Colorimetric determination of the fluoride ion based on interference with extractability

Summary The sensitivity of colorimetric determinations based on reduction of extinction by complex-forming anions can be increased by measuring the change of absorbancy in the organic phase after shaking with a suitable solvent, i. e. by determining the interference of the anion with extractability. This principle has been applied to the determination of the fluoride ion.

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Zusammenfassung Die Empfindlichkeit kolorimetrischer Bestimmungen, die auf Herabsetzung der Extinktion durch komplexbildende Anionen beruhen, kann durch Messung der Absorptionsänderung in der organischen Phase nach Schütteln mit einem geeigneten Lösungsmittel, das heißt durch Bestimmung der durch das Anion verminderten Extrahierbarkeit, erhöht werden. Dieses Prinzip wurde auf die Bestimmung von Fluoridion angewendet.

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Résumé La sensibilité des déterminations colorimétriques basée sur l'effet de diminution d'extinction dû à des anions donnant lieu à la formation de complexes peut être accrue par la variation de l'absorption dans la phase organique après agitation avec un solvant approprié, ce qui revient à déterminer l'effet d'empêchement d'extraction dû à l'anion. Ce principe a été appliqué au dosage de l'ion fluorure.

     

Einflu? der Wertigkeit bei der flammenabsorptionsspektrometrischen Bestimmung des Chroms

Zusammenfassung Die Intensität des flammenabsorptionsspektrometrischen Cr-Signals hängt in einer sehr komplexen Weise von der Wertigkeit des Chroms und der Flammentemperatur ab. Ferner ist ein ausgeprägter Kalium-Einfluß vorhanden. Alle diese Schwierigkeiten können am besten dadurch eliminiert werden, daß in der Lachgasflamme gearbeitet und die Analysenlösung mit einer höheren K-Konzentration gepuffert wird.

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Effect of valency on the determination of chromium by flame absorption spectrometry

The intensity of the chromium signal in AAS depends in a very complex manner strongly on the valency of the Cr and the flame temperature. It is furthermore influenced by potassium, if present. The best way to overcome all these interferences is to use the nitrous oxide flame and to buffer the solution with a higher concentration of potassium.

     

Die Reaktion von SeCl4 mit Übergangsmetalltetrachloriden. Synthese und Kristallstrukturen von (SeCl3)2MCl6 mit M = Zr,Hf, Mo,Re

The Reaction of SeCl₄ with Transition Metal Tetrachlorides. Synthesis and Crystal Structures of (SeCl₃)₂MCl₆ with M = Zr, Hf, Mo, Re The transition metal tetrachlorides ZrCl₄, HfCl₄ and MoCl₄ react with SeCl₄ in closed ampoules at temperatures of 140°C to (SeCl₃)₂MCl₆ (M = Zr, Hf, Mo) which are all isotypic and crystallize in the (SeCl₃)₂ReCl₆ structure type (orthorhombic, Fdd2, Z = 8, lattice constants for M = Zr: a = 1165.7(1)pm, b = 1287.2(2)pm, c = 2180.2(2)pm; for M = Hf: a = 1162.9(2)pm, b = 1285.0(2)pm, c = 2178.2(3)pm; for M = Mo: a = 1153.8(1)pm, b = 1267.7(1)pm, c = 2147.4(2)pm). The Cl^? ions form a hexagonal closest packing with one fourth of the octahedral holes filled by Se⁴⁺ and M⁴⁺ in an ordered way. The MCl₆ octahedra are regular, the SeCl₆ octahedra are distorted with 3 short and 3 long Se? Cl bonds (mean 215 pm and 287 pm). The structures can thus be regarded as built of SeCl₃⁺ and MCl₆^2? ions. Magnetic susceptibility measurements show for M = Zr the expected diamagnetic behavior, for M = Mo and Re paramagnetic behavior according to the Curie-Weiss law with magnetic moments of 2.5 B. M. for M = Mo and 3.7 B. M. for M = Re corresponding to 2 and 3 unpaired electrons respectivly.     

Synthesis of a digermane-containing tricylic nonadecadienedione incorporating an equivalent of ring-opened THF

The combination of 2 equiv of bis[bis(trimethylsilyl)amide]germylene (5) with 2 equiv of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) in tetrahydrofuran (THF) results in the ring-opening of 1 equiv of THF to form 2,2,8,8-tetrakis(1,1,1,3,3,3-hexamethyl-disilazan-2-yl)-5,16-diphenyl-7,9,14-trioxa-1,3,5,16,18,19-hexaaza-2,8-digerma-tricyclo[13.2.1.13,6]nonadeca-6(19),15(18)-diene-4,17-dione (6). This fast and nearly quantitative reaction builds a 15-membered ring from five different molecules. The new ring, structurally assigned by X-ray crystallography, contains a flexible methylene chain that moves rapidly on the NMR time scale.     

Metallorganische Lewis-Säuren. XLII. Carbonyl- und Nitrosyl-Komplexe von Mangan und Rhenium mit schwach koordinierten Anionen (Ph3P)2(ON)2MnX, (Ph3P)n(OC)5–nMX (M = Mn,Re; n = 1, 2; X = FBF3, OSO2CF3, OSO2F,OCORf)

Organometallic Lewis Acids. XLII. Carbonyl- and Nitrosyl Complexes of Manganese and Rhenium of Weakly Coordinated Anions (Ph₃P)₂(ON)₂MnX, (Ph₃P)_n(OC)_5–nMX (M = Mn, Re; n = 1, 2; X = FBF₃, OSO₂CF₃, OSO₂F, OCOR_f) The complexes (Ph₃P)₂(ON)₂MnX (X = FBF₃, OSO₂CF₃, OSO₂F, OCOCF₃, OCOC₃F₇) and (Ph₃P)_n(OC)_5–nMX (M = Mn, Re; n = 1, 2; X = FBF₃, OSO₂CF₃) have been obtained by reaction of (Ph₃P)₂(ON)₂MnH and (Ph₃P)_n(OC)_5–nMeMe with the corresponding acids HX or from (Ph₃P)_n(OC)_5–nReBr (n = 1, 2) with silver salts AgX, respectively. The compounds have been characterized by their IR and partially by ¹⁹F-NMR data. An efficient method for the preparation of the hydride (Ph₃P)₂(ON)₂MnH is reported.     

Fragmentation and reaction processes in cluster-surface collisions

We review the processes which have been observed from collisions between alkali-halide clusters and solid surfaces. Soft impact of nanocrystalline Na_nF _n?1 ⁺ clusters against solid surfaces causes them to cleave along the lowest energy (100) plane. At higher collision energies (E_i>1 eV/atom), an evaporative cascade occurs which is characteristic of a transformation of the nanocrystal to a molten state. Efficient F^? transfer from the cluster to the surface can occur for the larger clusters (>60 atoms) scattering from Si(111), in direct competition with the cleaving channel at low energies. In this regime, strong bonds can form between the F^? and silicon surface. The reaction probability increases with cluster size indicating that an impact-initiated shock wave is needed to enhance the reactive process.     

Über den sterischen Verlauf der Umsetzung von Enaminen aus offenkettigen Aldehyden und Ketonen mit Nitroolefinen zu 2,3-disubstituierten 4-Nitroketonen

On the Steric Course of the Reaction of Enamines Derived from Open-Chain Aldehydes and Ketones with Nitro-olefins Yielding 2,3-Disubstituted 4-Nitroketones The relative configuration of the nitro-ketone 12 obtained by the title reaction has been proved by a Baeyer-Villiger degradation and subsequent reduction to the amino-alcohol (±)-(u)- 20 , the relative configuration of which is identical with a sample prepared from 2-methyl-3-hydroxybutyrate of known configuration (Scheme 1). The stereochemical course of the title reaction is thus as predicted by our topological rule. It is assumed that the other nitro-ketones 13–18 described here are also formed by (lk)-combination of the trigonal centers of the educts (diastereoselectivity > 90%, see Formulae and Fig. 1). It is not possible to reverse this relative topicity by employing (Z)- instead of (E)-components of the starting materials, due to the reversibility of the primary step of these Michael additions (Schemes 2 and 3, and Fig. 2).     

Correlation of mercury concentrations in tree core and lichen samples in southeastern Louisiana

To determine if a correlation exists between mercury concentrations in lichens and wood from tree cores, tree core and lichen samples were taken from sites under mercury advisories and analyzed for mercury using a Bacharach 50B Mercury Analyzer System employing the Manual Cold Vapor Atomic Absorption EPA method 7471A. Wood from tree cores was dated using tree ring data. Wood samples from the cores were analyzed for various depths in the tree core (periods of time) to determine if variations occur throughout the cores. Preliminary data indicate that a strong correlation exists between mercury concentrations in tree core and lichen samples. Samples were analyzed for the 6-month period of summer 2003–winter 2004. A correlation coefficient of 0.882 was found between the tree core and lichen data sets. The derived correlations were used to estimate concentrations of mercury in tree rings for sites in lichen samples which were previously analyzed. These predicted values compared favorably to recently determined concentrations of Hg in tree cores. The strong correlation between lichen and tree core Hg concentrations suggests similar uptake mechanism for the two types of biota.     

The natural atomic orbital point charge model for PM3: Multipole moments and molecular electrostatic potentials

The natural atomic orbital/point (NAO-PC) model originally developed to calculate molecular electrostatic potentials (MEPs) and multiple moments based on the AM1 wave function has been extended to PM3. As for AM1, NAO-PC/PM3 reproduces dipole moments calculated by the standard PM3 method very well. There is also a surprisingly good correlation between experimental and calculated quadrupole moments. The MEPs calculated using PM3/NAO-PC are found to be in better agreement with those given by RHF/6-31G* than those obtained from the PM3 wave function using Coulson charges. On the other hand, the NAO-PC model is often slightly worse then the method implemented in MOPAC-ESP. The MEPs calculated using our model based on the PM3 wave function are often in better agreement with those given by RHF/6-31G* than those obtain with AM1. © 1994 by John Wiley & Sons, Inc.