Solid-Phase Substitution of Ammonia in Hexaamine Heteroligand Complexes of Chromium(III) with Cyclic Tetraamines

The solid-phase substitution of ammonia in heteroligand hexaamine complexes of chromium(III) with cyclic tetraamines was studied. The kinetic stability of these compounds, determined from the value of the activation energy, is lower than for other hexaamine compounds of chromium(III). This is due to the weakening of the Cr—NH₃ bonds and to the less close packing of the ions in the crystal lattice. For complexes with the trans structure the thermal stability increases in the series of tetraazamacrocyclic ligands teta < cyclam < TMC.     

Spectral studies with coordination behaviour of (NO3) and (NCS) anions and EPR parameters of chromium(III) complexes which have different chromospheres macrocyclic ligands: synthesis and electronic spectroscopy

New macrocyclic ligands were prepared and chromium(III) stability in the marcrocyclic cavities are reported. Two of them have four-coordinate [N2O2]:[N4], third one has five-coordinate [N2O2S] and the last one has six-coordinate [N4O2] donor macrocyclic cavities. These macrocyclic ligands have been synthesized with their chromium(III) complexes which have mononuclear nature and their structural features have been discussed on the basis of: elemental analysis, magnetic moment, electronic, IR, 1H NMR, and EPR spectral studies. All the chromium(III) complexes show magnetic moments in the range of 3.74-3.80 B.M. corresponding to high-spin configuration. However, the interaction of oxygen to the chromium ion in complexes is much weaker than that of other donor atoms. The spin-orbit coupling parameter, z, gives no significance because the splitting of doublet transition lines are too large to be explained by spin-orbit coupling. The beta values (0.75-0.79) indicate the covalent character, which is due to the presence of sigma bond between the metal/ligand. lambda values indicate that the complexes under study have substantial covalent character and their g-values have also been calculated by using spin-orbital coupling constant (lambda).     

The effect of Cr(III)-organic complexes on the determination of inorganic chromium species in groundwater by ammonium pyrrolidinedithiocarbamate–methylisobutylketone extraction procedure

Groundwater samples collected from a tannery contaminated area were analyzed for chromium species with the objective of investigating the interference of Cr(III)-organic complexes in the determination of Cr(VI) using APDC–MIBK extraction procedure. The contribution of Cr(III), Cr(VI) and Cr(III)-organic complexes towards total chromium ranged between 2 and 61%, 27 and 86%, and, 6 and 23%, respectively. The Cr(III)-organic complexes were not extractable by APDC–MIBK, however, HNO₃ digestion released the organic bound Cr(III). Interference of organic bound Cr(III) in Cr(VI) determination due to MIBK soluble Cr(III) was not observed. Significant difference between total dissolved chromium determined after appropriate digestion procedure, and the sum of dissolved Cr(III) and Cr(VI) determined indicates the presence of the Cr(III)-organic complexes. MIBK extraction of samples without APDC is an useful way to check the extractability of organic bound Cr(III). The presence of soluble Cr(III)-organic complexes thus add complexity to chromium speciation analysis by APDC–MIBK procedure.     

Über pentacyclische Azofarbstoff- Chrom (III)-und kobalt (III)-komplexe vom «DREW-PFITZNER»-Typus

For the first time pentacyclic azo dyestuff chromium(III) and cobalt(III) complexes with Drew-Pfitzner configuration have been produced. Comparison of their electronic spectra with those of analogous 1:2 complexes enables novel conclusions as to the shape of the octahedron formed by the metal-binding atoms.     

Comparative study of analytical methods for the determination of chromium in groundwater samples containing iron

Determination of chromium in groundwater samples containing iron may pose analytical problems due to sorption and fixation of chromium species onto Fe(III) hydroxides. Parks et al. (Water Res. 2004, 38, 2827) hypothesized that chromium species trapped inside Fe(III) hydroxides i.e. “fixed chromium” may not be soluble by HNO₃ digestion (APHA method 3030 B). In such cases, hydroxylamine digestion is required to release “fixed chromium”. To verify the hypothesis, we carried out this study on groundwater samples containing chromium and iron, using different methods of APHA and EPA. The results showed the presence of “fixed chromium”, ranged between 0.1 and 19.2 μg L^{− 1}, contributing 0.2 to 14.1% towards true total chromium. Digestion of samples with HNO₃ released Cr(III) bound to organic complexes, but not the “fixed chromium”. The hydroxylamine digestion released “fixed chromium”, but not the Cr(III) bound to organic complexes. Microwave digestion of samples with HNO₃ + HCl was effective for the release of both “fixed” and “Cr(III)-organic complexes”. Cr(III) was only adsorbed onto suspended matter, whereas Cr(VI), and Cr(III)-organic complexes were not adsorbed onto suspended matter due to their solubility. Sample pH, buffering capacity, and matrix have a significant influence on the adsorption and fixation of chromium species onto Fe(III) hydroxides.     

The effect of zinc(II) and some chromium complexes on the constant current chronopotentiometry of insulin

The constant current chronopotentiometry (CCCP) of zinc-free insulin was examined and the effect of additions of zinc(II) or either of two chromium complexes to the zinc-free zinc was studied. The zinc free insulin gave a constant current chronopotentiometric (CCCP) response which indicated that the freeze drying process, which was part of its preparation, may have denatured the insulin. The addition of zinc(II) appeared to reverse this since the response following zinc additions was similar to that of native insulin. Of the two chromium complexes investigated for their influence on insulin electrochemistry tripicolinato chromium(III) had no effect on the CCCP response, trans-Diaquoethylenebis-(salicylideneiminato) chromium(III) had an indirect effect by appearing to restore the native conformation of the insulin following the apparent denaturation caused by the removal of zinc.     

Metal-to-metal electron-transfer emission in cyanide-bridged chromium-ruthenium complexes: effects of configurational mixing between ligand field and charge transfer excited states

Irradiations of the transition metal-to-transition metal charge transfer (MMCT) absorption bands of a series of cyanide-bridged chromium(III)-ruthenium(II) complexes at 77 K leads to near-infrared emission spectra of the corresponding chromium(II)-ruthenium(III) electron transfer excited states. The lifetimes of most of the MMCT excited states increase more than 10-fold when their am(m)ine ligands are perdueterated. These unique emissions have weak, low frequency vibronic sidebands that correspond to the small excited-state distortions in metal-ligand bonds that are characteristic of transition metal electron transfer involving only the non-bonding metal centered d-orbitals suggesting that the excited-state Cr(II) center has a triplet spin configuration. However, most of the electronically excited complexes probably have overall doublet spin multiplicity and exhibit an excitation energy dependent dual emission with the near in energy Cr(III)-centered and MMCT doublet excited states forming an unusual mixed valence pair.     

Structural analysis of the solid amorphous binuclear complexes of iron(III) and aluminum(III) with chromium(III)-DTPA chelator using energy dispersive X-ray diffraction

This paper is concerned with the structural data obtained for two amorphous binuclear complexes of iron(III) and aluminum(III) with chromium(III)-diethylentriaminepentaacetic acid (chromium(III)-DTPA, CrL(2)(-)) using the energy-dispersive X-ray diffraction technique. Fe(OH)CrL(H(2)O)(6) and Al(OH)CrL(H(2)O)(6) are binuclear complexes, the metals ions being bridged via oxygen atoms. The metal ions are all octahedrally coordinated.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 microg/l for Cr(VI) and 5 microg/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Electrode processes and their kinetic parameters in the reduction and oxidation of Cr(III) and Cr(II) in molten CsCl

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.     

Mass spectrometric investigations of the kinetic stability of chromium and copper complexes with humic substances by isotope-labelling experiments

Isotope-labelling exchange experiments were carried out to investigate the kinetic stability of Cr(III) complexes with humic substances (HS). To compare the results with those of an ion, not expected to form kinetically stable HS complexes with respect to its electron configuration, Cu(II) was investigated under the same conditions. HS solutions of different origin were therefore spiked with ⁵³Cr(III) or ⁶⁵Cu(II) after saturation of HS with chromium and copper of natural isotopic composition. In fractions of metal/HS complexes with different molecular weight, obtained by ultrafiltration and HPLC/ICP-MS using size exclusion chromatography (SEC), respectively, the isotope ratios of chromium and copper were determined by ICP and thermal ionisation mass spectrometry. Distinct differences in the isotopic composition of chromium were found in the permeate of the ultrafiltration compared with the corresponding unseparated solution, which indicates kinetically stable Cr(III)/HS complexes. On the other hand, the copper isotopic composition was identical in the permeate and the unseparated solution, which shows that a total exchange of Cu²⁺ ions took place between free and HS complexed copper ions. The SEC/ ICP-MS experiments also resulted in a different isotopic distribution of chromium in the chromatographically separated complexes whereas the copper complexes, separated by SEC, showed identical isotopic composition. The kinetic stability of Cr(III)/HS complexes could be explained by the d³ electron configuration of Cr³⁺ ions, a fact which is well known from classical Cr(III) complexes, and influences substantially the mobility of this heavy metal in the environment.     

Investigation of an effect exerted by methods of production of chromium(III) oxides-hydroxides on their physicochemical properties

Results of a research of physical and chemical properties of chromium(III) oxides-hydroxides are reported produced from chromo-potassium alum by solid-phase hydrolysis and sol-gel method. Comparative assessment of structural properties of chromium oxides-hydroxides obtained by various techniques was suggested and the morphology was studied.     

Speciation of chromium in mineral waters and salinas by solid-phase extraction and graphite furnace atomic absorption spectrometry

A simple GF-AAS method for speciation analysis of chromium in mineral waters and salinas was developed. Cr(VI) species were separated from Cr(III) by solid-phase extraction with APDC (ammonium pyrrolidinedithiocarbamate). The APDC complexes were formed in the sample solution under proper conditions, adsorbed on Diaion HP-2MG resin and the resin was separated from the sample. After elution with concentrated nitric acid Cr(VI) was determined by GF-AAS. Total chromium was determined by GF-AAS directly in the sample and Cr(III) concentration was calculated as the difference between those results.

The detection limit of the method defined as 3 s of background variation was 0.03 μg l⁻¹ for Cr(VI) and 0.3 μg l⁻¹ for total chromium. RSD for Cr(VI) determination at the concentration of 0.14 μg l⁻¹ was 9%, and for total chromium at the concentration of 5.6 μg l⁻¹ was 5%. The recovery of Cr(VI) was in the range of 94–100%, dependently on type of the sample.

The investigation of recovery of the spiked Cr(VI) showed that at concentration levels near 1 μg l⁻¹ and lower recovery may be reduced significantly even by pure reagents that seem to be free from any reductants.     

Solvation of iron and chromium complexes in alcohol–water mixtures

Solubilities are reported for the perchlorates of five iron(II)-diimine complexes in t-BuOH–H₂O and one in MeOH–H₂O mixtures, for three iron(III)-3-hydroxy-4-pyranonate and three iron(III)-3-hydroxy-4-pyridinonate complexes in MeOH–H₂O and t-BuOH–H₂O, and for two chromium(III)-3-hydroxy-4-pyranonate complexes in MeOH–H₂O. Transfer chemical potentials are thence derived for the various iron(II), iron(III) and chromium(III) complexes, for transfer from H₂O into the respective mixed solvents (at 298.2 K). These results are combined with values reported earlier for related complexes, and for other alcohol–H₂O mixtures, to give an overall picture of solvation, expressed in the thermodynamic format of transfer chemical potentials, for iron(II)-diimine, iron(III)-3-hydroxy-4-pyridinonate and chromium(III)-3-hydroxy-4-pyranonate complexes in H₂O-rich aqueous-alcohol mixtures. Some spectroscopic (¹H-n.m.r.; i.r.) and kinetic (aquation rate constants at 298.2 K) data are reported for the chromium(III) complexes.     

Logistic Model of Ligand Selection for Chromium-Plating Electrolytes Based on Cr(III) Complexes

The effect of the ligand nature in chromium(III) complexes on chromium electrodeposition was studied. The predicting logistic model of ligand selection for chromium-plating electrolytes was constructed from experimental data. It was found that high-quality chromium coatings can be deposited from electrolytes of chromium(III) complexes with a ligand having the following acid–basic characteristics in the protonated form: pK ₁ < 4.0 and 4.0 < pK _n < 18.6. The proposed model was verified experimentally and used to prepare a chromium-plating electrolyte based on a chromium(III) malonate complex, which gives high-quality chromium coatings over a wide current density range.     

Mobilities of metal β-diketonato complexes in micellar electrokinetic chromatography

Electrically neutral acetylacetonato complexes of chromium(III), cobalt(III), rhodium(III), and platinum(II) (or palladium(II)) have been separated successfully by capillary zone electrophoresis in a micellar solution of sodium dodecyl sulfate (SDS). The distribution coefficient of each metal complex between the SDS micelle and the aqueous solution surrounding the micelle was calculated from the capacity factor. A linear log-log relationship was found between the distribution coefficient and the partition coefficient of the complex between dodecane and water. The linear relationship was effectively used for prediction of both the distribution coefficients and the migration times of other metal complexes, such as palladium(II) acetylacetonate and chromium(III) 3-methyl acetylacetonate.     

Effect of chromium(III) and of other ions on the absorptiometric determination of copper with 2, 2'-biquinolyl

In the determination of small amounts of copper in certain alloys by liquid-liquid extraction of the bis-chelate of copper(I) with 2, 2'-biquinolyl, recovery of copper has been reported to be low when chromium(III) is present. The adverse effect of chromium(III) could be overcome by adding iron(II). It is now shown that the inhibiting effect of chromium is attributable to the formation of a kinetically inert ternary complex of chromium(III), copper(II) and citrate ions containing an equal number of atoms of each of the two metals. Copper can be displaced from this complex by any of the transition cations Mn(II), Fe(II), Co(II), Ni(II) and Zn(II). Zinc is shown to form a ternary complex formally analogous to that of copper. The formation of the ternary complexes has been studied polarographically. The formation of binuclear complexes of various hydroxy-acids is reviewed and a probable structure for the ternary complex is proposed which explains its stability and kinetic inertness. Analogies are drawn between this complex and ternary complexes of UO(2)(VI)-Al(III)-citrate and Cu(II)-Al(III)-tartrate which also cause interference in established analytical procedures.     

Synthesis, characterization and magnetism of μ-chloranilato bi-nuclear chromium (III) complexes

Five new chloranilato-bridged binuclear chromium (III) complexes have been synthesized and identified as [Cr2(CA)L4]-(ClO4)4[L denotes 5-methyl-1,10-phenanthroline (Me-phen); 2,9-dimethyl-1, 10-phenanthroline ( Me2-phen); 5-chloro-1,10-phenanthroline(Cl-phen); diaminoethane (en) or 1,3-diaminopropane (pn)], where CA represents the dianion of chloranilic acid. Based on elemental analyses, molar conductivity and magnetic moment of room-temperature measurements, and IR and electronic spectral studies, it is proposed that these complexes have CA-bridged structures and consist of two chromium (III) ions, each in an octahedral environment. The complexes [Cr2(CA)(Me-phen)4](ClO4)4(1) and [Cr2(CA)(Me2-phen)4](ClO4)4(2) were further characterized by variable temperature (4.2-300 K) magnetic susceptibility measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, , giving the exchange parameter J = -7.8 cm-1 for (1) and J= -6.5 cm*1 for (2). This result     

Chromium speciation using an automated liquid handling system with inductively coupled plasma - mass spectrometric detection

The speciation of inorganic chromium in environmental samples is required for accurate assessment of pollution levels. Of the two chromium oxidation states, Cr (VI) is a known carcinogen, while Cr (III) is an essential element. Total chromium measurement cannot be used to determine actual environmental impact due to the considerable difference in toxicity of the two elemental forms. An automated liquid handling system, the PrepLab™, can be used with an inductively coupled plasma-mass spectrometer (ICP-MS) to quantify Cr (III) and Cr (VI) in liquid samples. An autosampler is used to introduce discrete sample volumes into a solid-phase chelation resin column. The Cr (III) and Cr (VI) species are separated and are introduced on-line into the VG PlasmaQuad 3 ICP-MS for detection. The chromatographic data are collected in time resolved analysis mode with the capability of simultaneous multiple-isotopic detection.     

The effects of chromium(III) coordination on the dissociation of acidic peptides

The complexes formed between chromium(III) and synthetic acidic peptides were studied by sustained off-resonance irradiation collision-induced dissociation (SORI-CID) in a Fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometer equipped with electrospray ionization (ESI). Neutral peptides and peptides containing one, two, and multiple acidic residues were studied. Formation of [M + Cr-2H]+ occurred for all peptides. Three noteworthy features were found in the CID spectra of [M + Cr-2H]+. The first is that fewer fragment ions were produced from [M + Cr-2H]+ than from [M + H]+. The reason may be that multiple coordination between chromium(III) and carboxylate or carbonyl groups hinders the production of fragment ions by continuing to bind pieces of the peptide to chromium(III) after cleavage of bonds within the peptide. The second feature is loss of CO from [M + Cr-2H]+ and [y(n) + Cr-H]+. A mechanism involving coordination of chromium(III) with carboxylate groups is proposed to rationalize elimination of CO. The third feature is that chromium(III) is retained in all fragment ions, indicating strong binding of the metal ion to the peptides. The complex [M + 2Cr-5H]+ is formed as the peptide chain length and number of acidic residues increases. Longer peptides have more sites to coordinate with chromium(III) and more conformational flexibility. In addition, formation of [M + Cr-2H]+ from AGGAAAA-OCH(3), which has no carboxylic acid groups, suggests that chromium(III) can coordinate with sites on the peptide backbone, albeit in low abundance. In the negative mode, [M + Cr-4H](-) was only found for peptides containing four or more carboxylic acid groups. This is consistent with deprotonated carboxylic acid groups being involved in chromium(III) coordination and with chromium existing in the 3 + state in the gas-phase ions.