Channel Inclusion Compound Research Articles

Hidden Degrees of Freedom in Aperiodic Materials

Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid-solid phase transition of an incommensurate host-guest system: the channel inclusion compound of nonadecane/urea. Strikingly, this phase transition generates a unit cell doubling that concerns only the modulation of one substructure by the other-an internal variable available only in superspace. This unanticipated pathway for degrees of freedom to rearrange leads to a second phase transition, which again is controlled by the higher dimensionality of superspace. These results reveal nature's capacity to explore the increased number of phases allowed in aperiodic crystals.

Organic channel inclusion compound featuring an open pore size of 12 Å

A first example of a purely organic material showing an open pore size of 12 Å for empty channels was obtained for micrometer sized crystals of 2,4,6-tris-(4-bromophenoxy)-1,3,5-triazine (BrPOT). The zeolitic-like form of the known inclusion compound was formed by a solid to solid transformation from micrometer large particles of the rhombohedral modification of BrPOT taking up gaseous CS 2. Long-term thermal stability of the empty channel structure was found up to about 60 °C. Functionalisation of the pore volume by including aromatic amines allowed sorption of molecular iodine. It is proposed that micrometer sized channel inclusion crystals are a promising entry to produce open pore modifications, which in the case of large crystallites are known to collapse into the solvent-free structure by the process of desolvation.

A new cryptophane receptor featuring three endo-carboxylic acid groups: synthesis, host behavior and structural study.

Examples of a new type of cryptophane molecule incorporating aromatic groups in the bridges (1-4) and, for the first time, being also supplied with three endo-positional ionizable carboxylic acid functions (1) have been synthesized and characterized. The cryptophane triester 2 yielded a solvate (channel inclusion compound) with trichloromethane and water, the X-ray crystal structure of which is reported. The complexation of 1 with low-molecular-weight alcohols in solution was studied, and the liquid-liquid extraction of different metal ions including alkali (Na(+), Cs(+)), alkaline earth (Mg(2+), Ca(2+), Sr(2+), Ba(2+)), and the lanthanide metal ions Eu(3+) and Yb(3+) in an extraction system containing metal nitrate buffer/H(2)O/1/CHCl(3) was examined. Molecular modeling calculations of the cryptophanes 1 and 2, and of the Eu(3+) complex of 1 were carried out contributing to the discussion.

NMR Cross-Relaxation Study of Ultraslow Motion of the DomainWall in Channel Inclusion Compound

We report on an NMR study of ultraslow motions in the channel thiourea-hexachloroethane inclusion compound, [2.95(NH2)2CS] C2Cl6. Temperature dependent 1H NMR relaxation measurements of the powder thiourea-hexachloroethane at different resonance frequencies, from 23 to 55.5 MHz, have been carried out. Significant reduction of the spin-lattice relaxation time at 38 and 47 MHz is caused by the cross-relaxation of protons via the quadrupole chlorine nuclei. We show that the effective 1H-35Cl cross-relaxation observed in a powder sample is due to a slow mode process, when the molecules of the domain wall exhibit a correlated translational and rotational motion over the channel. Such propagation of the domain wall is confirmed by atom-atomic potential calculation. - Pacs: 76.60-k, 76.60.Es, 61.44.Fw, 61.66.Hq

Crystal forms of torasemide: new insights

Crystallization from various organic solvents results in three crystal forms of torasemide: monotropically related mod. I (melting point, 158–161°C) and mod. II (melting point, 155–158°C), as well as a pseudopolymorphic crystal form (form A, channel inclusion compound with 1.9–4.2% water and alcohol). Physicochemical properties were determined by thermoanalysis (hot-stage microscopy, differential scanning calorimetry, thermogravimetry), Fourier transform infra-red and Raman spectroscopy, and X-ray powder diffractometry. The hygroscopicity, relative stability, true density, and heat of solutions were determined, respectively. The dissolution behaviour of mod. I and II was investigated as a function of pH, temperature, and in addition to surfactants. Mod. II is nearly three times more soluble than mod. I (mod. I, 0.34 mmol l −1; mod. II, 0.93 mmol l −1 at 20°C, pH 4.90) and proved to be highly kinetically stable. By crystallization from 1-butanol, a new compound was synthesized, which was identified as [[4-[(3-Methylphenyl)amino]-3-pyridinyl]sulfonyl]-carbamic acid, butyl ester (TOBC). The most important properties of this torasemide derivative are given. The present results give a thorough physicochemical characterization of the crystal forms of torasemide. They clearly indicate a mistaken identity of mod. II with crystal form A in formerly published articles.

Ultraslow motion of domain wall in channel inclusion compound studied by means of NMR cross-relaxation

We report temperature dependent 1H NMR relaxation measurements of the powder thiourea-hexachloroethane inclusion compound, [2.95(NH 2) 2CS]·C 2Cl 6, at different resonance frequencies, from 23 to 55.5 MHz. Significant reduction of spin–lattice relaxation time at 38–47 MHz is caused by the cross-relaxation of protons via the quadrupole chlorine nuclei. We conclude that the effective 1H– 35Cl cross-relaxation observed in powder sample is due to a slow mode process, when the molecules of the domain wall exhibit a correlated translational and rotational motion over the channel. Such a propagation of the domain wall was predicted by atom-atomic potential calculation. We show that the NMR cross-relaxation effect is an effective tool in studying ultraslow motions, in particular in incommensurate structures.

Urea–picoline N-oxide (4:2) cocrystal: an unusual channel inclusion compound

The crystal structure of urea–picoline N-oxide cocrystal reveals urea channel formation in which two independent picoline N-oxide molecules are stacked with their charge-transfer axes aligned approximately at 60° toward the crystallographic b-axis.

Phase Diagrams of Urea Inclusion Compounds 3. Pentadecanoic acid and urea

The phase diagram of the pentadecanoic acid and urea system consists of a combination of a binary system with two incongruently melting compounds and a system with a miscibility gap of the liquid phases. The first compound is a molecular addition compound of 1 molecule of pentadecanoic acid and 4 molecules of urea, which forms three polymorphic modifications. The second compound is a channel inclusion compound, which is known to be in a ratio of 1:12.2. In addition to the thermoanalytical investigations, FTIR spectroscopic and X-ray diffractometric analyses were also conducted for the inclusion compound as well as the stable form of the molecular addition compound.

Solid-state NMR Studies of Functional Group Recognition in Channel Inclusion Compound Formation

Abstract Solid-state 13C CP-MAS NMR spectra of urea inclusion compounds of methyl undecanoate (MUDA) show a significant bias in the relative alignment of guest molecules in the channels. In these spectra, asymmetric doublets are observed for C11 and methoxy carbons, while bands from internal carbons, including the carbonyl carbon, are unsplit. Band doubling is caused by differences in nearest neighbors, as shown by comparison with spectra of symmetric analogs, such as dimethyl sebacate/urea. During crystal formation of MUDA/urea from methanol, head to tail alignment is favored over head to head (plus tail to tail) alignment by a factor of 1.27±0.06, as shown by simulation of C11 resonances for spectra taken with a wide variety of cross polarization contact times. Adsorption of the ester group onto the growing face of the inclusion compound crystal probably gives rise to the observed bias.

Calorimetric studies on phase transitions arising from orientational order-disorder of the molecular axes of ferrocene and its derivatives

Heat capacities of the channel inclusion compound, Fe(C 5D 5) 2 · 3(NH 2) 2CS, and two ferrocenium salts, [Fe(C 5H 5)(C 6H 6)] + (PF 6) − and [Fe(C 5H 5) 2] + (PF 6) −, have been measured with adiabatic calorimeters between 13 and 393 K. Five phase transitions were found for Fe(C 5D 5) 2 · 3(NH 2) 2CS corresponding to those for Fe(C 5H 5) 2 · 3(NH 2) 2CS. The dominant phase transitions at 145.8 and 160.6 K are responsible for the onset of reorientational order-disorder of the molecular axis of Fe(C 5D 5) 2 in the clathrate cavity. The mass-effect of the guest ferrocene molecule on the phase transitions was not remarkable. The ferrocenium salt, [Fe(C 5H 5)(C 6H 6] +(PF 6) −, exhibited four phase transitions and two glass transition phenomena at low temperatures while its analog, [Fe(C 5H 5) 2] +(PF 6) −, brought about only three phase transitions without showing the glass transition. The higher-temperature phase transitions in these two salts have been assigned to the reorientational order-disorder mechanism of the molecular axes of the cations in the pseudo-cavities formed by eight PF − 6 anions. For the origin of the lower-temperature phase transitions in these two salts, three possibilities have been discussed. Among them, plausible origin is likely to be an order-disorder change of PF − 6 anion in the lattice. An important unsettled problem common to these three compounds is a question whether or not the Fe(C 5D 5) 2 and the cations, [Fe(C 5H 5)(C 6H 6)] + and [Fe(C 5H 5) 2] +, are still reorienting around their molecular axes even at the lowest-temperature phase.

Heat Capacity and Phase Transitions of Thiourea-Ferrocene Channel Inclusion Compound

Abstract The heat capacity of a 3:1 thiourea-ferrocene channel inclusion compound has been measured with an adiabatic-type calorimeter between 13 and 280 K. Five phase transitions were found at 147.2 (TC1), 159.79(TC2, 171.4(TC3, 185.5(TC4 and 220K(TC5. The enthalpy and entropy asssociated with these transitions have been determined. The two lowest-temperature transitions are responsitble for an order-disorder-type of reorientation of the molecular axis of ferocene in the thiourea host lattice. This reorientational disrodering was proved to proceed in two steps; in the first stage the reorientational motion is excited within the channel plane in a group of, say, three ferrocene molecules as a unit keeping the short-range order while in the second stage this restriction is lifted and the jump process between the channel plane and the channel axis is allowed. The remaining thre phase transitions with small entropy change have been attributed to unkonwn but intrinsic characters of the present clathrate. The dielectric constant measurements revealed no ferroelectric nature. The infrared and Raman spectra have also been recorde. Comparison of the transition mechanisms between solid ferrocene and the present clathrate has been maede.