Synthesis and Kinetic Study on the Chromium(III) Complex [Cr(ASA)(en)2]Cl·2H2O

In order to explore the transfer mechanism of chromium(III) in mammals, a novel complex [Cr(ASA)(en)₂]Cl· 2H₂O, bis(ethylenediamine‐ κ ² N,N′)(4‐aminosalicylic acid‐ κ ² O,O′) chromium(III) monochloride dihydrate was synthesized (4‐aminosalicylic acid=H₂ASA, ethylenediamine=en). The crystal structure belongs to orthorhombic system with the space group P2₁2₁2₁ by means of X‐ray diffraction. The characteristic for transfer of Cr³⁺ from the compound to the low‐molecular‐mass chelator EDTA and the iron‐binding protein apoovotransferrin (apoOTf) was followed by UV‐visible (UV‐Vis) and fluorescence spectra in 0.01 mol·L^?1 Hepes at pH 7.4. The second order rate constants were calculated. Those spectra in conjunction were used to obtain more accurate information about the interaction of chromium complex with apoOTf. The experimental results indicate that Cr³⁺ can be transferred from the complex to apoOTf with the retention of the 4‐aminosalicylic acid acting as a synergistic anion.     

New microstructured chromium doped poly(p‐toluidine) as a new acid–base indicator and precursor for chromic oxide nanostructured

New chromium doped poly(p‐toluidine) (Cr‐PPT) was synthesized via chemical oxidative polymerization of p‐toluidine with potassium dichromate as an initiator in acidic aqueous medium. The spectrophotometric behavior of Cr‐PPT in acetone and chloroform as different solvents was investigated. Cr‐PPT exhibits bathochromically red shift at 46‐nm value with the increasing of solvent polarity. The intermolecular charge transfer band peak for Cr‐PPT shifted from 422 nm in low‐polar solvent (chloroform) to high‐polar solvent (acetone) to 468 nm. Optical absorption measurements are used to obtain the energy gap of prepared Cr‐PPT. Cr‐PPT has an optical band gap (E_g = 1.90 to 2.05 eV) that is located in the semiconductor range. Pink color was observed using Cr‐PPT solution in acidic media while it changes sharply to yellow in basic medium. Based on intermolecular charge transfer, the Cr‐PPT was used as acid–base indicator. Cr‐PPT and phenolphthalein (phph) indicator were used for determination of normality of HCl using standard 0.1 N NaOH, the two indicators gave equal end point values. Using Cr‐PPT as a new molecular precursor for the production chromium oxide in nanoscale by thermal decomposition route was studied, and the average size of synthesized Cr₂O₃ was found in the range of 54–61 nm. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of Nitrogen and Fluorine Co‐substitution on the Structure and Magnetic Properties of Cr2O3

First‐principles density functional calculations were carried out to determine the structure as well as electronic and magnetic properties of N and F co‐substituted Cr₂O₃. The formation of strong Cr?N bonds upon substitution of oxygen with nitrogen leads to large distortions in the local structure and changes in magnetic moments, which are partly compensated by co‐substitution with fluorine. The effects of spin–orbit coupling are relatively weak, but its combination with local structural distortions gives rise to canting of spins and an overall magnetic moment in N, F co‐substituted Cr₂O₃. Experimentally, we observe spin canting in N, F co‐substituted Cr₂O₃ with considerable enhancement in the coercive field at low temperatures.     

One‐pot synthesis of polyaniline doped with transition metal ions using H2O2 as oxidant

Polyanilines (PANIs) doped with Zn²⁺ and Cu²⁺ were synthesized by H₂O₂ oxidative polymerization of aniline in the presence of corresponding metal chloride in solution. The products were characterized by elemental analysis, UV‐Vis‐NIR, FTIR and Raman spectroscopies. Scanning electron micrograph was employed to examine the morphology of PANIs fabricated in the presence of different transition metals. Experimental results showed that transition metal ions had been successfully incorporated into the polymer, and there was a strong interaction between the transition metal ions and the PANI chains. The electrical conductivity of PANI doped with Zn²⁺ and Cu²⁺ is 0.37 and 0.21 S/cm, respectively, which is higher than that of HCl doping PANI corresponding to 0.052 S/cm. The cyclic voltammetric study has indicated that incorporation of metal ions in PANI backbone results in increasing of specific capacitance compared to that of HCl doping PANI. Copyright © 2014 John Wiley & Sons, Ltd.     

Radar Absorption Properties of Ni0.5Zn0.5Fe2O4/PANI/epoxy Nanocomposites

A nitrate? citrate gel was prepared from metallic nitrates and citric acid by sol? gel process and was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄ nanocrystalline powder by auto‐combustion. Then, two novel 15 and 35% (w/w) magnetic Ni_0.5Zn_0.5Fe₂O₄ containing polyaniline nanocomposites, named as PANI‐Ni15 and PANI‐Ni35, respectively, were prepared via in‐situ polymerization of aniline in an aqueous solution containing proper amount of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder. The incorporation of the nanopowders to PANI matrix was confirmed by X‐ray diffraction (XRD), IR and SEM. Synthesized PANI‐NiZn ferrite composite particles were subsequently added to an epoxy resin matrix to produce related nanocomposites. The morphological properties of these nanocomposite materials were investigated by SEM and TEM. The electromagnetic‐absorbing properties were studied by measuring the reflection loss in the frequency range of 8.0 to 12.0 GHz. Results showed the reflection loss of the PANI‐Ni35 composite is higher than pure polyaniline and PANI‐Ni15. The good reflection loss of the nanocomposites suggests their potential applicability as radar absorber.     

[Cr8(PhCO2)16O4]·4CH3CN·2H2O: structural origin of magnetic anisotropy in a molecular spin cluster

The Cr₄O₄ hetero‐cubane‐centered octachromium(III) cluster [Cr₈(PhCO₂)₁₆O₄] crystallizes from fluorobenzene–acetonitrile as dodeca‐μ₂‐benzoato‐tetrabenzoatotetra‐μ₄‐oxido‐octachromium(III) acetonitrile tetrasolvate dihydrate, [Cr₈(C₇H₅O₂)₁₆O₄]·4C₂H₃N·2H₂O, (I). Crystals produced by this method are significantly more stable than the originally published dichloromethane pentasolvate, [Cr₈(PhCO₂)₁₆O₄]·5CH₂Cl₂ [Atkinson et al. (1999). Chem. Commun. pp. 285–286], leading to a significantly higher quality structure and allowing the production of large quantities of high‐quality nondeuterated and deuterated material suitable for inelastic neutron scattering (INS) measurements. Compound (I) reveals a higher symmetry structure in which the cluster sits on a twofold rotation axis, and is based on an asymmetric unit containing four crystallographically independent Cr positions, two oxide ligands, eight benzoate ligands, two acetonitrile solvent molecules and one disordered water molecule. All the Cr atoms are six‐coordinate, with an octahedral geometry for the inner cubane and a more highly distorted coordination environment in the outer positions. Despite the higher symmetry, the coordination geometries observed in (I) are largely similar to the dichloromethane pentasolvate structure, indicating that crystal‐packing effects have little influence on the molecular structure of [Cr₈(PhCO₂)₁₆O₄]. Close structural analysis reveals that the high magnetic anisotropy observed in the INS measurements is a consequence of the distorted coordination geometry of the four outer Cr atoms.     

Dipotassium tetra­chromate(VI), K2Cr4O13

The structure of dipotassium tetra­chromium(VI) trideca­oxide, K₂Cr₄O₁₃, has been determined from single‐crystal X‐ray data collected at 173 (2) K on a racemically twinned crystal with monoclinic Pc space‐group symmetry. The structure is composed of discrete [Cr₄O₁₃]²⁻ zigzag chains held together by the charge‐balancing potassium ions. The conformations adopted by the tetra­chromate anion in alkali metal salts and Cr₈O₂₁ are different and can be divided into three categories.     

Determination of Cr(VI) with Selective Sensing of Cr(VI) Anions by a PVC‐Membrane Electrode Based on Quinaldine Red

A dichromate‐selective PVC‐membrane electrode based on Quinaldine Red (an acridinium derivative) is described. The electrode exhibits rapid (< 30 s) and linear response to the activity of Cr(VI) anions in the range of 5.2 × 10^?6 ?1.0 × 10^?1 M dichromate with the limit of detection 2.5 × 10^?6 Mof Cr₂O₇^2?. The sensor is used as an indicator electrode in potentiometric determination of Cr(VI) anions and is also suitable for end‐point indication in the titrations of proper metal ions with dichromate under laboratory conditions. The proposed electrode has been applied to the direct potentiometric determination of Cr(VI) anions in water samples with satisfactory results.     

Beta‐lactoglobulin Electrochemical Detection Based with an Innovative Platform Based on Composite Polymer

In this work, we present a new electrochemical disposable platform based on poly(aniline‐co‐anthranilic acid) (PANI/PAA) composite polymer coupled with an aptamer for sensitive detection of β‐lactoglobulin. Firstly, PANI/PAA film was electrodeposited on the graphite screen‐printed electrode surface by cyclic voltammetry. The co‐polymer modified electrode was then employed as platform for the covalent immobilization of an amino‐modified aptamer. Various β‐lactoglobulin solutions, with a fixed amount of biotinylated oligonucleotide complementary sequence, were dropped onto the aptasensor surface. A streptavidin‐alkaline phosphatase conjugate was then employed to trace the affinity reaction. After the addition of 1‐naphthyl‐phosphate enzymatic substrate, 1‐naphthol electroactive product was detected by differential pulse voltammetry. A decrease in the signal was obtained when the target concentration was increased, in according to a signal‐off approach. After optimization of key experimental parameters, a dose‐response curve was obtained between 0.01–1.0 μg mL^?1 β‐lactoglobulin concentration range. The limit of detection of 0.053 μg L^?1 was obtained. Milk samples spiked with β‐lactoglobulin were analyzed.     

Preparation and characterization of PVC/PANI conductive composite with extremely low percolation threshold

Aniline was polymerized in the presence of poly(vinyl chloride) (PVC) powders in hydrochloric acid to in situ prepare poly(vinyl chloride)/polyaniline (PVC/PANI) composite particles. UV‐vis spectra and FT‐IR spectra indicate PANI in PVC/PANI composite particles possessed a higher oxidation state with decreased aniline content in reactants. Both conductivity and impact strength of the dodecylbenzenesulfonic acid (DBSA) doped PANI composites (PVC/PANI‐DBSA), which were compression molded from the in situ prepared PVC/PANI particles, increase with the pressing temperature and decrease with the increase of DBSA doped PANI (PANI‐DBSA) loading. An excellent electric conductivity of 5.06 × 10^?2 S/cm and impact strength of 0.518 KJ/m² could be achieved for the in situ synthesized and subsequently compression molded composite. Copyright © 2004 John Wiley & Sons, Ltd.     

Laser-induced luminescence of model Fe/Al2O3 and Cr/Al2O3 catalysts

The laser-induced luminescence of Cr³⁺ impurity ions in model Fe/Al₂O₃ and Cr/Al₂O₃ catalysts with different calcination temperatures was studied. It was found that an additional luminescence band at 770 nm appeared in the luminescence spectra of low-temperature samples as a result of the interaction of octahedrally coordinated Cr³⁺ ions with Fe³⁺ impurity ions. In the θ-Al₂O₃ phase with a concentration of Cr³⁺ ions higher than 0.1 wt %, the interaction of the Cr³⁺-Cr³⁺ ion pairs in the immediate surroundings resulted in the appearance of N _θ lines due to the splitting of R _θ lines. The differences of these lines from the N _α lines of α-Al₂O₃ were related to the individuality of the crystal lattice of the θ phase and the coordination of Cr³⁺ impurity ions in the immediate surroundings, which is different from that in the α phase. Based on the laser-induced luminescence spectroscopic data, it was found that regions with a local Cr³⁺ concentration higher than the average Cr³⁺ concentration in the bulk of a catalyst by one order of magnitude were formed in the α-Al₂O₃-Fe₂O₃ system with the bulk Fe and Cr concentrations of 2.5 and 0.04 wt %, respectively, which was calcined at 1220°C, as a result of the diffusion of chromium and iron ions.     

Analysis of highly resolved x‐ray photoelectron Cr 2p spectra obtained with a Cr2O3 powder sample prepared with adhesive tape

By using modern XPS systems it is possible to obtain spectra with well‐resolved spin orbit, multiplet and field splitting even with powder samples mounted using adhesive tape. Measurement of Cr₂O₃ powder with the latest generation of XPS spectrometers, which are able to analyse non‐conductive powders with ultimate energy resolution, revealed multiplet splitting features and satellite emission in the Cr 2p spectrum. Therefore, peak‐fit analysis of Cr 2p XPS spectra of Cr(III) compounds requires a more appropriate approach and common practice has to be reconsidered. One possible way to analyse this spectrum is proposed, based on the experimental and theoretical work of other authors. Copyright © 2004 John Wiley & Sons, Ltd.     

β‐K2Cr2O7

The monoclinic modification of dipotassium dichromate, β‐K₂Cr₂O₇, has been synthesized in the K₂Cr₂O₇–H₂O system. The structure consists of K⁺ cations and Cr₂O₇^2? dimers. In contrast with triclinic α‐K₂Cr₂O₇ [Kuz'min, Ilyukhin, Kharitonov & Belov (1969). Krist.Tech. 4 , 441–461], the Cr₂O₇^2? groups in β‐K₂Cr₂O₇ have twofold crystallographic symmetry and are parallel to each other.     

Effect Nd2O3 content on electrochemical performance of polyaniline/Nd2O3 composites

Polyaniline/neodymium(III) oxide (PANI/Nd₂O₃) composites were synthesized by in situ chemical oxidative polymerization method, and the new electrode materials were used for supercapacitor. The composites were characterized physically by scanning electron microscope (SEM), Fourier transform infrared spectra (FTIR) and X‐ray diffraction (XRD). SEM, IR and XRD results showed the existence of interactions between PANI and Nd₂O₃. The electrochemical capacitance performance of the composites was investigated by cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy with a three‐electrode system in 6 M KOH solution. Cyclic voltammetry and galvanostatic charge/discharge tests proved that the addition of Nd₂O₃ enhanced the capacitance of the composites. However, the conductivity of the composites decreases with increasing the amount of Nd₂O₃. Electrochemical impedance tests manifest that the charge‐transfer resistance of the composites is smaller than that of the pure PANI, which indicates the addition of Nd₂O₃ could lower resistance and facilitate the charge transfer of the active materials. All results support that Nd₂O₃ has a significant contribution to the performance of PANI and makes the composites have more active sites for faradiac reaction and larger specific capacitance than pure PANI. Copyright © 2014 John Wiley & Sons, Ltd.     

The Degradation of Indigo Sodium Disulphonate by Chromium Isomorphic Replacement in Magnetite

This study was designed to investigate the degradation of indigo sodium disulphonate (ISD, a kind of indigoiddyes) in heterogeneous Fenton system (H₂O₂/Fe_3‐xCr_xO₄). The co‐precipitation was employed to synthesize a series of Cr‐doped magnetite. The result of XRD indicated that Chromium isomorphic replacement will not cause significant changes in the structure of the magnetite. The thermogravimetric (TG) and differential scanning calorimetry analysis was applied in the samples. The adsorption data showed that strong acidic condition and high concentration Cr‐containing magnetite contributed to the enhancement of adsorbing capacity. The degradation experiment was carried out in consideration of 4 aspects, including pH, Fe_3‐xCr_xO₄, H₂O₂ concentration and catalyst dosage, stating that Cr‐doped magnetite made for degrading indigo sodium disulphonate.     

Solubility in the system Na2Cr2O7 + 2NH4Cl ⇆ (NH4)2Cr2O7 + 2NaCl-H2O

The solubility in the water-salt quaternary reciprocal system Na₂Cr₂O₇ + 2NH₄Cl ⇆ (NH₄)₂Cr₂O₇ + 2NaCl-H₂O has been investigated for the first time at 25, 50, and 75°C. Using a formal analytical model, the boundaries of the phase fields have been determined, and the univariant lines and invariant points have been calculated. The experimental data have been used to calculate the temperature and concentration parameters of the circular isohydric process of potassium dichromate preparation with the participation of ammonium salts as intermediates.     

Study of the [Cr(H2O)5NO]2+ Complex via Density Functional Theory

On the basis of density functional theory, the spin ground state of chromium‐nitrosyl complex [Cr(H₂O)₅NO]²⁺ (S = 1/2) is studied via B3LYP hybrid method. Its vibrational frequencies, atomic charges, and spin densities are analyzed. The excitation energies are evaluated using the CIS method. Our calculated N‐O stretching frequency and excitation energies are in good agreement with the IR and UV‐vis data. The related Cr^I(H₂O)₆⁺, Cr^II(H₂O)₆²⁺, and Cr^III(H₂O)₆³⁺ complexes are employed as the reference compounds to determine the characteristics of the central Cr. Results indicate that the effective Cr oxidation state is close to Cr(I).     

Hydrogen Storage and Selective,Reversible O2 Adsorption in a Metal–Organic Framework with Open Chromium(II) Sites

A chromium(II)‐based metal–organic framework Cr₃[(Cr₄Cl)₃(BTT)₈]₂ (Cr‐BTT; BTT³⁻=1,3,5‐benzenetristetrazolate), featuring coordinatively unsaturated, redox‐active Cr²⁺ cation sites, was synthesized and investigated for potential applications in H₂ storage and O₂ production. Low‐pressure H₂ adsorption and neutron powder diffraction experiments reveal moderately strong Cr–H₂ interactions, in line with results from previously reported M‐BTT frameworks. Notably, gas adsorption measurements also reveal excellent O₂/N₂ selectivity with substantial O₂ reversibility at room temperature, based on selective electron transfer to form Cr^III superoxide moieties. Infrared spectroscopy and powder neutron diffraction experiments were used to confirm this mechanism of selective O₂ binding.     

Speciation Analysis of Cr(III) and Cr(VI) after Solid Phase Extraction Using Modified Magnetite Nanoparticles

A new solid phase extraction (SPE) method has been developed for the speciation of Cr(III) and Cr(VI). This method is based on the adsorption of Cr(VI) on modified alumina‐coated magnetite nanoparticles (ACMNPs). Total chromium in different samples was determined as Cr(VI) after oxidation of Cr(III) to Cr(VI) using H₂O₂. The chromium concentration has been determined by flame atomic absorption spectrometric (FAAS) technique and amount of Cr(III) was calculated by substracting the concentration of Cr(VI) from total chromium concentration. The effect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, H₂O₂ concentration and cetyltrimethylammonium bromide (CTAB) concentration as modifier on the quantitative recovery of Cr(VI) were investigated. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation (RSD) of Cr(VI) were 140 (for 350 mL of sample solution), 0.083 ng mL^?1, 0.1‐10.0 ng mL^?1 and 4.6% (for 5.0 ng mL^?1, n = 7), respectively. This method avoided the time‐consuming column‐passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of chromium in different water and wastewater samples and suitable recoveries were obtained.     

Hydrogen Storage and Selective,Reversible O2 Adsorption in a Metal–Organic Framework with Open Chromium(II) Sites

A chromium(II)‐based metal–organic framework Cr₃[(Cr₄Cl)₃(BTT)₈]₂ (Cr‐BTT; BTT^3?=1,3,5‐benzenetristetrazolate), featuring coordinatively unsaturated, redox‐active Cr²⁺ cation sites, was synthesized and investigated for potential applications in H₂ storage and O₂ production. Low‐pressure H₂ adsorption and neutron powder diffraction experiments reveal moderately strong Cr–H₂ interactions, in line with results from previously reported M‐BTT frameworks. Notably, gas adsorption measurements also reveal excellent O₂/N₂ selectivity with substantial O₂ reversibility at room temperature, based on selective electron transfer to form Cr^III superoxide moieties. Infrared spectroscopy and powder neutron diffraction experiments were used to confirm this mechanism of selective O₂ binding.