Resolvable polymorphism in an intergrowth of two modifications of tris(diethyldithiocarbamato)antimony

Tris(diethyldithiocarbamato-κS)antimony(III), [Sb(C5H10NS2)3], is tentatively presumed to comprise a triclinic and a monoclinic polymorph intergrown into each other. The geometry in the triclinic phase is a ψ-capped octahedron and that in the monoclinic phase is a ψ-pentagonal bipyramid. The study also identifies the polyhedral symbols for a reported pair of polymorphs of another SbIII coordination compound, as well as for those of published polymorphic modifications of other BiIII and PbII coordination compounds; the symbols in the pair differ in most of these examples. When differentiating related structures of such classes of coordination compounds, lone-pair stereochemistry may be another informative variable, as stereochemical activity is not always apparent from bond distances and angles only.

Characterization of second-order bands in Raman scattering spectra of lead phthalocyanine thin films

The structure, optical absorption (500…950 nm) and resonance Raman spectra (within the range 100…3000 cm–1) of lead phthalocyanine (PbPc) thin solid films with the thickness 190 nm were studied. The films were deposited using thermal evaporation in vacuum 6.5 mPa onto silica substrates held at room temperature. It was found that in the process of depositing the PbPc thin solid films monoclinic and triclinic PbPc crystallites were grown, and the amount of crystallites in the triclinic phase in the as-deposited PbPc films was approximately two times less than those in the monoclinic one. The resonance Raman spectroscopy, with application of the He-Ne laser line 632.8 nm as an excitation source, was used for studying the 190-nm thick PbPc films. Due to resonance enhancement, the second-order Raman spectrum of PbPc films within the region 1700…2950 cm–1 was successfully registered and analyzed for the first time. It has been shown that the second-order PbPc Raman spectrum is mainly formed by the overtones and combination modes of B1 symmetry fundamental vibrations. The second-order Raman region of 2550…2900 cm–1 appeared to be highly specific for PbPc and could be used for its identification along with the finger-print region of fundamental vibrational modes.

Preparation of PPy-WO3 Nano-composite for Supercapacitor Applications

In this work, polypyrrole (PPy) composites were chemically prepared by a chemical oxidation method. Also, Tungsten Trioxide (WO3) nanoparticles were prepared and added in certain proportions to PPy. The structure properties were studied for the polypyrole and tungesten trioxide separately before mixing them together. The X-ray diffraction (XRD) analysis revealed a hexagonal WO3 and a triclinic PPy. It was observed that the nano-composite prepared by the addition of WO3 with 10 and 20% volume ratios to PPy shows a triclinic phase with the presence of hexagons. The molecular structures of PPy, WO3, and PPy–WO3 nano composites were depicted by Fourier-transform infrared spectroscopy (FTIR) in the scope of 400–4000 cm-1. The supercapcitors of PPy and PPy-WO3 were examined by calculating the figure of merit of the electrode (PPy and PPy-WO3) using cyclic voltammetry (CV), galvanostatic charge and discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. It was found that the highest value of capacity (266.62 F/g) is obtained at 20% WO3 ratio.

Polymorphism of dimethylaminoborane N(CH3)2-BH2

Dehydrocoupling of the adduct of dimethylamine and borane, NH(CH3)2-BH3 leads to dimethylaminoborane with formal composition N(CH3)2-BH2. The structure of this product depends on the conditions of the synthesis; it may crystallize either as a dimer in a triclinic space group forming a four-membered ring [N(CH3)2-BH2]2 or as a trimer forming a six-membered ring [N(CH3)2-BH2]3 in an orthorhombic space group. Due to the denser packing, the six-membered ring in the trimer structure should be energetically more stable than the four-membered ring. The triclinic structure is stable at low temperatures. Heating the triclinic phase above 290 K leads to a second-order phase transition to a new monoclinic polymorph. While the crystal structures of the triclinic and orthorhombic phases were already known in the literature, the monoclinic crystal structure was determined from powder diffraction data in this study. Monoclinic dimethylaminoborane crystallizes in space group C2/m with the boron and nitrogen atoms located on the mirror plane, Wyckoff position 4i, while the carbon and hydrogen atoms are on the general position 8j.

Single-crystal-to-single-crystal phase transitions of commensurately modulated sodium saccharinate 1.875-hydrate

This work reports reversible, single-crystal-to-single-crystal phase transitions of commensurately modulated sodium saccharinate 1.875-hydrate [Na(sac)(15/8)H2O]. The phases were studied in the temperature range 298 to 20 K. They exhibit complex disordered states. An unusual reentrant disorder has been discovered upon cooling through a phase transition at 120 K. The disordered region involves three sodium cations, four water molecules and one saccharinate anion. At room temperature, the structure is an eightfold superstructure that can be described by the superspace group C2/c(0σ20)s0 with q = (0, 3/4, 0). It demonstrates maximum disorder with the disordered chemical entities having slightly different but close to 0.50:0.50 disorder component ratios. Upon cooling, the crystal tends to an ordered state, smoothly reaching a unified disorder component ratio of around 0.90:0.10 for each of the entities. Between 130 and 120 K a phase transition occurs involving a sudden increase of the disorder towards the disorder component ratio 0.65:0.35. Meanwhile, the space group and general organization of the structure are retained. Between 60 and 40 K there is another phase transition leading to a twinned triclinic phase. After heating the crystal back to room temperature its structure is the same as before cooling, indicating a complete reversibility of the phase transitions.

Unveiling the crystallographic origin of mechanochemically induced monoclinic to triclinic phase transformation in WO3

This study reports the anomalously stabilized low-temperature triclinic phase (δ-WO3) during high energy ball milling (HEBM) of the monoclinic γ-WO3 phase.

Effect of Hydrothermal Conditions on Crystal Structure, Morphology and Visible-Light Driven Photocatalysis of WO3 Nanostructures

Tungsten trioxide (WO3) nanostructures were synthesized by a hydrothermal method, and the influence of essential hydrothermal conditions, temperature and time, on their crystal structure, morphology and visible-light driven photocatalysis was studied. The hydrothermal temperature was varied from 120 °C to 200 °C, and the hydrothermal time changed from 12 h to 32 h. The crystal structure, morphology and photocatalytic performance of WO3 nanostructures were characterized by XRD, SEM and UV-Vis. The crystal structure of WO3 nanostructure was triclinic phase and their morphology was mainly one dimensional nanorods. Methylene blue was used as the target to evaluate their photocatalytic performance under visible light (λ>420 nm). The photocatalytic results suggest the suitable hydrothermal conditions to synthesize WO3 nanostructures for the wastewater treatment application.

Synthesis and Structures of Bis- and Tris-(triphenylarsine)gold(I) Iodides

The title compounds [(Ph3As)2AuI] and [(Ph3As)3AuI] have been crystallized from equimolar solutions of Bu4NAuI2 and AsPh3 in dimethylformamide and structurally characterized by single crystal X-ray diffraction studies. [(Ph3As)2AuI] crystallizes in space group C2/c, Z 4, and is isomorphous with other [(Ph3E)2MX] (MX=coinage metal(i) salt) arrays, with the Au–I bond being disposed on a crystallographic 2-axis: Au–I, As 2.7008(2), 2.4337(2) Å, As–Au–As, I 125.736(8)°, 117.132(4)° (153K). [(Ph3As)3AuI] crystallizes as a triclinic phase in space group , Z 4, and is isomorphous with [(Ph3Sb)3CuI] and [(Ph3P)3AgI]: Au–As 2.4847–2.5049(10), Au–I 2.8518(8), 2.8597(7) Å with As–Au–As, I 109.67(3)–115.97(3)°, 101.33(2)–106.85(3)°. A second ‘[(Ph3As)3AuI]’ product was obtained as a co-crystalline phase in space group P21/n containing [(Ph3As)3AuI], and [(Ph3As)2AuI] accompanied by an additional unbound Ph3As molecule, i.e. [(Ph3As)3AuI]·[(Ph3As)2AuI·Ph3As], with structural parameters closely similar to those for the corresponding separate [(Ph3As)3AuI] and [(Ph3As)2AuI] complexes described above. Comparison of the bond lengths for these and related complexes show that they are generally consistent with the ‘gold is smaller than silver’ phenomenon caused by relativistic orbital contraction effects in gold, but the results also show that the magnitude of this effect is dependent on the nature of the metal–ligand bonds involved, and on changes in the metal coordination environment, which can in some circumstances yield trends in which the effect on particular bonds is partially masked or even reversed.

The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile

The crystal structure of 4-iodobenzonitrile, which is monoclinic (space group I2/a) under ambient conditions, contains chains of molecules linked through C≡N···I halogen-bonds. The chains interact through CH···I, CH···N and π-stacking contacts. The crystal structure remains in the same phase up to 5.0 GPa, the b axis compressing by 3.3%, and the a and c axes by 12.3 and 10.9 %. Since the chains are exactly aligned with the crystallographic b axis these data characterise the compressibility of the I···N interaction relative to the inter-chain interactions, and indicate that the halogen bond is the most robust intermolecular interaction in the structure, shortening from 3.168(4) at ambient pressure to 2.840(1) Å at 5.0 GPa. The π∙∙∙π contacts are most sensitive to pressure, and in one case the perpendicular stacking distance shortens from 3.6420(8) to 3.139(4) Å. Packing energy calculations (PIXEL) indicate that the π∙∙∙π interactions have been distorted into a destabilising region of their potentials at 5.0 GPa. The structure undergoes a transition to a triclinic ( P 1 ¯ ) phase at 5.5 GPa. Over the course of the transition, the initially colourless and transparent crystal darkens on account of formation of microscopic cracks. The resistance drops by 10% and the optical transmittance drops by almost two orders of magnitude. The I···N bond increases in length to 2.928(10) Å and become less linear [<C−I∙∙∙N = 166.2(5)°]; the energy stabilises by 2.5 kJ mol−1 and the mixed C-I/I..N stretching frequency observed by Raman spectroscopy increases from 249 to 252 cm−1. The driving force of the transition is shown to be relief of strain built-up in the π∙∙∙π interactions rather than minimisation of the molar volume. The triclinic phase persists up to 8.1 GPa.