Optical characteristics and intensity parameters of Sm3+ in GeO2, ternary germanate,and borate glasses

Absorption and fluorescence spectra of Sm3+ were measured in GeO₂, ternary germanate, and borate glasses. From these the intensity parameters were calculated by use of the Judd-Ofelt formula.Visible emission and decay times from the⁴G_5/2 level and its relative quantum efficiencies were measured The quantum efficiencies (QE) of the fluorescence in ternary germanate was higher by a factor of 20 than in GeO₂, The small QE in GeO₂, is explained by cross-relaxation between neighboring Sm³⁺ ions. The later process in hindered by the change in glass structure in the presence of modifier ions. A similar effect is observed in other glasses such as borate, where the addition of modifiers increases the QE of fluorescence.     

Ab initio characterization of several states of nitroxylium (NO). Comparison of fragmentation energies of nitroxylium,nitroxyl (NO3), and nitrate

Ab initio calculations have been performed at the self-consistent field (HF) level, and its perturbative extensions up to fourth-order (MPn), for several electronic states of nitroxylium (NO) as well as for a large number of reference species. Geometries are optimized at the HF/DZ and HF/DZP levels (double zeta and double zeta plus polarization bases). The ground state is found to be the D_3h ¹A₁′ state, with the C_2v ¹A₁ (closed Y) state higher by 0.94 eV. The relationship between adding electrons or oxygen atoms to NO⁺ and NO is explored, especially in relation to fragmentation energies of NO (q = 0 or 1). A comparison is drawn between NO and two isoelectronic species, CO₃ and C(CH₂)₃, where no surprises are found.     

Einfluß von Gitterstörungen des Graphits auf die Bildung von Graphithydrogensulfat

Influence of Lattice Defects of Graphite on the Formation of Graphite Hydrogensulfate Various natural and synthetic graphites were oxidized with chromic acid in sulfuric acid to the 1st stage of graphite hydrogensulfate with the intent of determining the inhibition of intercalation by lattice defects. More oxidant than required by stoichiometry is consumed because slow total oxidation to CO₂ is superimposed even at room temperature. The activation energy for total oxidation is reduced by lattice defects. With some graphites, separation of the intercalation reaction from total oxidation was accomplished using calorimetry. The reaction enthalpy in the oxidation of well-crystallized graphites to the graphite salt is ?3.05 kJ/mol C.     

Versuche zur Hydrolyse der Siloxan-Bindungen an Siliciumdioxid-Oberflächen

Zusammenfassung Am Beispiel des Aerosils wurde die Ver?nderung der Oberfl?che des Siliciumdioxids bei der Entwicklung verschiedener hydrolytischer Agentien untersucht. Die Oberfl?che des Aerosils enthielt ursprünglich neben Silanolgruppen in erheblichem Umfang Siloxangruppen. Mit kaltem Wasser, mit ammoniakalischer Brenzkatechin-L?sung und bei kürzerer Einwirkung von siedendem Wasser wurde eine teilweise Hydrolyse der Siloxan-Bindungen erreicht, doch, wurden nie mehr als 3.3 Silanolgruppen pro 100 ?² erhalten. Nach l?ngerer Einwirkung von siedendem Wasser wurde eine Abnahme der spez. Oberfl?che und der Zahl der Silanolgruppen pro Fl?cheneinheit beobachtet. Im Elektronenmikroskop zeigten die Teilchen dieser Aerosile Hüllen geringerer Dichte aus feinporigem Siliciumdioxid. Infolge der extrem engen Poren wurde ein erheblicher Teil der Oberfl?che und der Silanolgruppen bei den Messungen nicht erfa?t. Konz. Ammoniak und in geringerem Ma?e auch lange Lagerung an der Atmosph?re hatten ?hnliche Wirkung. überhitzter Wasserdampf katalysierte bei 200° die Abspaltung von Wasser aus Silanolgruppen. Die Pr?parate verloren dabei mehr Wasser als bei gleicher Temperatur im Hochvakuum. Die Ergebnisse und die Mechanismen der Ver?nderungen werden diskutiert.

---

Summary The influence of various agents on the surface of Aerosil, a fine particle size silicia was studied. Originally, siloxane as well as silanol groups were present in the Aerosil surface. Partial hydrolysis of the siloxane bonds was achieved with cold water, ammoniacal pyrocatechol solution and after shorter contact with boiling water. The number of silanol groups per 100 ?² never exceeded 3.3. On prolonged action of boiling water a significant decrease of the surface area and of the number of silanol groups was observed. Electron microphotographs show that the particles became coated by a layer of less dense porous silicia. As a result of the extremely narrow pores part of the surface and of the silanol groups escaped detection. Ammonia and, to a lesser extent, prolonged storing at atmospheric conditions had similar effects. At 200 °C the condensation of silanol groups to siloxane bonds was catalyzed by superheated steam as evidenced by a greater loss of silanol groups than in a high vacuum at the same temperature. The results and the mechanisms of the changes in the silica surface are discussed.

---

---

Herrn Prof.U. Hofmann zum 60. Geburtstag gewidmet.

---

Herrn Prof. Dr.U. Hofmann sind wir für stete F?rderung und gro?zügige Unterstützung unserer Arbeiten zu gro?em Dank verpflichtet. Dem Fonds der Chemie und dem Landesgewerbeamt des Landes Baden-Württemberg danken wir für finanzielle Unterstützung.     

Self‐Assembled Binary Mixtures of Partially Etched Nanowires

Arrays of anisotropic particles are sought after for applications in optics, electronics, and energy. Structures assembled from multiple micro‐ or nanoparticles could incorporate the distinct properties of each component to achieve functions not possible from single‐population assemblies. In mixed‐particle populations, the assembly forces may differ between the particle types, which will in turn influence the final assembled structures. Here, binary particle mixtures are studied and compared to assemblies formed from each of the component particles alone. The particles are partially etched nanowires (PENs, ≈300 nm diameter, and 3–8 μm overall length), which are formed by the silica coating and subsequent etching of striped metal nanowires, such that what remains are silica nanotubes containing segments of metal core (Au, Pt, Rh, or Pt/Au) with controllable location and number, spaced by “empty” regions that fill with water. Binary mixtures of PENs with different core metals and segment patterns are examined here to explore how the different core segment material, length, position, and number affects overall self‐assembly behavior.     

Palladium‐Catalyzed Chlorocarbonylation of Aryl (Pseudo)Halides Through In Situ Generation of Carbon Monoxide

An efficient palladium‐catalyzed chlorocarbonylation of aryl (pseudo)halides that gives access to a wide range of carboxylic acid derivatives has been developed. The use of butyryl chloride as a combined CO and Cl source eludes the need for toxic, gaseous carbon monoxide, thus facilitating the synthesis of high‐value products from readily available aryl (pseudo)halides. The combination of palladium(0), Xantphos, and an amine base is essential to promote this broadly applicable catalytic reaction. Overall, this reaction provides access to a great variety of carbonyl‐containing products through in situ transformation of the generated aroyl chloride. Combined experimental and computational studies support a reaction mechanism involving in situ generation of CO.