Loss Of Lattice Water Research Articles

Structure and Thermal Transformations of Methylammonium Tungstate

AbstractMethylammonium paradodecatungstate, (CH3NH3)10[H2W12O42] ⋅ nH2O, was prepared by the reaction of WO3 or H2WO4 in aqueous methylamine, followed by drying. The [H2W12O42]10− anion consists of two HW3O13 groups containing three edge‐sharing WO6 octahedra and two W3O14 groups having two edge‐sharing connections. On drying the produced material at 70 °C, some lattice water was released, but this did not affect the [H2W12O42]10− structure, although there was a decrease in the unit cell volume. By adding water, the loss of lattice water and structural changes were reversed. The existence of paradodecatungstate anions was confirmed by single‐crystal and powder X‐ray diffraction, Fourier transform infrared, Raman, 183W nuclear magnetic resonance, and ultraviolet‐visible spectroscopy. When the methylammonium paradodecatungstate was heated to more than 150 °C, CH3NH2 and H2O were released, and amorphous WO3 was observed as an intermediate product and monoclinic WO3 as the final product. These results reveal the structure of methylammonium tungstate, which was first reported in 1909 and now is used as an important negative staining reagent for virus observation, is methylammonium paradodecatungstate.

Lattice Water Controlled Photo- and Thermochromism of N-Protonated Carbomethoxypyridinium Iodoargentate Hybrids.

Two iodoargentate hybrids, {[HNOM][AgI2]·H2O} (1) and {[HINOM][AgI2]·H2O} (2) (HNOM+ = N-protonated 3-carbomethoxypyridinium; HINOM+ = N-protonated 4-carbomethoxypyridinium), have been designed and prepared, which were constructed from typical [AgI2]- inorganic chains and cationic hydrogen-bonding supramolecular networks (one-dimensional for 1 and three-dimensional for 2) of lattice water and positional isomeric N-protonated carbomethoxypyridinium. Two hybrids exhibit sensitive photochromism based on intermolecular electron transfer (ET) and thermochromism due to reversible hydration and dehydration and the consequent variation of intermolecular charge transfer (CT). Furthermore, loss of lattice water gives rise to improved photochromic dehydrated form 1T and optically inert dehydrated form 2T, suggesting a delicate modulating effect of lattice contraction on the intermolecular CT and ET as well as consequently photoresponsive behaviors.

Complexation of different transition metals with 4-(4-carboxyphenyl)-1,2,4-triazole: Synthesis, crystal structure and hirshfeld surfaces

Four new complexes based on the 4-(4-carboxyphenyl)-1,2,4-triazole (Hcpt) ligand, {[Co(cpt)2(H2O)4]·H2O}(1), {[Cr(cpt)2(H2O)4]·10H2O}(2), {[Fe(cpt)2(H2O)4]·10H2O}(3), {[Zn(cpt)2 (H2O)2]}(4) have been synthesized and characterized by elemental analysis, single crystal X-ray diffraction and TGA. For complexes 1, 2, and 3, they almost have the same coordination mode that only one nitrogen atom of triazole are involved in the coordination, while in the complex 4, only the group COO− participates in the coordination. In the crystal structure of 1, each structural unit[Co(cpt)2(H2O)4] is linked to another by hydrogen bonding formed by the lattice water molecules, thus forming a one-dimensional chain structure; In the crystal structure of 2 or 3, each structural unit[Cr(cpt)2(H2O)4] or [Fe(cpt)2(H2O)4] forms a two-dimensional layered structure by intermolecular hydrogen bonds from the coordinated water molecule and the group COO−. The results of thermogravimetric analysis show that the loss of lattice water and coordinated water molecules in 1, 2 and 3 is below 120 °C, while the loss of coordinated water molecules in 4 is in the temperature range of 190–260 °C. Hirshfeld surface shows that the NH⋯O hydrogen bonding interaction plays a significant role towards the conformation of the basic structure of these complexes.

Thermal properties of iopamidol

Three crystal forms of iopamidol, an iodinated contrast media used in radiology, have been so far elucidated: an anhydrous, a monohydrate and a pentahydrate form (labeled hereafter as W0, W1 and W5, respectively), which showed the occurrence of different conformations, atropisomeric in nature. Specifically, the anhydrous and monohydrate forms contain iopamidol with a “syn” conformation of the two symmetric sidearms, while an “anti” conformation was found in the pentahydrate, making it a conformational (pseudo)-polymorph of the first two. The three crystal forms have been here investigated by means of DSC, variable temperature X-ray powder diffraction and Raman spectroscopy. This study enabled us to highlight the thermal-induced transformations, leading to the discovery of new crystal forms, for a total of four hydrated and four distinct anhydrous phases. In particular, the DSC curve of W0 revealed only a reversible solid–solid transition at around 180 °C before melting, with subsequent degradation above 300 °C. W1, after the loss of lattice water around 100 °C, shows a characteristic split peak at about 250 °C, which is attributed to melting. Below 150 °C, powder diffraction of W1 suffers of minor changes, with a smooth variation of the lattice parameters, in agreement with a progressive loss of water in a reversible event, monitored also by DSC. At variance, W5 evidenced an irreversible loss of water in three distinct steps, for three, one and one H2O molecules each, respectively; subsequent transitions occur at 140 and 180 °C, before melting at 240 °C. Three clearly visible transformations were also detected by variable temperature powder diffraction measurements, where the loss of three molecules of water in a single step, generating a bis-hydrated species (W2), is followed by a second dehydration process leading, above 75 °C, to a new monohydrate phase W1′, different from the known W1 form. The Raman spectra of the three crystal forms, measured upon heating up to 160 °C, evidenced changes in spectral regions of amides that, according to our simulations of the vibrational properties, can be attributed to changes of the hydration properties and, more significantly, in terms of the “syn” and “anti” conformations.

Use of a TG/DTA/Raman System to Monitor Dehydration and Phase Conversions

Abstract Use of a TG/DTA/Raman system enabled real time collection of Raman spectra during the dehydration of Risedronate, the active pharmaceutical ingredient in the osteoporosis drug Actonel. Raman spectra collected during the dehydration of this material show a crystal lattice adjustment below the boiling point of water facilitating interpretation of the TG/DTA thermal profile. Raman spectra also revealed recrystallization processes subsequent to loss of lattice water that were not evident in the thermal analysis profile. Spectral evidence showing the formation and disappearance of a second hydrate form are observed during the dehydration of this material. In addition, spectral evidence indicating the presence of an anhydrate form of this material are observed prior to thermal induced degradation of this material.

The Fixation Phenomenon of Adsorbed Cations Caused by Drying of Kaolinite

Physico-chemical studies on the nature of adsorbed cations held on kaolinite surface, i.e. the change of the mean free bonding energy of adsorbed H+, and of the exchangeabilities of Li+, Na+, K+, Cs+ caused by drying the kaolinite below 600°C, were carried out.It was concluded that kaolinites, regardless of their morphological properties, have power to fix almost nonexchangeably a considerable amount of above cations. The ability of fixing the cations increases with the increasing degree of drying, until kaolinite decomposes with the loss of lattice water, when the decrease of fixing power is observed. The fixing power varies a great deal with the radii of cations as well as with the degree of losing the water of hydration at a definite temperature, the samller cation and the larger degree of dehydration causing the more powerful fixation.Drying brings with the decrease of ζ-potential of the clay surface suspended in water, and therefore the rehydration of adsorbed ions may not be reversible at normal temperature.A new theory of the fixation of adsorbed cations, being quite different from any current theories which have been introduced so far by soil scientists, is advanced by authors. As the fixation causes the change of ionic distribution in electrical diffuse double layer, it would be natural to consider that the fixation may affect the properties of kaolinite-water systems. The influences of drying on the sedimentation of clay-water suspension were investigated. It was noted that the kaolinite dried even at such a low temperature as below 50°C showed a remarkable differences in sedimentation volume and settling rate from those of non-dried, original suspension. The authors are going to point out that the fixation phenomenon, first unveiled by them, would be very significant for the colloid chemical or rheological study of clay minerals and for the proper control in clay industries.