Tatyana V. Rodionova

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.

The Structure of Tetrabutylammonium Bromide Hydrate (C4H9)4NBr·21/3H2O

Abstract The results of the investigation using single crystal X-Ray diffraction analysis of tetrabutylammonium bromide hydrate structure (C4H9)4NBr·21/3H2O, which was discovered in the tetrabutylammonium bromide–water binary system within the range of concentrated solutions, are presented in this communication. The (C4H9)4NBr·21/3H2O compound is crystallized in the trigonal space group R3c, a=16.609(1) A, c=38.853(2) A. The structure is a packing of tetrabutylammonium cations and clusters composed of hydrogen-bonded water molecules and bromide anions. The change of water functions is discussed within one binary system tetrabutylammonium bromide–water. In the clathrate formation region water plays the role of the host, forming the water–anion host framework in clathrate polyhydrates, while in the region of concentrated solutions, in the case of (C4H9)4NBr·21/3H2O compound, water functions as a guest, forming water-anion guest particle.

Calorimetric and structural studies of tetrabutylammonium chloride ionic clathrate hydrates.

In the present work, characteristic properties of tetrabutylammonium bromide (TBAB) ionic clathrate hydrates structures were studied by single-crystal X-ray structure analysis. The structures of three different tetragonal TBAB ionic clathrate hydrates that were formed in our experiments were based on the same water lattice of tetragonal structure I (TS-I) differing in the ways of including bromide anions and arranging tetrabutylammonium cations. We demonstrated that (1) Br(-) can be included into the water lattice, replacing two water molecules, (2) the butyl group of the cation can be inserted not only in large T and P cavities but also in small D cavities of the water lattice TS-I, and (3) one of the reasons for polytypism of ionic clathrate hydrates on the basis of TS-I is the occurrence of alternative modes of arrangements of four-compartment cavities in adjacent layers of the water framework. The compositions of three TBAB ionic clathrate hydrates TBAB·38.1H2O, TBAB·32.5H2O, and TBAB·26.4H2O were determined by chemical analysis, and their enthalpies of fusion were measured by differential scanning calorimetry (DSC). From the obtained results, the enthalpies of the TBAB hydrate formation from TBAB and water were calculated thermodynamically.

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.

Phase and X-ray study of clathrate formation in the tetraisoamylammonium fluoride-water system

The phase diagram of the binary (i-C5H11)4NF-water system has been studied in the clathrate formation region. Three polyhydrates have been discovered, two of which (1∶38.9 and 1∶32.7) are the known orthorhombic and tetragonal phases:Pbmn,a=11.88,b=21.53,c=12.70 Å,ρmeans=1.019 g cm-3 (0°C), m.p.=32.4°C andP42/m, a=23.729,c=12.466 Å,ρmeans=1.062 g cm-3, (0°C), m.p.=31.2°C, respectively. A single crystal X-ray analysis of the novel clathrate hydrate (i-C5H11)4NF·27 H2O is reported. This new clathrate hydrate is tetragonal,I4I/a, witha=16.894(5),c=17.111(2) Å,Z=4, (−50°C), and m.p.=34.6°C. Each (i-C5H11)4N+ cation occupies a four-chamber cavity built of 15-hedra 71635942 (idealized description), with small vacant 5444 cavities filling the intervening space.

The structure of the ionic clathrate hydrate of tetrabutylammonium valerate (C4H9)4NC4H9CO2·39.8H2O

For the first time the detailed crystal structure of the ionic clathrate hydrate of tetrabutylammonium valerate (C4H9)4NC4H9CO2·39.8H2O has been determined by single crystal X-ray analysis at 150 K. The idealized water–anion host framework consists of five-compartment polyhedral cavities 4T·P and small D cavities. Butyl chains of the cation and the anion of (C4H9)4NC4H9CO2 are included in the five-compartment cavities with displacement of two “inner” host water molecules. The inclusion of the guest entities leads to the distortion of D-cavities which are partially filled by additional “guest” water molecules. The other D-cages are empty. The structure exhibits significant disordering. The adequate model of disordering and inclusion mode of the guest moieties have been obtained. Special features of the crystal structures of ionic clathrate hydrates of tetraalkylammonium carboxylates are discussed.

Single crystal X-ray diffraction study of the cubic ionic clathrate hydrate of tetrabutyl ammonium propionate (C4H9)4NC2H5COO·27.0H2O

Single crystal X-ray diffraction is used for the first time to study the structure of the ionic clathrate hydrate of tetrabutyl ammonium propionate (C4H9)4NC2H5COO·27.0H2O with the host framework based on cubic arrangement I. The structural model is characterized by a high degree of disordering in both guest and host subsystems. The structural features indicate a colocation of cations and anions in multicell 4T·nD cavities with n = 0–4; the simplest option is a pairwise location of cations and anions in combined five-cell 4T·D cavities. The positional ordering of cations leads to the formation of a 2×2×2 supercell (space group

Semiclathrate Hydrates in Tri-n-butylphosphine Oxide (TBPO)–Water and TBPO–Water–Methane Systems

I\bar 43d