Dicyclohexylamine-Thiourea Clathrate

Abstract

The reaction of dicyclohexylamine (DCHA) with thiourea leads to the formation of the inclusion compound DCHA(6 Thiourea). Room temperature, single crystal X-ray diffraction analysis shows the product has a trigonal structure, α=β=90°, γ=120°, a=b=15.801(2)A, c=12.451(3)A, which may be described as a thiourea matrix defining hexagonal cavities where the di-cyclohexylamine molecules are accommodated. ¹³C-cross polarization magic angle spinning (CP-MAS) NMR study indicates the guest inside the cavities has a relatively free rotation and that the channels are, concerning this amine, perfect van der Waals cavities. Thermal studies indicates that the structural identity of the thiourea matrix endures after a partial loss of amine.     

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 of triisoamylbutylammonium iodide

The phase diagram of the (i-C₅H₁₁)₃C₄H₉NI?H₂O system is reported. Triisoamylbutylammonium iodide forms polyhydrates with hydration numbers of 36 (mp 12.5°C) and 32 (mp 13.2°C) and a dihydrate. Crystals of both polyhdrates have been isolated, and their compositions have been determined.     

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.     

Physicochemical Properties of Ionic Clathrate Hydrates

Ionic clathrate hydrates are known to be formed by the enclathration of hydrophobic cations or anions into confined cages and the incorporation of counterions into the water framework. As the ionic clathrate hydrates are considered for their potential applicability in various fields, including those that involve solid electrolytes, gas separation, and gas storage, numerous studies of the ionic clathrate hydrates have been reported. This review concentrates on the physicochemical properties of the ionic clathrate hydrates and the notable characteristics of these materials regarding their potential application are addressed.     

氮气笼型水合物的激光拉曼光谱

在253K和16MPa的压力下,于实验室内合成了氮气水合物,用显微共焦拉曼光谱对其N-N和O-H键伸缩振动的光谱特征进行了研究．结果表明,氮气水合物中的N-N和O—H键的拉曼峰分别为2322．4和3092．1cm^-1,与天然的空气水合物中的数据十分接近．另外,还测定了液氮和溶解于水中的氮分子中N—N键的拉曼峰值,分别为2326．6和2325．0cm^-1．氮气笼型水合物分解的拉曼谱图表明,氮分子同时进入水合物的大笼和小笼中,但由于氮分子在大、小笼中的环境氛围十分接近,其拉曼位移相差不大,故拉曼谱图只能显示N—N键伸缩振动一个峰．     

Hydrogen in Porous Tetrahydrofuran Clathrate Hydrate

The lack of practical methods for hydrogen storage is still a major bottleneck in the realization of an energy economy based on hydrogen as energy carrier. ¹ Storage within solid‐state clathrate hydrates, ² – ⁴ and in the clathrate hydrate of tetrahydrofuran (THF), has been recently reported. ⁵ , ⁶ In the latter case, stabilization by THF is claimed to reduce the operation pressure by several orders of magnitude close to room temperature. Here, we apply in situ neutron diffraction to show that—in contrast to previous reports^{[5, 6]}—hydrogen (deuterium) occupies the small cages of the clathrate hydrate only to 30 % (at 274 K and 90.5 bar). Such a D₂ load is equivalent to 0.27 wt. % of stored H₂. In addition, we show that a surplus of D₂O results in the formation of additional D₂O ice Ih instead of in the production of sub‐stoichiometric clathrate that is stabilized by loaded hydrogen (as was reported in ref. ⁶ ). Structure‐refinement studies show that [D₈]THF is dynamically disordered, while it fills each of the large cages of [D₈]THF?17D₂O stoichiometrically. Our results show that the clathrate hydrate takes up hydrogen rapidly at pressures between 60 and 90 bar (at about 270 K). At temperatures above ≈220 K, the H‐storage characteristics of the clathrate hydrate have similarities with those of surface‐adsorption materials, such as nanoporous zeolites and metal–organic frameworks, ⁷ , ⁸ but at lower temperatures, the adsorption rates slow down because of reduced D₂ diffusion between the small cages.     

Clathrate formation in water-peralkylonium salts systems

We discuss composition, stoichiometry and stability (phase diagrams) of peralkylonium salts and analogues (Alk₃XO, where X=N,P,As) polyhydrates depending on the dimensions and the configuration of the hydrophobic part of a guest-molecule and its ability to interact in a hydrophilic way with the framework.     

Adsorption-Inhibition of Clathrate Hydrates by Self-Assembled Nanostructures

The mechanism by which safranine O (SFO), an ice growth inhibitor, halts the growth of single crystal tetrahydrofuran (THF) clathrate hydrates was explored using microfluidics coupled with cold stages and fluorescence microscopy. THF hydrates grown in SFO solutions exhibited morphology changes and were shaped as truncated octahedrons or hexagons. Fluorescence microscopy and microfluidics demonstrated that SFO binds to the surface of THF hydrates on specific crystal planes. Cryo-TEM experiments of aqueous solutions containing millimolar concentrations of SFO exhibited the formation of bilayered lamellae with an average thickness of 4.2±0.2 nm covering several μm². Altogether, these results indicate that SFO forms supramolecular lamellae in solution, which might bind to the surface of the hydrate and inhibit further growth. As an ice and hydrate inhibitor, SFO may bind to the surface of these crystals via ordered water molecules near its amine and methyl groups, similar to some antifreeze proteins.     

Clathrate formation in the tetraisoamylammonium propionate-water system

In this paper we examine clathrate formation in the tetraisoamylammonium propionate-water binary system. We have found formation of four polyhydrates, two of which are metastable over the whole temperature range studied. All polyhydrate crystals were isolated and their compositions and densities determined; for (i-C₅H₁₁)₄NC₂H₅COO·36.5H₂O, unit cell parameters were additionally found. The results are compared with data for tetra-n-butylammonium carboxylate polyhydrates, and the structure of the title compounds is suggested. It is confirmed that the isoamyl radical stabilizes the tetradecahedral void of the clathrate hydrate framework better than the n-butyl radical. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 67–71, May–June, 1994. Translated by L. Smolina     

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.     

Clathrate Hydrates of Tetrabutylammonium and Tetraisoamylammonium Halides

Clathrate formation was considered for two series of systems: (C₄H₉)₄NG–H₂O and iC₅H₁₁)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.     

Clathrate Hydrates of Sulfur Hexafluoride at High Pressures

The pressure dependence (0.4 Mpa–1.3 GPa) of the hydrate decomposition temperatures in the sulfur hexafluoride-water system has been studied. In addition to the known low-pressure hydrate SF₆17H₂O of Cubic Structure II, two new high-pressure hydrates have been found. X-ray analysis in situ showed the gas hydrate forming in the sulfur hexafluoride-water system above 50 MPa at room temperature to be of Cubic Structure I. The ability of water to form hydrates whose structures depend on the guest molecule size under normal conditions and at high pressures is discussed.     

Clathrate hydrates of tetrabutylammonium carboxylates and dicarboxylates

Phase diagrams of the binary aqueous systems with tetra-n-butylammonium (TBA) carboxylates ((C₄H₉)₄NC_nH_{2 n+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.