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.     

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.     

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.     

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.     

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.     

The effect of σ-donation on the interactions of cis-diaqua(2-aminomethylpiperidine)platinum(II) complex with biomolecules in aqueous medium: synthesis,kinetic and mechanistic study

The kinetics of the interaction of dl-penicillamine with cis-[Pt(pipen)(OH₂)₂]²⁺ (pipen = 2-aminomethylpiperidine) have been investigated under pseudo-first-order conditions as a function of concentration and temperature at pH 4.0 in aqueous solution of 0.10 M NaClO₄ using UV–Vis spectrophotometry. The kinetic study has been supported by isolation and characterization of the product by IR and ESI–MS spectroscopic analysis. Thermodynamic and kinetic parameters for the reaction have been evaluated. The DNA-binding properties, pKa values and substitution rates of such complexes can be tuned through the σ-donation properties of the spectator ligand, which leads to potential applications in cancer therapy.     

Heteroligand polynuclear nickel(II) complexonates in aqueous solutions of 2,2′-dipyridyl

Formation of nickel(II) complexes with ethylenediaminetetraacetic acid (Edta) and 2,2′-dipyridyl (Dipy) has been studied by electronic absorption spectroscopy. Mathematical modeling has demonstrated that the most probable mathematical models to describe the experimental dependences of absorption on the medium acidity and concentration of solution components relies on the dissociation constants of the ligands (K _i ) and stability constants (β) of homoligand, heteroligand, and polynuclear complexes of general composition [Ni _m Dipy _n Edta _r ]^{2m ? 4r} (m = 1–4, n = 0–8, r = 0–1) as parameters. The reaction equilibrium constants and stability constants of the resulting complexes have been calculated. The structures of these complexes have been suggested.     

The thermodynamic parameters of complex formation between the copper(II) Ion and β-alanine in aqueous solution

The heats of formation of β-alanine complexes with the doubly charged copper(II) ion were determined calorimetrically. The heat effects of interaction of a solution of the amino acid with a solution of copper(II) were measured at 288.15, 298.15, and 308.15 K and ionic strengths of 0.50, 0.75, and 1.00 against the background of KNO₃. The heats of dilution of a solution of copper nitrate with solutions of the background electrolyte were also determined for the introduction of the corresponding corrections. The standard thermodynamic characteristics of complex formation were calculated. The influence of temperature on the thermal effects of complex formation in the β-alanine-copper(II) ions system were considered. The standard enthalpies of formation of CuAla⁺ and CuAla₂ complex particles in aqueous solution were calculated.     

Preparation of double pyrophosphates in aqueous systems chromium(III) salt−sodium pyrophosphate

The specifics of preparation of chromium double pyrophosphates in systems Cr(NO₃)₃–Na₄P₂O₇–H₂O, CrCl₃–Na₄P₂O₇–C₂O, and KCr(SO₄)₂–Na₄P₂O₇–H₂O are discussed. Changes in pH of the mentioned systems have been studied depending of the component ratio. The effects of the deposition duration and sodium pyrophosphate concentration on pH have been studied for system Cr(NO₃)₃–Na₄P₂O₇–H₂O. Phase composition has been determined for compounds prepared in systems Cr(NO₃)₃–Na₄P₂O₇–H₂O and KCr(SO₄)₂–Na₄P₂O₇–H₂O. It has been found that the acid residue anions do not substantially affect the formation of a continuous series of compounds consisting of hydroxy and hydro combinations of chromium ions and pyrophosphate ion, whereas cations can have an effect. System KCr(SO₄)₂–Na₄P₂O₇–C₂O is less sensitive to reaction conditions than systems in which normal salts Cr(NO₃)₃ and CrCl₃ act as a source of Cr³⁺ cation. A product stable over time can be prepared in system KCr(SO₄)₂–Na₄P₂O₇–C₂O; after heat treatment at 900°C, it is a mixture of KCrP₂O₇ and a-CrPO₄ phases.     

The kinetics of the solid-state dimerization of aquabis-N-acetyl-β-alaninatocopper(II)monohydrate

The simultaneous dehydration and dimerization of the blue monomeric complex of N-acetyl-β-alanine and copper(II) has been studied by isothermal thermogravimetry. The results are consistent with a two-stage loss of water from the dihydrate, dimerization being concurrent with the loss of the second water molecule.     

Partitioning of biomaterials in aqueous two-phase systems of mixed cationic-anionic surfactants

In a previous paper, we have showed that, when aqueous solutions of cationicand anionic surfactants at certain concentrations were mixed, the solution separatedspontaneously into two immiscible phases (aqueous two-phases), one phase was rich,and the other was poor in the mixed surfactants. A clear interfacial boundary existsbetween two phases.     

Regularities of copper(II) and nickel(II) distribution in an aqueous solution‒modified flax fiber heterophase system

Russian Journal of General Chemistry - The distribution of Cu2+ and Ni2+ ions in an aqueous solution — flax fiber heterophase system was investigated. The specific surface area of the sorbent...     

The degradation of polyacrylamide in aqueous solution induced by chemically generated hydroxyl radicals: Part II—Autoxidation of Fe2+

Hydroxyl radicals, generated by the autoxidation of Fe²⁺, have been shown to attack polyacrylamide molecules in solution and cause chain scission. In acid solution the extent of degradation is determined by the rate of autoxidation which is very dependent on pH and the chelation of the iron. In alkaline solution degradation is negligible.