L. S. Aladko

Clathrate Hydrates of Tetrabutylammonium and Tetraisoamylammonium Halides

Clathrate formation was considered for two series of systems: (C4H9)4NG–H2O and i‐C5H11)4NG–H2O G = F-, Cl-, Br-, I-). Clathrate hydrates of tetraisoamylammonium halides were shown to melt at higher temperatures than those of the butyl series. In passing from fluoride to bromide, the stability of compounds of the butyl series falls significantly and tetrabutylammonium iodide does not produce polyhydrates. In the isoamyl series, the melting points of polyhydrates vary insignificantly for different halides. In addition, the highest melting hydrate of tetraisoamylammonium bromide melts at a slightly higher temperature than chloride hydrates, indicating not only a hydrophilic effect of the anion on clathrate formation.

Effect of size and shape of cations and anions on clathrate formation in the system: Halogenides of quaterly ammonium bases and water

Abstract The effect of the hydrophobic and hydrophilic inclusion on the structure, stoichiometry and stability of polyhydrates of halogenides of quaternary ammonium bases is discussed. Phase diagrams of binary systems H2O-(i-C5H11)4−k(C4H9)kNA (k = 0, 1, 2, 3, 4; A = F−, Br−), H2O-(C4H9)4NA, −(i-C5H11)4NA (A = F−, Cl−, Br−, I−) and some structural and physico-chemical characteristics of polyhydrates forming in these systems are presented. A comparative analysis of presented data is given.

Stoichiometry of clathrates

Two aspects of clathrate stoichiometry are discussed: structural stoichiometry and variation in composition due to variable occupation of host cavities in the framework by guest molecules. The solid solutions that are due to the variable occupation of cavities (iskhoric solutions) are classified into two types according to the stability of the hollow clathrate framework of the host. The first type involves compounds with stable hollow frameworks (the occupancies change from zero), and the second type are compounds with metastable hollow frameworks (the occupancies change from certain positive values). Special attention is paid to a wide class of clathrate compounds of constant composition (currently all clathrates are regarded as nonstoichiometric compounds). Clathrates of constant composition are formed when the hollow framework of the host is absolutely unstable. Reasons for instability of the frameworks are discussed, and theoretical models designed on the basis of the available data are considered. Examples of alloxenic (with one guest replaced by another) and allokiric (with replacements in the host subsystem) solid clathrate solutions are given.

Clathrate Hydrates of Tetrabutylammonium Carboxylates and Dicarboxylates

Phase diagrams of the binary aqueous systems with tetra-n-butylammonium (TBA) carboxylates ((C4H9)4 NCn H2n+1 CO2, where n = 0÷5) and dicarboxylates ([(C4H9)4N]2(CH2)nC2O4,where n= 1÷3) including some branched carboxylate anions, have been studied in the field of crystallization of clathrate hydrates. Monocrystals of many hydrates have been prepared and their composition, densities, melting points and X-ray data have been determined. In the set of TBA carboxylate hydrates the stability increases towards TBA propionate or butyrate hydrates (for different structures) and then it decreases as sizes of anions grow, This is explained by additional stabilization of the framework caused by small cavities being occupied until the hydrophobic part of the anion is able to go in the cavity. In the set of hydrates of TBA dicarboxylates the change of the stability is easily accounted for by the modelling of the inclusion of dicarboxylate ions in the cavities, within known structures, different ways of hydrophilic inclusion being taken into account.

Hydrate formation in the system tetraethylammonium bromide-water

Hydrate formation in the binary system tetraethylammonium bromide-water was studied by differential thermal analysis. Three stable solid phases were detected, as well as two hydrates melting in metastable regions.

Clathrate Formation in Tetraisopentylammonium Bromide-Water System

Three polyhydrates of tetraisopentylammonium bromide with 38, 32, and 26 water molecules and also the dihydrate were found in the i-Pent4NBr-H2O system.

Diisoamyldibutylammonium Bromide Clathrate Hydrates

In the system i-Am2Bu2NBr-H2O, along with the known compound i-Am2Bu2NBr·38H2O, three new clathrate hydrates were revealed: i-Am2Bu2NBr·32H2O, i-Am2Bu2NBr·26H2O, and i-Am2Bu2NBr·24H2O. Crystals of all the hydrates were isolated, and their compositions and melting points were determined.

Clathrate Hydrates in the System Tetraisopentylammonium Iodide-Water

Two clathrate hydrates i-Pent4NI·36H2O and i-Pent4NI·32H2O were revealed in the system (i-Pent)4NI-H2O. The hydrates melt incongruently at 14.2 and 14.8°C, respectively. Along with the polyhydrates, tetraisopentylammonium dihydrate was found.

Formation of (CxH2x+1)4NBr·nH2O (x = 1–3) hydrate

The phase diagram of the binary system tetramethylammonium bromide-water was studied by the differential thermal analysis. In the stable region two phases, ice and the salt itself, were detected, and in the metastable region, three tetramethylammonium bromide hydrates (bromide-water, 1 : 4, mp 68.8°C, 1 : 5, mp 36.0°C, 1 : 7.5, mp −19.5°C) were found. Formation of (CxH2x+1)4NBr·nH2O (x = 1–3, n = 4, 5, 7.5) hydrates was revealed.

Clathrate Formation in the Series of Systems Diisopentyldibutylammonium Halide-Water

Three clathrate hydrates: (i-C5H11)2·(C4H9)2NCl·38H2O (mp 20.5°C), (i-C5H11)2·(C4H9)2NCl·32H2O (mp 22.2°C), and (i-C5H11)2·(C4H9)2NCl·27H2O (mp 23.8°C) were detected in the system diisopentyldibutylammonium chloride-water. Crystals of all the compounds were isolated, and their composition was determined. The size effect of the halide anions (F−, Cl−, and Br−) on the properties of related compounds was considered.