Chemoselective, Practical Synthesis of Cobaltocenium Carboxylic Acid Hexafluorophosphate

Cobaltocenium carboxylic acid (carboxycobaltocenium) hexafluorophosphate, a key compound for other monofunctionalized cobaltocenium salts, has been synthesized in >70% overall yield starting from cobaltocenium hexafluorophosphate by a synthetic sequence involving (i) nucleophilic addition of lithium (trimethylsilyl)­ethynide, (ii) hydride removal by tritylium hexafluorophosphate, and (iii) oxidative cleavage of the alkynyl substituent by potassium permanganate

Chemoselective, Practical Synthesis of Cobaltocenium Carboxylic Acid Hexafluorophosphate

Cobaltocenium carboxylic acid (carboxycobaltocenium) hexafluorophosphate, a key compound for other monofunctionalized cobaltocenium salts, has been synthesized in >70% overall yield starting from cobaltocenium hexafluorophosphate by a synthetic sequence involving (i) nucleophilic addition of lithium (trimethylsilyl)­ethynide, (ii) hydride removal by tritylium hexafluorophosphate, and (iii) oxidative cleavage of the alkynyl substituent by potassium permanganate

Separation of Hemicellulose and Cellulose from Wood Pulp by Means of Ionic Liquid/Cosolvent Systems

Pulp of high cellulose content, also known as dissolving pulp, is needed for many purposes, including the production of cellulosic fibers and films. Paper-grade pulp, which is rich in hemicellulose, could be a cheap source but must be refined. Hitherto, hemicellulose extraction procedures suffered from a loss of cellulose and the non-recoverability of unaltered hemicelluloses. Herein, an environmentally benign fractionation concept is presented, using mixtures of a cosolvent (water, ethanol, or acetone) and the cellulose dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc). This cosolvent addition was monitored using Kamlet–Taft parameters, and appropriate stirring conditions (3 h at 60 °C) were maintained. This allowed the fractionation of a paper-grade kraft pulp into a separated cellulose and a regenerated hemicellulose fraction. Both of these exhibited high levels of purity, without any yield losses or depolymerization. Thus, this process represents an ecologically and economically efficient alternative in producing dissolving pulp of highest purity

Dialkyl Phosphate-Related Ionic Liquids as Selective Solvents for Xylan

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from <i>Eucalyptus globulus</i> kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. ¹H NMR spectra of model solutions and Kamlet–Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by ¹³C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs

Structural Redetermination and Photoluminescence Properties of the Niobium Oxyphosphate (NbO)₂P₄O₁₃

The structure of (NbO)₂P₄O₁₃ was solved and refined based on new single-crystal diffraction data revealing considerably more complexity than previously described. (NbO)₂P₄O₁₃ crystallizes in the triclinic space group <i>P</i>1̅ with <i>Z</i> = 6. The lattice parameters determined at room temperature are <i>a</i> = 1066.42(4) pm, <i>b</i> = 1083.09(4) pm, <i>c</i> = 1560.46(5) pm, α = 98.55(1)°, β = 95.57(1)°, γ = 102.92(1)°, and <i>V</i> = 1.7213(2) nm³. The superstructure contains 64 unique atoms including two disordered semioccupied oxygen positions. An unusual 180° bond angle between two [P₄O₁₃]^6– groups was refined to form half-occupied, split positions in agreement with previous reports. The IR and Raman spectra reflect the appearance of overlapping bands assignable to specific group vibrations as well as P–O–P linkages present in the [P₄O₁₃]^6– entities. Investigation of the powdered product concerning its photoluminescence properties revealed an excitability in the UV at 270 nm assigned to O2p–Nb4d charge transfer transitions. A resulting broad-band emission with the maximum in the visible region at 455 nm was determined

Conformational Flexibility and Cation–Anion Interactions in 1-Butyl-2,3-dimethylimidazolium Salts

The butyl group in 1-butyl-2,3-dimethylimidazolium (BMMI) salts, a common group of low-melting solids, was found to exhibit different conformations in the solid state. Crystal structures of pure BMMI azide, thiocyanate, propynoate, hexachlorocerate­(IV), chlorocyanocuprate­(I), nonachlorodititanate­(IV), and mixed azide/chloride and cyanide/chloride salts were determined by single crystal X-ray diffraction, and their butyl chain conformations were examined. The twist angle of the C­(α)–C­(β) bond out of the plane of the imidazole ring ranges from 57° to 90°, whereas the torsion angle along the C­(α)–C­(β) bond determines the overall conformation: 63° to 97° (gauche) and 170° to 179° (trans). The preferred conformations of the butyl group are trans–trans and gauche–trans, but trans–gauche and gauche–gauche were also observed. More than one conformer was present in disordered structures. Numerous polar hydrogen bonds between cations and anions were identified. Five structures exhibit stacking of the aromatic imidazole systems, indicated by parallel alignment of pairs of cations with short centroid–centroid distances due to π–π interactions, which is surprisingly frequent. Not only imidazole ring protons are involved in the formation of short CH···X hydrogen bonds, but also interactions between methylene and methyl groups of the alkyl chain and the anion are visible. Hirshfeld surface analysis revealed that nonpolar H···H contacts represent the majority of interactions. The volume-based lattice potential energy, enthalpy, entropy, and free energy were calculated by density functional theory. Calculated and experimental molecular volumes in the range from 0.27 to 0.70 nm³ agreed favorably, thus facilitating reliable predictions of volume-derived properties

Synthetic Access to Cubic Rare Earth Molybdenum Oxides RE₆MoO_12−δ (RE = Tm–Lu) Representing a New Class of Ion Conductors

Materials crystallizing in highly symmetric structures are of particular interest as they display superior physical properties in many relevant technological areas such as solid oxide fuels cells (SOFCs), catalysis, or photoluminescent materials. While the rare earth molybdenum oxides RE₆MoO₁₂ with the large rare earth cations RE = La to Dy crystallize in a cubic defect fluorite structure type (<i>Fm</i>3̅<i>m</i>, no. 225), the compounds with the smaller cations RE = Tm–Lu could hitherto only be synthesized in the rhombohedral defect fluorite structure type (<i>R</i>3̅, no. 148). In the following, new low temperature access to the rare earth molybdenum oxides RE₆MoO_12−δ (RE = Tm–Lu) crystallizing in the highly symmetric cubic bixbyite structure type (<i>Ia</i>3̅, no. 206) will be discussed. The three-step method comprises preparation of the rhombohedral phases by solution combustion (SC) reactions, their reduction including simultaneous structural transitions from the rhombohedral to the cubic phases, and subsequent reoxidations while preserving their cubic structures. Detailed studies on this process were performed on the compound Yb₆MoO_12−δ using TG-DTA, XPS, EDX, and X-ray powder diffraction (XRPD) measurements. In contrast to the rhombohedral phase Yb₆MoO₁₂, which does not show any ionic conductivity, the cubic bixbyite structured compound can be classified as a promising ionic conductor. Electrochemical impedance spectroscopy (EIS) revealed that bulk and grain boundary activation energy determined to be 144.6 kJ mol^–1 and 150.4 kJ mol^–1, respectively, range in the same regime as the conventional ionic conductor 8-YSZ. Furthermore, the new cubic phase Yb₆MoO_12−δ displays improved coloristic properties (UV–Vis spectroscopy) with a yellow hue value (CIE-Lab) being enhanced from <i>b</i>* = 26.0 of the rhombohedral to <i>b</i>* = 46.1 for the cubic phase, which is relevant for the field of inorganic pigments