Structure and Stability of Quaternary Ammonium Interhalides: Experimental and Quantum-Chemical Study

The electronic structure of a series of ammonium interhalides [R¹R²R³R⁴N]XI₂, where R¹ = CH₃, C₂H₅, C₃H₇, F, H; R² = R³ = R⁴ = CH₃, H; X = Cl, Br, I, was studied by ab initio calculations (RHF/3-21G, RHF/HW, MP2/HW). The thermodynamic stability of these compounds correlates with the strength of the hydrogen bond N-H···X and three-center interhalide bond X-I-I. Calculations confirmed that, in polar solvents, these compounds preferably decompose to [R¹R²R³R⁴N]⁺ and XI₂ ^- (with subsequent decomposition of the anion), and in nonpolar solvents, to the neutral species [R¹R²R³R⁴N]X and I2. The calculation results were compared to the experimental data obtained by single crystal X-ray diffraction, ¹H NMR spectroscopy, and spectrophotometry.     

Spectrophotometric Determination of the Polyiodohalides of Organic Nitrogen-Containing Cations

The following biologically active diiodohalides of organic cations were studied: N-cetylpyridinium, trimethylbenzylammonium, triethylbenzylammonium, and N,N-dimethylmorpholinium diiodochlorides; N-cetylpyridinium, tetramethylammonium, tetrabutylammonium, and N,N-dimethylmorpholinium diiodobromides; and N,N-dimethylmorpholinium and butyroylcholinium triiodides. A simple and rapid procedure was proposed for the determination of the above compounds; it is based on the conversion of organic diiodohalides into the corresponding triiodides (_{300 nm} 4 × 10⁴; _{370 nm} 2 × 10⁴) in the presence of excess potassium iodide (RSD 2%). An extraction–spectrophotometric method was developed for the quantitative determination of the biologically active compounds in pharmaceutical dosage forms based on their ion associates with anionic dyes, erythrosine (m _min = 1.25–3.30 g; RSD 3%) and Bromothymol Blue (m _min = 3.85 g; RSD = 3%), or a cationic dye—1,3-dimethyl-2-(4-morpholinophenyl)azobenzimidazolium phenylsulfate (m _min = 2.32–8.26 g; RSD 4%). The developed procedures were used for monitoring drug substances in model pharmaceutical preparations (RSD 4%).     

Complex Formation in the System Bis[2-(trimethylammonio)ethyl] Succinate Diodide-Iodine in Solutions and in Crystal

The complex formation in the system bis[2-(trimethylammonio)ethyl] succinate diodide-iodine involves no more than two iodine molecules. The crystal structure of the salt [(CH3)3N(CH2)2OCOCH2]2(I3)2 is formed by layers of inorganic anions (I₃ ^-) and organic dications (centrosymmetric dications {[(CH₃)₃N · (CH₂)₂OCOCH₂]⁺}₂), evenly alternating along the a axis. The crystal structure of the salt [(CH₃)₃N(CH₂)₂·OCOCH₂]₂(I₃)₂(I₂)0.5 is formed by organic and inorganic layers evenly alternating along the [011] diagonal, with a centrosymmetric iodine molecule.     

Chromatographic Determination of Polyiodohalides of Organic Nitrogen Bases

The following biologically active polyiodohalides of organic nitrogen bases were synthesized and studied: trimethylbenzylammonium, triethylbenzylammonium, and N-cetylpyridinium diiodochlorides; tetramethylammonium, tetrabutylammonium, and N-cetylpyridinium diiodobromides; and butylcholinium triiodide. A method for the identification of the above compounds was proposed based on the dependence of their thin-layer chromatographic mobility and IR, UV, and NMR spectrometric properties and on the nature of the organic cation and the structure of the polyiodide anion. Reversed-phase high-performance liquid chromatography in a 1 : 1 methanol–water mixture (pH 6.86) was used for determining the compounds under study. The developed procedure is characterized by high sensitivity (0.09–0.51 g) at RSD of no worse than 10%.