György Pokol

Thermal, FTIR and XRD study on some 1:1 molecular compounds of theophylline

Thermal stability and structural features of three newly synthesized 1:1 lattice compounds of theophylline (th) with ethylenediamine carbamate (enCO2), 1,10-phenanthroline (phen), and 5-sulfosalicylic acid (sa-5-SO3H) have been studied in comparison with those of the theophylline compounds with ethanolamine (ea) and salicylic acid (sa). Simultaneous TG-DTA measurements, FTIR spectroscopy and X-ray diffraction have been carried out to get information on the various structural units of these solid inclusions, especially on the actual form (molecule, anion or cation) of theophylline moieties built in. Theophyllinate and theophyllinium ions have been found in the ethanolammonium-theophyllinate (1:1) (1, eaH+⋅th-) and the theophyllinium salicylic acid 5-sulfonate monohydrate (1:1:1), (5, thH+⋅saSO−3⋅H2O), respectively. Whilst the 1:1 complexes with 1,10-phenanthroline (2, th⋅phen), ethylenediamine carbamate (3, th⋅enCO2), and salicylic acid (4, th⋅sa) contain neutral theophylline moieties associated with H-bonds. In compound (3) the zwitterion of N-(2-ammonium-ethyl)carbamate (NH3+-CH2-CH2-NH-CO-2) is present.

Reaction of copper(II) with 1-carboxamide-3,5-dimethylpyrazole, 1-carboxamidine-3,5-dimethylpyrazole, 4-acetyl-3-amino-5-methylpyrazole and 5-amino-4-carboxamide-1-phenylpyrazole ☆

Abstract Complex formation of copper(II) bromide and acetate with 1-carboxamide-3,5-dimethylpyrazole (HL3) and copper(II) bromide with 5-amino-4-carboxamide-1-phenylpyrazole (L2), 4-acetyl-3-amino-5-methylpyrazole (HL4) and 1-carboxamidine-3,5-dimethylpyrazole (HL5), was studied. The obtained compounds, CuBr2(L2)2, Cu(L3)2, CuBr2(HL4)2, CuBr2(HL5)2 and [CuBr(HL1)(L3)]2 (HL1 denotes the 3,5-dimethylpyrazole), are characterized by elemental analysis, FT-IR spectrometry, molar conductivity, TG-MS and DSC. The X-ray structure of [CuBr(HL1)(L3)]2 and Cu(L3)2 is discussed. For [CuBr(HL1)(L3)]2 a dimeric penta-co-ordinated structure has been found; the co-ordination around the metal in Cu(L3)2 is trans-square planar. To CuBr2(L2)2 and CuBr2(HL4)2 a nearly tetrahedral, while for CuBr2(HL5)2 an octahedral geometry may be assumed. It means that the geometry of the compounds in the first place depends on the ligand substituents. The course of the complex formation reaction is anion-dependent and may be explained on the basis of Pearsons theory, taking into account the steric factors. A low stability intermediate formation was observed in the thermal decomposition of Cu(L3)2.

Quantitative determination of famotidine polymorphs: X-ray powder diffractometric and Raman spectrometric study

X-ray powder diffractometric and Raman spectrometric methods were developed for quantitative measurement of the polymorphic forms of famotidine in their mixtures. This study aims to deduce some useful conclusions regarding quantitative polymorph analysis, which could also be utilized in industrial practice. Both form A and form B of famotidine possess specific X-ray diffraction reflections as well as characteristic Raman vibrational bands, which permits simple determination of the phases in their mixtures. Keeping in mind that multivariate data processing by chemometric approach is thought of nowadays as superior over univariate one, the results of the two evaluation methods were compared by precision, accuracy as well as robustness. It was found that both approaches provide similar results provided analytically useful data regions are properly selected. Overcoming the common problems of quantitative X-ray powder diffractometry and solid state Raman spectrometry both permit accurate quantification of famotidine polymorphs; the latter, however, seems to be more favourable in regular laboratory practice.

Study of zinc thiocarbamide chloride, a single-source precursor for zinc sulfide thin films by spray pyrolysis

Thermal decomposition of the title compound, Zn(tu)2Cl2 (tu=thiourea), was studied up to 1200°C in dynamic inert (N2) and oxidative (air) atmospheres using simultaneous TG/DTA techniques. In addition, XRD and IR were employed ex situ to resolve the reaction mechanism and products. Cubic ZnS (sphalerite) is formed below 300°C in both atmospheres and is observed until 760°C, whereafter it transforms in nitrogen to the hexagonal ZnS (wurtzite). EGA by FTIR revealed the complexity of the decomposition reactions involving also the evolution of H2NCN, which reacts to form hexagonal ZnCN2 as revealed by an XRD analysis.

Evolved gas analysis of dichlorobis(thiourea)zinc(II) by coupled TG-FTIR and TG/DTA-MS techniques

Identification and monitoring of gaseous species released during thermal decomposition of the title compound 1, Zn(tu)2Cl2, (tu=thiourea, (NH2)2C=S) have been carried out in flowing air atmosphere up to 800°C by both online coupled TG-EGA-FTIR and simultaneous TG/DTA-EGA-MS. The first gaseous products of 1, between 200 and 240°C, are carbon disulfide (CS2) and ammonia (NH3). At 240°C, an exothermic oxidation of CS2 vapors occurs resulting in a sudden release of sulphur dioxide (SO2) and carbonyl sulphide (COS). An intense evolution of hydrogen cyanide (HCN) and beginning of the evolution of cyanamide (H2NCN) and isothiocyanic acid (HNCS) are also observed just above 240°C. Probably because of condensation and/or polymerization of cyanamide vapors on the windows and mirrors of the FTIR gas cell optics, some strange baseline shape changes are also occurring above 330°C. Above 500°C the oxidation process of organic residues appears to accelerate which is indicated by the increasing concentration of CO2, while above 600°C zinc sulfide starts to oxidize resulting in the evolution of SO2. All species identified by FTIR gas cell were also confirmed by mass spectrometry, except for HNCS.

Comparison of theophyllinato Cu(II) complexes of ethanolamine and diethanolamine. Part 2. Structure and thermal study of the dimeric complex with diethanolamine

Abstract There is now much evidence that anticancer drugs exert biological action by preferred binding of a transition metal to the N7 sites of the guanine residues of DNA. In our series of theophyllinato copper(II) complexes containing amine ligands, the structural effect of changing from ethanolamine to diethanolamine is examined. A new mixed ligand copper(II) complex, bis(μ-2-(2-hydroxyethyl)aminoethanolato-O,N,O′)bis(theophyllinato-N7)dicopper(II) (C22H34N10O8Cu2) (1) has been synthesized as model compound from aqueous solutions of CuSO4, theophylline, and diethanolamine (dea). Its distinct Me2L2L′2 structure has been determined by single crystal X-ray diffraction. The centrosymmetric binuclear complex contains two strongly distorted square pyramidally (or pseudooctahedrally) coordinated copper ions bound together by two alkoxo-bridges. The bridging O is a deprotonated oxygen of the monoalcoholate formed from diethanolamine. Both of the theophyllinate anions take part in N7/O6 chelation in the complex 1, while only one of the theophyllinate anions is able to perform it in the mononuclear complex (SPY-5-12)-(2-aminoethanol-N)(2-aminoethanol-N,O)bis(theophyllinato-N7)copper(II) dihydrate (2). The two copper(II) centres in 1 are found to be antiferromagnetically coupled. The combined thermogravimetric and evolved gas detection shows that the tridentate alcoholate anions are fragmented and evolved between 125 and 275°C, whilst the degradation of theophyllinate anions begins at 350°C. Structural, spectroscopic and thermal comparison to the previously published analogous monoethanolamine Cu(II) complex (2) is presented.

TRANSITION METAL COMPLEXES WITH PYRAZOLE-BASED LIGANDS Part 8. Characterization and thermal decomposition of zinc(II) complexes with di- and trisubstituted pyrazoles

We report the synthesis and the characterization (elemental analysis, FT-IR spectroscopy, thermal methods and molar conductivity measurements) of the mixed complexes of zinc with acetate and 3-amino-5-methylpyrazole, HL1, [Zn(OAc)2(HL1)2], or 3-amino-5-phenylpyrazole, HL2 [Zn(OAc)2(HL2)2], or 4-acetyl-3-amino-5-methylpyrazole, HL3, [Zn(OAc)(L3)(HL3)]2, with isothiocyanate and HL2 [Zn(SCN)2(HL2)2], or HL3 [Zn(SCN)2(HL3)2], and with nitrate, isothiocyanate and 3,5-dimethyl-1-carboxamidinepyrazole, HL4 [Zn(NO3)(NCS)(HL4)2].The thermal decomposition of the complexes is generally continuous resulting zinc oxide as end product,except [Zn(OAc)(L3)(HL3)]2 in which case a well-defined intermediate was observed between 570–620 K. On the basis of the IR spectra and elemental analysis data of the intermediate a decomposition scheme is proposed.

Combined DTA and XRD study of sintering steps towards YAl3(BO3)(4)

Sintering processes in the Y2O3–Al2O3–B2 O3 system and its subsystems (Y2O3–B2O3 and Al2 O3–B2O3) have been investigated by using combined DTA and XRD measurements to get a better understanding of solid state chemical changes resulting in the formation of yttrium aluminum borate (YAl3(BO3)4, YAB) phase and to study the possible role and contribution of various simple borates formed also in the former processes.Two new exothermic heat effects of YBO3 formation have been detected by DTA in the Y2O3–B2O3 system between 720 and 980°C. In the Al2O3–B2O3 system a new experimental XRD profile of Al4B2O9 was observed. Formation of these borates seems to promote the nucleation of double borate YAB below 1000°C. Conversion of Al4B2O9 to Al18B4 O33 was observed after a long term (10 h) sintering at 1050°C. Similarly, an increased formation of YAB has been observed as a product of the sintering reaction between YBO3 and Al18B4O33 at 1150°C. The two latter single borates are found to be identical with the high temperature decomposition products of YAB.

Studies on the reactions of aluminium oxides and hydroxides

The hydrothermal and decomposition reactions of differently ground gibbsite and its reaction products were studied. The samples were treated isothermally under hydrothermal conditions or in air, and the products were characterized by thermogravimetry and IR spectroscopy. It was found that the method and duration of grinding and the particle size of the starting gibbsite influenced the reactivity of the gibbsite itself and that of the primary reaction products. In a later step of the reaction sequence (hydrothermal rehydration ofγ-alumina), the effects of the differences in the properties of the starting gibbsites were insignificant.ZusammenfassungEs wurden die hydrothermischen und Zersetzungsreaktionen verschiedener Gibbsitproben und deren Reaktionsprodukten untersucht. Die Proben wurden unter hydrothermischen Bedingungen oder in Luft isothermisch behandelt, die Produkte mittels TG und IR beschrieben. Es wurde festgestellt, da\ Art und Weise der Zerkleinerung und Korngrö\e des Gibbsit-Ausgangsmateriales die ReaktivitÄt von Gibbsit selbst, aber auch die der primÄren Reaktionsprodukte beeinflu\t. In spÄteren Schritten des Reaktionsverlaufes (hydrothermische Rehydratation von-Aluminiumoxid) besitzen Unterschiede in den Eigenschaften des Gibbsit-Ausgangsmateriales keinen Einflu\.

Quantifying low levels of polymorphic impurity in clopidogrel bisulphate by vibrational spectroscopy and chemometrics

Vibrational spectroscopic methods were developed for quantitative analysis of Form II of clopidogrel bisulphate in Form I and Form II polymorphic mixtures. Results show that both IR and Raman spectroscopy combined with chemometrics are suitable to quantify low levels of Form II in Form I, down to 2 and 3%, respectively, with less than 1% limit of detection. Different preprocessing and multivariate methods were applied for spectral processing and were compared to find the best chemometric model. Common problems of quantitative vibrational spectroscopy in the solid phase are discussed; and procedures appropriate to eliminate them are proposed.