The thermal decomposition of some Cr(III) complexes

The thermal decomposition reactions of the following chromium(III) complexes were investigated: Cr(CH₃COO)₃·2 H₂O, [C_r3O(CH₃COO)₆(H₂O)₃]Cl·2 H₂O and [Cr₃O(CH₂ClCOO)₆(H₂O)₃]Cl·6H₂O. Simultaneous TG/DTG/DTA were applied nonisothermal conditions. From the recorded curves, the activation energiesE _a were calculated for all the thermal decomposition steps. Appropriate chemical reactions were attributed to the thermal effects, with consideration to the X-ray diffraction and IR spectra results.

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Zusammenfassung Für die Untersuchung der thermischen Zersetzungsreaktion der Chrom(III)-Komplexe Cr(CH₃COO)₃·2H₂O [C_r3O(CH₃COO)₆·(H₂O)₃]Cl2H₂O und [C_r3O(CH₂ClCOO)₆·(H₂O)₃]C₁₆H₂O wurde simultane TG/DTG/DTA unter nichtisothermen Bedingungen eingesetzt. Ausgehend von den aufgezeichneten Kurven wurden für alle Schritte der Zersetzungsreaktion die E_a-Werte berechnet. In Übereinstimmung mit röntgenographischen und IR-spektroskopischen Ergebnissen wurden den thermischen Effekten passende chemische Reaktionen zugeordnet.

     

Biotechnology of Cr(VI) transformation into Cr(III) complexes

The dose-dependent formation of Cr(III) complexes and uptake of chromium by Arthrobacter oxydans — a Gram-positive bacterium from contaminated Columbian basalt rocks (USA) — were studied along with the testing under aerobic conditions of two bacterial strains of Arthrobacter genera isolated from the polluted basalts from the Republic of Georgia. Instrumental neutron activation analysis (INAA) was used to track the accumulation of chromium in the bacterial cells. To monitor and identify Cr(III) complexes in these bacteria, electron spin resonance (ESR) spectrometry was employed.     

Ligand exchange reactions of some Cr(III) complexes investigated by cyclic voltammetry

From cyclic linear sweep voltammograms of some Cr(III) complexes it is evident that after electron transfer ligand groups are expelled relatively slowly inDMSO and the tetra coordinated complex is formed. The rate constants could be determined in some cases by the methods of cyclic voltammetry. The following compounds were examined: [Cr(en)₃]³⁺, [Cr(acac)(en)₂]²⁺, [Cr(acac)₃]. [Cr(dien)₂]³⁺, [Cr(DMSO)₆]³⁺, [Cr(ur)₆]³⁺. For [Cr(en)₃]³⁺ the energy of activation could be determined as well.The dependence of the velocity of ligand elimination on complex structure is discussed.

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Untersuchung von Ligandenaustauschreaktionen einiger Cr(III)-Komplexe mittels cyclischer Voltammetrie

Zusammenfassung Bei der Reduktion einiger der folgenden Cr(III)-Komplexe inDMSO läßt sich auf Grund der Voltammogramme auf eine Ligandenabspaltung und Bildung der vierfach koordinierten Cr(II)-Komplexe schließen: [Cr(en)₃]³⁺, [Cr(acac)(en)₂]²⁺, [Cr(acac)₃], [Cr(dien)₂]³⁺, [Cr(DMSO)₆]³⁺, [Cr(ur)₆]³⁺. Für das [Cr(en)₃]³⁺ konnten Geschwindigkeitskonstante und Aktivierungsenergie dieser nachgelagerten Reaktion bestimmt werden.Der Einfluß der Struktur des Komplexes auf die Zerfallsgeschwindigkeit wird diskutiert.

     

Mixed-ligand complexes of Ru(III) and Rh(III): ESR studies on some Ru(III) complexes

Reactions of 2-mercapto-3-phenyl-4-quinazolinone (LH) with RuCl₃·xH₂O and RhCl₃·xH₂O afforded the compounds [RuL₂Cl(H₂O)]H₂O, [RuL₂Cl·DMFI and RhL(LH)Cl₂·2H₂O. Reactions of LH with RuCl₃·xH₂O in the presence of N-heterocyclic bases led to the formation of complexes of type [RuL₂ClB]·H₂O (B = pyridine, 3-picoline or imidazole) and [RuLCl₂(o-phen)] H₂O (o-phen = 1, 10-phenanthroline). These complexes were characterized on the basis of analytical, conductivity, magnetic, IR and electronic spectral and ESR studies. Tentative structures for the complexes are proposed.     

Adduct formation of some tris(N,N dialkyldithiocarbamato)Cr(III) complexes with iodine

Spectrophotometric studies of dichloromethane solutions containing iodine and some Cr(S₂CNR₂)₃ complexes (where R₂NCS^?₂ are: OC₄H₈NCS^?₂ = modtc; (C₂H₅)₂NCS^?₂ = Et₂dtc; (C₆H₅CH₂)₂NCS^?₂ = Bz₂dtc) have shown the formation of 1:1 adducts whose spectral features were studied and which suggested that charge-transfer interaction involving iodine and a sulphur atom of a coordinated dithiocarbamato ligand occurred.A new BASIC non-linear least-squares program which performs an optimization of the absorbance data taken at several wavelengths was devised to evaluate reliable formation constants.The thermodynamic parameters have been calculated and compared with those obtained in the same conditions as above by a reinvestigation of the known 1:1 complex formation of iodine with the corresponding tetraalkylthiuram-disulphides, where the donor site is also the sulphur atom of the thiocarbonyl group. The ?ΔH° values related to the Cr(dtc)₃ · I₂ complexes are about 2 kcal lower than those of thiuram disulphides, showing a lowering of the donor strength of the thiocarbonyl sulphur as a consequence of the coordination to the metal.     

Photochemistry and photophysics of Cr(III) macrocyclic complexes

The phosphorescence and photochemical behavior of the macrocyclic complexes (1,4,7,10,13,16-hexaazacyclooctadecane)chromium(III) (Cr([18]-aneN(6))(3+); 1) and (4,4',4'-ethylidynetris(3-azabutan-1-amine)) chromium(III) (Cr(sen)(3+); 2) have been compared to each other and to the complex Cr(en)(3)(3+). For both macrocyclic complexes, phosphorescence from room temperature aqueous solutions is too weak to be observed, contrasting with Cr(en)(3)(3+), though both had somewhat longer 77 K lifetimes than Cr(en)(3)(3+). Phosphorescence lifetimes for these macrocyclics decreased with increasing temperature much faster than for Cr(en)(3)(3+) and a conventional extrapolation based on a fit of reciprocal lifetimes (corrected for the low-temperature contribution) to the Arrhenius equation gave estimated room temperature phosphorescence lifetimes of a few nanoseconds, consistent with the failure to observe room temperature emission. Fitting of the nonlinearity of the data seen in these plots suggested that two high-temperature processes were occurring with estimated activation parameters (E in kJ mol(-1) and A in s(-1)) for Cr([18]-aneN(6))(3+): E(1) = 40, A(1) = 1 x 10(16); E(2) = 24, A(2) = 1 x 10(14): Cr(sen)(3+); E(1) = 45, A(1) = 2 x 10(15); E(2) = 29, A(2) = 7 x 10(11). Cr([18]-aneN(6))(3+) was photochemically inert on irradiation. On irradiation into the lowest quartet ligand field absorption band, Cr(sen)(3+) photolyzes with a quantum yield of 0.098 +/- 0.001 at room temperature. Laser flash photolysis with conductivity detection showed that this photoreaction occurred faster than protonation of the liberated amine ligand at all practical proton concentrations. The quantum yield for irradiation directly into the doublet absorption band of Cr(sen)(3+) was 0.077 +/- 0.003. Photoaquation of Delta-Cr(sen)(3+) led to loss of optical activity and product analysis by capillary electrophoresis showed that both racemic and Delta-Cr(sen)(3+) photoaquate to a single main product, trans-Cr(sen-NH)(H(2)O)(4+). The product stereochemistry is shown to be consistent with predictions based on the angular overlap model for Cr(III) photochemistry, recognizing the additional constraints imposed by the ligand. The abnormally short room temperature solution lifetime of the doublet state is a result of a radiation-less process that competes with other processes depleting the doublet state. However, this doublet-state deactivation process does not lead to photoaquation but competes with BISC and photoaquation via the quartet state, resulting in an unprecedented reduction in photoaquation quantum yield on direct irradiation into the doublet state.     

Photoredox reactions of Cr(III) mixed-ligand complexes

Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O₂ and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C₂O₄^? radicals. The species undergo fast redox reactions dependent on the presence of O₂ and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to Cr^III. Then geminate recombination regenerates substrate, whereas competitive release of the C₂O₄^? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C₂O₄^? and pda^3?; the intermediate releases also e_aq^?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda.     

On the electrochemical reduction of some Cr(III) complexes inDMSO investigated by cyclic voltammetry

The compounds investigated were: [Cr(en)₃]³⁺, [Cr(ur)₆]³⁺, [Cr(DMSO)₆]³⁺, [Cr(dien)₂]³⁺, [Cr(en)₂(acac)]²⁺, [Cr(en) (acac)₂]⁺ and Cr(acac)₃.A distinctly different behaviour is caused by the introduction of one or moreacac ligands into the molecule. The first step is much more cathodic and quite irreversible, while it is reversible or quasi reversible for the first group of ions. This is due to a -type interaction between theacac ligand and the central ion. This interaction is responsible for a third peak occurring for the second group of compounds and may be attributed to the reduction of the Cr(I) ion.Some correlations were found e.g. between the extinction of thed-d band of the first group of ions and the potential of the first peak, and the number ofacac groups introduced in the second group of compounds and the shift of the potential of the first peak.The determined electrochemical data are tabulated.

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Untersuchungen zur elektrochemischen Reduktion einiger Cr(III)-Komplexe in DMSO mittels zyklischer Voltammetrie

Zusammenfassung Die elektrochemischen Daten einer Reihe von Cr(III)-Komplexen miten-, ur-, DMSO-, dien- undacac-Liganden werden präsentiert und einige Möglichkeiten der Korrelation der physikalischen Eigenschaften der Komplexe werden aufgezeigt.Die erste Stufe bei der Einführung vonacac-Liganden ist auf Grund einer -Wechselwirkung zwischen Ligand und Zentralion irreversibel.

     

Thermal decomposition of dinitrogen complexes of Cr(III)

The thermal behaviour of two dinitrogen complexes of chromium with EDTA and CDTA have been studied using DTA and TG. IR spectroscopy is used for the characterization of intermediate products. The loss of dinitrogen occurs at 240°C in both cases.     

Redox reactions of V(III) and Cr(III)picolinate complexes in aqueous solutions

Reactions of e_aq⁻, H-atoms, OH, (CH₃)₂COH, and CO₂⁻ radicals with V(III)picolinate and Cr(III)picolinate have been studied by the pulse radiolysis technique. The spectra of V(II)picolinate, V(IV)picolinate, Cr(II)picolinate, OH adduct of Cr(III)picolinate and Cr(IV)picolinate have been obtained and the rate constants of the reactions of various radicals with V(III) and Cr(III)picolinate have been determined. The implications of these results to the chemical decontamination of nuclear reactor systems are discussed.     

Crystal structure of barium isothiocyanato(ethylenediaminetetraacetato)cobaltate(III)

All-Union Scientific-Research Institute for Chemical Reagents and Highly Pure Chemical Substances. M. V. Lomonosov Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 4, pp. 120–127, July–August, 1988.     

Physicochemical model for choosing complexes for chromium-plating solutions based on Cr(III) compounds

A prognostic physicochemical model for choosing complexes for chromium-plating solutions is constructed on the basis of a combination of the thermodynamic principles and data on the kinetics of some electrochemical reactions. It is shown that high-quality chromium coating can be produced from solutions of Cr(III) complexes, whose logarithm of stability constants ranges from 10 to 20, and the logarithm of stability constants of Cr(II) complexes formed in electrolysis ranges from 7 to 10. The influence of the nature of ligands on chromium electrodeposition is studied. Using the model proposed, a chromium-plating solution based on a chromium(III) malonate complex is developed. This solution makes it possible to produce high-quality coatings in a wide interval of current densities.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 1, 2005, pp. 17–21.Original Russian Text Copyright © 2005 by Vinokurov, Demidov, Bondar.     

The synthesis of organo-imido complexes of Cr(IV) and Fe(III)

The reaction of p-tolylazide with (5,10,15,20- tetraphenylporphyrinato) chromium(II) (Cr(TPP)) yields the high spin chromium(IV) organo-imido complex, CH₃C₆H₄N=Cr(TPP). N,N′-ethylene- bis-(salicylideneiminato)iron(II), (Fe(salen)), however reacts with arylazides to produce iron(III) organo-imido-bridged compounds of general formula, [Fe(salen)]₂NR showing magnetic coupling between the Fe(III) centres.     

Thermal decomposition of Cr(III) complexes with urea and thiourea

The thermal decompositions of Cr(III) complexes with urea and thiourea were investigated. The courses of the decompositions were found to be anion- and ligand-dependent. Suggestions for a mechanism of decomposition of these complexes are presented. The final product of decomposition of the complexes investigated was chromium(III) oxide (Cr₂O₃).

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Zusammenfassung Die thermische Zersetzung der Komplexe von Cr(III) mit Karbamid und Thiokarbamid wurde untersucht. Der Verlauf der Zersetzung wurde für Anionen- und Liganden-abhängig gefunden. Vorstellungen über eine mechanische Zersetzung dieser Komplexe werden gegeben. Das Endprodukt der Zersetzung der untersuchten Komplexe war jeweils Chrom(III)oxid (Cr₂O₃).

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Résumé On a étudié la décomposition thermique des complexes du chrome(III) avec l'urée et la thiourée. On a trouvé que le processus de la décomposition dépend de l'anion et du ligand. On propose un mode de décomposition mécanique pour ces complexes. Le produit final de la décomposition des complexes étudiés est l'oxyde de chrome(III), Cr₂O₃.

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Cr (111) . , . . (111) (Cr₂O₃).

     

Structural studies and quantum chemical calculations of Cr(III), Fe(III) and Ru(III) bromazepam complexes

The reaction of bromazepam (7‐bromo‐1,3‐dihydro‐5‐(2‐pyridyl)‐2H ‐1,4‐benzodiazepin‐2‐one, BZM) with Cr(III) ( 1 ), Fe(III) ( 2 ) and Ru(III) ( 3 ) salts gives complexes of the type [M(BZM)₃]⋅3X (X = Cl or NO₃). Structural characterization was extensively carried out using various analytical and spectral tools such as infrared, ¹H NMR and UV–visible spectroscopies and magnetic, conductance, elemental and thermal analyses. BZM is a bidentate ligand and interacts with the metal ions via the pyridine and benzodiazepin‐2‐one nitrogen atoms. The magnetic and electronic properties of 2 and 3 are consistent with low‐spin octahedral complexes. The three BZM molecules are non‐isoenergetically coordinated to the metal ions and this is reflected in the values of the second‐order interaction energy. The antibacterial activity was studied using Staphylococcus aureus and Escherichia coli . Coordination of BZM to Cr(III) or Ru(III) ions leads to a marked increase in toxicity with respect to the inactive Fe(III) complex 2 .     

Studies of adsorption and solution of acetylacetonates of Cr(III), Co(III) and Al(III) by gas chromatography

Summary Specific retention volumes, adsorption isotherms, molar heats of solution and changes of the entropy were determined from chromatographic data, which was obtained by the gas chromatographic separation of metal acetylacetonates. The retention data for Cr(III), Co(III) and Al(III) acetylacetonates were measured at different temperatures and different flow rates. From the retention data other values associated with adsorption and solution phenomena were calculated.