Arsenic(III) oxide intercalate with ammonium chloride: crystal structure revision and thermal characterization.

According to the crystal structure determination by Edstrand & Blomqvist [Ark. Kemi (1955), 8, 245-256], intercalate NH4Cl·As2O3·0.5H2O ({\bf Y_{{NH}_{4}Cl}}) is not isostructural with compound KCl·As2O3·0.5H2O. This is very unlikely because both NH4Br·2As2O3 and KBr·2As2O3 as well as NH4I·2As2O3 and KI·2As2O3 are isostructural. Hence, intercalate {\bf Y_{{NH}_{4}Cl}} has been studied using single-crystal X-ray diffraction in addition to attenuated total reflection Fourier transform infrared (ATR-FTIR) and 15N solid-state magic-angle spinning nuclear magnetic resonance (ssNMR) spectroscopies. These techniques indicate that revising the previous crystal structure model is necessary. Compound {\bf Y_{{NH}_{4}Cl}} crystallizes in space group P6/mmm with unit-cell parameters a = 5.25420 (10) Šand c = 12.6308 (3) Šand is isostructural with KCl·As2O3·0.5H2O. The presence of two symmetry-independent ammonium cations in the structure has been unequivocally confirmed using 15N ssNMR spectroscopy. The 15N ssNMR spectrum of intercalate {\bf Y_{{NH}_{4}Cl}} has been compared with analogous spectra of NH4Br·2As2O3 and NH4I·2As2O3 which allowed for a probable assignment of signals to ammonium cations occupying particular sites in the crystal structures. Thermogravimetry, differential scanning calorimetry and variable-temperature ATR-FTIR spectra have revealed that intercalate {\bf Y_{{NH}_{4}Cl}} is dehydrated between 320 and 475 K. Upon cooling or standing in moist air water is re-absorbed. Dehydration leads to significant shortening of the c unit-cell parameter as revealed by powder X-ray diffraction [c = 12.1552 (7) Šat 293 K]. Compound {\bf Y_{{NH}_{4}Cl}} decomposes on prolonged heating above 490 K to arsenic(III) oxide and ammonium chloride.

Fast, solvent-free synthesis of ferrocene-containing organic cages via dynamic covalent chemistry in the solid state.

A simple, solvent-free synthetic protocol towards the synthesis of organic self-assembled macromolecules has been established. By employing mechanochemistry using glassware readily available to every organic chemist, we were able to synthesise three novel organic cage compounds exemplarily and to speed up the synthesis of a ferrocene-containing macrocycle by a factor of 288 compared to the solution-based synthesis. The structural investigation of the newly synthesised cages revealed different modes of connectivity from using ferrocene-containing aldehydes caused by the free rotation of the cyclopentadienyl units against each other. By extending the facile solvent-free synthesis to ball-milling, even compounds that show lower reactivity could be employed in the dynamic covalent formation of organometallic cage compounds. The presented protocol gives access to otherwise inaccessible structures, speeds up general synthetic workflows, and simultaneously reduces the environmental impact of supramolecular syntheses.

Influence of substituents in aryl groups on the structure, thermal transitions and electrorheological properties of zinc bis(diarylphosphate) hybrid polymers.

The structures and thermal properties of three new hybrid one-dimensional (1D) polymers based on zinc bis(diarylphosphate)s containing p-substituted phenyl rings are reported. The crystal structures of Zn[O2P(p-OC6H4NO2)2]2 (1), Zn[O2P(p-OC6H4OMe)2]2 (2) and Zn[O2P(p-OC6H4CO2Et)2]2 (3) differ from that of their unsubstituted analogue, Zn[O2P(OPh)2]2 (ZnDPhP). Compounds 1 and 3 consist of tetrahedrally coordinated zinc cations connected by double bridges of phosphate groups (2+2 bridging mode) and form polymeric chains that are packed in a distorted hexagonal lattice with six closest neighbours. In compound 2 zinc cations are linked by alternating single and triple phosphate bridges (3+1 bridging mode) and the resulting chains, having only four closest neighbors, are packed in a distorted tetragonal manner. DFT computations revealed that the 2+2 bridging mode, even at the highest energy conformation, is more stable than the 3+1 one. Simultaneous Thermal Analysis, Raman spectroscopy and powder XRD (PXRD) studies show that pyrolysis of the studied hybrid polymers begins above 260 °C, leading to a mixture of zinc condensed phosphates and carbonaceous deposits that may have electron-conducting properties. DSC and PXRD studies provide evidence that crystalline domains in 2 and 3 rearrange and/or disappear at a much lower temperature (ca. 150 °C) leading to an isotropic liquid (in the case of 3) or an amorphous solid material (in the case of 2). Electrorheological measurements indicate that 1-3 are polarized in an external electric field, and the type of electrorheological effect depends on the type of functional group attached to the phenyl ring; this feature can be utilized in designing new electrorheological devices.

1D and 2D hybrid polymers based on zinc phenylphosphates: synthesis, characterization and applications in electroactive materials.

The synthesis, structure and properties of three hybrid polymers based on zinc arylphosphates are described in this study. Zinc bis(diphenylphosphate) (ZnDPhP) was obtained as needle-like crystals containing hexagonally packed, homochiral 1 ∞[Zn(DPhP)2/2] helical chains. The XRD and DSC studies revealed that upon heating, ZnDPhP undergoes a reversible thermal transition at ca. 160 °C with expansion mainly perpendicular to its c-axis. Zinc phenylphosphate hydrate (ZnMPhP-H) formed plate-like particles with an average thickness of less than 1 µm and much thinner nanolayers with a basal spacing of 15.5 Å. ZnMPhP-H was easily and reversibly dehydrated to its anhydrous form, ZnMPhP-A, which exhibited a somewhat larger basal spacing of 16.5 Å and the capacity for amine intercalation. The thermal decomposition of ZnDPhP or ZnMPhP-A began around 250 °C, resulting in the formation of solid mixtures of zinc phosphates and electron-conducting carbonaceous phases. The bulk electrical conductivities of the poly(vinylidene fluoride)-based composites containing the ZnDPhP pyrolyzates reached 0.1-0.2 S cm-1. Upon mixing with silicone oil, all the synthesized hybrid polymers formed fluids that exhibit significant negative electrorheological effects and have potential for application in electroresponsive smart materials. The application of an electric field during the crosslinking of such systems affected the viscoelastic properties of the resultant solid composites, while the cured systems showed rather small electrorheological effects.

A Lanthanum-Filled Carbon-Boron Clathrate.

We report a carbon-boron clathrate with composition 2 La@B6 C6 (LaB3 C3 ). Like recently reported SrB3 C3 ,[1] single-crystal X-ray diffraction and computational modelling indicate that the isostructural La member crystallizes in the cubic bipartite sodalite structure (Type-VII clathrate) with La atoms encapsulated within truncated octahedral cages composed of alternating carbon and boron atoms. The covalent nature of the B-C bonding results in a hard, incompressible framework, and owing to the balanced electron count, La3+ [B3 C3 ]3- exhibits markedly improved pressure stability and is a semiconductor with an indirect band gap predicted near 1.3 eV. A variety of different guest atoms may potentially be substituted within Type-VII clathrate cages, presenting opportunities for a large family of boron-stabilized, carbon-based clathrates with ranging physical properties.

Crystal Structure and Non-Hydrostatic Stress-Induced Phase Transition of Urotropine Under High Pressure.

High-pressure behavior of hexamethylenetetramine (urotropine) was studied in situ using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier-transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure-transmitting media to study the effect of deviatoric stress on phase transformations. Up to 4 GPa significant damping of molecular librations and atomic thermal motion was observed. A first-order phase transition to a tetragonal structure was observed with an onset at approximately 12.5 GPa and characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by deviatoric or uniaxial stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and may be considered a common feature of such systems. DFT computations were performed to model urotropine equation of state and pressure dependence of vibrational modes. The first successful Hirshfeld atom refinements carried out for high-pressure diffraction data are reported. The refinements yielded more realistic C-H bond lengths than the independent atom model even though the high-pressure diffraction data are incomplete.

Synthesis and structural, electrochemical and photophysical studies of triferrocenyl-substituted 1,3,5-triphenylbenzene: a cyan-light emitting molecule showing aggregation-induced enhanced emission.

Triferrocenyl-substituted 1,3,5-triphenylbenzene was successfully synthesized in high yield. Single-crystal X-ray diffraction experiments revealed that the internal rotations of the ferrocenyl moieties are significantly restricted in the solid phase and that there are no significant π stacking interactions therein. The photoluminescence of the crystals is essentially the same as that of dilute chloroform solutions. However, studies of this cyan-light emitting substance in mixtures of chloroform and methanol revealed the aggregation-induced enhanced emission (AIEE) feature that boosts its fluorescence quantum yield from 13% up to 74%. We demonstrate the AIEE effect for a new class of easy-to-prepare aromatic molecules containing several metallocene units for the first time.

Raman studies of hydrogen trapped in As4O6·2H2 at high pressure and low temperature.

Raman spectroscopic measurements of the arsenolite-hydrogen inclusion compound As4O6·2H2 were performed in diamond anvil cells at high pressure and variable temperature down to 80 K. The experimental results were complemented by ab initio molecular dynamics simulations and phonon calculations. Observation of three hydrogen vibrons in As4O6·2H2 is reported in the entire temperature and pressure range studied (up to 24 GPa). While the experiments performed with protium and deuterium at variable temperatures allowed for the assignment of two vibrons as Q1(1) and Q1(0) transitions of ortho and para spin isomers of hydrogen trapped in the inclusion compound, the origin of the third vibron could not be unequivocally established. Low-temperature spectra revealed that the lowest-frequency vibron is actually composed of two overlapping bands of Ag and T2g symmetries dominated by H2 stretching modes as predicted by our previous density functional theory calculations. We observed low-frequency modes of As4O6·2H2 vibrations dominated by H2 "librations," which were missed in a previous study. A low-temperature fine structure was observed for the J = 0 → 2 and J = 1 → 3 manifolds of hydrogen trapped in As4O6·2H2, indicating the lifting of degeneracy due to an anisotropic environment. A non-spherical distribution was captured by molecular dynamics simulations, which revealed that the trajectory of H2 molecules is skewed along the crystallographic ⟨111⟩ direction. Last but not least, low-temperature synchrotron powder x-ray diffraction measurements on As4O6·2H2 revealed that the bulk structure of the compound is preserved down to 5 K at 1.6 GPa.

A ferrocene-templated Pd-bearing molecular reactor.

High-yield, chromatography-free syntheses of a ferrocene-templated molecular cage and its Pd-bearing derivative are presented. The formation of a symmetric cage-type structure was confirmed by single-crystal X-ray diffraction analysis. The Pd-bearing cage was used as an innovative catalyst for the efficient synthesis of 1,1'-biphenyls under mild conditions. The presented catalyst is reusable and 1,1'-biphenyls can be obtained efficiently in a gram scale process.

Effect of the substituent position on the electrochemical, optical and structural properties of donor-acceptor type acridone derivatives.

Three new donor-acceptor (D-A) compounds, positional isomers of phenoxazine-substituted acridone, namely 1-phenoxazine-N-hexylacridone (o-A), 2-phenoxazine-N-hexylacridone (m-A) and 3-phenoxazine-N-hexylacridone (p-A), were synthesized. The synthesized compounds showed interesting, isomerism-dependent electrochemistry. Their oxidation was reversible and their potential (given vs. Fc/Fc+) changed from 0.21 V for o-A to 0.36 V for p-A. In contrast, their reduction was irreversible, isomerism-independent and occurred at rather low potentials (ca. -2.25 to -2.28 V). The electrochemical results led to the following values of the ionization potentials (IPs) and electron affinities (EAs): 5.03 eV and -2.14 eV, 5.15 eV and -2.20 eV, and 5.20 eV and -2.28 eV for o-A, m-A and p-A, respectively. The experimentally obtained values were in very good agreement with those predicted by DFT calculations. All three isomers readily formed single crystals suitable for their structure determination. o-A and p-A crystallized in P1[combining macron] and P21/n space groups, respectively, with one molecule per asymmetric unit, while m-A crystallized in the P21/c space group with two molecules in the asymmetric unit accompanied by disordered solvent molecules. The UV-vis spectra of the studied compounds were isomerism and solvent independent, yielding absorption maxima in the vicinity of 400 nm. Their photoluminescence spectra, in turn, strongly depended on isomerism and the used solvent showing smaller Stokes shifts for the emission bands registered in toluene as compared to the corresponding bands measured in dichloromethane. The photoluminescence quantum yields (φ) were systematically higher for toluene solutions reaching the highest value of 20% for p-A. For all three isomers studied, stationary and time-resolved spectroscopic investigations carried out in toluene at different temperatures revealed spectral features indicating a contribution of thermally activated delayed fluorescence (TADF) to the observed spectroscopic behaviour. The measured photoluminescence quantum yields (φ) were higher for solid state films of pure compounds and for their dispersions in solid matrices (zeonex) than those recorded for toluene and dichloromethane solutions of the studied phenoxazine-N-hexylacridone isomers. The obtained experimental spectroscopic and structural data were confronted with theoretical predictions based on DFT calculations.

Carbon-boron clathrates as a new class of sp3-bonded framework materials.

Carbon-based frameworks composed of sp3 bonding represent a class of extremely lightweight strong materials, but only diamond and a handful of other compounds exist despite numerous predictions. Thus, there remains a large gap between the number of plausible structures predicted and those synthesized. We used a chemical design principle based on boron substitution to predict and synthesize a three-dimensional carbon-boron framework in a host/guest clathrate structure. The clathrate, with composition 2Sr@B6C6, exhibits the cubic bipartite sodalite structure (type VII clathrate) composed of sp3-bonded truncated octahedral C12B12 host cages that trap Sr2+ guest cations. The clathrate not only maintains the robust nature of diamond-like sp3 bonding but also offers potential for a broad range of compounds with tunable properties through substitution of guest atoms within the cages.

Integrating Activity with Accessibility in Olefin Metathesis: An Unprecedentedly Reactive Ruthenium-Indenylidene Catalyst.

Access to leading olefin metathesis catalysts, including the Grubbs, Hoveyda, and Grela catalysts, ultimately rests on the nonscaleable transfer of a benzylidene ligand from an unstable, impure aryldiazomethane. The indenylidene ligand can be reliably installed, but to date yields much less reactive catalysts. A fast-initiating, dimeric indenylidene complex (Ru-1) is reported, which reconciles high activity with scaleable synthesis. Each Ru center in Ru-1 is stabilized by a state-of-the-art cyclic alkyl amino carbene (CAAC, C1) and a bridging chloride donor: the lability of the latter elevates the reactivity of Ru-1 to a level previously attainable only with benzylidene derivatives. Evaluation of initiation rate constants reveals that Ru-1 initiates >250× faster than indenylidene catalyst M2 (RuCl2(H2IMes)(PCy3)(Ind)), and 65× faster than UC (RuCl2(C1)2(Ind)). The slow initiation previously regarded as characteristic of indenylidene catalysts is hence due to low ligand lability, not inherently slow cycloaddition at the Ru=CRR' site. In macrocyclization and "ethenolysis" of methyl oleate (i.e., transformation into α-olefins via cross-metathesis with C2H4), Ru-1 is comparable or superior to the corresponding, breakthrough CAAC-benzylidene catalyst. In ethenolysis, Ru-1 is 5× more robust to standard-grade (99.9%) C2H4 than the top-performing catalyst, probably reflecting steric protection at the quaternary CAAC carbon.

Towards a quantitative bond valence description of coordination spheres - the concepts of valence entropy and valence diversity coordination numbers.

Two novel definitions of chemical coordination numbers - valence entropy coordination number nVECN and valence diversity coordination number nVDCN - are proposed. Their originality stems from the fact that they are the first definitions based solely on bond valences. The expressions for them are derived from their definitions and their properties are studied. The unexpected close relationship of nVECN to Shannon entropy and nVDCN to diversity are revealed and the names of the new coordination numbers are taken therefrom. Finally, as an example, a study of arsenic(III) lone electron pair stereoactivity with respect to AsIII coordination number is carried out to demonstrate the usefulness and advantages of the new definitions as well as to compare them with the existing ones.

How and Why Does Helium Permeate Nonporous Arsenolite Under High Pressure?

Investigations into the helium permeation of arsenolite, the cubic, molecular arsenic(III) oxide polymorph As4 O6 , were carried out to understand how and why arsenolite helium clathrate As4 O6 ⋅2 He is formed. High-pressure synchrotron X-ray diffraction experiments on arsenolite single crystals revealed that the permeation of helium into nonporous arsenolite depends on the time for which the crystal is subjected to high pressure and on the crystal history. The single crystal was totally transformed into As4 O6 ⋅2 He within 45 h under 5 GPa. After release of the pressure, arsenolite was recovered and a repeated increase in pressure up to 3 GPa led to practically instant As4 O6 ⋅2 He formation. However, when a pristine arsenolite single crystal was quickly subjected to a pressure of 13 GPa, no helium permeation was observed at all. No neon permeation was observed in analogous experiments. Quantum mechanical computations indicate that there are no specific attractive interactions between He atoms and As4 O6 molecules at the distances observed in the As4 O6 ⋅2 He crystal structure. Detailed analysis of As4 O6 molecular structure changes has shown that the introduction of He into the arsenolite crystal lattice significantly reduces molecular deformations by decreasing the anisotropy of stress exerted on the As4 O6 molecules. This effect and the pΔV term, rather than any specific As⋅⋅⋅He binding, are the driving forces for the formation As4 O6 ⋅2 He.

Bis(Cyclic Alkyl Amino Carbene) Ruthenium Complexes: A Versatile, Highly Efficient Tool for Olefin Metathesis.

The state-of-the-art in olefin metathesis is application of N-heterocyclic carbene (NHC)-containing ruthenium alkylidenes for the formation of internal C=C bonds and of cyclic alkyl amino carbene (CAAC)-containing ruthenium benzylidenes in the production of terminal olefins. A straightforward synthesis of bis(CAAC)Ru indenylidene complexes, which are highly effective in the formation of both terminal and internal C=C bonds at loadings as low as 1 ppm, is now reported.

Soluble Flavanthrone Derivatives: Synthesis, Characterization, and Application to Organic Light-Emitting Diodes.

Simple modification of benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine-8,16-dione, an old and almost-forgotten vat dye, by reduction of its carbonyl groups and subsequent O-alkylation, yields solution-processable, electroactive, conjugated compounds of the periazaacene type, suitable for the use in organic electronics. Their electrochemically determined ionization potential and electron affinity of about 5.2 and -3.2 eV, respectively, are essentially independent of the length of the alkoxyl substituent and in good agreement with DFT calculations. The crystal structure of 8,16-dioctyloxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine (FC-8), the most promising compound, was solved. It crystallizes in space group P1‾ and forms π-stacked columns held together in the 3D structure by dispersion forces, mainly between interdigitated alkyl chains. Molecules of FC-8 have a strong tendency to self-organize in monolayers deposited on a highly oriented pyrolytic graphite surface, as observed by STM. 8,16-Dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines are highly luminescent, and all have photoluminescence quantum yields of about 80 %. They show efficient electroluminescence, and can be used as guest molecules with a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl host in guest/host-type organic light-emitting diodes. The best fabricated diodes showed a luminance of about 1900 cd m(-12) , a luminance efficiency of about 3 cd A(-1) , and external quantum efficiencies exceeding 0.9 %.

Spatial dispersion of lone electron pairs?--experimental charge density of cubic arsenic(III) oxide.

The first experimental charge density study of arsenolite, a cubic polymorph of arsenic(III) oxide, extended by periodic DFT calculations is reported. The presence of weak AsO interactions is confirmed and their topological characterization based on experimental electron density is provided. Spatial dispersion of arsenic lone electron pairs into three domains is observed in the Laplacian of electron density as well as in the electron localization function. It results from the clustering of As atomic cores in the crystal structure and/or from the presence of strong As-O bonds. A similar phenomenon is recognized in the crystal structures of antimonates(III) and bismuthates(III) of alkaline metals indicating that this could be a more general feature worthy of further investigations.

Indanthrone dye revisited after sixty years.

Indanthrone, an old, insoluble dye can be converted into a solution processable, self-assembling and electroluminescent organic semiconductor, namely tetraoctyloxydinaptho[2,3-a:2',3'-h]phenazine (P-C8), in a simple one-pot process consisting of the reduction of the carbonyl group by sodium dithionite followed by the substitution with solubility inducing groups under phase transfer catalysis conditions.

The structure and energetics of arsenic(III) oxide intercalated by ionic azides.

Unprecedented intercalates of arsenic(iii) oxide with potassium azide and ammonium azide have been obtained and characterized by single crystal X-ray diffraction. The compounds are built of As2O3 sheets separated by charged layers of cations and azide anions perpendicular to the sheets. The intercalates are an interesting example of hybrid materials whose structure is governed by covalent bonds in two directions and ionic bond in the third one. The obtained compounds are the first examples of As2O3 intercalates containing linear pseudohalogen anions. Periodic DFT calculations of interlayer interaction energies were carried out with the B3LYP-D* functional. The layers are held together mainly by ionic bonds, although the computations indicate that interactions between cations and As2O3 sheets also play a significant role. A comparison of cation and anion interaction energies with neutral As2O3 sheets sheds light on the crystallisation process, indicating the templating effect of potassium and ammonium cations. It consist in the formation of sandwich complexes of cations with crown-ether-resembling As6O12 rings. Raman spectra of both compounds are recorded and computed ab initio and all vibrational bands are assigned.

Anion exchange in [Ni(η(5)-C(5)H(4)R)(Cl)(NHC)]. Counterion effect on the structure and catalytic activity.

A series of novel complexes [Ni(η(5)-C5H4R)(L)(NHC)](+)A(-)2a-2j and [Ni(η(5)-C5H5)(A)(NHC)] 3a-3c has been obtained by anion metathesis from the corresponding chlorides 1a-1d, depending on the anion binding properties and reaction conditions. Solid-state structures of two cationic complexes (2c, 2j) and two complexes with a coordinated anion (3a, 3c) have been determined by X-ray diffraction revealing a trigonal planar geometry in all cases. Unexpectedly, 3c displayed unprecedented for this type of compounds temperature-dependent NMR spectra that were interpreted in terms of spin equilibrium. The cationic complexes 2 were less efficient in styrene polymerization than the parent chlorides 1. However, the activity of 2 and 3 in Suzuki cross-coupling did not depend considerably on the counterion.