The Four-Connected Net in the CeCu(2) Structure and Its Ternary Derivatives. Its Electronic and Structural Properties

The crystallochemistry of and the bonding in the orthorhombic four-connected nets of BaIn(2) (CeCu(2) structure) and of CaPtSn (TiNiSi structure, a derivative of the CeCu(2) structure) are analyzed with approximate molecular orbital calculations. Following the Zintl concept, in BaIn(2) the In(-) ions are isoelectronic with group IV tin and should adopt a four-connected structure. In contrast to alpha-tin, which has a cubic diamond structure, the indium ions in BaIn(2) build up an orthorhombic three-dimensional four-connected net containing distorted tetrahedra and ladder polymers of four-membered rings. In the CeCu(2) structure (space group Imma) two bond angles in these distorted tetrahedra are fixed at 90 degrees. The four-connected net in the CeCu(2) structure is topologically related to the layers in black phosphorus (space group Cmca). In CaPtSn (TiNiSi structure) the orthorhombic four-connected net is formed by (PtSn)(2)(-) ions in an ordered arrangement. Calculations on BaIn(2) and CaPtSn show that the four-connected nets are increasingly stabilized as the valence electron count is increased from 16 to 30 valence electrons per 4 formula units. For more than 30e, the nets are destabilized due to filling of M-E antibonding states. Structural data obtained by precise single crystal investigations for the TiNiSi series CaPdIn (20e), CaPdSn (24e), CaPdSb (28e), and CaAgSb (32e), confirm the results of the extended Hückel calculations. We find an interesting and understandable angular asymmetry of the tetrahedral sites in these ternary compounds.     

Particle analysis of car exhaust by ETV-ICP-MS

Particulates of platinum group elements (Pt, Rh, Pd, Ir) emitted in automotive catalyst exhaust were measured down to the pg/m(3) level. Samples were taken from a standard type three-way catalyst equipped gasoline engine, running on a computer controlled dynamometer. Particulates in catalyzed car exhaust were sampled fractionated according to size by using the cascade impactor with separate targets mounted underneath each nozzle. The targets, small flat discs made of pure graphite, were subsequently analyzed by ETV-ICP-MS without any preparatory steps.     

Vesicle phases from N-methyl-N-alkanoylglucamin and various co-surfactants

We have studied the phase behavior of N-methyl-N-alkanoylglucamin (GA) in water and the influence of various additives on the phases of GA. We find that GA forms a large L₁-phase that extends up to 60 wt.% of surfactant. The viscosity in this phase increases with increasing concentration and decreasing temperature. When solutions are cooled down below the Krafft-temperature (21–28 °C) T_k the samples transform into clear gels that are stable for several months. The transformation of the gel to the L₁-phase proceeds in two separate steps. Acid–base titration experiments show that the commercially produced GA is not a pure well defined compound but contains about 10% of an anionic surfactant, most likely dodecanoic acid. Solutions of GA can be continuously mixed with the anionic surfactant sodiumdodecylsulfate (SDS) or sodiumdodecylethoxysulfate (SDES) to clear and low viscous phases. Solutions of GA mixed with increasing amount of cationic surfactant tetradecyltrimethylamoniumbromide (TTABr) transform first into two phase systems and then again into low viscous single phases. The influence of several chemically different co-surfactants like n-alcohols, octanoic acid, oleic acid, 2-ethylhexylmonoglyceride (EHMG) and oleylmonoglyceride on the phase behavior of phases with 5% GA has been studied. With increasing mole fraction of the co-surfactants the well-known sequence of phases is observed, namely a L₁-phase, a two phase region L₁/L- and a L-phase. However, the properties of the L-phase for the different systems are very different. For samples with octanol the L-phase is an optically isotropic, transparent, highly viscoelastic gel. Without shear the gel like phase shows no birefringence. FF-TEM micrographs show that it consists of rather monodisperse, unilamellar vesicles with a diameter of about 500 Å. The L-phases for the other co-surfactants are turbid and have a rather low viscosity. They also contain vesicles but with a rather broad size distribution ranging from 200 to 1000 Å. For the same co-surfactant/surfactant ratio the various systems differ also in their conductivity. For some systems the conductivity is only about 20% lower than in the corresponding L₁-phase while in other systems the difference is more than a factor two. These results are an indication that small uni-lamellar vesicles contain more ionic groups at the outside than on the inside of the bilayer and that some systems are composed of uni-lamellar vesicles while others are composed of multilamellar vesicles (onions).     

Novel [2 + 2] photocycloaddition-induced rearrangement of bichromophoric naphthalene-tethered resorcinol ethers

The first examples of sequential photocycloaddition-rearrangement reactions of naphthalene-tethered resorcinol ethers are described. Bichromophoric aromatic compounds with naphthalene and resorcinol ether moieties were irradiated in the presence/absence of a small amount of acid to give the corresponding cycloaddition-rearrangement products. From the determination of quantum yields, steady-state fluorescence spectral studies, and fluorescence lifetime measurements, the mechanism of this novel photoinduced multistep reaction was elucidated to involve the initial intramolecular exciplex formation, followed by the intramolecular [2 + 2] photocycloaddition between the two aromatic rings and the subsequent acid-catalyzed skeletal rearrangement of the resulting cyclobutane derivative leading to the final products.     

The use of chloranilic acid salts in micro analysis

Summary The use of chloranilic acid salts is recommended for the micro determination of aluminium salts, sulphides, thiosulphates, cyanides and fluorides. The methods are based on the reaction of an insoluble chloranilate with the ion to be determined to form an insoluble compound of this ion and an equivalent of liberated chloranilic acid which can be measured. The procedures are simple and rapid.

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Zusammenfassung Zur Mikrobestimmung von Aluminiumsalzen, Sulfiden, Thiosulfaten, Cyaniden und Fluoriden wird die Verwendung von Salzen der Chloranilsäure empfohlen. Die Methoden beruhen auf der Reaktion unlöslicher Chloranilate mit dem zu bestimmenden Ion unter Bildung einer unlöslichen Verbindung dieses Ions und Freisetzung einer äquivalenten Menge Chloranilsäure, die gemessen wird. Die Bestimmungen lassen sich einfach und schnell durchführen.

     

Complicated goings-on in the metal-manipulated ring-opening of cyclobutene

Most reported examples of transition metal-mediated pericyclic reactions have been shown to proceed by nonpericyclic mechanisms. However, the conversion of Fe(CO)(4)-cyclobutenes to Fe(CO)(3)-butadienes and CO is thought to proceed through a mechanism involving an electrocyclic ring-opening step. We have examined this and possible alternative mechanisms for the parent Fe(CO)(4)-cyclobutene complex using hybrid HF-DFT calculations. In this system there is an inherent preference for a pathway that avoids metal-templated electrocyclic ring-opening, but the pericyclic pathway is predicted to dominate for more elaborate substrates and under certain experimental conditions.