Structures and photophysical properties of 3,4-diaryl-1H-pyrrol-2,5-diimines and 2,3-diarylmaleimides

Structural features of 3,4-diaryl-1H-pyrrol-2,5-diimines and their derivatives have been studied by molecular spectroscopy techniques, single-crystal X-ray diffraction, and DFT calculations. According to the theoretical calculations, the diimino tautomeric form of 3,4-diaryl-1H-pyrrol-2,5-diimines is more stable in solution than the imino-enamino form. We also found that the structurally related 2,3 exist in the solid state in the dimeric diketo form. 3,4-Diary1-1H-pyrrol-2,5-diimines and 2,3-diarylmaleimides exhibit fluorescence in the blue region of the visible spectrum. The fluorescence spectra have large Stokes shifts. Aryl substituents at the 3,4-positions of 1H-pyrrol-2,5-diimine do not significantly affect fluorescence properties. The insertion of donor substituents into 2,3diarylmaleimides leads to bathochromic shift of emission bands with hyperchromic effect. (C) 2017 Elsevier B.V. All rights reserved

The Crystal Structure of Sergeysmirnovite, MgZn₂(PO₄)₂·4H₂O, and Complexity of the Hopeite Group and Related Structures

The crystal structure of sergeysmirnovite, MgZn2(PO4)2·4H2O (orthorhombic, Pnma, a = 10.6286(4), b = 18.3700(6), c = 5.02060(15) Å, V = 980.26(6) Å3, Z = 4), a new member of the hopeite group of minerals, was determined and refined to R1 = 0.030 using crystals from the Këster mineral deposit in Sakha-Yakutia, Russia. Similar to other members of the hopeite group, the crystal structure of sergeysmirnovite is based upon [Zn(PO4)]– layers interlinked via interstitial [MO2(H2O)4]2– octahedra, where M = Mg2+. The layers are parallel to the (010) plane. Within the layer, the ZnO4 tetrahedra share common corners to form chains running along [001]. Sergeysmirnovite is a dimorph of reaphookhillite, a mineral from the Reaphook Hill zinc deposit in South Australia. The relations between sergeysmirnovite and reaphookhillite are the same as those between hopeite and parahopeite. Topological and structural complexity analysis using information theory shows that the hopeite (sergeysmirnovite) structure type is more complex, both structurally and topologically, than the parahopeite (reaphookhillite) structure type. Such complexity relations contradict the general observation that more complex polymorphs possess higher physical density and higher stability, since parahopeite is denser than hopeite. It could be hypothesized that hopeite is metastable under ambient conditions and separated from parahopeite by a structural and topological reconstruction that requires an essential energy barrier that is difficult to overcome

Dynamic Disorder of Fe3+ Ions in the Crystal Structure of Natural Barioferrite

A natural barioferrite, BaFe3+12O19, from a larnite–schorlomite–gehlenite vein of paralava within gehlenite hornfels of the Hatrurim Complex at Har Parsa, Negev Desert, Israel, was investigated by Raman spectroscopy, electron probe microanalysis, and single-crystal X-ray analyses acquired over the temperature range of 100–400 K. The crystals are up to 0.3 mm × 0.1 mm in size and form intergrowths with hematite, magnesioferrite, khesinite, and harmunite. The empirical formula of the barioferrite investigated is as follows: (Ba0.85Ca0.12Sr0.03)∑1(Fe3+10.72Al0.46Ti4+0.41Mg0.15Cu2+0.09Ca0.08Zn0.04Mn2+0.03Si0.01)∑11.99O19. The strongest bands in the Raman spectrum are as follows: 712, 682, 617, 515, 406, and 328 cm−1. The structure of natural barioferrite (P63/mmc, a = 5.8901(2) Å, c = 23.1235(6) Å, V = 694.75(4) Å3, Z = 2) is identical with the structure of synthetic barium ferrite and can be described as an interstratification of two fundamental blocks: spinel-like S-modules with a cubic stacking sequence and R-modules that have hexagonal stacking. The displacement ellipsoids of the trigonal bipyramidal site show elongation along the [001] direction during heating. As a function of temperature, the mean apical Fe–O bond lengths increase, whereas the equatorial bond lengths decrease, which indicates dynamic disorder at the Fe2 site

Merohedral Mechanism Twining Growth of Natural Cation-Ordered Tetragonal Grossular

Garnet supergroup minerals are in the interest of different applications in geology, mineralogy, and petrology and as optical material for material science. The growth twins of natural tetragonal grossular from the Wiluy River, Yakutia, Russia, were investigated using single-crystal X-ray diffraction, optical studies, Raman spectroscopy, microprobe, and scanning electron microscopy. The studied grossular is pseudo-cubic (a = 11.9390 (4), c = 11.9469 (6) Å) and birefringent (0.01). Its structure was refined in the Ia3¯d, I41/acd, I41/a, and I4¯2d space groups. The I41/a space group was chosen as the most possible one due to the absence of violating reflections and ordering of Mg2+ and Fe3+ in two independent octahedral sites, which cause the symmetry breaking according to the group–subgroup relation Ia3¯d → I41/a. Octahedral crystals of (H4O4)4−-substituted grossular are merohedrally twinned by twofold axis along [110]. The mechanism of twining growth led to the generation of stacking faults on the (110) plane and results in the formation of crystals with a long prismatic habit

Thermal Behavior and Phase Transition of Uric Acid and Its Dihydrate Form, the Common Biominerals Uricite and Tinnunculite

Single crystals and powder samples of uric acid and uric acid dihydrate, known as uricite and tinnunculite biominerals, were extracted from renal stones and studied using single-crystal and powder X-ray diffraction (SC and PXRD) at various temperatures, as well as IR spectroscopy. The results of high-temperature PXRD experiments revealed that the structure of uricite is stable up to 380 °C, and then it loses crystallinity. The crystal structure of tinnunculite is relatively stable up to 40 °C, whereas above this temperature, rapid release of H2O molecules occurs followed by the direct transition to uricite phase without intermediate hydration states. SCXRD studies and IR spectroscopy data confirmed the similarity of uricite and tinnunculite crystal structures. SCXRD at low temperatures allowed us to determine the dynamics of the unit cells induced by temperature variations. The thermal behavior of uricite and tinnunculite is essentially anisotropic; the structures not only expand, but also contract with temperature increase. The maximal expansion occurs along the unit cell parameter of 7 Å (b in uricite and a in tinnunculite) as a result of the shifts of chains of H-bonded uric acid molecules and relaxation of the π-stacking forces, the weakest intermolecular interactions in these structures. The strongest contraction in the structure of uricite occurs perpendicular to the (101) plane, which is due to the orthogonalization of the monoclinic angle. The structure of tinnunculite also contracts along the [010] direction, which is mostly due to the stretching mechanism of the uric acid chains. These phase transitions that occur within the range of physiological temperatures emphasize the particular importance of the structural studies within the urate system, due to their importance in terms of human health. The removal of supersaturation in uric acid in urine at the initial stages of stone formation can occur due to the formation of metastable uric acid dihydrate in accordance with the Ostwald rule, which would serve as a nucleus for the subsequent growth of the stone at further formation stages; afterward, it irreversibly dehydrates into anhydrous uric acid

Eudialyte Group Minerals from the Lovozero Alkaline Massif, Russia: Occurrence, Chemical Composition, and Petrogenetic Significance

The Lovozero Alkaline Massif intruded through the Archean granite-gneiss and Devonian volcaniclastic rocks ca. 360 Ma ago and formed a large laccolith-type body. The lower part of the massif (the Layered complex) is composed of regularly repeating rhythms: melanocratic nepheline syenite (lujavrite, at the top), leucocratic nepheline syenite (foyaite), foidolite (urtite). The upper part of the massif (the Eudialyte complex) is indistinctly layered, and lujavrite enriched with eudialyte-group minerals (EGM) prevails there. In this article, we present the results of a study of the chemical composition and petrography of more than 400 samples of the EGM from the main types of rock of the Lovozero massif. In all types of rock, the EGM form at the late magmatic stage later than alkaline clinopyroxenes and amphiboles or simultaneously with it. When the crystallization of pyroxenes and EGM is simultaneous, the content of ferrous iron in the EGM composition increases. The Mn/Fe ratio in the EGM increases during fractional crystallization from lujavrite to foyaite and urtite. The same process leads to an increase in the modal content of EGM in the foyaite of the Layered complex and to the appearance of primary minerals of the lovozerite group in the foyaite of the Eudialyte complex

Fe(II)/Et3N-Relay-catalyzed domino reaction of isoxazoles with imidazolium salts in the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates, its ylide and betaine derivatives

A simple approach was developed for the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates from easily available compounds, 5-methoxyisoxazoles and phenacylimidazolium salts under hybrid Fe(II)/Et3N relay catalysis. The products were easily transformed into the corresponding 3-(5-methoxycarbonyl-1H-imidazol-3-ium-3-yl)pyrrol-1-ides, which in turn can be hydrolyzed under basic conditions into the corresponding betaines. A carbene tautomeric form of the 4-methoxycarbonyl-substituted imidazolylpyrrolides was trapped by reaction with sulfur affording the corresponding imidazolethiones under very mild conditions

Jahn-Teller Distortion and Cation Ordering: The Crystal Structure of Paratooite-(La), a Superstructure of Carbocernaite

The crystal structure of paratooite-(La) has been solved using crystals from the type locality, Paratoo copper mine, near Yunta, Olary Province, South Australia, Australia. The mineral is orthorhombic, Pbam, a = 7.2250(3) Å, b = 12.7626(5) Å, c = 10.0559(4) Å, V = 927.25(6) Å3, and R1 = 0.063 for 1299 unique observed reflections. The crystal structure contains eight symmetrically independent cation sites. The La site, which accommodates rare earth elements (REEs), but also contains Sr and Ca, has a tenfold coordination by seven carbonate groups. The Ca, Na1, and Na2 sites are coordinated by eight, eight, and six O atoms, respectively, forming distorted CaO8 and Na1O8 cubes, and Na2O6 octahedra. The Cu site is occupied solely by copper and possess a distorted octahedral coordination with four short (1.941 Å) and two longer (2.676 Å) apical Cu–O bonds. There are three symmetrically independent carbonate groups (CO3)2− with the average <C–O> bond lengths equal to 1.279, 1.280, and 1.279 Å for the C1, C2, and C3 sites, respectively. The crystal structure of paratooite-(La) can be described as a strongly distorted body-centered lattice formed by metal cations with (CO3)2− groups filling its interstices. According to the chemical and crystal-structure data, the crystal-chemical formula of paratooite-(La) can be described as (La0.74Ca0.11Sr0.07)4CuCa(Na0.75Ca0.15)(Na0.63)(CO3)8 or REE2.96Ca1.59Na1.38CuSr0.28(CO3)8. The idealized formula can be written as (La,Sr,Ca)4CuCa(Na,Ca)2(CO3)8. The structure of paratooite is a 1 × 2 × 2 superstructure of carbocernaite, CaSr(CO3)2. The superstructure arises due to the ordering of the chemically different Cu2+ cations, on one hand, and Na+ and Ca2+ cations, on the other hand. The formation of a superstructure due to the cation ordering in paratooite-(La) compared to carbocernaite results in the multiple increase of structural complexity per unit cell. Therefore, paratooite-(La) versus carbocernaite represents a good example of structural complexity increasing due to the increasing chemical complexity controlled by different electronic properties of mineral-forming chemical elements (transitional versus alkali and alkaline earth metals)

Crystal structure of natural phaeosphaeride A

The asymmetric unit of the title compound, C15H23NO5, contains two independent molecules. Phaeosphaeride A contains two primary sections, an alkyl chain consisting of five C atoms and a cyclic system consisting of fused five- and six-membered rings with attached substituents. In the crystal, the molecules form layered structures. Nearly planar sheets, parallel to the (001) plane, form bilayers of two-dimensional hydrogen-bonded networks with the hydroxy groups located on the interior of the bilayer sheets. The network is constructed primarily of four O—H...O hydrogen bonds, which form a zigzag pattern in the (001) plane. The butyl chains interdigitate with the butyl chains on adjacent sheets. The crystal was twinned by a twofold rotation about the c axis, with refined major–minor occupancy fractions of 0.718 (6):0.282 (6)