Synthesis and crystallographic, spectroscopic and computational characterization of 3,3',4,4'-substituted biphenyls: effects of OR substituents on the intra-ring torsion angle.

Presented here are the synthesis, characterization and study (using single crystal X-ray diffraction, Raman scattering, quantum mechanics calculations) of the structures of a series of biphenyls substituted in positions 3, 3', 4 and 4' with a variety of R (R = methyl, acetyl, hexyl) groups connected to the biphenyl core through oxygen atoms. The molecular conformation, particularly the torsion angle between aromatic rings has been extensively studied both in the solid as well as in the liquid state. The results show that the compounds appearing as rigorously planar in the solid present instead a twisted conformation in the melt. The solid versus melt issue strongly suggests that the reasons for planarity are to be found in the packing restraints. A `rule of thumb' is suggested for the design of biphenyls with different molecular conformations, based on the selection of the OR substituent.

Iron-based nanoparticles prepared from yerba mate extract. Synthesis, characterization and use on chromium removal.

Iron-based nanoparticles were synthesized by a rapid method at room temperature using yerba mate (YM) extracts with FeCl3 in different proportions. Materials prepared from green tea (GT) extracts were also synthesized for comparison. These materials were thoroughly characterized by chemical analyses, XRD, magnetization, SEM-EDS, TEM-SAED, FTIR, UV-Vis, Raman, Mössbauer and XANES spectroscopies, and BET area analysis. It was concluded that the products are nonmagnetic iron complexes of the components of the extracts. The applicability of the materials for Cr(VI) (300 µM) removal from aqueous solutions at pH 3 using two Cr(VI):Fe molar ratios (MR), 1:3 and 1:0.5, has been tested. At Cr(VI):Fe MR = 1:3, the best YM materials gave complete Cr(VI) removal after two minutes of contact, similar to that obtained with commercial nanoscale zerovalent iron (N25), with dissolved Fe(II), and with a likewise prepared GT material. At a lower Cr(VI):Fe MR (1:0.5), although Cr(VI) removal was not complete after 20 min of reaction, the YM nanoparticles were more efficient than N25, GT nanoparticles and Fe(II) in solution. The results suggest that an optimal Cr(VI):Fe MR ratio could be reached when using the new YM nanoparticles, able to achieve a complete Cr(VI) reduction, and leaving very low Cr and Fe concentrations in the treated solutions. The rapid preparation of the nanoparticles would allow their use in removal of pollutants in soils and groundwater by direct injection of the mixture of precursors.

Thermal, spectroscopic and structural analysis of a thermosalient phase transformation in tapentadol hydrochloride.

Presented herein are detailed optical, thermal, spectroscopic and structural analyses of the phase transformation occurring in tapentadol hydrochloride (C14H24NO+·Cl-), a phenomenon already reported [Fischer et al. (2006); Patent: WO 2006000441 A2]. The thermal behaviour of the compound was studied using single-crystal X-ray diffraction, differential scanning calorimetry and Raman scattering measurements. The compound undergoes a first-order reversible phase transition at Theat = 318.0 (1) K, Tcool = 300.0 (1) K, as assessed by the coexistence of both phases in the vicinity of the transition and the abrupt changes observed in the unit-cell parameters with temperature. The process is accompanied by clear thermosalient behaviour, with a conspicuous movement of the samples. On cooling, the transformation leads from a P212121 symmetry (Z' = 1) to P21, with an abrupt change in ß [90 ↔ 94.78 (1)°] and duplication of the asymmetric unit contents (Z' = 2). The main structural differences observed across the transition are extremely small, with almost no changes in the stronger, non-covalent interaction scheme involving the `conventional' (N-H...Cl, O-H...Cl) hydrogen bonds.

Structure and electrical properties of a one-dimensional polymeric silver thiosaccharinate complex with argentophilic interactions.

Among the potential applications of coordination polymers, electrical conductivity ranks high in technological interest. We report the synthesis, crystal structure and spectroscopic analysis of an AgI-thiosaccharinate one-dimensional coordination polymer {systematic name: catena-poly[[[aquatetrakis(µ3-1,1-dioxo-1,2-benzisothiazole-3-thiolato-κ3N:S3:S3)tetrasilver(I)]-µ2-4,4'-(propane-1,3-diyl)dipyridine-κ2N:N'] dimethyl sulfoxide hemisolvate]}, {[Ag4(C7H4NO2S2)4(C13H14N2)(H2O)]·0.5C2H6OS}n, with the 4,4'-(propane-1,3-diyl)dipyridine ligand acting as a spacer. A relevant feature of the structure is the presence of an unusually short Ag...Ag distance of 2.8306 (9) Å, well within the range of argentophilic interactions, confirmed experimentally as such by a Raman study on the low-frequency spectrum, and corroborated theoretically by an Atoms in Molecules (AIM) analysis of the calculated electron density. Electrical conductivity measurements show that this complex can act as a semiconductor with moderate conductivity.

A combined crystallographic, thermal, Raman and computational study on polymorphism and phase transition in 1-(4-hexyloxy-3-hydroxyphenyl)ethanone.

The crystal structure of the triclinic polymorph of 1-(4-hexyloxy-3-hydroxyphenyl)ethanone, C14H20O3, differs markedly from that of the orthorhombic polymorph [Manzano et al. (2015). Acta Cryst. C71, 1022-1027]. The two molecular structures are alike with respect to their bond lengths and angles, but differ in their spatial arrangement. This gives rise to quite different packing schemes, even if built up by similar chains having the hydroxy-ethanone O-H...O hydrogen-bond synthon in common. Both phases were found to be related by a first-order thermally driven phase transformation at 338-340 K, which is discussed in detail. The relative stabilities of both polymorphs are explained on the basis of both the noncovalent interactions operating in each structure and quantum chemical calculations. The polymorphic phase transition has also been studied experimentally by means of differential scanning calorimetry (DSC) experiments, conducted on individual single crystals, Raman spectroscopy and controlled heating under a microscope of individual single crystals, which were further characterized by powder and single-crystal X-ray diffraction.

A New, More Stable Polymorphic Form of Otilonium Bromide: Solubility, Crystal Structure, and Phase Transformation.

A new polymorphic form of otilonium bromide is presented (Form I), and a thorough analysis of its crystal and molecular structure is performed. The compound suffers a temperature-driven first-order phase transition at about 396 K, which transforms it into the polymorph reported by Dapporto P and Sega A (Acta Cryst. 1986;C42:474-478) (Form II). Through thermal analysis and solubility experiments the relative stability of both crystal modifications were determined, confirming that at room temperature this new Form I is the more stable one, Form II existing just in a metastable state.

A polymeric silver thiosaccarinate complex with a two-dimensional triply entangled mesh and argentophilic interactions.

Silver(I) complexes with sulfur-donor ligands have a broad range of pharmacological applications. One of the most important factors for tuning the biological activity is the type of donor atom and the ease of ligand replacement. Silver thiosaccharinates display a wide range of structures from mono- to polynuclear complexes. We report the synthesis, crystal structure and vibrational spectroscopic analysis of a two-dimensional Ag(I)-thiosaccharinate coordination polymer, namely poly[tris(µ2-4,4'-bipyridine-κ(2)N:N')bis(µ3-1,1-dioxo-1,2-benzisothiazole-3-thiolato-κ(3)N:S(3):S(3))bis(µ2-1,1-dioxo-1,2-benzisothiazole-3-thiolato-κ(2)S(3):S(3))tetrasilver(I)], [Ag2(C7H4NO2S2)2(C10H8N2)1.5]n, with 4,4'-bipyridine acting as a spacer. A relevant feature of the structure is the presence of an unusually short Ag...Ag separation of 2.8859 (10) Å, well within the range of argentophilic interactions and confirmed as such by Raman analysis of the low-frequency spectrum. From a topological point of view, the structure presents interpenetration in the form of a threefold entangled 2D→2D mesh (2D is two-dimensional).

A temperature-induced order-disorder phase transition in a 4-substituted 4,2':6',4''-terpyridine.

Crystals of 4'-(isoquinolin-4-yl)-4,2':6',4''-terpyridine (iqtp), C24H16N4, grown from an ethanol solution, undergo a reversible first-order single-crystal to single-crystal phase transition at Tc in the range 273-275 K, from a disordered higher-temperature phase [form (I)] in the space group P21/c, with one single molecule in the asymmetric unit, to an ordered lower-temperature one [form (II)] in the space group P21/n, with two independent molecules in the asymmetric unit. There is a group-subgroup relationship linking (I)-(II), due to cell doubling and the disappearance of a number of symmetry operations. In addition to X-ray diffraction, the transition has been monitored by Raman spectroscopy and differential scanning calorimetry, the latter disclosing an enthalpy change of 0.72 (6) kJ mol(-1). Variations of the unit-cell parameters with temperature between 170 and 293 K are presented. The evolution of diffraction spots in the vicinity of the transition temperature shows the coexistence of both phases, confirming the first-order character of the transition. Structural details of both phases are analyzed and intermolecular interactions compared in order to investigate the mechanism of the phase transition. A three-dimensional Hirshfeld surface analysis was performed to corroborate the significant changes in the intermolecular features.