Polysulfonylamine. LVII. Zwei Silber(I)-di(organosulfonyl)-amide mit einer Silber-η2-Aryl- beziehungsweise einer Silber-Silber-Wechselwirkung: Kristallstrukturen von Silberdi(benzolsulfonyl)-amid-Wasser (1/0,5) und von wasserfreiem Silberdi(4-toluolsulfonyl)-amid

Polysulfonyl Amines. LVII. Two Silver(I) Di(organosulfonyl)-amides with Silver-η²-Aryl or Silver-Silver Interactions: Crystal Structures of Silver Di(benzenesulfonyl)amide-Water (1/0.5) and of Anhydrous Silver Di(4-toluenesulfonyl)-amide Crystals of [(PhSO₂)₂NAg(μ-H₂O)AgN(SO₂Ph)₂]_n ( 5 ) and [(4-Me? C₆H₄SO₂)₂NAgAgN(SO₂C₆H₄-4-Me)₂]_n ( 6 ) were obtained from aqueous solutions. The crystallographic data are for 5 (at ?95°C): monoclinic, space group C2/c, a = 2 743.8(5), b = 600.49(12), c = 1 664.5(3) pm, β = 101.143(15)°, V = 2.6908 nm³, Z = 8, D_x = 2.040 Mg m^?3; for 6 (at ?130°C): monoclinic, space group P2₁/n, a = 1 099.8(5), b = 563.7(3), c = 2 487.7(13) pm, β = 99.68(4)°, V = 1.5203 nm³, Z = 4, D_x = 1.888 Mg m^?3. In both crystals, the silver atom has a fivefold coordination. The structure of 5 displays [(RSO₂)₂N? Ag(μ-H₂O)Ag′? N(SO₂R)₂] units with Ag? N 226.9 pm, Ag? O 236.7 pm and Ag? O? Ag′ 95.3°; the water oxygen lies on a crystallographic twofold axis. These units are extended to two fused six-membered rings by intramolecular dative bonds (S)O → Ag′ and S(O)′ → Ag (249.3 pm). One phenyl group from each (PhSO₂)₂N moiety is η²-coordinated with its p-C and one m-C atom to a silver atom of a neighbouring bicyclic unit related by a glide plane to form infinite parallel strands (p-C? Ag 252.2, m-C? Ag 263.9 pm). The strands are interconnected into parallel layers through hydrogen bonds between H₂O and sulfonyl oxygens [O …? O(S) 276.1 pm]. These layers consist of a hydrophilic inner region containing metal ions, N(SO₂)₂ fragments and water molecules, and hydrophobic surfaces formed by phenyl groups. The structure of 6 features centrosymmetric [(RSO₂)₂N? Ag? Ag′? N(SO₂R)₂] units with two intramolecular dative bonds (S)O → Ag′ and (S)O′ → Ag (Ag? Ag′ 295.4, Ag? N 226.0, Ag? O 229.4 pm). These bi-pentacyclic units are associated by translation parallel to y into infinite strands by two dative (S)O → Ag bonds per silver atom (Ag? O 243.2 and 253.3 pm).     

Optical sensors for dissolved sulfur dioxide

Colorimetric sensing membranes for the determination of sulfur dioxide were developed and characterized. These films can be used for sensing trace amounts of sulfur dioxide both in the gas phase and in aqueous solutions. Lipophilic pH indicator ion pairs were immobilized in hydrophobic gas-permeable silicone and phenyl substituted ormosil. On exposure to SO₂ the films undergo a visually detectable color change from blue to yellow. No cross-sensitivity to pH and CO₂ was observed. Response times depend on the thickness of the sensing membranes, the indicator concentration in the film as well as on the respective SO₂ concentration. Membranes with response times of < 1 min (t₉₀) were developed. The sensitivity to sulfur dioxide depends on the pK_a of the indicator. An increase in the pK_a results in a lower detection limit. The new optical SO₂ sensors are chemically and mechanically stable and are easy to manufacture. The storage stability of the membranes is at least 7 months if stored in the dark. Received: 17 December 1997 / Revised: 12 June 1998 / Accepted: 15 June 1998     

K11[HSn(PWO34)2] · 27 H2O – Synthese und Struktur

K₁₁[HSn (PW O₃₄)₂] · 27 H₂O – Synthesis and Structure K₁₁[HSn (PWO₃₄)₂] · 27 H₂O 1 can be synthesized in an “one-pot reaction” from commercially obtainable educts (SnCl₂; Na₂HPO₄ · 7 H₂O, Na₂WO₄ · 2 H₂O) in high yields and has been characterized by elemental analysis, IR/Raman-, UV/Vis-spectroscopy as well as by X-ray crystal structure analysis. The example of 1 again demonstrates the validity of our working hypothesis, that polyoxometalates can be obtained by linking highly charged, transferable building blocks by cationic centres within the scope of an optimal charge control. For structural details see “Inhaltsübersicht”.     

Nanoscale vibrational analysis of single-walled carbon nanotubes

We use near-field Raman imaging and spectroscopy to study localized vibrational modes along individual, single-walled carbon nanotubes (SWNTs) with a spatial resolution of 10-20 nm. Our approach relies on the enhanced field near a laser-irradiated gold tip which acts as the Raman excitation source. We find that for arc-discharge SWNTs, both the radial breathing mode (RBM) and intermediate frequency mode (IFM) are highly localized. We attribute such localization to local changes in the tube structure (n, m). In comparison, we observe no such localization of the Raman active modes in SWNTs grown by chemical vapor deposition (CVD). The direct comparison between arc-discharge and CVD-grown tubes allows us to rule out any artifacts induced by the supporting substrate.     

Determination of benzothiazoles from complex aqueous samples by liquid chromatography-mass spectrometry following solid-phase extraction

A method was developed for the determination of benzothiazoles from municipal wastewater, which may originate from their use as corrosion inhibitors, vulcanization accelerators or fungicides. Extraction is performed by SPE using a polymeric sorbent, followed by LC-MS analysis with electrospray ionization. Due to the diversity of the analytes, two LC-MS runs are required: 2-aminobenzothiazole, benzothiazole and 2-methylthiobenzothiazole are detected in the positive ion mode, while benzothiazole-2-sulfonic acid (BTSA), 2-mercaptobenzothiazole and 2-hydroxybenzothiazole are determined in the negative ion mode. Limits of quantification range from 20 to 200 ng/L in treated wastewater. Reliable quantification with R.S.D.s below 25% is achieved by standard addition in a limited number of samples of each sample series. A significant reduction of matrix effects in positive electrospray ionization is achieved by reducing the flow directed into the ESI-interface. When applied to untreated municipal wastewater most analytes were found at concentrations in the high ng/L- to low microg/L-range with the most polar BTSA being the dominant compound of this class. Removal of benzothiazoles in biological wastewater treatment appears to be limited.     

Cis-/Trans-Isomerie bei Bis-(trisalkoxy)-hexavanadaten: cis-Na2[VO7(OH)6{(OCH2)3CCH2OH}2] · 8 H2O,cis-(CN3H6)3[VIVVO13{(OCH2)3CCH2OH}2] · 4,5 H2O und trans-(CN3H6)2[VO13{(OCH2)3CCH2OH}2] · H2O

Cis-/Trans-Isomerism of Bis-(trisalkoxy)-hexavanadates: cis-Na₂[V O₇(OH)₆{(OCH₂)₃CCH₂OH}₂] · 8 H₂O, cis-(CN₃H₆)₃[V^IVV O₁₃{(OCH₂)₃CCH₂OH}₂] · 4.5 H₂O and trans-(CN₃H₆)₂[V O₁₃{(OCH₂)₃CCH₂OH}₂] · H₂O Polyoxovanadates with distorted Lindquist-structure, in which six of the twelve μ₂-oxygen atoms are formally replaced by the oxygen atoms of two coordinated pentaerythritol ligands, can be prepared by a simple method in an aqueous medium. The “fully reduced”, six-fold protonated compound cis-Na₂[VO₇(OH)₆{(OCH₂)₃CCH₂OH}₂] · 8 H₂O ( 1 ), the mixed valence species cis-(CN₃H₆)₃[V^IVVO₁₃{(OCH₂)₃CCH₂OH}₂] · 4.5 H₂O ( 2 ) containing one localized V^IV centre and the “fully oxidized” compound trans-(CN₃H₆)₂[VO₁₃{(OCH₂)₃CCH₂ · OH}₂] · H₂O ( 3 ) have been synthesized and characterized by UV/VIS-, IR- and EPR-spectroscopy, by magnetic measurements, cyclic voltammetry and by a single-crystal X-ray structure analysis. The organic {(CH₂)₃CCH₂OH}³⁺-groups tend to cap the triangular faces formed by μ₂-oxygen atoms of the central approximately octahedral {V₆O₁₉}-unit. Therefore the anions of bis-(trisalkoxy)-hexavanadates can exist in a trans-form as well as in an isomeric cis-form referring to a “basic” plane of four vanadium atoms of the {V₆}-octahedron. The different relative positions of the ligands have a significant influence on the redox potentials of the compounds. For structural details see “Inhaltsübersicht”.     

Metal incorporation in modified PNA duplexes

Substitution of bipyridine for a nucleobase leads to modified peptide nucleic acid (PNA) single strands that are bridged in the presence of Ni2+ into a duplex containing a combination of hydrogen and coordinative bonds. CD experiments demonstrate that the duplex adopts a structure similar to that of an unmodified 10-bp PNA duplex, and UV melting experiments show a very sensitive dependence of the duplex stability on the substitution of a nucleobase pair with a pair of ligands or a metal-ligand alternative base pair.     

Cation-independent electron transfer between ferricyanide and ferrocyanide ions in aqueous solution

Electron transfer between Fe(CN)(6)(3-) and Fe(CN)(6)(4-) in homogeneous aqueous solution with K(+) as the counterion normally proceeds almost exclusively by a K(+)-catalyzed pathway, but this can be suppressed, and the direct Fe(CN)(6)(3)(-)-Fe(CN)(6)(4-) electron transfer path exposed, by complexing the K(+) with crypt-2.2.2 or 18-crown-6. Fe((13)CN)(6)(4-)-NMR line broadening measurements using either crypt-2.2.2 or (with extrapolation to zero uncomplexed [K(+)]) 18-crown-6 gave consistent values for the rate constant and activation volume (k(0) = (2.4 +/- 0.1) x 10(2) L mol(-1) s(-1) and Delta V(0) = -11.3 +/- 0.3 cm(3) mol(-1), respectively, at 25 degrees C and ionic strength I = 0.2 mol L(-1)) for the uncatalyzed electron transfer path. These values conform well to predictions based on Marcus theory. When [K(+)] was controlled with 18-crown-6, the observed rate constant k(ex) was a linear function of uncomplexed [K(+)], giving k(K) = (4.3 +/- 0.1) x 10(4) L(2) mol(-2) s(-1) at 25 degrees C and I = 0.26 mol L(-1) for the K(+)-catalyzed pathway. When no complexing agent was present, k(ex) was roughly proportional to [K(+)](total), but the corresponding rate constant k(K)' (=k(ex)/[K(+)](total)) was about 60% larger than k(K), evidently because ion pairing by hydrated K(+) lowered the anion-anion repulsions. Ionic strength as such had only a small effect on k(0), k(K), and k(K)'. The rate constants commonly cited in the literature for the Fe(CN)(6)(3-/4-) self-exchange reaction are in fact k(K)'[K(+)](total) values for typical experimental [K(+)](total) levels.