Thermoanalytical studies of imidazole-substituted coordination compounds

Four manganese(II) coordination compounds with bis(1-methylimidazol-2-yl)ketone (BIK) of general formula Mn(BIK)₂X₂ (X = Cl, Br, NO₃, ClO₄) were synthesized and characterized by elemental analysis, by UV–vis, and FTIR spectroscopies to be compared with the literature data. Following our previous thermoanalytical studies on imidazole-substituted coordination compounds, the thermal behavior of the synthesized Mn(II) complexes was investigated using TG and DTG techniques: the thermal profile is characterized by three substantial consecutive releasing steps for all the three complexes and the releasing supposed behavior is confirmed by EGA analysis performed by coupling the TG analyzer to an MS spectrometer. In particular, the first step is ascribed to the release of the two anions, followed by the loss of four methyl groups (side chains of the ligand) and two bridge-carbonyl groups. The residual tetra-imidazole manganese compound decomposes in a final step to give MnO as the final residue. Both the initial decomposition temperatures and the kinetic rate constants associated to the first decomposition step indicated a higher stability of the Mn(BIK)₂Cl₂ complex, the bromide complex being very close to the chloride one (first-step thermal stability: ClO₄ ⁻ <NO₃ ⁻ ≤Br⁻ <Cl⁻). Finally, the three-dimensional diffusion reaction model (D3) was selected to describe the first decomposition step for all the four complexes examined.     

Thermoanalytical approach to the study of the kinetic and thermodynamic stability of coordination compounds and clathrates

The possibilities of the modern thermoanalytical methods for the study of the kinetic lability and thermodynamic stability of coordination compounds and inclusion compounds are discussed. The nonisothermal kinetics allowed to obtain the kinetic stability series of compounds (iso-entropy, iso-enthalpy and with iso-kinetic temperature), these series are considered from the point of view of the ligands substitution mechanism. The quasi-equilibrium thermogravimetry was used for the forming of thermodynamic stability series and for the search of the iso-equilibrium temperature.

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Zusammenfassung Es werden die Möglichkeiten moderner thermoanalytischer Methoden für die Untersuchung der kinetischen Labilität und der thermodynamischen Stabilität von Koordinations- und Einschlußverbindungen diskutiert. Die nichtisotherme Kinetik erlaubt die Erstellung von kinetischen Stabilitätsreihenfolgen der Verbindungen (Iso-Entropie, Iso-Enthalpie und mit isokinetischer Temperatur). Diese Reihenfolgen wurden auch vom Gesichtspunkt des Mechanismus der Ligandensubstitution her bewertet. Eine quasi-Gleichgewichts-Thermogravimetrie wurde zur Erstellung der Reihenfolge der thermodynamischen Stabilität und zur Ermittlung der iso-Gleichgewichtstemperatur benutzt.

     

Supramolecular isomerism in coordination compounds: nanoscale molecular hexagons and chains

A nanoscale supramolecular hexagon, 1, and its supramolecular isomeric chain structure, 2, have been prepared from self-assembly of 5-NO2-bdc and Cu(II) cations. The hexagon is neutral and soluble and has outer and inner diameters of 3.1 and 0.8 nm, respectively.     

Linkage isomerism in coordination polymers

The use of the recently prepared polynitrile ligand tcnopr3OH(-) ([(NC)(2)CC(OCH(2)CH(2)CH(2)OH)C(CN)(2)](-)) with different salts of Fe(II), Co(II), and Ni(II) has led to a very rare example of linkage isomerism in a coordination chain. These pairs of linkage isomers can be formulated as [M(tcnopr3OH-κN,κO)(2)(H(2)O)(2)]; M = Fe (1), Co (3), and Ni(5) and [M(tcnopr3OH-κN,κN')(2)(H(2)O)(2)]; M = Fe (2), Co (4), and Ni (6). Compounds 1-2, 3-4, and 5-6 are three pairs of linkage isomers since they present the same formula and chain structure and they only differ in the connectivity of the polynitrile ligand bridging the metal ions in the chain: through a N and an O atom (1κN:2κO-isomer) or through two N atoms (1κN:2κN'-isomer). The magnetic properties show, as expected, very similar behaviors for both isomers.     

Quantum-chemical study of the coordination isomerism of P(V)-P(IV) in chlorophosphoric heterocyclic compounds

Using the RHF/6-31G method calculations have been carried out on the isomeric chlorophosphoric heterocyclic molecules C₆H₄O₂PCl₂N=CClX₃ and C₆H₄O₂PCl=NCCl₂CX₃ (X = F and Cl) with full optimization of their geometries. Conclusions are drawn regarding the chlorotropic conversion of these isomers which contain phosphorus with coordination numbers V and IV. The relative stabilization energies of the isomeric compounds have been determined for variation of X. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 294–298, February, 2007.     

Structural isomerism in CuSCN coordination polymers

CuSCN reacts with the angular ligand 2,4-bis(4-pyridyl)-1,3,5-triazine (dpt) to afford rare examples of coordination polymer structural isomers including a non-centrosymmetric three-dimensional framework with Cd(SO4) topology constructed from tetrahedral metal cations.     

Thiocyanate linkage isomerism in a ruthenium polypyridyl complex

Ruthenium polypyridyl complexes have seen extensive use in solar energy applications. One of the most efficient dye-sensitized solar cells produced to date employs the dye-sensitizer N719, a ruthenium polypyridyl thiocyanate complex. Thiocyanate complexes are typically present as an inseparable mixture of N-bound and S-bound linkage isomers. Here we report the synthesis of a new complex, [Ru(terpy)(tbbpy)SCN][SbF(6)] (terpy = 2,2';6',2'-terpyridine, tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine), as a mixture of N-bound and S-bound thiocyanate linkage isomers that can be separated based on their relative solubility in ethanol. Both isomers have been characterized spectroscopically and by X-ray crystallography. At elevated temperatures the isomers equilibrate, the product being significantly enriched in the more thermodynamically stable N-bound form. Density functional theory analysis supports our experimental observation that the N-bound isomer is thermodynamically preferred, and provides insight into the isomerization mechanism.     

cis-trans isomerism of indolyl-enaminocarbonyl compounds

Analysis of the PMR spectra of a series of indolylenaminocarbonyl compounds: 3-(indolylamino)vinyl ketones, β-indolylaminocrotonates, N-(indolyl)aminomethylenemalonates have been performed. We have established that in the solvents used to record the spectra, the studied enamines exist in the cis-S-cis form. Mordovian State Pedagogical Institute, Saransk 430007, Russia; e-mail:mgpi@si.moris.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1336–1344, October, 1999.     

Supramolecular isomerism and solvatomorphism in a novel coordination compound

Three different crystal forms were obtained from the crystallisation of a flexible imidazole based ligand and CdBr(2) under different conditions. Structural analysis reveals that the correlation between the three metallocyclic compounds can be described in terms of isostructurality, solvatomorphism and supramolecular isomerism.     

Thermoanalytical studies of organic compounds. part V

This paper deals with the thermal analysis of the new benzoyl, methoxy- and ethoxycarbonyl-3-hydroxybenzisoxazoles by means of derivatograph. In the serial stages of tautomeric, isomeric and decarboxylic transformation, the newN-acylated benzisoxazolin-3-ones, benzoxazolin-2-ones and 3-alkylbenzoxazolin-2-ones were obtained.

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Zusammenfassung Der Artikel befasst sich mit der Thermoanalyse der neuen Benzoyl-, Methoxy- und Äthoxycarbonyl-3-hydroxybenzisoxazolen unter Anwendung der derivatographischen Methode. Die neuen N-acylierten Benzisoxazolin-3-one, Benzoxazolin-2-one und 3-Alkylbenzoxazolin-2-one wurden an Hand der Stufenfolge tautomerer, isomerer und Decarboxilierungs-Umwandlungen erhalten.

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Résumé Le comportement thermique de nouveaux benzoyl, méthoxy et éthoxycarbonyl-3-hydroxybenzisoxazoles a été étudié à l'aide d'un Derivatograph. Lors des étapes successives correspondant aux transformations tautomères, isomères et de décarboxylation, il se forme de nouvelles N-acétylées benzisoxazoline-3-ones, benzoxazoline-2-ones et 3-alkylbenzoxazoline-2-ones.

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-, - -3- -3- . , , , N-a -3-, -2- 3- -2-.

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Part IV. E. Domagalina, T. Sawik, Acta Pol. Pharm. 33/1976/623.

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Work partly supported by Faculty of Medicine, Polish, Academy of Sciences.     

Thermoanalytical study of fluoxetine hydrochloride

The thermal decomposition of two inclusion compounds Mn(HCOO)₂·1/3C₄H₈O₂ and Mn(HCOO)₂·1/3C₄H₈O was studied in the inert atmosphere. The process of both dioxane, and tetrahydrofurane removal has two steps; the intermediate phase is unstable and kinetically hindered. Manganese formate is stable up to 330°C. Thermogravimetric data (obtained at different rates of linear heating) were processed with computer program (with ‘Model free’ approach). Kinetic parameters were calculated for the first decomposition step, and the process is described by equation of n-order reaction with autocatalysis.     

Thermoanalytical study of hydrolytic lignin

Possibility of using thermal analysis for studies of temperature-time parameters of the kinetics of thermochemical reactions of hydrolytic lignin was examined in a wide temperature range.     

Pressure-tuning of magnetism and linkage isomerism in iron(II) hexacyanochromate

A pressure-induced linkage isomerization of the cyanide anion has been observed in single crystals of a chromium(III)-iron(II) Prussian blue analogue of formula K0.4Fe4[Cr(CN)6]2.8 square1.2.16H2O (1). Upon application of pressure in the 0-1200 MPa range, the cyanide ligand rotates and becomes C-bonded to the iron(II) cations, leading to a stabilization of their diamagnetic low-spin states. The result is a decrease of magnetization and magnetic ordering temperatures from TC = 19 K at ambient pressure to 13 K at 1200 MPa. The initial magnetic properties can be restored on pressure release. The reversible movement of cyanide in the solid state can be exploited as a switch of the magnetic interaction at the molecular level.     

Thermoanalytical study of glibenclamide and excipients

Summary Taking into account the problems of desertification and agricultural practices able to provide income to the population at the semi-arid region of North-East Brazil, this work presents the results of the chemical and thermal characterization by TG and DSC of the seed derivatives of Cnidoscolus quercifolius, hereinafter called faveleira, aiming at the application of these materials as an alternative of food source for animals and for the human population at this region. The faveleira seed derivatives present thermodynamic properties similar to the ones of other foods utilized for human use, as well as an acceptable calorific value. According to TG and DSC results, was verified that the faveleira derivatives presents good thermal and oxidative stabilities.     

Thermoanalytical study of an aged XLPE-pipe

A high quality pipe made of XLPE (Engel method) for industrial applications was used for the study of the material deterioration process upon accelerated aging. A sample aged at 110°C while submitted to an hydrostatic pressure of 0.53 MPa, giving a hoop stress of 2.66 MPa, was studied by means of Thermal Analysis, Density, and Gel Content measurements. The effects of aging are compared to a reference unexposed sample and the experimental results are discussed in terms of annealing effects, free volume and structural relaxation processes.