Thermodynamics of the Extraction of U(VI) by N,N′-Didecanoylpiperazine

A novel extractant, N, N-didecanoylpiperazine (DDPEZ), was synthesized for the first time. The extraction of U(VI) by DDPEZ from aqueous nitric acid media in carbon tetrachloride has been studied. The dependence of extraction distribution ratio on concentration of aqueous nitric acid, extractant, salting-out agent and temperature was investigated and the enthalpy of the extraction was calculated.     

Stability constants of the complexes of Zn(II) and Mn(II) with N,N′-bis(2-hydroxyethyl) aminomethyl

The acid dissociation constants of N,N′-bis(2-hydroxyethyl) aminomethyl phosphonic acid (BHAMP) and the stability constants with Zn⁺⁺ and Mn⁺⁺ were determined at 25°C and at an ionic strength of 0.10 by means of potentiometric methods. The existence of a stable chelate species YM is illustrated. The equilibrium constants reported were calculated by the method developped by Schwartzenbach.     

Diastereomeric Difference of the Self-Inclusion Complex of N(N′-Formyl-Phenylalanyl)-Deoxyamino-β-Cyclodextrin Caused by the Interaction between the Arm and the Rim of the Cavity

A complete assignment of proton resonances for N(N-formyl d-phenylalanyl)-deoxyamino--cyclodextrin (1d) was performed by means of 1D and 2D NMR,¹H–^1H-COSY, ¹H–^13C-COSY, TOCSYand NOESY spectroscopy. Based on 2D-NMR ROESY and circular dichroism spectroscopy, the conformation of 1d was determined; the phenyl group stays inside the distorted cyclodextrin (CyD) cavity forming a self-inclusion complex, which is almost the same as N(N-formyl l-phenylalanyl)-deoxyamino--CyD (1l). The remarkable diastereomeric difference was observed in the chemical shifts of H(5) and H(6) protons at the narrow rim of the CyD cavity and induced circular dichroism spectra. These results suggest the existence of hydrogen bonds between the hydroxyl group on CyD and the amide groups on the arms, which provides the difference in the molecular recognition properties.     

Crystal Structure of the Addition Compound of N,N′-Bi(2-pyridylmethyl)-Oxamide and the Complex of Copper with 1,10-Phenanthroline

ＩｎｔｒｏｄｕｃｔｉｏｎＨｅｔｅｒｏｂｉｎｕｃｌｅａｒｃｏｍｐｌｅｘｅｓａｒｅｅｒｙｖｅｒｙｉｍｐｏｒｔａｎｔｉｎａｎａｔｅｍｐｔｔｏｍｉｍｉｃｔｈｅｓｔｒｕｃｔｕｒａｌａｎｄｆｕｎｃｔｉｏｎａｌｐｒｏｐｅｒｔｉｅｓｏｆｂｉｏｌｏｇｉｃａｌｓｙｓｔｅ...     

Kinetics of the oxidation of [N-(2-hydroxyethyl)-ethylene-diamine-N,N′,N′-triacetato]cobalt(II) by N-bromosuccinimide

The kinetics of the oxidation of [N-(2-hydroxyethyl)-ethylene-diamine-N,N,N-triacetato] cobalt(II), [Co^II-(HEDTA)]^–, by N-bromosuccinimide, NBS, have been studied in aqueous solutions and water-methanol solvent mixtures under various conditions. The reaction stoichiometry indicates that one mole of NBS reacts with one mole of [Co^II(HEDTA)]^–. In aqueous solutions the reaction obeys the following rate law:

Coupling of ν(NH⋯N) vibrations with the γ(NH⋯N) overtone in solid imidazole derivatives

The IR spectra of a number of imidazole derivatives were studied in the solid state at room and liquid nitrogen temperatures. The bands ascribed to stretching and out-of-plane deformation vibrations of NH groups involved in strong NH⋯N hydrogen bonds were analysed. The energy of this bond reflected in the position of the ν(NH⋯N) band changes over a broad range so that it was possible to investigate band shaping due to the overlap with the overtone band of the γ(NH⋯N) mode. The correlation between the γ(NH⋯N) and ν(NH⋯) frequencies shows that the γ(NH⋯N) value for strong NH⋯N bridges only slightly depends on ν(NH⋯N).     

Kinetics of solvolysis of the trans-dichlorobis(R-ethylenediamine)cobalt(III) ion (R = N-methyl or N,N′-dimethyl) in urea–water mixtures

First order solvolysis rates of the trans-dichlorobis(R-ethylenediamine)cobalt(III) ion (R=N-Me or N,N-Me₂) complex have been investigated in mixtures formed by adding urea to H₂O, which enhances the dielectric constant and decreases solvent structure. Differential effects of the changes in solvent structure on the initial and transition states are found to be important factors controlling changes in the rate constant with solvent composition. The variation of the enthalpy and the entropy of activation with solvent composition are contrasted with their variations found for the solvolysis of the complexes in mixtures where solvent structure is enhanced by additions of a co-solvent to water. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the cationic cobalt(III) complexes in the transition state are more stable than the cationic cobalt complexes the initial state in the water+urea mixtures.     

Dependence of the chemical properties of macrocyclic [Ni(II)(2)L(μ-O(2)CR)](+) complexes on the basicity of the carboxylato coligands (L(2-) = macrocyclic N(6)S(2) ligand)

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.     

In vitro biological studies of heteroleptic Ag(I) and Cu(I) unsymmetrical N,N′-diarylformamidine dithiocarbamate phosphine complexes; the effect of the metal center

A series of five dithiocarbamate and their respective Ag(I) and Cu(I) triphenylphosphine complexes of the general formula [Ag/Cu(PPh₃)₂L] were synthesized and characterized. The dithiocarbamate ligands were synthesized from formamidines with substituents in the 2 and/or 6 positions of the phenyl rings, intentionally keeping substituents on one ring different from those of the second phenyl ring while investigating the structure-activity relationship of Ag(I) and Cu(I) dithiocarbamate complexes. All Ag(I) and Cu(I) complexes with the general formula [Ag(PPh₃)₂L] (1–5) or [Cu(PPh₃)₂L] (6–10), displayed distorted tetrahedral geometry around the metal centers with coordination via two S atoms of the dithiocarbamate ligand and two P atoms from the PPh₃ units. Complexes 1–5 showed better inhibition values against Gram-positive, Staphylococcus aureus (methicillin resistant) and Staphylococcus aureus than the standard used, ciprofloxacin. Complexes 1 and 2 generally had good activity against all bacterial strains but were not active against Salmonella typhimurium. All Cu(I) complexes were either of low activity or inactive against all bacterial strains tested. Complex 2 was found to be more active with IC₅₀ values of 1.34 × 10⁻³ mM and 0.25 mM as agents for antioxidant activity against DPPH and NO free radical scavengers, respectively. The metal center played a vital role in their biological activity as the Ag(I) complexes displayed better antibacterial and antioxidant activity than Cu(I) complexes.     

Critical phenomena in the topochemical reaction of water vapor with solid N,N′-ethylenebis (acetylacetoniminato)copper (II)

The effects of water vapor and temperature on the phase transition between anhydrous N,N-ethylenebis(acetylacetoniminato) copper (II) and the monohydrate have been studied by a piezoelectric microbalance method. The presence of a branch point and critical deceleration of the phase transition dynamics near that point have been observed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 149–153, March–April, 1993.This work was supported by a fundamental research grant from the State Committee on Science and Technology, Ukraine Council of Ministers.     

Electrochemical synthesis and spectroscopy of the polymeric form of N,N′-bis(3-methoxysalicylidene)-1,3-propylenediamine

Electrochemical oxidation of N,N′-bis(3-methoxysalicylidene)-1,3-propylenediamine leads to the formation of a conducting polymer on the electrode surface. The diffusion coefficient and activation barrier of the charge transfer in the bulk of the polymer in an electrolyte medium were determined. The Schiff base and its polymeric form in the oxidized and reduced states were characterized by IR, X-ray photoelectron, and electronic absorption spectroscopy. Reversible changes in the polymer structure, accompanying its electrochemical oxidation-reduction, are substantiated.     

Spectrophotometric Method for the Determination of Cobalt with N,N′-Bis(2-Aminobenzoyl)Ethylenediamine

 A simple and direct spectrophotometric method has been developed for the determination of cobalt(II) using N,N′-Bis(2-aminobenzoyl)ethylenediamine (Baben). The method is based on the colour reaction between Baben and cobalt(II) in borax buffer (pH 9.2). The studies are carried out at 470 nm at which the calculated value of molar absorptivity is found to be 1.102 × 10⁴ L mol⁻¹ cm⁻¹. The system obeys Beer’s law over a wide range of concentration (2–20 μg/ml). The effect of interfering ions has been studied and the method was applied to the determination of cobalt in water, industrial effluents and in alloys and the results were highly satisfactory. Received May 8, 2000. Revision January 30, 2001.     

Synthesis and X-ray crystal structures of N,N,N′,N′-tetraalkylpyridine-2,6-dithiocarboxamides (S-dapt) complexes of cobalt(II) and nickel(II)

Reactions of anhydrous CoX₂ (X?=?Br^?, SCN^?) and Ni(ClO₄)₂ with N,N,N′,N′-tetraisobutylpyridine-2,6-dithiocarboxamides (S-dbpt), N,N,N′,N′-tetraisopropyl pyridine-2,6-dithiocarboxamides (S-dppt), and N,N,N′,N′-tetraethylpyridine-2,6-dithiocarboxamides (S-dept) lead to the formation of [Co(S-dbpt)Br₂] (1), [Co(S-dppt)(SCN)₂] (2), and [Ni(S-dept)₂]·(ClO₄)₂·H₂O (3), respectively. The X-ray crystal structures of the three S-dapt ligands and three complexes along with spectroscopic analyzes are presented. The molecular structure investigations of the S-dapt ligands show that the thiamide planes are twisted with respect to the pyridine ring, which is more in the case of phenyl groups. The structures of the Co(II) complexes reveal that an increase in steric crowding on the amide side arms of the ligands has no substantial effect on the geometry adopted by the corresponding complexes. The Co(II) gives only 1?:?1 five-coordinate, ion-paired complexes with a distorted square pyramidal geometry. Ni(II), on the other hand, prefers an octahedral geometry with 1?:?2 metal–ligand ratio. The coordination behavior of S-dapt has been compared to the analogous oxo(O-daap) ligands. Lesser propensity of S atom to get involved in H-bonding interactions ensures an S-N-S type of tridentate coordination by S-dapt.     

Complexation of the N,N′,O-donor ligand N-trans-(2′-hydroxycyclohexyl)-2-aminomethylpyridine

The potentially tridentate N,N′,O-donor N-trans-(2′-hydroxycyclohexyl)-2-aminomethylpyridine (1) forms ML₂ complexes with M(II)?=?Cu, Ni, and Zn. X-ray crystal structures of the isostructural Ni(II) and Zn(II) complexes confirm bis-tridentate coordination in significantly distorted octahedral geometries as the all-cis facial isomer. Structural comparisons with the previously reported all-trans facial Cu(II) and cis,cis,trans(N_py) facial Co(III) complexes are presented. Protonation constants for 1 and stability constants with Cu(II), Ni(II), and Zn(II) are reported, with both ML and ML₂ species defined. The trend for ML (log K ₁ values for Cu, Ni, and Zn of 8.3, 6.9, and 5.3, respectively) is conventional. Protonation and stability constants with Cu(II) for N,N-bis(2-pyridylmethyl)amine (2) were also defined. The log K ₁ value measured for 2 of 7.4 is very similar to that found for 1 of 8.3, despite the marked difference in the third donor group; it appears that the third donor of the tridentate ligand generally binds only poorly to Jahn–Teller elongated Cu(II) in solution.     

Study on the Mechanism of the Radiation-Induced Chain Oxidation of N,N,N,N-Tetramethyl-4,4′-diaminodiphenylmethane by Tetrabromomethane in Poly(vinyl chloride) Films

Kinetics and mechanism of the radiation-induced chain oxidation of N,N,N,N-tetramethyl-4,4-diaminodiphenylmethane (Am) by tetrabromomethane in poly(vinyl chloride) (PVC) films were studied by ESR and optical spectroscopy. The quantitative analysis of the ESR spectra of PVC films containing Am and CBr₄ irradiated with -rays at 77 K was performed. The nature of radical species involved in the chain process was established. It was shown that the heating of the films after their irradiation at 77 K resulted in the formation of free radicals Am^·, which initiated the chain oxidation of amine with a chain length of 100. The kinetic features of the chain oxidation–reduction reactions occurring in vacuum and in the presence of oxygen were compared.     

The characterization of some square planar Ni(II) complexes of N,N′-ethylenebis (isonitrosoacetylacetoneimine)

The ligand (H₂L) is prepared by the condensation of 2 molecules of isonitrosoacetylacetone with 1 molecule of ethylenediamine. The dimeric nature of the ligand is compatible with the types of the square planar Ni(II) complexes it produces with NiX₂(X  Cl, NO₃, CH₃CO₂). The 1:1 up to 5:1 molar ratio reaction of nickel chloride with the ligand produced the same complex H₂LNiCl₂ · HLNiCI(I) which did not react with pyridine, while the 1:2 and 1:3 molar ratio reaction afforded the complexes LNi · HLNiCl(II) and (LNi)₂(III) respectively. The reaction of nickel nitrate with (H₂L)₂ led to the formation of the complex LNi · HLNiNO₃(IV). The Ni(II) complex LNi(V) of the monomeric ligand was obtained by either the reaction of nickel acetate with (H₂L)₂ (1:1 or 5:1) or by reacting nickel chloride with the neutral solution of the ligand (1:1 or 2:1). The two anions of the ligand are linked together through either (a) hydrogen bonding formation that involves the oxime groups (H₂L and complex I), (b) coordination of one on the oximato group of a ligand's anion with the chelated metal ion to another ligand's anion (complex III), or (c) by both types of linkages (complexes II and IV). The suggested molecular formulations are based on analytical, spectral and magnetic moment evidence.