AHPCS is a pre-ceramic polymer utilised as a precursor to SiC. An initial polymerisation to a cross-linked network is followed by a complex sequence of processes ultimately leading to amorphous SiC. Using thermal volatilisation analysis (TVA) accompanied with solid-state NMR (SSNMR), FTIR, MS, DSC and TGA the complete thermal profile was identified. Between 160 – 300 °C, AHPCS cross-links through the allyl group and undergoes some carbon-silicon rearrangement, with a volatilisation of low mass oligomeric material and significant volumes of hydrogen released from dehydrocoupling of SiH moieties. By 300 °C the allyl group is completely cross-linked but the polymer starts to undergo pyrolytic degradation of the network, with the release of chain fragments and low molar mass species such as methane, ethane, methanol, propane, propene and silane species. Hydrogen once again becomes the major volatile product above 400 °C due to higher proportion of dehydrocoupling forming Si–C and Si–Si bonds. Small chain fragments are seen in the form of larger alkyl silanes. These fragments come from the chain scission of the polymer at weaker parts of the network. The process of side group scission leads to further radical recombination reactions of silicon and carbon atoms to build the SiC network. By 500 °C higher proportion of dehydrocoupling occurs with recombination of Si–Si and Si–C species. The Si–H bonds in -SiH3 groups have completely cleaved along with C-H bonds in the CH3 and CH2 groups leaving SiC, -SiH and HCSi3 present in the material. This bond cleavage leads the silicon and carbon radical species to undergo radical recombination in the network with the volatile release being dominated by H2. By 650 °C the cleavage and recombination of remaining -SiH2-, -SiH- and HCSi3 groups ultimately form amorphous SiC. The volatiles released are mostly hydrogen with very few condensable products seen. Finally, SiC is then crystallised at higher temperatures forming β-SiC at 1100 °C and then subsequently α-SiC above 1500 °C.

With rising interest in organic-based functional materials, it is important to understand the nature of magnetic and electrical transitions within these types of systems. One intriguing material is triethylammonium bis-7,7,8,8-tetracyanoquinodimethane (TEA(TCNQ)2) where there is an order-disorder transition at ∼220 K. This work focuses on novel neutron scattering techniques to understand the motion of the TEA cations at this transition and explain why we see the dielectric behaviour and possible ferroelectricity within this type of system. We show that the motion of the methyl groups of the TEA cation is spatially restricted below 220 K, whereas above the dielectric anomaly at 220 K, they are free to re-orientate, which ultimately leads to some rich behaviour that could be further exploited. Lastly, we also study the dynamics at this transition using a variety of additional techniques, helping to provide a consistent picture of the motions of the cations.

The photocatalytic and dielectric behaviors of Aurivillius oxyfluorides such as Bi2TiO4F2 depend sensitively on their crystal structure and symmetry but these are not fully understood. Our experimental work combined with symmetry analysis demonstrates the factors that influence anion order and how this might be tuned to break inversion symmetry. We explore an experimental approach to explore anion order, which combines Rietveld analysis with strain analysis.

The esterification of levulinic acid under acidic conditions to produce levulinate esters is of current significant interest due to the potential of these compounds as fuels and fuel additives. While a number of bespoke heterogeneous catalysts have been reported to be effective for this transformation, the use of widely available commercial catalysts has generally proved to be ineffective, with only low conversions to ester products being achieved. Herein, we report a novel strategy for the efficient synthesis of levulinate esters from levulinic acid in the presence of trialkyl orthoformates or dialkyl acetals and ketals catalyzed by commercial catalysts, such as ZSM-5 and Amberlyst-15. These reactions proceed under mild conditions and in short reaction times to selectively produce high yields of levulinate esters.

This work presents an updated solid-form discovery approach to the polymorphism of the antiarrhythmic drug mexiletine hydrochloride, in which experimental and computational techniques are combined to provide a rigorous characterization of the solid-form landscape of this compound. The resulting solid forms were characterized by powder and single-crystal X-ray diffraction, IR spectroscopy, differential scanning calorimetry, and C-13 solid-state NMR. This approach reveals five solid-form types of mexiletine hydrochloride. Forms 1, 2, and 3 are mutually enantiotropically related anhydrous polymorphs, with Form 1 the room temperature stable form, Form 2 the high-temperature form, and Form 3 the thermodynamically stable polymorph between 148 and 167 degrees C. The final two forms termed Types A and B comprise two large families of isomorphous channel solvates, including a fourth nonsolvated form isostructural to the Type A solvates. We report 11 modifications of each solvate, in which a diverse range of solvents are included in the channels, without changing the fundamental structure of the drug framework. These experimental results go hand-in-hand with computational crystal structure prediction (using the AstraZeneca crystal structure prediction approach), which together suggest that it is unlikely further nonsolvated forms, at least with Z' = 1, will be discovered under ambient conditions.

Wide-dose-range 2D radiochromic films for radiotherapy, such as GAFchromic EBT, are based on the lithium salt of 10,12-pentacosadiynoic acid (Li-PCDA) as the photosensitive component. We show that there are two solid forms of Li-PCDA—a monohydrated form A and an anhydrous form B. The form used in commercial GAFchromic films is form A due to its short needle-shaped crystals, which provide favorable coating properties. Form B provides an enhanced photoresponse compared to that of form A, but adopts a long needle crystal morphology, which is difficult to process. The two forms were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, CP-MAS 13C solid-state NMR spectroscopy, and thermogravimetric analysis. In sum, these data suggest a chelating bridging bidentate coordination mode for the lithium ions. The sodium salt of PCDA (Na-PCDA) is also reported, which is an ionic cocrystal with a formula of Na+PCDA–·3PCDA. The PCDA and PCDA– ligands display monodentate and bridging bidentate coordination to the sodium ion in contrast to the coordination sphere of the Li-PCDA forms. In contrast to its lithium analogues, Na-PCDA is photostable.

This study reports an organic salt prepared from an antibacterial drug, levofloxacin and antioxidant γ-resorcylic acid. A simple preparation method leads to a crystal with disordered structure. The idea is to prepare an organic salt comprising of pharmaceutically acceptable acidic and basic components. The salt is characterised by IR, solid state NMR, and single crystal XRD. Crystal data for C25H26N3O8F: triclinic, space group P-1 (no. 2), a = 7.0037(8) Å, b = 12.764(3) Å, c = 13.909(3) Å, α = 104.821(4)°, β = 92.039(4)°, γ = 95.334(4)°, V = 1194.6(4) Å3, Z = 2, T = 296(2) K, μ(MoKα) = 0.113 mm-1, Dcalc = 1.433 g/cm3, 16879 reflections measured (5.048° ≤ 2Θ ≤ 54.186°), 5139 unique (Rint = 0.0663, Rsigma = 0.0975) which were used in all calculations. The final R1 was 0.1121 (I>2σ(I)) and wR2 was 0.2505 (all data). SC-XRD analysis shows that the crystal packing is stabilized by strong H-bonding of type N-H···O and comparatively weak interactions of type C-H···O, C-H···π and off-set π···π stacking.

In this work we develop photoreactive cocrystals/salts of a commercially-important diacetylene, 10,12-pentacosadiynoic acid (PCDA, 1) and report the first X-ray crystal structures of PCDA based systems.

To account for the charge transfer and covalent character in bonding between P and Bi centers, the electronic structures of [P(C6H4-o-CH2SCH3)3BiCln](3–n)+ (n = 0–3) model species have been investigated computationally. On the basis of this survey a synthetic target compound with a dative P→Bi bond has been selected. Consecutively, the highly reactive bismuth cage [P(C6H4-o-CH2SCH3)3Bi]3+ has been accessed experimentally and characterized. Importantly, our experiments (single-crystal X-ray diffraction and solid-state NMR spectroscopy) and computations (NBO and AIM analysis) reveal that the P···Bi bonding in this trication can be described as a dative bond. Here we have shown that our accordion-like molecular framework allows for tuning of the interaction between P and Bi centers.

Struvite-K (MgKPO4·6H2O) is a magnesium potassium phosphate mineral with naturally cementitious properties, which is finding increasing usage as an inorganic cement for niche applications including nuclear waste management and rapid road repair. Struvite-K is also of interest in sustainable phosphate recovery from wastewater and, as such, a detailed knowledge of the crystal chemistry and high-temperature behavior is required to support further laboratory investigations and industrial applications. In this study, the local chemical environments of synthetic struvite-K were investigated using high-field solid-state 25Mg and 39K MAS NMR techniques, alongside 31P MAS NMR and thermal analysis. A single resonance was present in each of the 25Mg and 39K MAS NMR spectra, reported here for the first time alongside the experimental and calculated isotropic chemical shifts, which were comparable to the available data for isostructural struvite (MgNH4PO4·6H2O). An in situ high-temperature XRD analysis of struvite-K revealed the presence of a crystalline-amorphous-crystalline transition that occurred between 30 and 350 °C, following the single dehydration step of struvite-K. Between 50 and 300 °C, struvite-K dehydration yielded a transient disordered (amorphous) phase identified here for the first time, denoted δ-MgKPO4. At 350 °C, recrystallization was observed, yielding β-MgKPO4, commensurate with an endothermic DTA event. A subsequent phase transition to γ-MgKPO4 was observed on further heating, which reversed on cooling, resulting in the α-MgKPO4 structure stabilized at room temperature. This behavior was dissimilar from that of struvite exposed to high temperature, where NH4 liberation occurs at temperatures >50 °C, indicating that struvite-K could potentially withstand high temperatures via a transition to MgKPO4.

The hydroxy-pyrazole and 3-hydroxy-oxindole motifs have been utilised in several pharma and agrochemical leads but are distinctly underrepresented in the scientific literature due to the limited routes of preparation. We have developed a one-pot procedure for their synthesis starting from simple isatins. The method employs cheap and easy-to-handle building blocks and allows easy isolation.

The influence of the intrapore cation on the fluorination of zeolite Y from dilute fluoride solutions has been studied, revealing fluoride reacts with the zeolite framework in the presence of a Brønsted acid to form [SiO3F] and [AlO3F] moieties. 29Si{1H} Cross-polarised MAS NMR indicates the reaction proceeds by the substitution of surface hydroxide moieties for fluoride. The fluorination reaction is strongly influenced by the nature of the intrapore cation. Intrapore Brønsted acids facilitate fluorination of the framework by in situ ion-exchange, releasing the acidic ions to the zeolite surface. The fluorination reaction may be further promoted by the presence of intrapore alkaline earth cations (viz. Mg2+, Ca2+, Sr2+ and Ba2+). The conclusions of this work are significant to the preparation of fluorinated zeolite catalysts, the application of zeolites in defluoridation and the labelling of zeolite-based tracers with 18F for application in positron imaging techniques.

In Situ high-temperature powder X-ray diffraction experiments were undertaken for the coarse crystalline natural layered double hydroxides (LDHs) quintinite, hydrotalcite, stichtite, and iowaite in the temperature range 25–1000 °C, with thermal analyses of these minerals and their annealed forms carried out in parallel. In the temperature range from 25 °C to 170–210 °C quintinite, hydrotalcite, and stichtite (carbonate members of the LDH family) demonstrated contraction of the basal d00n-value of 0.1–0.3 Å, followed by a sharp contraction of 1.0–1.1 Å at T > 170–210 °C. The high-temperature modified states were stable up to 380–420 °C, before decomposing to an amorphous phase. Iowaite (chloride member of the family) was stable up to 320 °C and transformed to an amorphous phase at higher temperature. Iowaite experiences continuous contraction of the d00n-value of up to 0.5 Å in the temperature range 25–200 °C, reaching a plateau at a temperature range of 200–320 °C. Assessing the reversibility of thermal transformation shows complete reconstruction of the crystal structure of the hydrotalcite and iowaite heated to 300 °C. Solid-state nuclear magnetic resonance analysis shows that some Al changes coordination from 6- to 4-fold, synchronously with quintinite transformation to the amorphous phase. All phases transform to periclase and a spinel-type compound upon further heating. Thermal analysis of samples annealed at 125 °C shows that carbonate members do not have a tendency to form dehydrated phases, whereas for iowaite, a dehydrated phase having 0.9 apfu lesser water content as in the initial sample has been obtained. Thermal evolution of LDHs is found to depend on the nature of the interaction of interlayer species and water molecules to H atoms of the metal-hydroxide layer.

The first selective oxidation of methane to methanol is reported herein for zinc-exchanged MOR (Zn/MOR). Under identical conditions, Zn/FER and Zn/ZSM-5 both form zinc formate and methanol. Selective methane activation to form [Zn-CH3 ]+ species was confirmed by 13 C MAS NMR spectroscopy for all three frameworks. The percentage of active zinc sites, measured through quantitative NMR spectroscopy studies, varied with the zeolite framework and was found to be ZSM-5 (5.7 %), MOR (1.2 %) and FER (0.5 %). For Zn/MOR, two signals were observed in the 13 C MAS NMR spectrum, resulting from two distinct [Zn-CH3 ]+ species present in the 12 MR and 8 MR side pockets, as supported by additional NMR experiments. The observed products of oxidation of the [Zn-CH3 ]+ species are shown to depend on the zeolite framework type and the oxidative conditions used. These results lay the foundation for developing structure-function correlations for methane conversion over zinc-exchanged zeolites.

We report the solid-state structural properties and phase transition behavior of 1,4-dibromo-2,3,5,6-tetramethylbenzene, demonstrating that this material undergoes an order disorder phase transition below ambient temperature (at ca. 154 K on cooling and ca. 160 K on heating). In both the high-temperature and low-temperature phases, the crystal structure is based on pi-stacking of the molecules. In the crystal structure of the high-temperature phase, the bromine occupancy in each substituent site is ca. 1/3 and the methyl group occupancy in each substituent site is ca. 2/3, consistent with statistical orientational disorder of the molecule between six distinct orientations. Natural-abundance solid-state H-2 NMR spectroscopy confirms that, at ambient temperature, this disorder is dynamic via rapid molecular reorientation about an axis perpendicular to the aromatic ring. In the low-temperature phase, the bromine and methyl substituents occupy preferred sites within the crystal structure, with the distribution of site occupancies becoming progressively more ordered on decreasing temperature.

To study pnictogen bonding involving bismuth, flexible accordion-like molecular complexes of the composition [P(C6H4-o-CH2SCH3)3BiX3] , (X = Cl, Br, I) have been synthesised and characterised. The strength of the weak and mainly electrostatic interaction between the Bi and P centres strongly depends on the character of the halogen substituent on bismuth, which is confirmed by single-crystal X-ray diffraction analyses, DFT and ab initio computations. Significantly, Bi–P through-space coupling (J = 2560 Hz) is observed in solid-state P NMR spectra, which is so far unprecedented in the literature, delivering direct information on the magnitude of this pnictogen interaction. Weak interactions are elementary bonding forces, which have an impact on the structure of molecular assemblies. The properties of materials strongly depend on the strength and orientation of noncovalent interactions; thus, a fundamental understanding of their nature is essential for the design of new molecular assemblies with bespoke physical and chemical properties. Besides the well-known hydrogen bonding, more recently the concepts of other “element-specific” interactions such as triel, tetrel, pnictogen, chalcogen, halogen and aerogen bonding for group 13–18 elements, respectively, have been established. Although interactions between pnictogen centres had been observed much earlier, some pioneering works at the beginning of this decade, 8] initiated a vivid scientific discussion on the theoretical aspects of pnictogen bonding. Analogously to the definition of a halogen bond, a pnictogen bond is defined as a weak, attractive interaction between the electrophilic region of a pnictogen atom (termed as pnictogen bond donor) and a Lewis base (termed as pnictogen bond acceptor, which is not necessarily another pnictogen centre). Because the strength of pnictogen interactions can be comparable to that of hydrogen bonds, pnictogen bonding can be envisioned to be a potential linking motif in molecular assemblies. Very recently the idea of employing pnictogen bonds in organocatalysis arose and was successfully realised experimentally. A plethora of computational studies have revealed two main interactions, that contribute to pnictogen bonds (besides minor effects such as dispersion forces): 1) The electrostatic interaction, whereby the lone pair of a Lewis base (the pnictogen bond acceptor) interacts with the positively charged belt around the lone pair of a pnictogen, is considered to make the leading contribution. Due to this anisotropic electron density distribution around the pnictogen centre the pnictogen bond belongs to the so-called s-hole interactions. 2) To a lesser extent, charge transfer also contributes to the pnictogen bonding: the lone pair of a Lewis base donates electron density into the s*(Pn@X) antibonding orbitals at the pnictogen Pn. 8a, 15] In contrast to the large number of theoretical studies that have been disclosed, experimental investigations on pnictogen bonding are mainly limited to single-crystal X-ray studies. 17] Notably, only a few spectroscopic investigations have been reported 13a, 18] even though methods such as NMR spectroscopy are ideally suited for gaining fundamental understanding of pnictogen bonding. However, minor changes in chemical shifts may only be expected due to the weak nature of these interactions. In contrast, coupling patterns and spin–spin coupling constants derived therefrom can be very meaningful ; however, their observation is usually limited to systems with spin I = =2 nuclei whereas coupling to quadrupolar nuclei (I> =2) is seen comparatively rarely due to fast relaxation. Here, we present our experimental and theoretical studies on pnictogen interaction in a series of accordion-like, bridged compounds 2 a–c shown in Scheme 1, which were designed based on the following considerations: Phosphorus and bismuth were chosen as bridge-head atoms and in our hypothesis the linkers are flexible enough to allow electronic communication between the pnictogens. On one hand, phosphorus has outstanding NMR properties among the pnictogens and may act as a pnictogen bond acceptor (electron pair donor). On the other hand, the strongest pnictogen interaction is expected for bismuth (due to its largest polarisability), and its electronic properties may be tuned by the halogen substituents. To obtain the target molecules, we first developed a facile and reproducible two-step synthetic protocol for the preparation of the tris-g-substituted thioether phosphine 1 (P(C6H4-oCH2SCH3)3, Scheme 1) as the central building block. [19] This involves metallation of the commercially available tris(o-tolyl)phosphine with Schlosser’s base and subsequent reaction with dimethyl disulfide. Compound 1 (P d =@36.8 ppm) can be isolated as a colourless solid in moderate yield (36 %). We attempted to synthesise the 1:1 complexes of 1 with all the four bismuth trihalides (BiX3, X = F, Cl, Br, I). The reaction of Scheme 1. Synthesis of ligand 1 and compounds 2 a–c. i) hexane, rt; ii) toluene, @78 8C; iii) toluene (2 a,b)/THF (2 c), rt. [a] R. Mokrai, Dr. Z. Benkő Budapest University of Technology and Economics H-1111 Budapest (Hungary) E-mail : zbenko@mail.bme.hu [b] J. Barrett, Dr. D. C. Apperley, Dr. A. S. Batsanov, Dr. D. Heift Department of Chemistry, Durham University, DH1 3LE Durham (UK) E-mail : dominikus.heift@durham.ac.uk Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under : https ://doi.org/10.1002/chem.201900266. T 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial, and no modifications or adaptations are made. Chem. Eur. J. 2019, 25, 4017 – 4024 www.chemeurj.org T 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4018 Communication

To study pnictogen bonding involving bismuth, flexible accordion-like molecular complexes of the composition [P(C6H4-o-CH2SCH3)(3)BiX3], (X=Cl, Br, I) have been synthesised and characterised. The strength of the weak and mainly electrostatic interaction between the Bi and P centres strongly depends on the character of the halogen substituent on bismuth, which is confirmed by single-crystal X-ray diffraction analyses, DFT and ab initio computations. Significantly, Bi-209-P-31 through-space coupling (J=2560 Hz) is observed in solid-state P-31 NMR spectra, which is so far unprecedented in the literature, delivering direct information on the magnitude of this pnictogen interaction.

To overcome the critical limitations of liquid-electrolyte-based dye-sensitized solar cells, quasi-solid-state electrolytes have been explored as a means of addressing long-term device stability, albeit with comparatively low ionic conductivities and device performances. Although metal oxide additives have been shown to augment ionic conductivity, their propensity to aggregate into large crystalline particles upon high-heat annealing hinders their full potential in quasi-solid-state electrolytes. In this work, sonochemical processing has been successfully applied to generate fine Co3O4 nanoparticles that are highly dispersible in a PAN:P(VP-co-VAc) polymer-blended gel electrolyte, even after calcination. An optimized nanocomposite gel polymer electrolyte containing 3 wt % sonicated Co3O4 nanoparticles (PVVA-3) delivers the highest ionic conductivity (4.62 × 10-3 S cm-1) of the series. This property is accompanied by a 51% enhancement in the apparent diffusion coefficient of triiodide versus both unmodified and unsonicated electrolyte samples. The dye-sensitized solar cell based on PVVA-3 displays a power conversion efficiency of 6.46% under AM1.5 G, 100 mW cm-2. By identifying the optimal loading of sonochemically processed nanoparticles, we are able to generate a homogenous extended particle network that effectively mobilizes redox-active species through a highly amorphous host matrix. This effect is manifested in a selective 51% enhancement in photocurrent density (JSC = 16.2 mA cm-2) and a lowered barrier to N719 dye regeneration (RCT = 193 Ω) versus an unmodified solar cell. To the best of our knowledge, this work represents the highest known efficiency to date for dye-sensitized solar cells based on a sonicated Co3O4-modified gel polymer electrolyte. Sonochemical processing, when applied in this manner, has the potential to make meaningful contributions toward the ongoing mission to achieve the widespread exploitation of stable and low-cost dye-sensitized solar cells.