The Modification of Hydroxyl Surfaces of Formamide-Intercalated Kaolinites Synthesized by Controlled Rate Thermal Analysis

Controlled rate thermal analysis (CRTA) technology made possible the separation of adsorbed formamide from intercalated formamide in formamide-intercalated kaolinites. X-ray diffraction shows that the CRTA-treated formamide-intercalated kaolinites remain expanded after CRTA treatment. The Raman spectra of the CRTA-treated formamide-intercalated kaolinites are significantly different from those of the intercalated kaolinites with both intercalated and adsorbed formamide. An intense band is observed at 3629 cm(-1), attributed to the inner surface hydroxyls hydrogen bonded to the formamide. Broad bands are observed at 3600 and 3639 cm(-1) and are attributed to the inner surface hydroxyls, which are hydrogen bonded to the adsorbed water molecules. The hydroxyl stretching band of the inner hydroxyl is readily observed at 3621 cm(-1) in the Raman spectra of the CRTA-treated formamide-intercalated kaolinites. The results of thermal analysis show that the amount of intercalated formamide between the kaolinite layers is independent of the presence of water. The Raman bands of the formamide in the CRTA-treated intercalated kaolinites are readily observed. Copyright 2001 Academic Press.     

Cyclodextrins and the liquid-liquid phase distribution of progesterone, estrone and prednicarbate

The purpose of the present work was to investigate the interaction of drugs and octanol with hydroxypropyl β- (HPβCD) and γ- (HPγCD) cyclodextrin, sulfobutyl ether β-cyclodextrin (SBEβCD) and randomly methylated-β-cycoldextrin (RMβCD) and to describe the interaction by theoretical models. The poorly soluble steroid drugs progesterone, estrone and prednicarbate were used as model compounds in this study. Hexane and chloroform were also investigated in combination with HPβCD. Octanol formed a complex with all cyclodextrins and the saturation of the aqueous solution with this solvent therefore had a significant effect on the solubilization and extraction potential of cyclodextrins. Hexane had less affinity for cyclodextrins, but the drugs were poorly soluble in this solvent and it could therefore not be used in phase-distribution investigations. Previously we have derived equations that can be used to account for the competitive interaction between two guest compounds that compete for space in the cyclodextrin cavity. These equations were rearranged to calculate the complexation efficacy from phase-solubility data. An equation was derived that obtains intrinsic solubility (S ₀) and intrinsic partition coefficient (P) from the slopes of the phase-solubility and phase-distribution profiles. Investigation of the data showed that the results could not be sufficiently explained by the “classical” drug/cyclodextrin complex model that recognizes the possibility of competitive interactions but ignores any contribution from higher order complexes or aggregation of the cyclodextrin complexes. Relative difference in solubilization potential of different cyclodextrins cannot be translated to relative differences in extraction efficacy. Thus, for these three steroid compounds, RMβCD and SBEβCD gave the best solubilization potential whereas the best extraction efficacy was observed with HPγCD.     

Copper oxalate complexes: synthesis and structural characterisation

Six copper(II) oxalate complexes, namely {K₂[Cu(ox)₂]} _n (1), {(Hiz)₂[Cu(ox)₂]} _n (2), {[Cu(ox) (N-Bzliz)₂]} _n (3), (HMeiz)₂[Cu(ox)₂] (4), {[Cu(ox)(Meiz)₂]} _n (5), and [Cu(Hox)₂(H₂O)₂](N-Bzliz) (6) where ox = oxalate ion, iz = imidazole, N-Bzliz = N-benzylimidazole, Meiz = 2-methylimidazole, were synthesised and characterised by single crystal X-ray diffraction (complexes 1–5) or powder X-ray diffraction (compound 6). The three-dimensional crystal packing structures of 2, 4, and 5 are consolidated by intermolecular hydrogen bonds linking the oxygen atom of the oxalate group and the amine or imine group of the imidazole-based part into chains. The molecules of complex 6 are held together by intermolecular hydrogen bonds between the oxygen atoms of the oxalate group and coordinated water molecules.     

Studies on the Chemistry of [Cd(NH3)4](MnO4)2. A Low Temperature Synthesis Route of the CdMn2O4+x Type NOx and CH3SH Sensor Precursors

Abstract. [Tetraamminecadmium(II)] bis(permanganate) ( 1 ) was prepared and its crystal structure was elucidated with XRD‐Rietveld refinement and vibrational spectroscopic methods. Compound 1 has a cubic lattice consisting of a 3D hydrogen‐bonded network built as four by four distorted tetrahedral blocks of [Cd(NH₃)₄]²⁺ cations and MnO₄^– anions, respectively. The other four permanganate ions are located in a crystallographically different environment, placed in the cavities formed by the attachment of the building blocks. A low‐temperature (≈100 °C) solid phase quasi‐intramolecular redox reaction producing ammonium nitrate and amorphous CdMn₂O₄ could be established. Neither solid phase nor aqueous solution phase thermal deammoniation of compound 1 can be used to prepare Cd(MnO₄)₂ and [Cd(NH₃)₂(MnO₄)₂]. During deammoniation of compound 1 in aqueous solution a precipitate consisting of Cd(OH)₂ forms. Additionally, solid MnO₂ and ammonium permanganate (NH₄MnO₄) forms. The solid phase deammoniation reaction (toluene used as heat convecting medium) with subsequent aqueous leaching of the ammonium nitrate formed has proved to be an easy and convenient technique for the synthesis of amorphous CdMn₂O_4+x type NO_x and MeSH sensor precursors. The 1 ‐ D perdeuterated complex was also synthesized to distinguish the N–H(D) and O–H(D) fragment signals in the TG‐MS spectra and to elucidate the vibrational characteristics of the overlapping Mn–O and Cd–N frequencies.     

Thermal decomposition of hydrotalcite with hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.5·7H₂O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.66·9H₂O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite.     

Thermoanalytical studies of silver and lead jarosites and their solid solutions

Dynamic and controlled rate thermal analysis has been used to characterise synthesised jarosites of formula [M(Fe)₃(SO₄)₂(OH)₆] where M is Pb, Ag or Pb–Ag mixtures. Thermal decomposition occurs in a series of steps. (a) dehydration, (b) well defined dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of water formation reveal the subtle nature of dehydration and dehydroxylation. CRTA offers a better resolution and a more detailed interpretation of the decomposition processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal separation of the dehydroxylation steps, since in these cases a higher energy (higher temperature) is needed to drive out gaseous decomposition products through a decreasing space at a constant, pre-set rate.     

Book review

Summary Handbook of Thermal Analysis and Calorimetry, Volume 2, Applications to Inorganic and Miscellaneous Materials, by Michael E. Brown and Patrick K. Gallagher (Editors). Elsevier B.V., Amsterdam, 2003, 905 pp, ISBN 0 444 82086 8;