A self-generating third-order electrode: Part II. Analytical applications of the silver—silver sulphide electrode

Analytical applications of the silver—silver sulphide electrode are illustrated by potentiometric determinations of Cd(II) and Pb(II) ions. The stability of the electrode potential in the presence of oxidizing agents is demonstrated by various titrations with silver(I) solutions. The influence of pH on the electrode potential in pure acidic solutions is noted. The electrode used was prepared by electrolytic deposition of silver sulphide on a silver rod; after 2 years, it remained reliable, and was unaffected by light under normal laboratory conditions.     

Racemic dipeptide glycyl‐dl‐leucine at 120 K

The structure of glycyl‐dl ‐leucine, C₈H₁₆N₂O₃, has been determined at 120 K by single‐crystal X‐ray diffraction. In addition to three N—H?O‐type hydrogen bonds of the positively charged RNH₃⁺ group of the zwitterionic mol­ecule, an intermolecular N—H?O contact exists between the peptide bond and the carboxyl­ate group. Four hydrogen‐bond cycles were identified, giving a complex pattern.     

Hydrogen ADPs with Cu Kα data? Invariom and Hirshfeld atom modelling of fluconazole

For the structure of fluconazole [systematic name: 2‐(2,4‐difluorophenyl)‐1,3‐bis(1H‐1,2,4‐triazol‐1‐yl)propan‐2‐ol] monohydrate, C₁₃H₁₂F₂N₆O·H₂O, a case study on different model refinements is reported, based on single‐crystal X‐ray diffraction data measured at 100 K with Cu Kα radiation to a resolution of sin θ/λ of 0.6 Å⁻¹. The structure, anisotropic displacement parameters (ADPs) and figures of merit from the independent atom model are compared to `invariom' and `Hirshfeld atom' refinements. Changing from a spherical to an aspherical atom model lowers the figures of merit and improves both the accuracy and the precision of the geometrical parameters. Differences between results from the two aspherical‐atom refinements are small. However, a refinement of ADPs for H atoms is only possible with the Hirshfeld atom density model. It gives meaningful results even at a resolution of 0.6 Å⁻¹, but requires good low‐order data.     

Motion of positrons in metals

In this review we discuss the different aspects of positron annihilation in metals that involve the dynamics of positron motion before annihilation. The emphasis is on the theory, but also some experimental evidence is quoted. The topics covered are: slowing down and thermalization, effective mass, temperature dependence of positron vacancy trapping, positron channeling, and escape of low energy positrons from metal surfaces.     

Donor-acceptor stabilized silaformyl chloride

Formyl chloride (H(Cl)C=O) is unstable at room temperature and decomposes to HCl and CO. Silicon analogue of formyl chloride, silaformyl chloride IPr·SiH(Cl)=O·B(C(6)F(5))(3) (3) (IPr = 1,3-bis(2,6-diisopropyl-phenyl)imidazol-2-ylidene), was stabilized by Lewis donor-acceptor ligands. Compound 3 is not only the first stable acyclic silacarbonyl compound but also the first silacarbonyl halide reported so far.