Thermodynamics of interactions between organic ammonium ions and sulfonatocalixarenes

Calorimetric titration and NMR experiments in aqueous phosphate buffer (pH 7.2) at 298.15 K have been done to determine the binding mode, complex stability constants and thermodynamics (ΔG°, ΔH°, and TΔS°) for 1:1 inclusion complexation of water-soluble calix[n]arenesulfonates (CnAS, n = 4 and 6) and thiacalix[4]arene tetrasulfonate (TCAS) with acethylcholine, carnitine, betaine and benzyltrimethylammonium ion. The results show the inclusion complexations are driven by enthalpy (ΔH° < 0), accompanied by negative entropic changes (ΔS° < 0). The binding affinities (C4AS > C6AS > TCAS) are discussed from the viewpoint of CH-π/π-π interactions, electrostatic interactions and size/shape-fit relationship between host and guest.     

Zn(II), Cd(II) and Hg(II) complexes of 8-aminoquinoline.: Structure,spectra and photoluminescence property

The reaction of 8-aminoquinoline (8-aq) with M(NO₃)₂ and M(ClO₄)₂ (where M = Zn, Cd and Hg) has synthesized complexes of the composition [M(8-aq)₂(H₂O)₂](X)₂ (X = NO₃, ClO₄) whereas MCl₂ has isolated M(8-aq)Cl₂ type non-ionic compounds. The reaction of M(OAc)₂, 8-aq and NaN₃/NH₄CNS in a 1:1:2 mole ratio has separated polynuclear complexes of the composition [M(8-aq)(Y)₂]_n (Y = N₃, NCS). The complexes have been characterized by spectroscopic data and have been structurally confirmed by single crystal X-ray diffraction study in some representative cases. The X-ray structure of [Zn(8-aq)₂(H₂O)₂](NO₃)₂ shows C–H–π, and π–π interactions and forms a H-bonded sheet (with interactions between the oxygen of NO₃ and C(9)–H of 8-aq/coordinated H₂O). A novel one-dimensional cadmium(II) azido complex, [Cd(8-aq)(N₃)₂]n (9), in which the azido takes on an end-on (EO) bridging mode, has been synthesized and characterized. The presence of π–π interactions result in a supramolecular two-dimensional behaviour for the structure. The complexes are photoluminescent at room temperature.     

Facile one-pot synthesis of a photo patternable anthracene polymer

A polycyclic aromatic compound, anthracene, was covalently connected through a methylene bridge via Friedel-Crafts alkylation reaction. Thus, a highly fluorescent anthracene polymer (PMAn) linked by a methylene unit was prepared in one step to produce a conjugated-nonconjugated spacer-type polymer through its reaction with chloromethyl methyl ether (CME) and FeCl₃ at 0 °C. The resultant polymer was soluble in organic solvents and showed significantly higher fluorescence (quantum yield = 0.80) compared to monomeric anthracene, 9-methylanthracene, in chloroform solution. Fluorescent thin films of PMAn as solid media were prepared with high film uniformity. The emission of the film was extinguished when the film was exposed to a UV source, due to the photodimerization of anthracene unit. A fluorescent gap electrode pattern was formed on the polymer film-forming average step depth of 8 nm and 14 nm, after 30 and 60 min irradiation with a UV light, respectively. The photo patternable fluorescent polymer afforded a convenient method of image formation and patterning.     

Preparation, crystal structure, and spectroscopic, chemical, and electrochemical properties of (2E,4E)-4-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1,3-butadiene compared with those of (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene

Wittig reaction of 3-[4-(dimethylamino)phenyl]propanal (5) with (3-guaiazulenylmethyl)triphenylphosphonium bromide (4) in ethanol containing NaOEt at 25 °C for 24 h under argon gives the title (2E,4E)-1,3-butadiene derivative 6E in 19% isolated yield. Spectroscopic properties, crystal structure, and electrochemical behavior of the obtained new extended π-electron system 6E, compared with those of the previously reported (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene (12), are documented. Furthermore, reaction of 6E with 1,1,2,2-tetracyanoethylene (TCNE) in benzene at 25 °C for 24 h under argon affords a new Diels-Alder adduct 8 in 59% isolated yield. Along with spectroscopic properties of the [π4+π2] cycloaddition product 8, the crystal structure, possessing a cis-3,6-substituted 1,1,2,2-tetracyano-4-cyclohexene unit, is shown. Moreover, reaction of 6E with (E)-1,2-dicyanoethylene (DCNE) under the same reaction conditions as the above gives no product; however, this reaction in p-xylene at reflux temperature (138 °C) for four days under argon affords a new Diels-Alder adduct 9 in 54% isolated yield. Although reaction of 6E with DCNE in toluene at reflux temperature (110 °C) for four days under argon provides 9 very slightly, reaction of 6E with dimethyl acetylenedicarboxylate (DMAD) in toluene at reflux temperature for two days under argon yields a new Diels-Alder adduct 10, in 58% isolated yield, which upon oxidation with MnO₂ in CH₂Cl₂ at 25 °C for 1 h gives 11, converting a (CH₃)₂N-4″ into CH₃NH-4″ group, in 37% isolated yield. The crystal structure of 11 supports the molecular structure 10 possessing a partial structure cis-3,6-substituted 1,2-dimethoxycarbonyl-1,4-cyclohexadiene. The title basic studies on the above are reported in detail.     

Photodimerization of Solid Pleiadiene; Isomerization and Cycloreversion of the Dimer

Irradiation (λ>400 nm) of solid pleiadiene ( 1 ) yields a single, head-to-head [_π4_s+_π4_s]-photodimer ( 2 ) the structure of which was determined by X-ray analysis. The formation of 2 is entirely suppressed at 77 K, since properly oriented pairs of molecules arise only from thermal disorder in crystals of 1 . Upon pyrolysis (80°), the strained photodimer 2 rearranges to the [_π2_s + _π4_s] dimer 3 by a ‘forbidden’ suprafacial [1,3]-C-atom migration. Both 2 and 3 are reconverted to 1 by UV. irradiation in solution, but the latter, ‘forbidden’ photoreaction is suppressed at 77 K . Discrepancies of the experimental observations with the predictive schemes of Kaupp or Michl are discussed.     

Near-infrared solid-state fluorescent naphthooxazine dyes attached with bulky dibutylamino and perfluoroalkenyloxy groups at 6- and 9-positions

No solid-state fluorescence is observed for 9-(diethylamino)benzo[a]phenoxazin-5-one (Nile Red). However, 9-dibutylamino-6-{perfluoro[4-methyl-3-(1-methylethyl)-2-penten]-2-oxy}benzo[a]phenoxazin-5-one showed fluorescence maximum at 717 nm in solid state with fluorescence quantum yield 0.024. X-ray crystallographic analysis suggests that prevention of network π−π interactions by the bulky fluorine-containing and dibutylamino groups is essential to show solid-state fluorescence.     

Synthesis of 1,2-dihydroisoquinolines via the reaction of ortho-alkynylarylimines with bis-π-allylpalladium

The reaction of the ortho-alkynylarylimines 1 with allyltributylstannane and allyl chloride in the presence of allylpalladium chloride dimer (5 mol %) and Cu(OAc)₂ (20 mol %) in CH₃CN at 50 °C gave the 1,4-diallyl-1,2-dihydroisoquinolines 2 in good yields. Most probably, the reaction proceeds through tandem bis-allylation of the imine-alkyne functional groups with bis-π-allylpalladium.     

Crystal structures of anti- and syn-9,10-di(1′-naphthyl)anthracene and isomerization in solid state

9,10-Di-(1′-naphthyl)anthracene is often used as electroluminescence materials in organic light-emitting diodes. Because of the hindered rotation about the σ-bond between naphthyl and anthracene chromophore, two possible stereoisomers can be isolated. HPLC, ¹H NMR, and ¹³C NMR spectra gave two different sets of peaks and the X-ray single crystal analysis confirmed the structures of the two isomers, anti and syn. syn was more soluble than anti in THF as well as toluene and the thermal properties of the two were quite different. Differential scanning calorimetry study and HPLC analysis showed that the isomerization between anti and syn in the solid state took place at >370 °C.     

Synthesis and structure of the monometallic cationic complex [Cp(CO)2Fe{η-(CH2CHCH2CH3)}]PF6 (Cp = η-C5H5)

The bimetallic carbocation complex [{Cp(CO)₂Fe}₂(μ-C₄H₇)]PF₆ reacted with trifluoroacetic acid to give the mononuclear cationic complex [Cp(CO)₂Fe{η²-(CH₂CHCH₂CH₃)}]PF₆, which formed yellow orthorhombic crystals in the space group P2₁2₁2₁ with a = 7.652(4), b = 13.422(7), c = 14.037(7); α = β = γ = 90.00 and Z = 4. The carbocation is coordinated to the metal in a η²-fashion forming a chiral metallacyclopropane type structure. The β-CH carbon (C9) is disordered over two positions (C9A and C9B), each having about 50% occupancy. This is attributed to there being both the R and S enantioface isomers in equal amounts in the crystal sample. NMR data indicate that the metallacyclopropane structure observed in the solid state is preserved in solution.     

Magnetic single-component molecular conductors exhibiting strong π-d interactions

Single-component molecular conductors [M(tmdt)₂] (tmdt = trimethylenetetrathiafulvalenedithiolate; M = Ni, Au, Pt, Cu), exhibit a variety of electromagnetic properties, which originate from the differences of the metal’s d-orbitals role in the band structure formation. The [Au(tmdt)₂] crystal undergoes an antiferromagnetic transition at 110 K, while maintaining a metallic state at lower temperatures. The Au analog has a high magnetic transition temperature as compared to traditional magnetic molecular conductors due to the strong three-dimensional (3-D) structure and the contribution of the metal d-orbitals. The single-component molecular conductor, [Cu(tmdt)₂], with π- and d-like frontier orbitals is isostructural with other metallic [M(tmdt)₂] systems (M = Ni, Pt, Au). The Cu(tmdt)₂ molecule is planar, which strikingly contrasts the tetrahedral coordination of Cu(dmdt)₂ (dmdt = dimethyltetrathiafulvalenedithiolate) with similarly extended TTF type ligands. Interestingly, unlike other [M(tmdt)₂] with metallic behavior, [Cu(tmdt)₂] shows semiconducting behavior at room temperature (σ(RT) = ∼7 S cm⁻¹). The RT conductivity increased linearly with increased pressure to 110 S cm⁻¹ at 15 kbar despite the compressed pellet sample. The magnetic susceptibility indicates one-dimensional (1-D) Heisenberg behavior with J = 117 cm⁻¹ and shows antiferromagnetic ordering at 13 K. The [Cu(tmdt)₂] is a new multi-frontier π-d system, which introduces a d(σ)-type frontier orbital around the Fermi level of the π-like metal bands.     

Crystal structures,optical properties and theoretical calculation of novel two-photon polymerization initiators

Three novel A–π–D–π–A type compounds 3,6-bis[2-(4-pyridyl)ethenyl]-9-ethylcarbazole (1), 3,6-bis[2-(2-pyridyl)ethenyl]-9-ethylcarbazole (2), 3,6-bis[2-(4-pyridyl)ethenyl]-9-ethylpyridylcarbazole (3) were conveniently synthesized by Pd-catalyzed Heck coupling methodology and characterized by single crystal X-ray diffraction determination. One-photon fluorescence, one-photon fluorescence quantum yields, one-photon fluorescence lifetime, and two-photon fluorescence have been investigated. The calculated two-photon absorption cross-sections for the three initiators by quantum chemical method are as high as 947, 943 and 815 × 10⁻⁵⁰ cm⁴ s photon⁻¹, respectively. Two-photon initiating polymerization microfabrication experiments have been carried out and the possible polymerization mechanism was also discussed. The results show that they are good two-photon absorbing chromophores and effective two-photon photopolymerization initiators.     

A novel series of iridium complexes with alkenylquinoline ligands: Theoretical study on electronic structure and spectroscopic property

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of a novel series of neutral iridium(III) complexes with cyclometalated alkenylquinoline ligands [(C^N)₂Ir(acac)] (acac = acetoylacetonate; C^N = 2-[(E)-2-phenyl-1-ethenyl]pyridine (pep) 1; 2-[(E)-2-phenyl-1-ethenyl]quinoline (peq) 2; 1-[(E)-2-phenyl-1-ethenyl]isoquinoline (peiq) 3; 2-[(E)-1-propenyl]pyridine (pp) 4; 2-[(E)-1-fluoro-1-ethenyl]pyridine (fpp) 5) were investigated by DFT and CIS methods. The highest occupied molecular orbital is composed of d(Ir) and π(C^N) orbital, while the lowest unoccupied molecular orbital is dominantly localized on C^N ligand. Under the TD-DFT with PCM model level, the absorption and phosphorescence in CH₂Cl₂ media were calculated based on the optimized ground and triplet excited state geometries, respectively. The calculated lowest-lying absorptions at 437 nm (1), 481 nm (2), 487 nm (3), 422 nm (4), and 389 nm (5) are attributed to a {[d_x²-y²(Ir) + d_xz(Ir) + π(C^N)] → [π∗(C^N)]} transition with metal-to-ligand/intra-ligand charge transfer (MLCT/ILCT) characters, and the calculated phosphorescence at 582 nm (1), 607 nm (2), 634 nm (3), 515 nm (4), and 491 nm (5) can be described as originating from the ³{[d_x²-y²(Ir) + d_xz(Ir) + π (C^N)] [π∗(C^N)]} excited state with the ³MLCT/³ILCT characters. The calculated results revealed that the phosphorescent color of these new Ir(III) complexes can be tuned by changing the π-conjugation effect strength of the C^N ligand.     

Heterometallic Pt-Ag and Pt2Ag transition metal complexes

Complexes of type {cis-[Pt](μ-σ,π-CCPh)₂}AgX (3a, [Pt] = (bipy′)Pt, X = FBF₃; 3b, [Pt] = (bipy′)Pt, X = FPF₅; 3c, [Pt] = (bipy)Pt, X = OClO₃; 3d, [Pt] = (bipy′)Pt, X = BPh₄; bipy′ = 4,4′-dimethyl-2,2′-bipyridine; bipy = 2,2′-bipyridine) are accessible by combining cis-[Pt](CCPh)₂ (1a, [Pt] = (bipy′)Pt; 1b, [Pt] = (bipy)Pt) with equimolar amounts of [AgX] (2a, X = BF₄; 2b, X = PF₆; 2c, X = ClO₄; 2d, X = BPh₄). In 3a-3d the platinum(II) and silver(I) ions are connected by σ- and π-bonded phenyl acetylide ligands. When the molar ratio of 1 and 2 is changed to 2:1 then trimetallic [{cis-[Pt](μ-CCPh)₂}₂Ag]X (8a, [Pt] = (bipy)Pt, X = BF₄; 8b, [Pt] = (bipy′)Pt, X = PF₆; 8c, [Pt] = (bipy)Pt, X = BF₄) is produced. The solid state structure of 8a was determined by single X-ray crystal structure analysis. In 8a the silver(I) ion is embedded between two parallel oriented cis-[Pt](CCPh)₂ units. Within this structural arrangement the phenyl acetylides of individual [Pt](CCPh)₂ entities possess a μ-bridging position between Pt(II) and Ag(I). In addition, a very weak dative Pt → Ag interaction is found (Pt-Ag 2.8965(3) Å). The respective silver carbon distances Ag-C_α (2.548(7), 2.447(7) Å) and Ag-C_β (3.042(7), 2.799(8) Å)(PtC_αC_βPh) confirm this structural motif.Complexes 8a-8c isomerize in solution to form trimetallic [{cis-[Pt](μ-σ,π-CCPh)₂}₂Ag]X (9a, [Pt] = (bipy)Pt, X = BF₄; 9b, [Pt] = (bipy′)Pt, X = PF₆; 9c, [Pt] = (bipy)Pt, X = ClO₄). In the latter molecules the organometallic cation [{cis-[Pt](μ-σ,π- CCPh)₂}₂Ag]⁺ is set-up by two nearly orthogonal positioned [Pt](CCPh)₂ entities which are hold in close proximity by the group-11 metal ion. Within this assembly all four PhCC units are η²-coordinated to silver(I). A possible mechanism for the formation of 9 is presented.     

Oligothiophene-2-yl-vinyl bridged mono- and binuclear ruthenium(II) tris-bipyridine complexes: Synthesis, photophysics, electrochemistry and electrogenerated chemiluminescence

A series of mono- and binuclear ruthenium(II) tris-bipyridine complexes tethered to oligothienylenevinylenes have been synthesized and characterized by ¹H NMR, ¹³C NMR and TOF-MS spectrometry. Photophysics, electrochemistry and electrogenerated chemiluminescence (ECL) properties of these complexes are investigated. The electronic absorption spectra of the mononuclear ruthenium complexes show a significant red shift both at MLCT (metal-to-ligand charge transfer) and π-π^∗ transitions of oligothienylenevinylenes with increase in the number of thiophenyl-2-yl-vinyl unit. For the binuclear complexes these two absorption bands are overlapped. All the metal complexes have very weak emission compared to that of the reference complex Ru(bpy)²⁺₃. The first reduction potentials of all mononuclear ruthenium complexes are less negative than that of Ru(bpy)²⁺₃, due to the moderate electron-withdrawing effect of oligothienylenevinylenes. For binuclear ruthenium complexes, only one Ru(II/III) oxidation peak (E_1/2 = 0.96 V vs. Ag/Ag⁺) was observed, suggesting a weak interaction between two metal centers. Three successive reduction processes of bipyridine ligands are similar among all ruthenium complexes except for RuTRu, which has a very sharp peak owing to the accumulation of neutral product on the electrode surface. All these ruthenium complexes exhibited different ECL property in CH₃CN solution without any additional reductant or oxidant. For three mononuclear ruthenium complexes, the ECL intensity strengthens with increase in the number of thiophene-2-yl-vinyl unit. However, the ECL efficiency dramatically decreased in the binuclear ruthenium complexes. The ECL efficiencies of all the reported complexes do not exceed that of Ru(bpy)²⁺₃, where the ECL efficiency decreases in the order of RuTRu > Ru3T > Ru2T > RuT > Ru2TRu (RuT,bis-2,2′-bipyridyl-(4-methyl-4′-(2-thienylethenyl)-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru2T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru3T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}}-2,2′-bipyridine) ruthenium dihexafluorophosphate; RuTRu, bis-2,2′-bipyridyl-ruthenium-bis-[2-((E)-4′-methyl-2, 2′-bipyridinyl-4)-ethenyl]-thienyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate; Ru2TRu, bis-2,2′-bipyridyl-ruthenium-(E)-1,2-bis-{2-[2-((E)-4′-methyl-2,2′-bipyridinyl-4)-ethenyl]-thienyl}-ethenyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate).     

Synthesis of a pillar[5]arene dimer by co-oligomerization and its complexation with n-octyltrimethyl ammonium hexafluorophosphate

A pillar[5]arene dimer was successfully prepared by co-oligomerization of 1,4-dimethoxybenzene and 1,6-bis(4-butoxyphenoxy)hexane. It was demonstrated that it forms 1:2 complexes with n-octyltrimethyl ammonium hexafluorophosphate both in chloroform and the gaseous state. A Scatchard plot indicated that the complexation between them is statistical with an average association constant of 6.0 (±0.4) × 10² M⁻¹ in chloroform.     

High temperature synthesis of some strontium and barium 2,6-dibenzylphenolates

Direct treatment of HOdbp (= 2,6-dibenzylphenol) with strontium or barium metal in the absence of solvent at high temperature provides the corresponding phenolates Sr(Odbp)₂ and Ba(Odbp)₂. Recrystallisation of Ba(Odbp)₂ from THF gave a good yield of the crystalline dimer [Ba(Odbp)₂(THF)]₂ · 2THF. Attempted recrystallisation of Sr(Odbp)₂ from THF mostly yielded microcrystalline material characterized as [Sr(Odbp)₂]_n but on one occasion gave a small crop of crystalline [Sr₉(Odbp)₈(O₂SiMe₂)₄(OH)₂(THF)₆(OH₂)₂] · 6THF derived from the adventitious reaction of Sr(Odbp)₂ with dimethylsilicone grease ({OSiMe₂}_∞). In the solid-state [Ba(Odbp)₂(THF)]₂ · 2THF displays significant intramolecular Ba?π-arene interactions with the pendant benzyl substituents. [Sr₉(Odbp)₈(O₂SiMe₂)₄(OH)₂(THF)₆(OH₂)₂] · 6THF features a square prismatic [Sr(O₂SiMe₂)₄]⁶⁻ core capped by two inverse crown-like square [Sr₄(Odbp)₄(OH)(L)₄]³⁺ units, where L = OH₂ or THF, that are staggered with respect to the cuboidal core.     

Gas-phase electron diffraction study of cyclic dimer of dimethylphosphinic acid (Me2P(O)OH)2 using quantum chemical data and a priori force field

The molecular structure of the hydrogen bonded cyclic dimer of dimethylphosphinic acid (Me₂P(O)OH)₂ was determined by gas-phase electron diffraction (GED) at 433 K. The presence of monomer cannot be determined at this temperature within the error limits for the GED method. Structural analysis was performed with consideration of non-linear kinematic effects at the first-order level of perturbation theory (h1). The vibrational characteristics of internuclear distances were calculated from a priori scaled quantum chemical (RHF/6-311G**) force field. The analysis aided by a constraint based on the RHF/6-311G** calculations yielded the following r_h1-parameters of the C₂-symmetry dimer configuration: PO 1.497(3); P-O 1.573(4); P-C 1.806(1) and 1.811(1) Å; (C-H)_av. 1.109(3) Å; ∠O-PO 120(1)°. Unlike PO and P-O bonds, whose lengths in the gas phase and in the solid state differ insignificantly, the -O?O distance in the gas phase (r_h1 2.81(4) Å) is considerably longer than in the solid state (r_α 2.48(2) Å). The latter is in accordance with the conclusion based on the IR spectra that transition from gas to a solid sample leads to strengthening of the H-bonds. Due to its small contribution to the diffraction pattern, the donor O-H bond length (r_h1 0.99(1) Å) was forcedly bound up with the parameters of C-H bonds. With this assumption, the other geometrical parameters characterizing the H-bond fragment have the following r_h1 values: O?H 1.84(4) Å, ∠-OHO164(6)°, and ∠P-O-H 117(4)°. Conformational flexibility of the non-planar eight-atom ring of the dimer is experimentally verified by absence of any apparent peaks of the f(r) curve at the r-region of more than 4.2 Å.     

Conversion of pentynol to pentanone catalysed by Pd(II) metal centres

The cyclization of 3- or 4-pentyn-1-ol is catalysed by PdCl₂ or trans-[PdCl₂L₂] (L = R-camphorimine; R = Ph; Prⁱ; NMe₂) complexes at room temperature affording heterocyclic compounds, respectively, 2-methyl-2-pent-3-ynyloxy-tetrahydrofuran or 2-methyl-2-pent-4-ynyloxy-tetrahydrofuran which subsequently add water to give selectively 5-(2-methyl-tetrahydrofuran-2-yloxy)-pentan-2-one from both starting materials. By hydrolysis 5-(2-methyl-tetrahydrofuran-2-yloxy)-pentan-2-one undergoes ring cleavage to form 5-hydroxy-2-pentanone. The catalytic activity and selectivity of complexes trans-[PdCl₂L₂] (L = R-camphorimine) depend on the characteristics of the R group (NMe₂ > Prⁱ > Ph). The catalytic activity of PdCl₂ is comparable to that of trans-[PdCl₂L₂] (L = Ph-camphorimine) which is the less efficient catalyst.     

Adduct formation in LC-ESI-MS of nonylphenol ethoxylates: mass spectrometrical, theoretical and quantitative analytical aspects

The analysis of nonylphenol ethoxylate (A₉PEO_n) surfactants with LC-ESI-MS was investigated in a detailed study of the formation of different types of adducts. Part of the observations was explained by calculating their relative stabilities using molecular dynamics techniques.Strong differences in adduct formation behaviour were found for different oligomers.Beside the common sodium adducts, surfactant dimer adducts [2 × A₉PEO_1,2 + Na]⁺, adducts including a solvent molecule [A₉PEO_1,2 + MeOH + Na]⁺ and doubly charged adducts [A₉PEO_>11 + 2 × Na]²⁺ were found.Molecular dynamics calculations showed that the A₉PEO_n molecule wraps itself around the complexing sodium ion in a way that negative electronic charges on oxygen have optimum electrostatic interaction with this ion. van der Waals interactions between alkyl chains are of less importance for the stability of these adducts. Both [2 × A₉PEO_2,5 + Na]⁺ dimer and [A₉PEO_2,5 + Na]⁺ monomer adducts turned out to be stable from an energetic point of view with adducts of A₉PEO₅ being more stable than adducts of A₉PEO₂. Only for the monomer adduct the latter is in accordance with experimental observations.Consequences of the formation of several adducts per A₉PEO_n oligomer for the quantitative analysis of environmental samples were evaluated. In clean samples, it was found that the presence of short-chain A₉PEO_1,2 can cause an overestimation of long-chain A₉PEO_>2. In real environmental extracts, other processes like matrix effects have a stronger influence on the quantitative result, and therefore no significant influence of adduct formation processes could be observed. However, inclusion of [A₉PEO_1,2 + MeOH + Na]⁺ adduct signals does improve the detection limits of the two short-chain oligomers.Correct quantitative results are obtained when A₉PEO₁ and A₉PEO₂ are quantified separately, and longer oligomers with a molar calibration followed by correction of the average molar weight of the A₉PEO_>2 in the sample.     

Highly active new α-diimine nickel catalyst for the polymerization of α-olefins

A new silylated α-diimine ligand, bis[N,N′-(4-tert-butyl-diphenylsilyl-2,6-diisopropylphenyl)imino]acenaphthene 3, and its corresponding Ni(II) complex, {bis[N,N′-(4-tert-butyl-diphenylsilyl-2,6-diisopropylphenyl)imino]acenaphthene}dibromonickel 4, have been synthesized and characterized. The crystal structures of 3 and 4 were determined by X-ray crystallography. In the solid state, complex 4 is a dimer with two bridging Br ligands linking the two nickel centers, which have square pyramidal geometries. Complex 4, activated either by diethylaluminum chloride (DEAC) or methylaluminoxane (MAO) produces very active catalyst systems for the polymerization of ethylene and moderately active for the polymerization of propylene. The activity values are in the order of magnitude of 10⁷ g PE (mol Ni [E] h)⁻¹ for the polymerization of ethylene and of 10⁵ g PP (mol Ni [P] h)⁻¹ for the polymerization of propylene. NMR analysis shows that branched polyethylenes (PE) are obtained at room or higher temperatures and almost linear PE is obtained at 0 °C with 4/DEAC.