Synthesis and X-ray structural analysis of a unique Co-crystallization complex of [NaSal]2DB24C8 and [KSal]2DB24C8

Sodium salicylate (NaSal where Sal=2-hydroxybenzoate), when mixed with dibenzo-24-crown-8 (DB24C8) yields a bimetallic complex [NaSal]₂DB24C8 in most polar organic media, while potassium salicylate (KSal) under similar conditions shows a tendency to yield 11 or 21 complexes depending upon medium or synthesis. However, the presence of both NaSal and KSal together results in a unique mixed cation complex of composition NaKSal₂DB24C8. This product melts sharply (190-92°C) without decomposition, displays IR spectral characteristics comparable to those of [Na(Sal)]₂DB24C8, and is stable in aqueous media as shown by the detectable cation effect on the UV absorption bands of Sal and DB24C8. Single crystal X-ray analysis of NaK(Sal)₂DB24C8 reveals that the system represents a co-crystallization complex of individual (KSal)₂DB24C8 and (NaSal)₂DB24C8 molecules. The crystals are monoclinic,P2₁/c,a=19.976(2) Å,b=9.031(1) Å,c=25.541(5) Å,=122.065(9)°, ų,T=298 K,Z=2+2, CuK =1.5418 Å, and 2 (2.5°–100°). FinalR factor for the 3012 observed reflections (F>3) is 0.092. Both the Na₂- and K₂-molecules possess crystallographic centers of symmetry with one metal and its associated anion on each side of the crown ring. However, the conformations of the crowns are very different in the two molecules, with the K₂-crown being nearly planar and the Na₂-crown being quite puckered. Four oxygen atoms from the DB24C8 (KO, 2.680–2.908 Å) and three carboxyl oxygen atoms (KO, 2.472–2.708 Å) from separate salicylate ions coordinate with each potassium. Three oxygens from the crown (NaO, 2.536–2.65 Å) and three carboxyl oxygens (NaO, 2.31–2.563 Å) coordinate with each sodium. The salicylate ions lie on opposite sides and nearly perpendicular (77.2°, Na₂-molecule; 82.7° K₂-molecule) to each crown but coordinate to both of the metal ions within a molecule. The K⁺K⁺ and Na⁺Na⁺ distances in the respective molecules are 3.95 and 3.34 Å. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82044 (18 pages).     

Ultrathin films of functionalised single-walled carbon nanotubes: a potential bio-sensing platform

ABSTRACT

The Langmuir monolayer is a special class of lyotropic liquid crystalline system wherein phase transition essentially depends on surface density, temperature and ion-content in the aqueous medium. The variety of surface phases can be transferred onto devices by the Langmuir–Blodgett (LB) technique. The Langmuir monolayer of pristine single-walled carbon nanotubes (SWCNTs) exhibited gas and liquid-like phases. The LB film of SWCNTs shows target surface pressure dependent interesting morphologies. The methane gas sensing using parallel alignment of SWCNTs was found to be better than that of randomly oriented SWCNTs. The SWCNTs can be functionalised chemically to enhance the ease of film processability and affinity towards analytes. These are essential parameters for the development of a sensor. In this article, we present our work on Langmuir monolayer and LB films of octadecylamine functionalised SWCNTs (ODACNTs) and its sensing application towards bio-analytes, e.g. L-aspartic acid and bovine serum albumin. The sensing performance of LB film of ODACNTs was compared with that of spin-coated films of ODACNTs. The sensing performance of LB films of ODACNTs indicated a potential platform for bio-sensing application.     

Targeting the Rich Conformational Landscape of N-Allylmethylamine Using Rotational Spectroscopy and Quantum Mechanical Calculations

The highly variable conformational landscape of N-allylmethylamine (AMA) was investigated using Fourier transform microwave spectroscopy aided by high-level theoretical calculations to understand the energy relationship governing the interconversion between nine stable conformers. Spectroscopically, transitions belonging to four low energy conformers were identified and their hyperfine patterns owing to the ¹⁴N quadrupolar nucleus were unambiguously resolved. The rotational spectrum of the global minimum geometry, conformer I, shows an additional splitting associated with a tunneling motion through an energy barrier interconnecting its enantiomeric forms. A two-step tunneling trajectory is proposed by finding transition state structures corresponding to the allyl torsion and NH inversion. Natural bond orbital and non-covalent interaction analyses reveal that an interplay between steric and hyperconjugative effects rules the conformational preferences of AMA.     

Qualitative cation analysis without removing interfering anions

Summary A scheme of cation analysis is presented where phosphate and organic acids do not interfere with the course of analysis. The method is standardised on 2–3 mg level, and the procedure is rapid. Group separations are neat and in no case the precipitate is gelatinous. Some confirmatory tests of the elements have been modified.

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Zusammenfassung Ein Analysengang für Kationen wird angegeben, der durch Phosphat und organische Säuren nicht gestört wird und mit 2 bis 3 mg Probe rasch durchführbar ist. Die Gruppentrennungen verlaufen sauber, die Niederschläge sind in keinem Fall gallertig. Einzelne Nachweisreaktionen wurden modifiziert.

     

Crystal and molecular structure of sodium picrate monohydrate

Na⁺ [C₆H₂(NO₂)₃O]^– H₂O,M _r=269.11, monoclinic,C2/m (No. 12),a=13.065(1),b=20.065(2),c=3.6957(4) Å,=90.75(1)°,V=968.7(1) ų,Z=4,D _m=1.848 g cm^–3 (by flotation),D _x=1.845 g cm^–3, (CuK)=1.54184 Å,(CuK)=17.5 cm^–1,F(000)=540,T=295 K,R=0.055,wR=0.060 for 879 observed reflections withI2.5(I). p]In the structure the picrate anion has exact twofold symmetry, the water molecule has exact mirror symmetry and the two sodium cations occupy special positions on inversion centers at (0, 1/2, 0) and (1/2, 1/2, 1/2). The phenyl ring together with the four substituent N and O atoms is strictly planar, but the phenyl ring is severely distorted from hexagonal symmetry, as is commonly observed in structures containing the picrate fragment. Both sodium ions are eight-coordinated with Na(1) and Na(2) in a cubic and distorted cubic arrangement, respectively. Na(1) coordinates to four charged phenoxide O atoms and four O atoms of nitro groups, and Na(2) to four O atoms of nitro groups and four water molecules. The water molecule donates two hydrogen bonds to symmetry-related O(2) atoms ofortho nitro groups. Two symmetry-related O(3) atoms ofortho nitro groups serve as acceptors in a very unusual asymmetric bifurcated C-HO hydrogen bond.