Designing Fluorinated Cinchona Alkaloids for Enantioselective Catalysis: Controlling Internal Rotation by a Fluorine‐Ammonium Ion gauche Effect (φNCCF)

The C9 position of cinchona alkaloids functions as a molecular hinge, with internal rotations around the C8? C9 (τ₁) and C9? C4′ (τ₂) bonds giving rise to four low energy conformers ( 1 ; anti‐closed, anti‐open, syn‐closed, and syn‐open). By substituting the C9 carbinol centre by a configurationally defined fluorine substituent, a fluorine‐ammonium ion gauche effect (σ_C?H→σ_C?F*; F^δ????N⁺) encodes for two out of the four possible conformers ( 2 ). This constitutes a partial solution to the long‐standing problem of governing internal rotations in cinchonium‐based catalysts relying solely on a fluorine conformational effect.     

X-ray photoelectron spectroscopy as detection tool for coordinated or uncoordinated fluorine atoms demonstrated on fluoride systems NaF,K2TaF7, K3TaF8, K2ZrF6, Na7Zr6F31 and K3ZrF7

While systems K₃TaF₈ and K₃ZrF₇ were prepared by modified molten salt method modified wet pathway was used for reproducible preparation of Na₇Zr₆F₃₁. Its congruently melting character was demonstrated on simultaneous TG/DSC measurements and XRD patterns. X-ray photoelectron spectroscopy was applied for identification of differently bonded fluorine atoms in series of compounds NaF, K₂TaF₇, K₃TaF₈, K₂ZrF₆, Na₇Zr₆F₃₁ and K₃ZrF₇. Three different types of fluorine atoms were described qualitatively and quantitatively. Uncoordinated fluorine atoms (F⁻) provide signals at lowest binding energies, followed by signals from terminally coordinated fluorine atoms (M–F) and then bridging fluorine atoms (M–F–M) at highest energy. Based on XPS F 1s signals assigned to fluorine atoms in compounds with correctly determined structure it was suggested that fluorine atoms in K₃ZrF₇ have partially bridging character.     

Synthesis and characterization of tetramethylammonium trifluorosulfate

[Me₄N]⁺[SO₂F₃]^?, the first example of a [SO₂F₃]^? salt, has been prepared from Me₄NF and SO₂F₂. The colorless, microcrystalline solid was characterized by its infrared and Raman spectra. The trigonal bipyramidal structure of C_2v symmetry of the [SO₂F₃]^? anion is predicted by ab initio calculations. Two oxygen atoms with d(SO)=143.2 pm and one fluorine atom with d(SF)=157.9 pm occupy the equatorial plane. The two fluorine atoms in the axial position with d(SF)=168.5 pm are repulsed by the two oxygen atoms forming a bent axis with ?(F_axSF_ax)=165.2°.     

健那绿B的荧光猝灭研究及作为核酸测定探针的应用

用紫外可见光谱、稳态荧光发射及荧光寿命测定研究了核酸猝灭十二烷基磺酸钠胶束中的健那绿荧光。水溶液中弱的健那绿荧光在十二烷基磺酸钠胶束中被大大加强，其最大发射从425纳米移至410纳米，核酸的加入将猝灭健那绿的荧光，当健那绿浓度为2.5×10^–5 mol•L^-1时，荧光猝灭(F₀/F)分别与小牛胸腺DNA及鱼精DNA在2.4×10^–8 到 1.08×10^–7及 1.9×10^–8 到 3.8×10^–8 mol•L^-1范围内成正比, 检测限分别为1.3×10^–8 mol•L^-1 (小牛胸腺DNA)及6.3×10^–9 mol•L^-1 (鱼精DNA)。当DNA浓度较高时, 将系统偏离Stern-Volmer方程。这是因为动态猝灭和静态猝灭同时存在。方法已应用于鸡血提取液中DNA的测定, 测定结果与紫外法一致。     

Synthesis and Structure of the Ordered Modification of Ba6EuF12Cl2

Crystals of ordered Ba₆EuF₁₂Cl₂ were found to form during high temperature flux growth. The structure was refined in the hexagonal space group P 6 to R^F(R ) = 0.024(0.024) for 326 reflections and 46 parameters. Lattice parameters are a = b = 1059.27(8) pm and c = 416.36(2) pm; Z = 1. The structure is isotypic to Ba₇F₁₂Cl₂. No solid solution of Ba/Eu was observed, the Eu²⁺ ions are located in the channels formed by 3 + 6 fluorine ions, occupying only one of the three metal sites of the Ba₇F₁₂Cl₂ structure.     

Darstellung und Struktur von Sn(NH2)2F2

Synthesis and Structure of Sn(NH₂)₂F₂ Diamido-difluoro-tin Sn(NH₂)₂F₂ can be produced by ammonolysis from (NH₄)₂SnF₆ at 613 K. The compound is a product from Sn(NH₃)₂F₄ formed during the ammonolysis reaction. Sn(NH₂)₂F₂ crystallizes in space group C2/m (No. 12) with lattice constants a = 1070.18(7), b = 325.38(3) pm, c = 505.02(3) pm and β = 105.728(3)° (V = 169.271(6) · 10⁶ pm³) containing two formula units per unit cell. Data refinement by the Rietveld method yields a Bragg R-value of R_Bragg = 0.0514 (Profile R-value R_wp = 0.177). Tin is octahedrally coordinated by two fluorine atoms and for amido groups. The octahedra are connected to one-dimensional strings by edge sharing. The NH₂ groups are in the bridging position whilst the fluorine atoms are terminal.     

A New Cu, Al Fluoride Disilicate CuAl2F2(Si2O7) and its Relations to Topaz

CuAl₂F₂(Si₂O₇) has been prepared by hydrothermal synthesis and its crystal structure was determined by single crystal X‐ray diffraction: space group Pnma, a = 8.8697(9), b = 14.084(2), c = 4.7553(5) Å, wR₂ = 0.056, R = 0.022. Cu²⁺ shows elongated square pyramidal coordination. Edge‐ and corner‐sharing [AlO₄F₂] octahedra with fluorine atoms in cis position form layers parallel to the ac plane. Along b these layers are linked by Si₂O₇ groups to form a three‐dimensional framework [Al₂F₂(Si₂O₇]^2–. In addition, the [CuO₅] pyramides connect two Al octahedra of neighbouring layers. The crystal structure is discussed as a derivative from topaz structure. The modular (or polysomatic) approach is used for this purpose, and for modelling hypothetical related compounds.     

ErF3‐reiche ternäre Erbiumfluoride mit den schweren Alkalimetallen: I. KEr3F10 und RbEr3F10

ErF₃‐Rich Ternary Erbium Fluorides with the Heavy Alkali Metals: I. KEr₃F₁₀ and RbEr₃F₁₀ The conversion of erbium trifluoride (ErF₃) with chlorides of the heavy alkali metals (ACl; A = K, Rb and Cs) at 700–800 °C in tantalum capsules sealed by arc‐welding surprisingly results in the formation of ErF₃‐rich ternary alkali‐metal erbium(III) fluorides with the compositions AEr₃F₁₀ (A = K and Rb) or CsEr₂F₇, respectively. The first‐mentioned compounds are characterized by high coordination numbers at the alkali‐metal cation (CN(A⁺) = 15 and 16) as well as by a uniform surrounding of the Er³⁺ cation (CN = 8, square antiprism). In KEr₃F₁₀ (cubic, Fm3m; a = 1154.06(7) pm, Z = 8) eight (F1)^? anions always arrange as a cube, whose six faces are each capped by an Er³⁺ cation. These [(F1)₈Er₆]¹⁰⁺ groups constitute a cubic closest sphere‐packing with K⁺ cations in all of the tetrahedral interstices. The [Er₆(μ₃‐F1)₈]¹⁰⁺ units are interconnected via the remainder fluoride anions (F2) to build up a three‐dimensional framework so that the characteristic [ErF₈]^5? polyhedra (d(Er³⁺?F^?) = 220 – 235 pm) emerge. In RbEr₃F₁₀ (hexagonal, P6₃mc; a = 818.43(5), c = 1336.54(8) pm, Z = 4) the analogous [ErF₈]^5? polyhedra (d(Er³⁺?F^?) = 219 – 237 pm) initially convene to triple groups [Er₃F₁₉]^10? through cis‐edge condensation, which are then further connected via F^? corners to arrange as a two‐dimensional network perpendicular to the c axis. Finally, the cross‐linking of these layers is achieved by common F^? vertices again, such that large cavities apt to take up the Rb⁺ cations are formed. A second part of these series will report on the syntheses and crystal structures of the ErF₃‐poorer AEr₂F₇‐type representatives with A = K, Rb and Cs.     

Enantioselective Aziridination of Cyclic Enals Facilitated by the Fluorine‐Iminium Ion Gauche Effect

The enantioselective, organocatalytic aziridination of small, medium and macro‐cyclic enals is reported using (S)‐2‐(fluorodiphenyl methyl)‐pyrrolidine. Central to the reaction design is the reversible formation of a β‐fluoroiminium ion intermediate, which is pre‐organised on account of the fluorine‐iminium ion gauche effect. This conformational effect positions the fluorine substituent synclinal‐endo to the electropositive nitrogen centre thus benefiting from favourable stereoelectronic and electrostatic interactions (σ_C?H→σ_C?F*; F^δ?…?N⁺). Consequently, one of the shielding groups on the fluorine‐bearing carbon atom is positioned above the π‐system, forming the basis of an enantioinduction strategy. Treatment of this intermediate with a “nitrene” source furnished a series of novel, optically active aziridines (e.r. up to 99.5:0.5). Further derivatisation of the product aziridines gives facile access to various amino acid derivatives, including β‐fluoroamino acids. Crystallographic analyses of both the aziridines and their derivatives are disclosed.     

Radiative lifetimes of the Rb(n 2 F)(n=6, 7, 8) states measured with the stepwise dipole-quadrupole excitation scheme

We report measurements of lifetimes of the Rb(n ² F)(n=6, 7, 8) states performed in a vapour cell. TheF-states were excited in a two-step sequence of an electric-dipole transition followed by an electric-quadrupole transition. Single photon counting was used for detection. The results are: (6² F)=171(4), (7² F)=262(15), (8² F)=387(12) (in ns). These lifetimes, have been compared with theoretical values given by different authors. An estimate of the cross sections for quenching due to collisions with ground-state Rb atoms is also given.This work was supported by the Polish Committee for Scientific Research under grant No. 2 2341 92 03     

Die Kristallstrukturen von (DDI)2[Sb2F6O] und (DDI)2[Sb3F7O2] (DDI = 1, 3‐Diisopropyl‐4, 5‐dimethylimidazolium) — Ein Beitrag zur Hydrolyse von SbF3 [1]

The Crystal Structures of (DDI)₂[Sb₂F₆O] and (DDI)₂[Sb₃F₇O₂] (DDI = 1,3‐Diisopropyl‐4,5‐dimethylimidazolium) — a Contribution to the Hydrolysis of SbF₃ [1] The salts (DDI)₂[Sb₂F₆O] ( 2 ) and (DDI)₂[Sb₃F₇O₂] ( 3 ), (DDI = 1,3‐diisopropyl‐4,5‐dimethylimidazolium) are obtained by hydrolysis of C₁₁H₂₀N₂SbF₃ ( 1 ). The anion [Sb₂F₆O]^2? consists of two SbF₂ fragments linked by a symmetrical oxygen bridge and two unsymmetrical fluorine bridges to form a distored ψ‐octahedral coordination sphere at the antimony atoms. In [Sb₃F₇O₂]^2?, two SbF₂ units are linked by a symmetrical fluorine bridge, while the third antimony atom is connected with each SbF₂ fragment by a symmetrical oxygen and an unsymmetrical fluorine bridge. The antimony atoms adopt the centres of strongly distored ψ‐polyhedra.     

Characterization of Mercury – Humic Acids Interaction by Potentiometric Titration with a Modified Carbon Paste Mercury Sensor

Stability constant for mercury binding by commercial and natural humic acids (HA) were determined using a new potentiometric mercury(II) sensor based on dithiosalicylic acid modified carbon paste electrode. The sensor present a high selective and sensitive response to mercury(II) ions, and a low detection limit of 1.8×10^?8 M. The potentiometric titrations curves of humic acids against mercury(II) ions were modeled. For 1.00×10^?7 to 3.00×10^?4 M mercury(II) ion concentration levels the results are consistent with the presence of two different binding sites in the humic acid macromolecule. The strongest binding sites (log K₁ ranging from 10.1 to 6.8) are probably due to interaction with carboxylic acid and amine groups in the molecule, whereas weakest binding sites (log K₂ ranging from 8.8 to 4.5) can be associated to phenolic groups.     

Nickel(0) Complexes with Fluorinated Alkyne Ligands and their Reactivity towards Semihydrogenation and Hydrodefluorination with Water

The current work describes the synthesis and full characterization of zerovalent nickel complexes of the type [(dippe)Ni(η²‐C,C‐F_n‐alkyne)] (dippe=1,2‐bis(di‐isopropylphosphino‐ethane), F_n‐alkyne=fluorinated aromatic alkyne, n=1, 3, 5; 3a , 3b , 3c ) and [{(dippe)Ni}₂(μ²‐C,C‐F_n‐alkyne)] ( 4 ). Reactions with complexes 3a , 3b , 3c , and water as the hydrogen source, yield selective semihydrogenation of the bound alkyne to the corresponding alkene, accompanied by partial hydrodefluorination of the aromatic ring. Different alkynes were tested; on using the alkyne with five fluorine atoms over the aromatic ring, partial defluorination was achieved under the mildest reaction conditions, followed in reactivity by the alkyne with three fluorine atoms. The alkyne with only one fluorine atom was barely defluorinated. The use of triethylsilane as a sacrificial hydride source resulted in an overall increase in reactivity towards defluorination.     

The transformation of Sn(ND3)2F4 into Sn(ND2)2F2. Synthesis and neutron crystal structure determination of Sn(ND2)2F2

Diamido-difluoro-tin Sn(ND₂)₂F₂ can be produced by ammonolysis from (NH₄)₂SnF₆ at 633 K. The compound is a product formed from Sn(ND₃)₂F₄ during the ammonolysis reaction. Sn(ND₂)₂F₂ isostructural with Sn(NH₂)₂F₂ crystallizes in space group C2/m with lattice constants a = 1072.92(7), b = 325.97(1) pm, c = 505.79(4) pm and β = 105.713(6) ° (V = 170.28(1) ·10⁶ pm³) containing two formula units per unit cell. Data refinement by the Rietveld method of neutron time-of-flight data collected at POLARIS yields a weighted profile R-value R_wp = 0.022. Tin is octahedrally coordinated by two fluorine atoms and four amido groups. The octahedra are connected to one-dimensional chains by edge sharing. The ND₂ groups are in the bridging position whilst the fluorine atoms are terminal. Nearly linear (175.2(4) °) and angular (134.35(8) °) N-D···F hydrogen linkages connect the chains.     

Fluorinated α-Diimine Nickel Mediated Ethylene (Co)Polymerization

Fluorine substituents in transition metal catalysts are of great importance in olefin polymerization catalysis; however, the comprehensive effect of fluorine substituents is elusive in seminal late transition metal α-diimine catalytic system. In this contribution, fluorine substituents at various positions (ortho-, meta-, and para-F) and with different numbers (F_n; n=0, 1, 2, 3, 5) were installed into the well-defined N-terphenyl amine and thus were studied for the first time in the nickel α-diimine promoted ethylene polymerization and copolymerization with polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity, polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given. As a notable result, the ortho-F substituted α-diimine nickel catalyst produced highly linear polyethylenes with an extremely high molecular weight (M_w=8703 kDa) and a significantly low degree of branching of 1.4/1000 C; however, the meta-F and/or para-F substituted α-diimine nickel catalysts generated highly branched (up to 80.2/1000 C) polyethylenes with significantly low molecular weights (M_w=20-50 kDa).     

Röntgenstrukturanalytische Untersuchungen von Diazadiphosphetidinen

X‐Ray Structure Analysis of Diazadiphosphetidines Various diazadiphosphetidines are synthesized by a modified Kirsanov reaction and subjected to X‐ray crystal structure analysis, the results of which show steric hindrance in the cyclohexyl‐substituted compound 4 . A comparison of its structure to that of the fluorine compound 12 shows that the steric hindrance occurs only in the case of chlorophosphoranes. During the Kirsanov reaction with aliphatic amines branched at the α‐position, a further reaction is observed if the amine is added in excess. The phosphonium salt 11 is characterized by ¹H‐, ¹³C‐ and ³¹P‐NMR‐spectra, FAB‐mass spectrum, elemental analysis and X‐ray crystal structure analysis.     

Influence of stereoelectronic effects on the 1JC─F spin–spin coupling constant in fluorinated heterocyclic compounds

The Perlin effect and its analog for fluorinated compounds (the fluorine Perlin-like effect) manifest on one-bond C─H (C─F for the fluorine Perlin-like effect) spin–spin coupling constants (SSCCs) in six-membered rings. These effects can be useful to probe the stereochemistry (axial or equatorial) of the C─H and C─F bonds, respectively. The origin of these effects has been debatable in the literature as being due to hyperconjugative interactions, dipolar effects, and induced current density. Accordingly, a variety of model compounds has been used to probe such effects since the cyclohexanone carbonyl group and the endocyclic heteroatom lone pairs play different roles on the above-mentioned effects. Thus, the ¹J_C─F SSCC in fluorinated lactams and lactones were theoretically studied to gain further insight on the nature of the fluorine Perlin-like effect. In addition, because the intramolecular α-effect has recently gained attention for its importance in the reactivity and stereoelectronic interactions in peroxide compounds, some fluorinated 1,2-dioxanes and 1,2-dithianes were studied to evaluate the role of the α-effect on the behavior of ¹J_C─F SSCCs. Differently from fluorinated ketones and ethers, the fluorine Perlin-like effect in the amides and esters cannot be explained by hyperconjugative or dipolar interactions alone, because the resonance in these groups affect the ¹J_C─F values. The O─O and S─S-containing systems exhibit a strong fluorine Perlin-like effect, but unlike the α-effect, this behavior cannot be explained neither by hyperconjugation nor by dipolar interactions alone; the spatial proximity of the C─F and O─O/S─S bonds is proposed to affect the magnitude of the ¹J_C─F SSCC.     

Fluorine addition to polychlorinated and polybrominated ethenes and arenes using vanadium pentafluoride

Reaction of vanadium pentafluoride with trichloroethene, tetrabromoethene, hexachlorobenzene, and octachloronaphthalene at −20 to 50 °C gave products from fluorine addition, CFCl₂CFClH, C₂Br₄F₂, C₆Cl₆F₆, and C₁₀Cl₈F₈, respectively. The fluorine addition to pentachloropyridine and hexabromobenzene was accompanied by the partial replacement of halogen atoms by fluorine and led to products C₅Cl₄F₅N and C₆Br₄F₈, respectively.     

Luminescence de l'europium divalent dans les composés α- et β-RbLu3F10

The effect of the crystal structure upon the luminescence of the divalent europium within the RbLu₃F₁₀ dimorphous matrix has been investigated. The obtained results essentially show that the difference between the rubidium coordination numbers in both α- and β-RbLu₃F₁₀ phases (15 or 16 and 8 or 10 respectively) is responsible for the change over from a 4f⁷ → 4f⁷ emission to a 4f⁶5d¹ → 4f⁷ emission.     

Constitution moléculaire d' α,ω-difluoro-μ-oxo-poly(méthylphosphanoxy diméthylsilanes): Mise en evidence d'une forte tendance à l'alternance régulière des centres siliciés et phosphorés à l'equilibre

The purpose of this study was to gain a closer knowledge of the molecular constitution of the linear fluorine-terminated oxygen-bridged methylphosphanoxy/dimethylsilane polymers, for example, to find evidence for preferential sorting (or, on the contrary, for random scattering) of the substituents and building units. The title polymers were prepared by reaction of MeP(O)F₂ with cyclic dimethylsiloxanes (Me₂SiO)_n (n = 3 or 4). An equilibrium is reached in the redistribution of fluorine vs. bridging oxygen atoms among the phosphorus and silicon-based centers, and among the resulting building units, after about 2 months at 120°C. The excellent resolution of the ¹H-NMR spectra (Fig. 2), even at 60 MHz, allowed identification of seventeen different fragments (Table II). Nineteen equilibrated samples of varied overall compositions (R = F/(Si + P); R′ = P/(Si + P)) have been analyzed (Table IV), and their molecular constitution is described by a set of four basic constants. The fundamental features which govern the structure of these polymers are as follows. (a) The regular (Si-O-P) alternation of the two different centers, which is thermodynamically favored, as shown by the linkage constant K₀ = [Si-O-Si][P-O-P]/[Si-O-P]² ? 10⁴, which describes the sorting of the silicon and phosphorus atoms on the bridging oxygens, and which deviates by four orders of magnitude from its random value of 0.25. (b) A somewhat surprising lack of preferential distribution of fluorine and oxygen between the two centers (K_I = [MeP(O)F₂][Me₂SiO_1/2]₂/[Me₂SiF₂]-[MeP(O)(O_1/2)₂]) differs little from (a), which contrasts with the preferential affinity of fluorine for silicon and oxygen for phosphorus (K_I ? 10⁷) that was found when F atoms and OCH₃ groups were exchanged between the same centers. (c) The sorting of the fluorine atoms and oxygen bridges on each center, to give neso molecules and the terminal and medium building units, resulting in a slight preference for the formation of the terminal units, as expressed by