首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
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 CrIII. 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 pda3?; the intermediate releases also eaq?, 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.  相似文献   

2.
Hot atom chemical reaction by50Cr/n, /51Cr and52Cr/, n/51Cr reactions, and recoil implantation reaction by51V/p, n/51Cr reaction were investigated using geometrical isomers /mer and fac/ of tris/benzoylacetonato/ chromium/III/ /Cr/ba/3/. The production of counter isomer was observed for both mer- and fac-targets, although the yield of labelled parent isomer was larger. The observed mer/fac yield ratio suggests that the main formation mechanism of51Cr/ba/3 is the reaction of ba and Cr/ba/ 2 + which has the same geometrical configuration of target complex, and the substitution reaction of central metal atom by recoil51Cr. Furthermore, implantation gave rise to a much higher yield of labelled Cr/ba/3 compared to the case of in situ nuclear recoils.  相似文献   

3.
Summary Rhenium(VII) can be separated on a column of Al2O3 from a 500-fold excess of Mo(VI) and W(VI) and a 250-fold excess of Cr(III), Mn(II), Ni(II), Co(II), and Fe(III) by elution with 0.1M Nad. For photometric determination, rhenium(VII) is reduced with Sn(II), extracted as the thiocyanate complex into isopropyl ether, and measured at 430 nm. The sensitivity is 0.04 g/ml, if 10-mm cells are used. The interferences were examined statistically and found to be negligible.
Zusammenfassung Rhenium(VII) läßt sich von einem 500fachen Überschuß an Mo(VI) und W(VI) sowie von einem 250fachen Überschuß an Cr(III), Mn(II), Ni(II), Co(II) und Fe(III) mit Hilfe einer Aluminiumoxidsäule trennen und daraus mit 0,1-m Kochsalz eluieren. Für die photometrische Bestimmung wird Rhenium(VII) mit Sn(II) reduziert, dann als Rhodanidkomplex mit Isopropyläther extrahiert und bei 430 nm gemessen. Bei Verwendung von 10-mm-Küvetten beträgt die Empfindlichkeit 0,04 g Re/ml. Störungen wurden statistisch geprüft und als unbeachtlich erkannt.
  相似文献   

4.
We have recently reported that the organic bilayer of 3,4,9,10-perylenetetracarboxyl-bisbenzimidazole (PTCBI, n-type semiconductor) and 29H,31H-phthalocyanine (H2Pc, p-type semiconductor), which is a part of a photovoltaic cell, acts as a photoanode in the water phase (Abe et al., ChemPhysChem 5:716, [2004]); in that case, the generation of the photocurrent involving an irreversible thiol oxidation at the H2Pc/water interface took place to be coupled with hole conduction through the H2Pc layer, based on the photophysical character of the bilayer. In the present work, the photoelectrode characteristics of the bilayer were investigated in the water phase containing a redox molecule , where the photo-induced oxidation and reduction for the couple were found to take place at the bilayer. The photoanodic current involving the oxidation efficiently occurred at the interface of H2Pc/water, similar to the previous example. In the view of the voltammograms obtained, it was noted that there are pin-holes in the H2Pc layer of the bilayer, leading to a cathodic reaction with at the PTCBI surface especially in the dark; that is, the band bending at the PTCBI/water interface can essentially be reduced by applying a negative potential [e.g., < ∼ 0 V (vs Ag/AgCl)] to the PTCBI, when the cathodic reaction may take place through the conduction band of the PTCBI. Moreover, under that applied potential condition of irradiation, the photogenerated electron carrier part can move to the PTCBI surface, thus enhancing the reduction of .  相似文献   

5.
Three novel -oxalato-bridged Cu 3 II CrIII-type heterotetranuclear complexes described by the overall formula [Cu3Cr(ox)3L3](ClO4)3, where ox represents the oxalato dianions, L stands for diaminoethane (en), 1,3-diaminopropane (pn), and 1,2-diaminopropane (ap) respectively, have been synthesized and characterized by elemental analyses, molar conductivity and magnetic moment (room-temperature) measurements, i.r., e.s.r. and electronic spectral studies. It is proposed that these complexes have oxalato-bridged structures consisting of three copper(II) ions and a chromium(III) ion, in which the chromium(III) ion has an octahedral environment and the three copper(II) ions have square-planar environments. Variable temperature magnetic susceptibility (4.2–300 K) measurements and studies of complexes [Cu3Cr(ox)3(en)3](ClO4)3 (1) and [Cu3Cr(ox)3(pn)3](ClO4)3 (2) revealed the occurrence of an intramolecular ferromagnetic interaction between the copper(II) and chromium(III) ions through the oxalato-bridge within each molecule. The magnetic data have been used also to deduce the indicated -oxalato-bridges [Cu 3 II CrIII] heterotetranuclear structure. On the basis of the spin Hamiltonian operator, , the magnetic analyses were carried out for the two CuII—CrIII heterotetranuclear complexes and the spin-coupling constants (J) were evaluated as +6.36 cm–1 for (1) and +7.02 cm–1 for (2). The results indicate that the bridging oxalato entity should be able to transmit ferromagnetic interactions in the strict orthogonality [Cu 3 II CrIII] system.  相似文献   

6.
The possibilities and limitations of the RRDE method in recording and identifying intermediate and target products of chromium dissolution in sulfuric acid solutions of pH 0.3–2 are analyzed on the basis of own and literature data. From the experimental data, partial currents of chromium dissolution to Cr(II) ions in the region of active dissolution of chromium and its transition into a passive state are computed. The Cr(III) ions can be discovered through the reaction of their reduction on an Hg(Au) ring electrode only at pH 1.8. The current efficiency of reactions that lead to the formation of Cr(II) and Cr(III) ions near the anodic-dissolution peak is other than 100%. Assumptions as to the causes of this effect are made. In the solutions studied, Cr(VI) ions are recorded with a 100-% current efficiency on a gold ring electrode in a transpassive region of the chromium disk potentials.  相似文献   

7.
Summary A new colour reaction for the detection of cerram(IV) which can be carried out both in a test tube and on a spot plate has been described. The test solution is treated with methylene blue in nitric acid solution (11) to form a rose-red colour. This simple procedure has an advantage over the existing tests in that it is applicable in the presence of oxidising agents like chromium(VI), vanadium(V), nitrate, perchlorate and of coloured ions like copper(II), cobalt(II), nickel(II), chromium(III), iron(III), vanadium(IV), uranium(VI).
Zusammenfassung Eine neue, sowohl in der Eprouvette wie auf der Tüpfelplatte ausführbare Farbreaktion zum Nachweis von Cer(IV) wurde angegeben. Die Probelösung wird mit salpetersaurer Methylenblaulösung behandelt und gibt eine rosarote Färbung. Die Reaktion hat gegenüber bekannten Tests den Vorteil, in Gegenwart von Oxydationsmitteln wie Cr(VI), V(V), NO3 , ClO4 bzw. in Anwesenheit gefärbter Ionen wie Cu(II), Co(II), Ni(II), Cr(III), Fe(III), V(IV) oder U(VI) anwendbar zu sein.
  相似文献   

8.
Summary Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 2001 and 1 ml sample volumes were 120 and 60 h–1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50g ml–1 and 0.67% for Cr(III) (0.10,g ml–1) and the corresponding limits of detection were 85 ng ml–1, and 16 ng ml–1, respectively.On leave from University of Belgrade.  相似文献   

9.
Zusammenfassung Nach Extraktion von Chrom(III)-Lösungen mit geschmolzenem Oxin ist die polarographische Bestimmung nach Nitrierung des gebildeten Chrom(III)-oxinats möglich. Die experimentellen Bedingungen für die Nitrierung und die polarographische Bestimmung von 1–25 g Cr/25 ml werden mitgeteilt. Ein kurzer Vergleich mit der spektralphotometrischen Bestimmung als Chrom(III)-oxinat wird gegeben. Das polarographische Verfahren ist um den Faktor 5–10 empfindlicher. Nur Kobalt stört und muß durch eine vorausgehende Extraktion abgetrennt werden.
Polarographic determination of chromium(III) after extraction as chromium(III) oxinate with an oxine melt
Summary After extraction of chromium(III) solutions with molten oxine the polarographic determination is possible by nitration of the Cr(III) oxinate. Experimental conditions for the nitration and for the polarographic determination of 1–25 g Cr/25 ml are described. A short comparison with the spectrophotometric determination as Cr(III) oxinate is also given. The polarographic method is more sensitive by a factor of 5–10. The only interference is caused by cobalt, which must be separated by a preceding extraction.
Die Untersuchungen wurden in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbands der Chemischen Industrie unterstützt.  相似文献   

10.
The reduction of chromium ions in the CsCl-CrCl3 melt in wide concentration and temperature ranges is reported. It is assumed that the melt contains polynuclear chromium complexes. The reduction of Cr(III) to Cr(II) is a reversible one-electron process. The electroreduction of divalent chromium to chromium metal is an irreversible process involving dinuclear and mononuclear chromium complex ions. The electron transfer rate constant has been calculated for various temperatures and chromium chloride concentrations in the salt melt. The activation energy of electron transfer and its dependence on the CrCl3 concentration in the electrolyte have been determined for the Cr(III) ↔ Cr(II) process.  相似文献   

11.
Summary The kinetics of anation of chromium(III) species, [Cr(H2O)6]4+ and [Cr(H2O)5OH]2+, by L-phenylalanine in aqueous acid has been studied spectrophotometrically. Effects of varying [substrate], [ligand], [H+], , % ethanol and temperature were investigated. The kinetic data suggest a mechanism where outersphere-associations [between chromium(III) species and phenylalanine in the zwitterionic form] precede anation. Comparison of the results with published data suggest an Ia path for the [Cr(H2O)6]3+ reaction and Id path for the [Cr(H2O)5OH]2+ reaction.  相似文献   

12.
The nature and composition of complexes formed by the reaction of Fe(III), Cr(III), Zn(II), and Co(II) with potassium pentacyanonitrosyl manganate K3 [Mn(CN)5NO] has been investigated by radiometric method. The metals form 1∶1 complexes with K3 [Mn(CN)5NO], the optimum pH for maximum precipitation being 3.6 for Fe(III), 7.3 for Cr(III), 5.4 for Zn(II), and 8.3 for Co(II). The solubility of the complexes as computed from activity at maximum precipitation point follows the order: chromium complex > iron complex > cobalt complex > zinc complex. The radiometric titration curves also show the formation of colloidal precipitates with dilute Zn(II) solutions.  相似文献   

13.
Summary The ionic behaviour of 1-phenyl-3-pyrazolidinone (phenidone) at different pH values and its complexes with a selected group of metal ions such as Mg(II), Al(III), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) were investigated in the pH range of 1–13 by paper electrophoresis. pH-mobility curves were determined for phenidone, the nine metal ions and 21 metal-ligand systems with 1, 110 and 1100 metal: ligand ratios. The effect of the pH on complex formation and the influence of the phenidone concentration on the metal ion mobilities are discussed.Presented at the XXII International Conference on Coordination Chemistry, August 23–27, 1982, Budapest (Hungary).  相似文献   

14.
The self-quenching of chromium phosphorescence in K3[CrxCo1-x(CN)6] mixed crystals has been studied in the range of very high chromium concentration and a minimum in emission quantum yield has been found at about 80% Cr. Comparison of the Cr emission intensities from K3[Cr(CN)6] doped with 1% of various impurities suggests that the impurity quenching observed in the range 90 to 100% Cr may be a result of the site asymmetry introduced by the impurity. It is suggested that at least two mechanisms of self-quenching are operative in this concentration range and the nature of these is discussed in relationship to present theories of radiationless transitions.
Zusammenfassung Die Eigenlöschung der Cr(III)-Phosphoreszenz wurde in K3[CrxCo1-x(CN)6]-Mischkristallen im Bereich hoher Cr-Konzentrationen untersucht. Die Quantenausbeuten der Emission zeigten ein Minimum bei etwa 80% Cr. Ein Vergleich der Lumineszenzintensitäten von K3[Cr(CN)6] mit 1% verschiedener Zusätze läßt vermuten, daß die im Bereich von 90–100 % Cr beobachtete Löschung von einer durch die Verunreinigung verursachten Gitterstörung herrührt. — Es wird angenommen, daß in dem untersuchten Konzentrationsbereich mindestens zwei Mechanismen der Eigenlöschung wirksam sind, die anhand der gegenwärtigen Theorien der strahlungslosen Übergänge diskutiert werden.

Résumé L'auto étouffement du chrome phosphorescent à partir de K3[CrxCo1-x(CN)6], cristaux mélanges avait été étudié dans la région de très haute concentration de chrome et un minimum d'émission quantique, il en résultait environ 80% Cr. Comparé à l'intensité d'émission de chrome à partir de K3[Cr(CN)6] contaminé par 1% de diverses impuretés indique que l'étouffement d'impureté qui était observé dans la région de 90 à 100% Cr, peut être le résultat de l'emplacement assimétrique introduit par l'impureté. — II a été suggéré qu'au moins deux mécanismes d'auto étouffement sont à l'oeuvre dans cette région de concentration et leur nature décrite en relation avec les présentes théories de transitions sans radiation.


Dedicated to the memory of Professor Hans-Ludwig Schläfer.  相似文献   

15.
Natural and chemically modified zeolites from the Slovak Republic and Ukraine have been investigated as the adsorbents for the uptake of Cr(III). Model water solution of low radioactivity was used. The adsorption and desorption kinetics of chromium were established with the gradual radioexchange technique (tracer 51Cr) and flame AAS. The effect of the factors studied are examined and explained. The sorption coefficient , distribution coefficient K D , sorption capacity , sorption rate S, and leachability of Cr were calculated in neutral, alkaline and acidic aqueous solutions. The sorption capacity of the modified zeolites was found to be greater by a factor of 2 to 16 than that of the unmodified ones depending on the modifying solution applied. The leachability of chromium from loaded zeolites into the neutral solution was negligible. The leachability into alkaline and acidic solutions increased over 40%.  相似文献   

16.
A novel bis(oxalato)chromium(III) salt of a ferromagnetically coupled, oxalato-bridged dinuclear chromium(III)-cobalt(II) complex of formula [CrL(ox)(2)CoL'(H(2)O)(2)][CrL(ox)(2)]·4H(2)O (1) has been self-assembled in solution using different aromatic α,α'-diimines as blocking ligands, such as 2,2'-bipyridine (L = bpy) and 2,9-dimethyl-1,10-phenanthroline (L' = Me(2)phen). Thermal dehydration of 1 leads to an intriguing solid-state reaction between the S = 3/2 Cr(III) anions and the S = 3 Cr(III)Co(II) cations to give a ferromagnetically coupled, oxalato-bridged trinuclear chromium(III)-cobalt(II) complex of formula {[CrL(ox)(2)](2)CoL'} (2). Complex 2 possesses a moderately anisotropic S = 9/2 Cr(III)(2)Co(II) ground state, and it exhibits slow magnetic relaxation behavior at very low temperatures (T(B) < 2.0 K).  相似文献   

17.
Methods for the on-line chromatographic preconcentration of Cr(III) and Cr(VI) have been developed. Cr(VI) has been preconcentrated on an RP C18 silica based column with tetrabutylammonium-bromide (TBABr) as ion-pairing agent. Specially for Cr(III) a new and effective preconcentration technique based on the sorption of Cr(III)-ions in a C18 column in presence of KH-phthalate has been developed. The efficiency of sample introduction into the atomic emission spectrometer could be improved by hydraulic high pressure nebulization. For the detection of chromium the acetylene/N2O flame has been used as a powerful emission spectrometric source. Applying these steps the detection limit (3) could be improved to 25 pg/mL for Cr(III) and to 20 pg/mL for Cr(VI). The method has been applied for the chromium speciation in natural water samples.  相似文献   

18.
Synthesis and crystal structure of a new structure type of mixed Cr(III)/Cr(VI) chromates is reported. NH4Cr(CrO4)2 was prepared from CrO3 in the presence of (NH4)2Ce(NO3)6. Since this is the first preparation of mixed valence ternary chromium oxides from aqueous solution, a reaction pathway for this synthesis is suggested. The crystal structure of NH4Cr(CrO4)2 has been determined from three-dimensional X-ray data collected at low temperature, 173 K. The structure belongs to the orthorhombic space group Pnma, with a=14.5206(10), b=5.4826(4), and Z=4. The title compound consists of corner-sharing chromium(III) octahedra and chromium(VI) tetrahedra forming a three-dimensional network with the composition [Cr(CrO4)2]nn-, containing channels in which zigzag rows of ammonium ions balance the net charge.  相似文献   

19.
Summary The structural parameters of chromium sulfide selenides are intermediate between those of the sulfides and the selenides. The nature of the dependence of the magnetic properties of the sulfide selenides on temperature and composition has much in common with that for the sulfides. The presence of selenium atoms in the sulfide lattice leads merely to some distortion of the anomalies which are observed for the pure sulfides. In the mixed chalcogenides of chromium, gradual oxidation of the monosulfide by selenium takes place, with the conversion of Cr(II) into Cr(III). The principal contribution to the magnetic moments is made by the spin values, equal to 4.9 B for Cr(II) and 3.87 B for Cr(III). The slight increase in the lattice parameters of the sulfide selenides (increase in the Cr–Cr distances) compared with the sulfides leads to a decrease in the exchange interactions in the sulfide selenides compared with the sulfides. This is indicated by the change in the paramagnetic Curie temperature with change in composition.Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 14, No. 1, pp. 163–166, January–February, 1973.  相似文献   

20.
Summary Quantum chemical calculations based on density functional theory have been performed on Cr(CO)6, (6-C6H6)Cr(CO)3 and (6-C6H6)Cr(CO)2(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal-ligand binding energies. In particular, a comparison of metal-arene bond energies calculated for the (6-C6H6)Cr(CO)3 and (6-C6H6)Cr(CO)2(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger -backbonding charge transfer to the CS ligand as compared with CO.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号