substituents correlate the fraction of the adduct population that is tetrahedral. The fraction of tetrahedral intermediate is greatest for those systems in which the negative charge is most highly stabilized. The structures of the adducts are determined on the basis of collisionally activated decomposition mass spectra. These spectra show that both the adducts of the ion-molecule reactions and deprotonated reference compounds, which have a structure that is similar to the tetrahedral intermediate, decompose by elimination of water and by a retro-aldol reaction. The adducts formed from the ion-molecule reactions show a greater propensity to reform the acetone enolate, whereas the deprotonated reference compounds eliminate H₂O readily. The reaction constant ρ from the Hammett correlation is +1.6, which substantiates that the production of tetrahedral intermediates is facilitated by electron-withdrawing substituents.     

Increasing Chemical Diversity of B2N2 Anthracene Derivatives by Introducing Continuous Multiple Boron-Nitrogen Units

Increasing the chemical diversity of organic semiconductors is essential to develop efficient electronic devices. In particular, the replacement of carbon-carbon (C−C) bonds with isoelectronic boron-nitrogen (B−N) bonds allows precise modulation of the electronic properties of semiconductors without significant structural changes. Although some researchers have reported the preparation of B₂N₂ anthracene derivatives with two B−N bonds, no compounds with continuous multiple BN units have been prepared yet. Herein, we report the synthesis and characterization of a B₂N₂ anthracene derivative with a BNBN unit formed by converting the BOBN unit at the zigzag edge. Compared to the all-carbon analogue 2-phenylanthracene, BNBN anthracene exhibits significant variations in the C−C bond length and a larger highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap. The experimentally determined bond lengths and electronic properties of BNBN anthracene are confirmed through theoretical calculations. The BOBN anthracene organic light-emitting diode, used as a blue host, exhibits a low driving voltage. The findings of this study may facilitate the development of larger acenes with multiple BN units and potential applications in organic electronics.     

Tetrathiafulvalene‐Based Macrocycles Formed by Radical Cation Dimerization: The Role of Intramolecular Hydrogen Bonding and Solvent

Compounds 1 a and 1 b were prepared by appending two tetrathiafulvalene (TTF) units to an aromatic amide segment that is driven by six or two intramolecular N? H???O hydrogen bonds to adopt a folded conformation. UV/Vis absorption experiments revealed that if the TTF units were oxidized to TTF^.+ radical cations, the two compounds could form a stable single molecular noncovalent macrocycle in less polar dichloromethane or dichloroethane or a bimolecular noncovalent macrocycle in a binary mixture of dichloromethane with a more polar solvent owing to remarkably enhanced dimerization of the TTF^.+ units. The stability of the (TTF^.+)₂ dimer was evaluated through UV/Vis absorption, electron paramagnetic resonance, and cyclic voltammetry experiments and also by comparing the results with those of control compound 2 . The results showed that introduction of the intramolecular hydrogen bonds played a crucial role in promoting the stability of the (TTF^.+)₂ dimer and thus the noncovalent macrocyclization of the two backbones in both uni‐ and bimolecular manners.     

Charge-Separated and Lewis Paired Metal–Organic Framework for Anion Exchange and CO2 Chemical Fixation

Charge-separated metal–organic frameworks (MOFs) are a unique class of MOFs that can possess added properties originating from the exposed ionic species. A new charge-separated MOF, namely, UNM-6 synthesized from a tetrahedral borate ligand and Co²⁺ cation is reported herein. UNM-6 crystalizes into the highly symmetric P43n space group with fourfold interpenetration, despite the stoichiometric imbalance between the B and Co atoms, which also leads to loosely bound NO₃⁻ anions within the crystal structure. These NO₃⁻ ions can be quantitatively exchanged with various other anions, leading to Lewis acid (Co²⁺) and Lewis base (anions) pairs within the pores and potentially cooperative catalytic activities. For example, UNM-6-Br, the MOF after anion exchange with Br⁻ anions, displays high catalytic activity and stability in reactions of CO₂ chemical fixation into cyclic carbonates.     

Relationships between Retention Factors and Analyte Hydrophobicity on Cyanopropyl and n‐Octadecyl Bonded Silicas,Cross‐Linked Polymers and Porous Graphitic Carbon Stationary Phases. Consequences for the Trace Analysis of Highly Polar Organic Compounds

LC retention data have been measured using various stationary phases with an emphasis on highly polar to moderately polar neutral organic compounds having octanol‐water partition coefficients (K_ow) in log units between 0 and 3. The relationships between the retention factor measured in water and the octanol‐water partition coefficient are linear but with different slopes for octadecyl (C₁₈) silicas, and two polystyrene divinylbenzene (PS‐DVB) phases with low and high surface areas. These relationships confirm that highly cross‐linked polymers can provide more than 1000‐times higher retention values than C₁₈ silicas for moderately polar analytes but close values for highly polar ones. They also explain why C₁₈ silicas and polymers are equivalent for the separation of very polar analytes. In contrast, due to a different retention mechanism, no relation exists between the retention shown by porous graphitic carbons (PGC) and analyte hydrophobicity, but highly polar analytes are in general much more strongly retained than by any other sorbent. The potential of PGC for both the extraction and the separation of analytes is shown. Due to the difference in separation mechanism, PGC is the analytical phase that should be used for confirmation of the identity of analytes instead of a cyanopropylsilica column as recommended in some environmental procedures. Applications are presented for the trace‐determination of triazines and polar degradation products in ground and surface water with detection limits below the 0.1 μg/L level.     

Influence of B<Subscript>2</Subscript>O<Subscript>3</Subscript> on the structure and crystallization of soil active glasses

Glasses of the SiO₂–P₂O₅–K₂O–MgO–CaO–B₂O₃ system acting as nutrients carriers in the soil environment were synthesised by the melt-quenching technique. Thermal properties were studied using DTA/DSC methods and the influence of B₂O₃ and P₂O₅ content on thermal stability and crystallization process of these glasses was examined. The structure of the glass network was characterized by FTIR, ³¹P, and ¹¹B MAS NMR. The chemical activity of the glasses in the 2 mass% citric acid solution was measured by the ICP-AES method. The analysis indicated that the formation of P–O–B units with chemically stable tetrahedral borate groups decreases the glass solubility in conditions simulating the soil environment.     

Low-temperature modification of dienic polymers via the “Ene” reaction with 4-substituted-1,2,4-triazoline-3,5-diones

4-Substituted-1,2,4-triazoline-3,5-diones have been used to synthesize a series of new polydienes by the “ene” reaction at ambient temperatures. The extent of chemical conversion can be varied widely and up to 93% of the diene-repeating units of the parent polymer chain undergo reaction. Yields of the new polymers based on the reactant range from 90 to 95% at room temperature; their physical properties range from secondary crosslinking effects or elasticity at low degrees of conversion to rigid, amorphous polymers with high softening points at high degrees of conversion. The new polymers show a predictable correlation between the extent of conversion and the softening point. A similar correlation exists between the polarity of the new polymers and the extent of conversion. Polydienes with conversions to the extent of 45% or greater are soluble in aqueous solutions of sodium hydroxide and those with conversions of 60% or greater are soluble in aqueous sodium bicarbonate. Thus, in general, the new polymers (1) have higher T_g, (2) become increasingly polar, hence are soluble in polar solvents, and (3) possess a reasonably acidic proton, hence form salts. Bistriazolinediones result in room temperature crosslinking. A kinetic study with model compounds suggests that the rate of the reaction can be varied, depending on the electronic nature of the 4-substituent.     

A tetrahedral coordination compound for second-order nonlinear optics: synthesis,crystal structure and SHG of Zn(2-NH2py)2Cl2

A coordination compound with a tetrahedral molecular configuration, Zn(NH₂py)₂Cl₂(2-NH₂py=2-aminopyridine), was prepared. It is transparent in the visible region and shows second harmonic generation (SHG) effect 8.0 times as strong as that of KDP. X-ray single crystal structure analysis reveals that all Zn(NH₂py)₂Cl₂ molecules are aligned in a fully parallel direction. The advantages and disadvantages of tetrahedral zinc coordination compounds as nonlinear optical (NLO) materials are discussed. The results may represent a novel strategy for designing a new class of transparent NLO materials.     

Thermal analysis of the Bi2O3-Y2O3-ZrO2 pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new colour inorganic pigments. Chemical compounds of the Bi_2-xY_x/2Zr_3x/₈O₃ type were synthetised. The host lattice of these pigments is Bi₂O₃ that is doped by Y³⁺ and Zr⁴⁺ ions. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.     

Columnar mesomorphism of bent-rod mesogens containing 1,2,4-oxadiazole rings

In this study, the synthesis, characterization, and mesomorphic properties of ten new bent-rod compounds containing two units of 1,2,4-oxadiazoles are reported. In order to understand the relationship between the structure and the mesomorphic behavior, molecules containing a variety of polar substituents (i.e., I, NO₂, NH₂, OH) on the central rigid core were prepared. The hexagonal columnar mesomorphism was characterized by DSC and POM and the nature of the mesophases was established through XRD studies. The driving force for self-assembly can be explained by microsegregation between the aliphatic parts and the polar parts, producing a dimer, trimer, and tetramer inside a single disc.     

Thermal analysis of the Bi2O3-Er2O3-Zro2 pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new ecological inorganic pigments. Chemical compounds of the Bi_2−xEr_x/2Zr_3x/8O₃ type were synthetized. The host lattice of these pigments is Bi₂O₃ that is doped by Er³⁺ and Zr⁴⁺ ions. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.     

(Li6Si5)2–5: The Smallest Cluster-Assembled Materials Based on Aromatic Si56− Rings

Extensive explorations of their potential energy surfaces, combined with high-level quantum chemical computations, strikingly show that the lowest energy structures of the (Li₆Si₅)_2–5 systems consist of 2–5 Si₅⁶⁻ aromatic units, surrounded by Li⁺ counterions, respectively. These viable gas-phase compounds are the pioneering reported cases of oligomers made by planar aromatic silicon rings. Based on the key evidence that these oligomers are energetically favored, and that their silicon rings aromaticity is thoroughly preserved, the Li₆Si₅ cluster is proposed as a potential assembly unit to build silicon-lithium nanostructures, thus opening new paths to design Zintl compounds at the nanoscale level.     

Disordered structures,vibrational spectroscopy,thermal behavior,and electrical properties of two new tetrachlorometallates complexes [(CH3CH2CH2)4N]2MIICl4 with MII = Co and Mn

The two new hybrids single crystals having the general formula [(CH₃CH₂CH₂)₄N]₂M^IICl₄ with M^II = Co (1) and Mn (2) have been synthetised by the slow evaporation process in aqueous solutions. In this article, these compounds were described by the following characterization techniques: X-rays diffraction, thermal analysis (TGA-TDA), vibrational spectroscopy, nuclear magnetic resonance (NMR), and electrical properties. From the crystallographic study, the crystals (1) and (2) have been disclosed to be crystallized too in the centrosymmetric monoclinic systems, with space group P2₁/c (Z = 4) and C2/c (Z = 8), respectively. Their crystal structures consist of [MCl₄]²⁻ anions and two different cations [(CH₃CH₂CH₂)₄N]⁺, which are connected by a three dimensional network of C-H···Cl hydrogen bonds. In both crystals, each M^II center atom being surrounded by four chloride ligands forming a slightly distorted tetrahedral geometry. The tetrahedral [CoCl₄]²⁻ is ordered, while the tetrahedral [MnCl₄]²⁻ is disordered. Some tetrapropylammonium cations of these compounds are found to be disordered. The thermal analysis studies made in the temperature range (298–473 K) did not show any phase transition for the two crystals. Furthermore, the electrical properties of the two compounds are studied by using the complex impedance spectroscopy technique in the temperature and frequency field varied of 290–363 K and 1 kHz–13 MHz, respectively.     

Shape- and Size-Tunable Synthesis of Covalent Organic Cages through Rh-Catalyzed Regioselective [2+2+2] Cycloaddition

Covalent organic cages have potential applications in molecular inclusion/recognition and porous organic crystals. Bridging arene units with sp³ atoms enables facile construction of rigid isolated internal vacancies, and various prismatic arene cages have been synthesized by kinetically controlled covalent bond formation. However, the synthesis of a tetrahedral one, which requires twice as much bond formation as prismatic ones, has been limited to a thermodynamically controlled dynamic S_NAr reaction, and this reversible covalent bond formation made the resulting cage product chemically unstable. Here we report the Rh-catalyzed high-yielding and highly 1,3,5-selective room temperature [2+2+2] cycloaddition of push-pull alkynes and its application to the synthesis of chemically stable aryl ether cages of various shapes and sizes, including prismatic and tetrahedral forms. These aryl ether cages are highly crystalline and intertwine with each other to form regular packing structures. Some aryl ether cages encapsulated isolated water molecules in their hydrophobic cavity by hydrogen bonding with the multiple ester moieties.     

Syntheses and Molecular Structures of 2-(1-Methyliminoethyl)phenolato Zinc Complexes

2-(1-Methyliminoethyl)phenol ( 1 a ) reacts with diethyl zinc to give bis[2-(1-methyliminoethyl)phenolato]zinc ( 3 ) via [2-(1-methyliminoethyl)phenolato]ethylzinc ( 2 ) as an intermediate. The complex 3 is also formed in the reaction of bis(trimethylsilyl)amide zinc with 1 a . The compounds were characterized by microanalysis, NMR (¹H, ¹³C) and IR spectroscopy. X-ray structure analysis of the compounds 2 and 3 revealed that both compounds form in the solid state dimeric species where the monomeric units are bridged via two oxygen atoms forming a planar Zn₂O₂ ring with tetrahedral [ZnO₂NC] and trigonal-bipyramidal [ZnO₃N₂] coordination of the zinc atom, respectively.