2,3,4,5,6‐Penta­nitro­aniline 1,2‐dichloro­ethane disolvate: `push–pull' deformation of aromatic rings by intra­molecular charge transfer

The title compound, C₆H₂N₆O₁₀·2C₂H₄Cl₂, forms layered stacks of penta­nitro­aniline mol­ecules, which possess twofold symmetry. The voids between these stacks are occupied by dichloro­ethane mol­ecules, which reside near a 2/m symmetry element and display pseudo‐inversion symmetry. The C atoms in one of the two solvent mol­ecules are threefold disordered. In the penta­nitro­aniline mol­ecule, considerable distortion of the benzenoid ring, coupled with the short C—N(H₂) bond and out‐of‐plane NO₂ twistings, point to significant intra­molecular `push–pull' charge transfer at the amino‐ and nitro‐substituted (ortho and para) positions, as theoretically quantified by natural bond orbital analysis of the π‐electron density.     

TeSe3]2- and [TeSe2]2- as synthons

The [Au2(TeSe2)2]2- anion has been prepared from the reaction of [TeSe3]2- with AuCN in DMF in the presence of PEt3 and from the reaction of [TeSe2]2- with AuCN in DMF. Reaction of [TeSe2]2- with AuCN in DMF in the presence of PEt3 leads ultimately to the [Au2(Te2)2]2- anion.     

Layer-by-layer adsorption of polyelectrolyte and surfactant and adsorption of their complexes on solid surface

The capillary electrokinetics method (measurement of streaming potential and current in a capillary with a radius of 5–7 μm made of fused quartz) is employed to study the structure formation at interfaces between quartz and solutions containing a cationic polyelectrolyte (poly(diallyldimethylammonium chloride) with molecular mass M = 100000−200000) and an anionic surfactant (sodium dodecyl sulfate). The kinetics of surface layer formation is studied upon the layer-by-layer adsorption of the components and the adsorption of their complexes at the same component ratios. It is established that the formation time and the electrokinetic potentials of the surface layers are almost independent of the procedure of their formation. In the case of the layer-by-layer adsorption, the first layers of the polyelectrolyte appear to be virtually undeformed, thus indicating that molecules with a planar conformation prevail in the adsorption layer. Surfactant adsorption enhances the deformation (layer loosening), which decreases with time (layer aging). Layers formed from the complexes have a denser (less deformable) structure. Variations in the electrokinetic potentials of the layers during the long-term pumping of a background electrolyte solution through a capillary witnesses the prevailing desorption of the anionic surfactant, with the desorption being noticeably more pronounced for the layers resultant from the adsorption of the complexes.     

Experimental Study of Zirconium(IV) Extraction from Fluoride-Containing Acid Solutions

Zirconium(IV) extraction from acid solutions was studied, and the optimal parameters of the process were found. Extractants for zirconium(IV) recovery from nitric and sulfuric acid solutions in the presence of fluoride ions were selected. The distribution coefficients of zirconium(IV) and fluoride ion were determined.     

Crystal‐Structure‐Guided Design of Self‐Assembling RNA Nanotriangles

RNA nanotechnology uses RNA structural motifs to build nanosized architectures that assemble through selective base‐pair interactions. Herein, we report the crystal‐structure‐guided design of highly stable RNA nanotriangles that self‐assemble cooperatively from short oligonucleotides. The crystal structure of an 81 nucleotide nanotriangle determined at 2.6 Å resolution reveals the so‐far smallest circularly closed nanoobject made entirely of double‐stranded RNA. The assembly of the nanotriangle architecture involved RNA corner motifs that were derived from ligand‐responsive RNA switches, which offer the opportunity to control self‐assembly and dissociation.     

Synthesis and Crystal Structure of a Novel Heterocycle, 2-Oxa-4,7-Diazabicyclo[3.3.1]Non-3-Ene

Abstract  

The compound 5, containing the novel heterocycle 2-oxa-4,7-diazabicyclo[3.3.1]non-3-ene, has been obtained in a synthetic approach toward oxazoles and 1,3-diazepanes of natural product-like complexity from cyclization and rearrangement of δ-lactam cyanamides. When this procedure was applied to a silyl-protected N-((3S,4S,5S)-4,5-dihydroxy-2-oxopiperidin-3-yl)cyanamide (2b) formation of the novel heterobicyclic scaffold 5 was observed along with the expected oxazole (3b) and diazepane (4b) products. The crystal structures of 5 and diazepane 4b are described. Compound 5 crystallized from methanol in the monoclinic system, P2₁ space group with unit cell parameters a = 15.3402(9), b = 7.2717(4), c = 22.5803(13), β = 106.8620(10) and a cell volume of 2410.5(2) A³.     

Synthesis and structural characterization of some selenoruthenates and telluroruthenates

The reaction of solid [RuClCp(PPh(3))(2)] with TeSe(3)(2-) or Se(n)(2-) in DMF leads to the formation of [RuCp(PPh(3))(mu(2)-Se(2))](2) (1). In the structure of this compound the two bridging Se(2) groups lead to a six-membered Ru(2)Se(4) ring in a chair conformation. Attached to each Ru center is a PPh(3) ligand in an equatorial position and a Cp ring in an axial position. The compound is diamagnetic. The compound [Ru(2)Cp(2)(mu(3)-Se(2))(mu(3)-Se)](2) (2) is obtained under similar conditions in the presence of air. This structure comprises a centrosymmetric Ru(4)Se(6) dimer formed from the two bridging Se groups and the two bridging Se(2) groups. Each Ru center is pi-bonded to a Cp ring. The reaction of solid [RuClCp(PPh(3))(2)] with a Te(n)(2-) polytelluride solution in DMF leads to the diamagnetic compound [(RuCp(PPh(3)))(2)(mu(2)-(1,4-eta:3,6-eta)Te(6))] (3). Here the Ru centers are bound to a bridging Te(6) chain at the 1, 4, 3, and 6 positions, leading to a bicyclic Ru(2)Te(6) ring. Each Ru atom is bound to a Cp ring and a PPh(3) group. This dimer possesses a center of symmetry. The structure of 3 is the first example of a bicyclic complex where fusion occurs along a Te-Te bond. If the same reaction is carried out in DMF/CH(2)Cl(2), rather than DMF, then [(RuCp(PPh(3)))(2)(mu(2)-(1,4-eta:3,6-eta)Te(6))].CH(2)Cl(2) (4) is obtained. In the solid state it possesses the same Ru(2)Te(6) structural unit as does 3, but the unit lacks a crystallographically imposed center of symmetry. The electronic structures of 3 and 4 have been analyzed with the use of first principles density functional theory. Bond order analysis indicates that the Te-Te bond where fusion occurs has a shared bonding charge of about (2)/(3) of that found for Te-Te single bonds.     

Crystallographic view of fluidic structures for room‐temperature ionic liquids: 1‐butyl‐3‐methyl­imidazolium hexa­fluoro­phosphate

Shock‐induced crystallization of the supercooled ionic liquid 1‐butyl‐3‐methyl­imidazolium hexa­fluoro­phosphate, C₈H₁₅N₂⁺·PF₆⁻, allows for the first time precise X‐ray diffraction analysis directly pertinent to the fluid state. This inter­mediate‐chain‐length structure shows features of both short‐ and long‐chain analogs. Two types of inter­planar distances between imidazolium rings are observed. The anions are located in channels formed by the imidazolium rings and alkyl chains.     

Isolation of Rare Earth Element's Radionuclides from Phosphoric Acid Solutions on Cerium (III) Phosphate

Abstract

The isolation of the lanthanide phosphates by crystallization from the solutions of phosphoric acid with the concentration of 2–5 mol·dm^?3, produced during destruction of the apatite, was investigated. The kinetic parameters of crystallization of the lanthanide phosphates and the values of their solubility in phosphoric acid with various impurities under temperatures between 60–90°C have been obtained from the data on distribution of Ce¹⁴⁴ and Eu^152–154 radio- nuclides between the solution and the solid phase. The wide region of supersaturated solution metastability has been determined. The possibility to remove supersaturation in the metastable region by introduction of the cerium (III) phosphate seeds has been proved. Separation of the lanthan-ides from calcium and other accompanying elements in the apatites by crystallization of the phosphates on the CePO₄ ·0.5H₂O seed in the region of small supersaturation of strongly acid solutions has been studied. Calcium phosphate demonstrates the “salting out” effect on the lanthanide phosphates. By thermodynamic computations the ionic compositions of the produced solutions from breaking down the apatite and the solubilities of the lanthanide phosphates were obtained, which agrees with the experimental data. The distribution coefficients for the solid phase and the liquid phase are 1.1.10⁴ for cerium and 4–10³ for europeum. The lanthanides/calcium separation coefficient is 1.3·10³.