Thermodynamic characteristics of complex formation in the nickel(II) ion-β-alanine systems in aqueous solution

Heats of reactions between a nickel(II) ion and β-alanine were measured calorimetrically at 288.15, 298.15, and 308.15 K and ionic strengths of 0.5, 1.0, and 1.5 (KNO₃). Thermochemical data were processed with account for stepwise equilibria; attendant protolytic processes were taken into account together with complexing reactions. Extrapolation to the zeroth ionic strength with the use of a one-parameter equation gave standard thermodynamic characteristics of complex formation in the system. The influence of the supporting electrolyte and temperature on the heats of complex formation reactions was considered. Standard enthalpies of formation were calculated for NiAla⁺, NiAla₂, and NiAla₃⁻ species. Original Russian Text ? L.A. Kochergina, O.V. Platonycheva, O.M. Drobilova, V.V. Chernikov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 2, pp. 377–384.     

The chemistry of tin (II) chelates—II The tin (II)-ethylenediaminetetra-acetic acid system in aqueous solution

The tin (II)-EDTA system in aqueous solution has been investigated by potentiometry and polarography. The system is very sensitive to oxidation, changes in pH, and presence of electrolytes. Both mono and bi-nuclear complexes exist in solution.     

Benzoyl peroxide-cobalt(II) vinyl-β-diketonate systems as initiators of styrene and methyl methacrylate polymerization

New cobalt(II) vinyl-β-diketone-benzoyl peroxide [or azobis(isobutyronitrile)] binary systems were studied as initiators of polymerization of styrene and methyl methacrylate.     

Steric effect on the formation of columnar phases in β-diketonate copper(II) complexes

A systematic study of the mesomorphic properties of three series of copper(II) complexes based on β-diketonate ligands containing branched side chains is reported. These disc-like compounds have four, six and eight flexible alkoxy side chains appended to the central core, in which two or four side chains were substituted by bulkier secondary alkoxy groups: 1-methylbutyloxy R ' = C₅(2°) or 1-methylheptyloxy R ' = C₈(2°). The mesomorphic results indicated that at least eight side chains are required to form stable columnar mesophases; other compounds with four or six side chains are not mesogenic regardless of the combination of the carbon length on the alkoxy or secondary alkoxy groups of the side chains. The compounds 3 with shorter R ' = C₅(2°) side chains were all non-mesogenic regardless of the carbon length of three alkoxy side chains (R = C₈, C₁₀, C₁₂) used. However, when the longer 1-methylheptyloxy side chain R ' = C₈(2°) was substituted, the compounds 3b-3e with various alkoxy groups (R = C₆, C₇, C₈, C₁₀, C₁₂) exhibited columnar phases. The mesophases were characterized and identified as columnar hexagonal phases (Col_h), as expected, by thermal analysis and optical polarized microscopy. The presence of the introduced secondary alkoxy groups apparently appeared to influence the formation of columnar phases. The clearing points were relatively lower than other similar copper(II) compounds not substituted by secondary alkoxy side chains.     

Recognition of dicarboxylates in aqueous acetonitrile by a dinuclear zinc(II) complex of 2,2’-binaphthalene-based receptor

Molecular recognition of dicarboxylates by a dinuclear zinc(II) complex of 2,2?-binaphthalene bearing di(2-pyridyl)aminomethyl groups at 8- and 8?-positions ([Zn₂L]⁴⁺) by UV-vis and fluorescence spectral titrations in an aqueous solvent was investigated. In a series of α,ω-dicarboxylate, receptor [Zn₂L]⁴⁺ showed the highest binding affinity for succinate and UV-vis and fluorescence changes were also largest upon the addition of this guest. In a series of phthalate derivatives, phthalate was strongly bound by [Zn₂L]⁴⁺. The characteristic UV-vis and fluorescence changes strongly depend on the dihedral angle of two naphthyl groups of the complex [Zn₂L]⁴⁺· dicarboxylate estimated by spectral titrations and DFT calculations.     

The Szilard-Chalmers effect in solid-state systems containing octa-μ3-chloro-octahedro-hexamolybdenum(II) clusters

The Szilard-Chalmers effect for the ⁹⁹Mo radioisotope was measured for various systems containing the Mo₆Cl₈⁴⁺ cluster. Chromatrographic sepaations have indicated the production of four chemical species although the major component recovered was molybdate(VI). Retention as the target cluster was determined by recrystallization to constant specific activity. Retention was only 0.63% for an aqueous solution of (Mo₆Cl₈)Cl₆²⁻ in 1.5 . M HCl. Retention in solid-state systems was inversely dependent upon the degree of hydration and appeared to be inhibited somewhat by air. Thermal annealing of irradiated samples gave marginally measurable increases in retention up to temperatures where some decomposition of the compounds occurred.     

Study of spectroscopic properties of Europium (III) Tris(β-diketonate) complex and α-Cyclodextrin in aqueous medium

The solubilization of an europium (III) β-diketonate chelate in aqueous medium and the changes in its photophysical properties upon its inclusion into an α-cyclodextrin hydrophobic cavity are described. The complex [Eu(tta)₃·(H₂O)₂] (tta = 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione) was synthesized, characterized, and incorporated into the hydrophobic cavity by stirring in an α-cyclodextrin aqueous solution. The inclusion was confirmed by ¹H NMR, and the stoichiometry of association was obtained by the Job method. The maximum in the excitation spectrum of the α-CD inclusion compound in aqueous solution was shifted 28 nm compared with the maximum of non α-CD complex. The emission spectrum of the association is similar to that of the free solid complex and displays the characteristic ⁵D₀ → ⁷F_0-4 Eu³⁺ transitions.     

Thermochemical study of coordination equilibria in the zinc(II)-β-alanine-water system in aqueous solution

The heats of formation of β-alanine (HAla) complexes with Zn²⁺ ion at temperatures of 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 mol/l (KNO₃) were determined by calorimetry; the heats of dilution of a zinc nitrate solution in supporting electrolyte solutions were found for introduction of appropriate corrections. The standard heats of complexation in the zinc(II)-β-alanine-water system were determined. The standard thermodynamic characteristics of zinc(II) complexation with β-alanine and standard enthalpies of formation of ZnAla⁺ and ZnAla₂ complex species were calculated.     

Structural investigations of copper(II) complexes containing unsymmetrical β-diketonate and monothio-β-diketonate ligands

The crystal structures of the complexes Cu(txhd)₂ and Cu(S-tmhd)₂ (where txhd is the anion of 2,2,6-trimethylheptane-3,5-dione and S-tmhd is the anion of 5-mercapto-2,2,6,6-tetramethyl-4-hepten-3-one) were determined. In the solid state, both complexes are square planar. In each case, only one geometrical isomer (trans or cis) was observed in the crystals; arguments are presented that both isomers are present in bulk samples of Cu(txhd)₂, while from electronic considerations, the monothio-β-diketonate ligands probably have cis geometry in Cu(S-tmhd)₂. Calculations of molecular volumes for structurally similar Cu[t-BuC(O)CHC(O)R]₂ complexes showed that there is a slight decrease in packing efficiency as the steric bulk of R increases. More importantly, strong ring-stacking interactions, such as those found for Cu(acac)₂ are not observed, or are greatly attenuated, in complexes with bulkier peripheral substituents. [Cu(txhd)(μ₃-OEt)]₄, an impurity that co-sublimed with Cu(txhd)₂, was isolated in low yield. The tetrameric structure, which is isomorphous with known [Cu(tmhd)(μ₃-OEt)]₄ (where tmhd is the anion of 2,2,6,6-tetramethylheptane-3,5-dione), has a cubane-like core.     

Standard enthalpies of formation of bis(β-diketonate)cobalt(II) complexes: The mean (CoO) bond-dissociation enthalpies

The standard enthalpies of formation, at 298 K, of the 1-phenyl-1,3-butanedione (HBZAC) and 1,1,1-trifluoro-2,4-pentanedione (HTFAC) crystalline complexes of cobalt(II) were determined by precise solution—reaction calorimetry: ΔH⁰_f{Co(BZAC)₂,cr} = −632±6.0 kJ mol⁻¹ ΔH⁰_f{Co(TFAC)₂,cr} = −2140±10 kJ mol⁻¹. The average molar bond-dissociation enthalpies, <D>(CoO) were derived.     

Disposition of copper(II) inβ-cyclodextrin

Distances of glucose protons in-cyclodextrin (BCD) from copper(II) in copper(II)--cyclodextrin have been determined from¹H NMR spin-lattice relaxation time (T ₁) measurements for the first time. Very lowT _1p /T _2p values indicated the dipolar mechanism to be the most dominant one in determining the paramagnetic contribution to relaxation. The distances of copper(II) from BCD glucose protons indicated copper(II) to be present almost in the centre, inside the cavity in the same plane as H-1 and H-4. An average distance of about 5.0–5.9 Å was obtained for copper(II) from the H-2, H-3, H-1, H-4 and H-6 a and b protons in BCD.     

The effect of Fe(II) ions on the 1,10-phenanthroline and neocuproine intercalates of γ-zirconium phosphate

1,10-Phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neocuproine), and 4,7-dimethyl-1,10-phenanthroline have been intercalated between layers of -zirconium phosphate (-ZrP). The observed interlayer distances are not a simple function of the size of guest molecules. Despite the fact that -ZrP takes up very few Fe²⁺ ions, the phen and neocuproine intercalates do take up some Fe²⁺ ions without further changes in the interlayer distances. The chemical environments around Fe²⁺ ions between layers of the intercalates were investigated by⁵⁷Fe Mössbauer spectroscopy. A fairly large fraction of the Fe²⁺ ions was found to be in a high-spin state. The low-spin [Fe(phen)₃]²⁺ ions are also ion exchanged on -ZrP, with the expansion of the interlayer up to 19.9 Å.     

The effect of čerenkov light in the radiation-induced luminescence of aqueous solutions

The yield of luminescence from indole in an equivolume mixture of glycol and water observed during irradiation with ⁶⁰Co γ-rays is found to be considerably larger than that obtained during exposure to 220 kV X-rays. The difference is attributed to the γ-induced Čerenkov light which is absorbed by the solute and thereby causes additional luminescence. Thus, about 80 percent of the singlet excitation in a 10⁻² mol dm⁻³ indole solution is due to this effect. The yields of the fluorescence and phosphorescence induced by Čerenkov light are determined as a function of solute concentration. The yield of Čerenkov light in water is calculated as a function of the radiation energy for various sample sizes. The results indicate that because of this effect radiations having sufficient energy to produce Čerenkov light are not suited for studies of radiation-induced solute excitation in systems where energy transfer from the solvent does not contribute to the luminescence yield.     

Structure of the hexanuclear Cu(II) β-diketonate complex

The structure of the hexanuclear copper(II) β-diketonate complex with gfa (hexafluoroacetylacetone) and dpm (dipivalylmethanate) ligands was studied by low-temperature (T = 100 K) X-ray diffraction. Crystal data for Cu₆(gfa)₄(dpm)₄(OH)₄ [C₆₄H₈₄Cu₆F₂₄O₂₀]: a = 28.2364(7) Å, b = 12.8072(3) Å, c = 24.7199(7) Å, β= 115.900(1)°, V = 8041.5(4) ų, space group C2/m, Z = 4, d _calc 1.661 g/cm³. The coordination polyhedra of the copper atoms — squares and octahedra — are formed by the oxygen atoms of the gfa and dpm ligands and groups. In all cases, the Cu-O distances vary from 1.89 Å to 2.13 Å. The complexes follow the sites of the rhombohedral sublattice with the parameters a _c ≈ 14.4 Å and a _c ≈ 61.5°.     

X-ray photoelectron study of electron density distribution in palladium(II) β-diketonate complexes

This work is devoted to experimental (X-ray photoelectron) and theoretical investigations of electron density distribution in Pd(II) β-diketonate complexes. Data about the electronic structure (effective charges, core level energies) of the compounds are compared with their thermodynamic parameters (thermal stability, vaporization enthalpy). In molecular crystals of Pd(II) β-diketonates, the volatility of the complexes and vaporization enthalpy ΔH _T ⁰ depend not only on van der Waals interactions, but also on electrostatic interactions of molecules in crystal.     

Synthesis and electron transfer studies of redox active trans-β-diketonate Ni(II) complexes

The synthesis of trans-[Ni(dbm)₂(RN=C(Me)NHR)₂] (dbm?=?1,3-diphenylpropanedionate; R?=?phenyl, p-tolyl, 3,5-dimethylphenyl, 3,5-dichlorophenyl) has been achieved by reaction of [Ni(dbm)₂(H₂O)₂] with two equivalents of the amidine ligands, RN=C(Me)NHR. X-ray crystallographic studies reveal that trans-[Ni(dbm)₂(RN=C(Me)NHR)₂] (R?=?3,5-dimethylphenyl) exhibits an intramolecular N?CH···O hydrogen bond, which along with the large steric bulk of the amidine ligands may enforce the trans geometry. Electrochemical studies show a strong dependence of the oxidation potential on the substituent groups despite their remote position. DFT calculations indicate that the HOMO consists of Ni-ligand ??* orbitals with a significant contribution from the amidine ligands.     

The effect of SCN− on the extraction of Fe(III)-TTA

The extraction of iron from perchloric acid solution into TTA-benzene is known to be very slow and does not reach equilibrium within a practical contact time of the two phases. The addition of thiocyanate was found to enhance the rate considerably. From the results of detailed investigation, the reason for this effect is considered to be the replacement of a slow step, the direct formation of Fe-TTA complex, by a series of fast reactions, i.e. the formation of Fe-SCN complex in aqueous phase, followed by its extraction into the organic phase and the replacement of SCN⁻ in the complex with TTA in the organic phase. The possibility for a synergistic effect based on this phenomenon is suggested.     

Improvement of synthesis conditions of dispersed polymetallic Fe–Al–Mo systems in aqueous solutions

Kinetic dependences describing the processes occurring on aluminum microparticles in aqueous solutions containing iron and molybdenum ions were determined. It was shown that the samples obtained contain iron, molybdenum, and aluminum in the elementary state in the absence of an oxide phase.