Structural and spectroscopic properties of trans-difluoro(1,4,8,12-tetraazacyclopentadecane)chromium(III) perchlorate hydrate

The structure of [CrF(2)([15]aneN(4))]ClO(4).H(2)O ([15]aneN(4)=1,4,8,12-tetraazacyclopentadecane) has been determined by a single-crystal X-ray diffraction study at 173 K. The complex crystallizes in the space group P1- of the triclinic system with two mononuclear formula units in a cell of dimensions a=9.6117(7) A, b=10.2882(7) A, c=11.0001(7) A and alpha=99.7570(10) degrees, beta=105.6080(10) degrees and gamma=113.7130(10) degrees. The complex cation unit has its central Cr atom in an octahedral coordination with four nitrogen atoms and two fluorine atoms in a trans position. Three six-membered and one five-membered chelate rings of the [15]aneN(4) ligand are in a chair-twist(skew)-chair-gauche conformation sequence. The gauche five-membered ring is disordered with the twist six-membered ring opposite. The four H atoms in the chiral N atoms have the trans-II (CTCg) type configuration. The mean Cr-N and Cr-F bonds are 2.095(2) and 1.8752(13) A, respectively. The IR and visible spectral properties are consistent with the result of X-ray crystallography. The resolved band maxima of the electronic d-d spectrum are fitted with secular determinant for quartet state energy of d(3) configuration in tetragonal field including configurational but neglecting spin-orbit coupling. It is confirmed that the fluoride has strong sigma- and pi-donor properties toward the chromium(III) ion and the nitrogen atoms of the [15]aneN(4) ligand also have a strong sigma-donor character.     

Enhanced electrocatalytic oxidation of dyes in aqueous solution using cobalt phthalocyanine modified activated carbon fiber anode

Cobalt tetra(2,4-dichloro-1,3,5-triazine)aminophthalocyanine(CoPc)was immobilized covalently on activated carbon fiber(ACF)felt to obtain CoPc-modified ACF(CoPc-ACF)catalyst,and an electrocatalytic oxidation system using CoPc-ACF as the anode was constructed.The electrocatalytic oxidation of Acid Red 1(AR1)was investigated in aqueous solution by an UV-vis spectrophotometer and UPLC.The results indicated that AR1 could be eliminated efficiently in this electrocatalytic oxidation system.In addition,the results of FTIR,TOC and GC-MS suggested that the electrocatalytic oxidation experienced the decoloration achieved by destroying the azo linkage and the further mineralization due to the cleavages of benzene ring and naphthalene ring.The intermediates were mainly small molecular compounds such as maleic acid and succinic acid,etc.Repetitive tests showed that CoPc-ACF can maintain high electrocatalytic activity over several cycles.The further EPR spin-trap experiments indicated that the hydroxyl radicals did not dominate the reaction in this electrocatalytic system,which was completely different from the traditional electro-Fenton system.Based on the non-radical reaction mechanism,the CoPc-modified ACF electrocatalyst has potential application in treating actual dyestuffs wastewaters,which are accompanied with high concentration of hydroxyl radical scavengers such as chlorine ions and additives in the textile printing and dyeing industry.     

The kinetics of cobalt(II) complexation with o-phthalate in aqueous solution

The rate constants for the formation and dissociation of cobalt(II) complexes with o-phthalate in aqueous solution have been determined by a pressure-jump technique. The forward and reverse rate constants obtained are k_f = 1.1 x 10⁶ M⁻¹ s⁻¹ and k_r = 1.6 x 1O³ s⁻ at 25°C, respectively. The activation parameters of the reaction were also obtained from the temperature variation study. The results indicate that chelate ring closure and rupture are affected by the rigidity of the benzene ring of the ligand, and thus the rate determining step of the reaction is the chelate ring closure process.     

Removal of cobalt(II) from aqueous solution by spent green tealeaves

Journal of Radioanalytical and Nuclear Chemistry - The removal of Co2+ in aqueous solution by spent green tealeaves (SGTL) was studied in batch conditions. The bio-sorbent was characterized by the...     

Thermodynamic studies on the addition of molecular oxygen to Co(II)-1,4,8,12 tetraazacyclopentadecane in aqueous solution at 25°C

Aqueous solutions containing Co²⁺ and the macrocyclic ligand 1,4,8,12-tetraazacyclopentadecane (L) are able to bind reversibly molecular oxygen to form the species Co₂L₂O ₂ ⁴⁺ between pH 5 and 7. This species at pH greater than 8 is replaced by the complex Co₂L₂O₂ (OH) ₂ ²⁺ whose concentration in the solution increases to about pH 10.5. At pH greater than 10.5, Co(II) exists totally in this -peroxobisydroxo complex. Both the above mentioned oxygenated forms suffer a relatively slow irreversible oxidation to Co(III). From oxygen binding curves, approximate values of the equilibrium constants were calculated for the addition of oxygen to CoL²⁺ to form the -peroxo and the -peroxo-bishydroxo complexes. The enthalpies of formation of this latter complex starting from both Co²⁺ or CoL²⁺ have been obtained by means of calorimetric measurements. The effects of the size of the macrocyclic ligand on the affinity and the enthalpy of oxygen binding have been considered.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples, December 4–7, 1984.     

The kinetics of complexation of nickel(II) and cobalt(II) with cinchomeronate in aqueous solution

The pressure-jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are k_f = 2.27 × 10⁶ M^?1 s^?1 and k_r = 3.81 × 10¹ s^?1 for the nickel(II) complex and k_f = 1.23 × 10⁷ M^?1 s^?1 and k_r = 2.66 × 10² s^?1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.     

Radiolysis of aqueous solutions of cobalt(II) and cobalt(III)

Radiolysis of aqueous solution of di and trivalent cobalt with 1:2 (bis) carboxymethylaminodiethyltetraacetic acid (EGTA) was investigated, both in absence and in presence of oxygen. A radiolytic mechanism has been proposed. It has been shown that the degradation at the ligand of the chelate is due to OH only.     

Reaction of pentaammine(urea-O)cobalt(III) cation with chlorine and hypochlorous acid in aqueous solution

Summary The Co(NH₃)₅[OC(NH₂)₂]³⁺ cation in aqueous acid reacts with chlorine and hypochlorous acid, with two sequential steps observed in each case. Rate constants for both steps show a first-order dependence on [oxidant], with k₁/k₂ always <20, but varying with the choice of reactant and acid. Rate constants with Cl₂ as reactant are faster than with HOCl, possibly related to preferential attack by Cl⁺ compared with OCl^– on the bound urea. Competition by ions (HSO ₄ ^– , Cl^– or NO ₃ ^– ) measured by product analysis of reactions conducted in 1 M acid produced competition ratios R (R=[CoX]/[CoOH₂][X]) which are similar to values determined with a range of leaving groups previously, indicating a mechanistic constancy. No formation of Co(NH₃)₅Cl²⁺ was observed in reactions conducted in H₂SO₄ or HNO₃, implying that free Cl^– is not generated at the reaction site and captured by the metal ion. Electronic and vibrational spectra of the intermediate formed in the two stage reaction is indicative of a change from an O-bound to an N-bound ligand in forming that intermediate, although it cannot be a simple isomerization due to the dependence on [oxidant]. A possible mechanism is discussed.     

Acid-base properties of poly(1-vinylazoles) in aqueous solution

The interaction of poly(1-vinylimidazole) and poly(1-vinyl-1,2,4-triazole) with HCl and alkalies in aqueous and water-salt solutions was investigated by potentiometric titration, viscosimetry, ¹H and ¹³C NMR, and UV spectroscopy. The effect of the nature and concentration of low-molecular counterions was found. The interaction of poly(1-vinylazoles) with the acid results in the protonation of the azole cycle. The interaction of poly(1-vinylazoles) with alkalies is stipulated by the capability of the pyridine N atom of forming a coordination bond with the metal ion and that of the unsaturated pi-system of the heterocycle of coordinating with the anions.     

Heteroleptic cobalt(II) and nickel(II) complexes with iminodiacetic and dicarboxylic acids in aqueous solution

Equilibria in binary and ternary systems containing cobalt(II) and nickel(II) salts, iminodiacetic acid, and dicarboxylates were studied by spectrophotometry at I = 0.1 (NaClO₄) and T = 20 ± 2°C. The molar and proton compositions of the resulting complexes and the pH ranges of their existence were determined. The stability constants of the homo- and heteroleptic complexes were calculated. The pH-distribution of the detected complexes was obtained. The experimental data were analyzed using the mathematical models that predict the existence of a wide spectrum of complex species in solution and allow ignoring those species that are negligible for accurate reproduction of the observed pattern.     

Rates of water exchange for two cobalt(II) heteropolyoxotungstate compounds in aqueous solution

Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the catalytic sites, the rates of which are unknown. Here we report the exchange rates of water ligated to Co(II) atoms in two polyoxotungstate sandwich molecules using the (17)O-NMR-based Swift-Connick method. The compounds were the [Co(4)(H(2)O)(2)(B-α-PW(9)O(34))(2)](10-) and the larger αββα-[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-) ions, each with two water molecules bound trans to one another in a Co(II) sandwich between the tungstate ligands. The clusters, in both solid and solution state, were characterized by a range of methods, including NMR, EPR, FT-IR, UV-Vis, and EXAFS spectroscopy, ESI-MS, single-crystal X-ray crystallography, and potentiometry. For [Co(4)(H(2)O)(2)(B-α-PW(9)O(34))(2)](10-) at pH 5.4, we estimate: k(298)=1.5(5)±0.3×10(6) s(-1), ΔH(≠)=39.8±0.4 kJ mol(-1), ΔS(≠)=+7.1±1.2 J mol(-1) K(-1) and ΔV(≠)=5.6 ±1.6 cm(3) mol(-1). For the Wells-Dawson sandwich cluster (αββα-[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-)) at pH 5.54, we find: k(298)=1.6(2)±0.3×10(6) s(-1), ΔH(≠)=27.6±0.4 kJ mol(-1) ΔS(≠)=-33±1.3 J mol(-1) K(-1) and ΔV(≠)=2.2±1.4 cm(3) mol(-1) at pH 5.2. The molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions. This dissociation is detectable by EPR spectroscopy as S=3/2 Co(II) species (such as the [Co(H(2)O)(6)](2+) monomer ion) and by the significant reduction of the Co-Co vector in the XAS spectra.     

Structure of iron (II) and cobalt (II) bromide complexes in aqueous solution by X-ray diffraction analysis

Structures of bromo-metal complexes in concentrated aqueous solutions of FeBr₂ and of CoBr₂ were investigated by X-ray diffraction analysis. The complexes possess an octahedral geometry coordinating Br^– along with H₂O ligands. The frequency factors of metal-Br contacts per one atom of metal were 0.325 for the 2.7M (mol-dm^–3) and 0.747 for the 4.5M FeBr₂ solutions, and 0.280 for the 2.8M and 0.595 for the 4.3M CoBr₂ solutions. The frequency factors suggested that the tendency of metal ions to forming monobromo complexes is in the order, Fe>Co>Ni相似文献   

Complexes of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with chloride,nitrate, iodate,and sulfate ions in aqueous media: I. Formation constants,thermodynamic properties,and bonding mechanisms

Complexation stoichiometries and formation constants of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with NO ₃ ^– , Cl^–, IO ₃ ^– and SO ₄ ^2– ions are determined by pH potentiometric and¹³C NMR spectrometric measurements. Estimates of H and S are obtained from the values of the temperature dependent formation constants and acid dissociation constants. All four anions form only 1 : 1 complexes with the triprotonated amine species. NO ₃ ^– and Cl^– form 1 : 1 complexes only with the tetraprotonated amine, while IO ₃ ^– and SO ₄ ^2– form both 1 : 1 and 2 : 1 complexes. The complexation behavior is interpreted in terms of solvation and internal hydrogen bonding interactions.     

Kinetics and mechanism of an unique hydrolysis reaction of (hexafluoroacetylacetonato)bis(ethylenediamine)cobalt(III) in aqueous solution

Summary Addition of base to the title complex results in the rapid reversible formation of the hydrolysed species Co(en)₂-(hfac · OH)⁺ in which the coordinated hexafluoroacetylacetonato ligand contains a hydroxyl group on the carbonyl carbon atom. The kinetics of both the forward hydrolysis and reverse acidolysis reactions were followed spectrophotometrically using stopped-flow and T-jump techniques. The corresponding rate constants areca. 3×106 and 1×10⁸ M^–1s^–1, respectively, for various buffer systems at 25 °C and ionic strength 1.0 M. A combination of the kinetic and equilibrium data enables the estimation of the uncatalyzed (spontaneous) forward and reverse reaction components. The results are discussed with reference to similar data reported for the hydrolysis and reverse acidolysis reactions of the uncoordinated acetylacetonato ligand.     

Spectroscopic properties of neodymium(III)-containing polyoxometalates in aqueous solution

The spectroscopic properties of the neodymium(III)-containing polyoxometalates (POMs) [Nd(PW(11)O(39))(2)](11-), [Nd(PMo(2)W(9)O(39))(2)](11-), [Nd(PMo(4)W(7)O(39))(2)](11-), [Nd(PMo(6)W(5)O(39))(2)](11-), [Nd(SiMo(2)W(9)O(39))(2)](13-), [Nd(P(2)W(17)O(61))(2)](17-), [NdW(10)O(36)](9-), [NdP(5)W(30)O(110)](12-) and [NdAs(4)W(40)O(140)](25-) are described. Absorption spectra of aqueous solutions of the complexes have been recorded and the transition intensities are parameterised in terms of the Judd-Ofelt intensity parameters Omega(lambda) (lambda=2, 4, 6). Marked differences were found between the luminescence lifetimes of the complexes of the type Nd(POM) and those of the type Nd(POM)(2), due to a better shielding of the neodymium(III) ions from the bulk water molecules in the latter type of complexes.     

Oxygen binding of water-soluble cobalt porphyrins in aqueous solution

Water-soluble cobalt porphyrin 1Co and imidazole ligand 2 were synthesized. 1Co binds dioxygen in the presence of imidazole ligand 2 in aqueous solution. The formation of the oxygen adduct 2-1Co(O(2)) was studied using UV-vis and EPR spectroscopy. The impact of pH on the kinetic stability of the oxygen adduct was examined.     

4,7,10,13-Tetrakis(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane and properties of its metal complexes

A new N-carboxymethyl derivative of the oxa-tetraaza macrocyle, 4,7,10,13-tetrakis-(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane, has been synthesised. The protonation constants of this compound and the stability constants of its complexes with several di- and trivalent metal ions were determined by potentiometric or spectrophotometric methods, at 25°C and ionic strength 0.10 M in tetramethyl ammonium nitrate. The ligand exhibits two high or fairly high values of protonation constants and two low ones, and its overall basicity is about 27 in log units. Mono- and dinuclear complexes were found. The stability constant values of the 1:1 complexes with most of the metal ions studied are lower than expected, but not those of the dinuclear complexes. This was interpreted, in the case of mononuclear complexes, as the non-involvement in the co-ordination to these metal ions of two nitrogen atoms of the macrocycle backbone and, probably also, of one or two carboxylate groups. The Cu²⁺ ion has an exceptional behaviour, its 1:1 complex exhibits a high stability constant value. Spectroscopic data have indicated, for the last complex, the presence of two octahedral isomers in solution, one of them having only two nitrogens in the co-ordination sphere, while in the other three nitrogen donor atoms of the macrocyclic framework are co-ordinated in the equatorial plane. A third species appears at pH values higher than 7. These features suggest that the presence of four carboxymethyl arms and the relatively large size of the macrocycle severely constrains the geometric arrangement of the nitrogen donor atoms of the macrocyclic backbone around the metal centre decreasing the co-ordination number or leading to a preferred co-ordination with oxygen atoms. Another consequence of these structural features, is their easy ability to form dinuclear complexes, as found in the equilibria studies in solution and also by EPR spectroscopy of the Cu²⁺ complexes where the presence of two types of signals in the ΔM_s=1 and ΔM_s=2 regions, clearly reveals the presence of the dinuclear complex.