Synthesis and structural characterization of tris (methacrylato)chromium(III)

A straightforward synthetic route to produce tris(methacrylato)chromium(III), Cr(O₂C(CH₃)C=CH₂)₃, by reacting sodium methacrylate with an aqueous solution of CrCl₃ gave a blue microcrystalline powder, insoluble in most common solvents. Electronic spectroscopy (UV-Vis), electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), were employed to characterize Cr(O₂C(CH₃)C=CH₂)₃. Morphology and elemental composition of this compound were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), respectively. Spherical particles of approximately 2.5 µm in diameter were obtained. Thermal stability of the product was investigated via thermogravimetric analysis (TGA). The spectroscopic studies revealed that the coordination sphere around the chromium ion corresponds to a chelating bidentate carboxylate-Cr(III) complex. Thermal stability above 350°C, and spherical shape particles of few micrometers in diameter, suggest a potential application of this novel compound as a catalyst in oxidation reactions.     

Growth, structure, and characterization of tris(thiourea)silver(I) nitrate

Single crystals of tris(thiourea)silver(I) nitrate have been grown by slow evaporation solution growth technique from an aqueous solution at 25 °C. The single crystal X-ray diffraction study reveals that the crystal belongs to tetragonal system and cell parameters are a = b = 14.2790(4) Å, c = 24.8900(7) Å, and V = 5074.8(2) Å³. The various functional groups present in the molecule are confirmed by Fourier transformed infrared spectroscopy (FT-IR). The structure and the crystallinity of the materials were further confirmed by powder X-ray diffraction analysis. Thermogravimetric and differential thermal analysis reveal the purity of the sample and no decomposition is observed up to the melting point. The crystal is further characterized by UV–Vis and Vickers microhardness analysis.     

Thermal racemization of tris(1,10-phenanthroline) chromium(III)

The thermal racemization of (+)₅₈₉-Cr phen₃(ClO₄)₃ has been examined under a variety of medium conditions. The racemization rate constant in water at 75°C, for example, is 8·5 × 10⁻⁵ sec⁻¹, with an energy and entropy of activation of 23·5 kcal mole⁻¹ and −10·9 e.u., respectively. The effect of acid, hydroxide, and various other added ions on the rate constant has been investigated, and the results compared with other tris-phenanthroline systems. An intramolecular twist process is considered the most probable mechanism of racemization.     

Probing the R lines in tris(acetylacetonato) chromium(III) and tris(3-bromo-acetylacetonato) chromium(III) by luminescence and excitation line narrowing spectroscopy

Site-selective and narrowed luminescence and excitation spectra in the region of the (2)E <-- (4)A 2 transitions are reported for single crystals of Al(acac) 3/Cr(III) and Al(3-Br-acac) 3/Cr(III) (where acac is acetylacetonate). The R 2 line is pronounced in the brominated system and displays a comparable oscillator strength as the R 1 line. The (2)E splitting is found to be 138 cm (-1), and the (4)A 2 ground-state splitting is 1.39 cm (-1). However, in the case of the Al(acac) 3/Cr(III) system the R 2 line is not a distinct feature. We propose that vibronic coupling via a second-order Jahn-Teller effect leads to a redistribution of R 2 intensity over several vibrational sidelines. An upper limit for the R 1 line width Gamma h = 15 MHz is deduced for the Al(acac) 3/Cr(III) 1% system at 1.5 K. This line width is limited by direct and indirect electron-spinelectron-spin interactions. Accurate zero-field splittings (1.20, 1.19, 1.17 cm (-1)) for the three sites in Al(acac) 3/Cr(III) are determined and compared with previously published electron paramagnetic resonance (EPR) data.     

Polythermal solubility of chromium(III) and cobalt(III) tris(acetylacetonates) in water-tert-butanol mixtures

Solubility data for chromium(III) and cobalt(III) tris(acetylacetonates) in water and water-tert-butanol mixtures over a wide range of temperatures and alcohol concentrations were obtained, and thermodynamic parameters of solution were calculated. The dependences of solubility on the concentration of tert-butanol have an inversion point corresponding to a change in the hydration mechanism, when the solvent structure changes from water to aqueous alcohol.     

Precursor trichloroeth anoato-chromium (III) species in the formation of tris (2,4-pentanedionato) chromium (III)

Two precursor species have been identified as responsible for the catalyzing effect of the trichloroethanoate (TCE) anion on the formation of tris(2,4-pentanedionato)chromium(III), Cr(acac)₃. The first one is the green intermediate species (GIS) identified as tetrahydroxodecakis-μs-trichloroethanoato-trichloroethanoato-tetraaquopentachro-mium(III), Cr₅(OH)₄(CCl₃COO)₁₁(H₂)₄. This appears to be the first pentanuclear species reported among the polynuclear alkanoato metal complexes. It reacts at a rapid rate with the 2,4-penaanedtonate, acac, anion to produce a second precursor, the violet-green intermediate species (VGIS) identified as bis(2,4-pentanedionato)-trichloroethanoato-aquochromium(III), Cr(C₅H₇O₂)₂(CCl₃COO)(H₂O). This is attacked by the remainigg acac anion to ultimaelly produce the Cr(acac)₃. Thus the effect of the TCE anion in facilitating the formation of Cr(acac)₃ is through the ligand coordination catalytic mechanisms.     

Synthesis,characterization and dynamic stereochemistry of thermochromic tris(dithiocarbamato)vanadium(III) complexes stereochemistry of thermochromic tris(dithiocarbamato)vanadium(III) complexes

The vanadium(III) complexes, V(S₂CNMe₂)₃ (1) and V(S₂CN ⁱ Pr₂)₃ (2) were prepared and characterized by analysis, IR, electronic and ¹H NMR spectra. The complexes show reversible thermochromic behaviour. MM2 calculations were used to simulate the molecular structure of 1. For 2, variable temperature ¹H NMR revealed hindered rotation about C–N bonds. The rotational energy barrier (38?kJ?mol^?1) was obtained by molecular mechanics force-field calculations.     

Preparation and characterization of tris(1, 10-phenanthroline) technetium(III)

The [Tc(phen)₃] (PF₆)₃ complex has been synthesized by ligand substitution on [Tc(tu)₆]³⁺. The reaction proceeds quickly in aqueous solution. A pure compound is obtained with 40% yield. It was characterized by Tc elemental analysis, cerimetric titration, conductometry and electrophoresis. The corresponding spectroscopic properties (UV, Vis, IR and NMR) are also reported and discussed.     

Triamidoamine complexes of chromium(III) and chromium(IV)

Treatment of [CrCl3(THF)3] with slightly more than 1 equiv of Li3(N3N) [(N3N)(3-) = ((Me3SiNCH2CH2)3N)(3-)] affords the triamidoamine complex [Cr(N3N)] (1) in 75% yield. 1 is oxidized by PhICl2, CuCl2, or AgCl to give the chromium(IV) complex [Cr(N3N)Cl] (2) in moderate yields. Alternatively, complex 2 is obtained directly from [CrCl3(THF)3] in 50% yield after treatment with 0.5 equiv of Li3(N3N). Both compounds are high-spin complexes bearing three and two unpaired electrons, respectively. Their molecular structures are described revealing a trigonal monopyramidal and trigonal bipyramidal coordination geometry of the chromium center, respectively.     

Spectro-thermal characterization of chromium(III) and manganese(II) complexes with carboxyamide

Complexes of Cr(III) and Mn(II) with N′,N″-bis(3-carboxy-1-oxopropanyl) 2-amino-N-arylbenzamidine (H₂L¹) and N′,N″-bis(3-carboxy-1-oxophenelenyl) 2-amino-N-arylbenzamidine (H₂L²) have been synthesized and characterized by various physico-chemical techniques. The vibrational spectral data are in agreement with coordination of amide and carboxylate oxygen of the ligands with the metal ions. The electronic spectra indicate octahedral geometry around the metal ions, supported by magnetic susceptibility measurements. The thermal behavior of chromium(III) complexes shows that uncoordinated nitrate is removed in the first step, followed by two water molecules and then decomposition of the ligand; manganese(II) complexes show two waters removed in the first step, followed by removal of the ligand in subsequent steps. Kinetic and thermodynamic parameters were computed from the thermal data using Coats and Redfern method, which confirm first order kinetics. The thermal stability of metal complexes has been compared. X-ray powder diffraction determines the cell parameters of the complexes.     

The synthesis and characterization of some titanium (III) tris N,N-dialkyldithiocarbamates

It has been demonstrated that the reaction of sodium salts of dialkyldithiocarbamates with titanium trichloride in ethanol gives a yellow-green solid, which shows a three to one stoichiometry indicating a tris coordination. Infrared spectral data indicate the complexes to be approximately of D₃h symmetry, bonded through the sulfur atoms as chelates. Magnetic data show that the d¹ state is retained.     

Heterogeneous effects on the thermal and photoreactivities of tris(1,2-diaminoethane)chromium(III) cation and hexathiocyanatochromate(III) anion in aqueous media

The ground- and excited-state reactivities of the [Cr- (en)3]3+ (en=1,2-diaminoethane) and [Cr(NCS)6]3− ions in a polyacrylamide (PAA) environment are reported. The aquation kinetics of these complexes has been studied to identify the effect of added PAA with varying molecular weight. Aquation of the complexes in aqueous acid containing PAA yielded the respective substituted products. The macromolecule in solution was found to decrease significantly the rate of ligand replacement. Similarly, photolysis of the cationic and anionic complexes in water–PAA mixtures revealed a decrease in aquation quantum yield. Possible explanations for the decrease in reaction rates and quantum yields are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cyclopentadienyl mesityl complexes of chromium(II) and chromium(III)

Chromium(III) mesityl complexes were synthesized by protonolysis of chromocene with 1,3-diisopropylimidazolium chloride or DBU hydrochloride, salt metathesis with MesMgBr, and single electron oxidation with iodine.     

Microscopic detection of chromium as chromium(III)

Summary Trisodium phosphate is recommended as a reagent for the microscopic detection of chromium (III). Sensitivity of the test is 6 of chromium (III) in a volume of 0.01 ml. Of particular importance is the fact that aluminum and iron (III) do not react with the reagent to form crystalline precipitates.

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Zusammenfassung Tertiäres Natriumphosphat gibt mit Chrom(III)-Lösungen eine charakteristische Fällung, in der unter dem Mikroskop rechteckige Kristalle zu erkennen sind. Weder Aluminium noch Eisen(III) gibt mit diesem Reagens einen kristallinen Niederschlag. Die Reaktion gestattet den Nachweis von 6 Chrom in 0,01 ml Lösung. Auch Quecksilber(II) gibt charakteristische Kristalle.

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Résumé On recommande le phosphate trisodique comme réactif pour la recherche microscopique du chrome-III. La sensibilité de l'essai est 6 de chrome-III dans un volume de 0,01 ml. Le fait que l'alumine et le fer-III ne se combinent pas avec le réactif pour former des précipités cristallins présente une importance particulière.

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With 2 figures.