The thermodynamic characteristics of step complex formation in the (5,10,15,20-tetraphenylporphyrinato)(chloro)indium(III)-pyridine-toluene system

The thermodynamic characteristics, step mechanism, and spectral manifestations of step reactions between (5,10,15,20-tetraphenylporphyrinato)(chloro)indium(III) ((Cl)InTPP) and organic base pyridine (Py) in inert toluene were studied using spectrophotometric titration and physicochemical analysis of intermediate forms. The coordination of Py molecule (K ₁ = 9.45 × 10² l/mol at 298 K) with the formation of (Cl)(Py)InTPP, the substitution of Cl^? in (Cl)(Py)InTPP with the second Py molecule (K ₂ = 2.3 × 10² l/mol), and the coordination of the third Py molecule to produce [(Py)₃ InTPP]⁺ · Cl^? (K ₃ = 8.7 l/mol) were observed at the first, second, and third steps, respectively. The fourth reaction stage most likely corresponds to π?π complex formation equilibrium between the aromatic complex and pyridine with a 1: 2 stoichiometry. The thermodynamic parameters of step reactions ΔH ^° and ΔS ^° well correspond to the stoichiometric mechanism of the reaction. Prospects for the use of the metalloporphyrin as a receptor of organic N-bases are considered.     

Kinetics of thermal reaction HOCl ⇄ H(<Superscript>2</Superscript><Emphasis Type="Italic">S</Emphasis>) + OCl(<Emphasis Type="Italic">X</Emphasis><Superscript>2</Superscript>Π<Subscript><Emphasis Type="Italic">i</Emphasis></Subscript>) in gas phase

The kinetics of gas reaction \(HOCl\underset{{k_r }}{\overset{{k_f }}{\longleftrightarrow}}H(^2 S) + OCl(X^2 \Pi _i )\) was analyzed by the MP4 method. In the temperature range of 100–373 K the rate constants k _f and k _r and equilibrium constant K were changed from 1.10 × 10^?220 to 1.17 × 10^?52 s^?1, from 2.89 × 10^?16 to 1.68 × 10^?5s^?1 and from 3.80 × 10^?205 to 6.96 × 10^?48 respectively. In the above temperature range, the activation energy of the forward reaction (E _f) is 105.05 kcal/mol. In the same temperature interval there are two kinetic domains for the reverse reaction with activation energies (E _r1 = 5.53 kcal/mol when T is 100–273 K and E _r2 = 14.50 kcal/mol when T is 273–373 K, respectively.     

Germane decomposition: Kinetic and thermochemical data

Rate constants for the two stages of germane dissociation (GeH₄ → GeH₂ + H₂(I) and GeH₂ → Ge + H₂(II) have been derived from the studies of the chemiluminescence kinetics during germane dissociation in the presence of nitrous oxide behind shock waves at 1060–1300 K and the full density equal to ～10^?5 mol/cm³. Analysis in terms of the RRKM model gave the following expressions for the rate constants of these reactions in the high and low pressure limits: k _{1, ∞} = 2.0 × 10¹⁴exp(?208.0/RT) s^?1; k _{1, 0} = 1.7 × 10¹⁸(1000/T)^3.85exp(?208.0/RT) cm³/(mol s); and k _{2, 0} = 2.8 × 10¹⁵(1000/T)^1.32exp(?135.0/RT) cm³/(mol s). The results, in combination with the available enthalpies of formation of radical GeH₂, show that the back reaction for stage (I) has an energy barrier of about 66 kJ/mol.     

Mixed-Ligand Complexation of Zinc and Cobalt(II) Complexonates with Amino Acids in an Aqueous Solution

The formation of mixed-ligand complexes in the M(II)–Nta and Ida–L systems (M = Co, Zn; L = His, Orn, Lys, Gly, Im, en), where Ida and Nta are the residues of iminodiacetic and nitrilotriacetic acids, was studied by pH-metry, calorimetry, and NMR spectroscopy. The thermodynamic parameters (logK, Δ _r G⁰, Δ _r H, Δ _r S) of formation for these complexes were determined at 298.15 K and an ionic strength I = 0.5 (KNO3). The most probable pattern of coordination between a complexone and an amino acid in mixed-ligand complexes was revealed.     

Reaction Equilibrium and Kinetics of Synthesis of Polyoxymethylene Dimethyl Ethers from Formaldehyde and Methanol

Polyoxymethylene dimethyl ethers (PODE _n ) are environmentally friendly diesel fuel additives. They belong to alkyl ethers that could reduce solid particulate matter formation and emissions of carbon monoxide and nitrogen oxide when added into diesel fuels. This work aimed to researching chemical equilibrium and reaction kinetics of the synthesis of polyoxymethylene dimethyl ethers from formaldehyde and methanol catalyzed by an ion-exchange resin at the reaction temperatures 313, 333, 343 and 353 K. In the reversible reaction, the K_{n ≥ 2}/K₂ ratio was equal to one. The reaction orders of methanol, formaldehyde, water and PODE _n were 0.2638, 0.1328, 0.1565 and 0.0048, respectively. At a 10 wt % dosage of H-SIR1 resin, the rate constants of the methylal (dimethoxymethane) formation and depolymerization were 1.04 × 10⁴ and 3.43 × 10⁶ min^–1, respectively, and the pre-exponential factor for the PODE_{n + 1} formation was 2.50 × 10³ min^–1. Activation energies for the methylal propagation and depolymerization and PODE_{n > 1} formation were 30.46, 48.40 and 27.10 kJ/mol, respectively. The results indicated that the equilibrium constants of PODE_{n > 1} formation reactions were consistent. The exothermic reaction of methylal formation was easier than the reverse reaction and more difficult than the formation of PODE_{n > 1}.     

The catalytic properties of alkaline phosphatases under various conditions

A comparative study was performed to examine the catalytic properties of alkaline phosphatases from bacteria Escherichia coli and bovine and chicken intestines. The activity of enzyme dimers and tetramers was determined. The activity of the dimer was three or four times higher than that of the tetramer. The maximum activity and affinity for 4-nitrophenylphosphate was observed for the bacterial alkaline phosphatase (K _M = 1.7 × 10^?5 M, V _max = 1800 μmol/(min mg of protein) for dimers and V _max = 420 μmol/(min mg of protein) for tetramers). The Michaelis constants were equal for two animal phosphatases in various buffer media (pH 8.5) ((3.5 ± 0.2) × 10^?4 M). Five buffer systems were investigated: tris, carbonate, hepes, borate, and glycine buffers, and the lowest catalytic activity of alkaline phosphatases at equal pH was observed in the borate buffer (for enzyme from bovine intestine, V _max = 80 μmol/(min mg of protein)). Cu²⁺ cations formed a complex with tris-(oxymethyl)-aminomethane (tris-HCl buffer) and inhibited the intestine alkaline phosphatases by a noncompetitive mechanism.     

A novel 3D energetic coordination polymer containing Co(II) atoms in a pentanuclear cluster

A novel coordination polymer [Co₅(OH)₂(dnbpdc)₄(H₂O)₆]·16H₂O (1) (dnbpdc = 6,6′-dinitro-4,4′-biphenyldicarboxylic acid) is obtained from a hydrothermal reaction. The structure of complex 1 is characterized by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction analysis. The title compound (C₅₆H₇₀Co₅N₈O₅₆, M _r = 2045.85) crystallizes in the triclinic space group P-1 with a = 11.9349(2) Å, b = 12.1895(2) Å, c = 15.420(2) Å, α = 109.390(7)°, β = 94.786(1)°, γ = 108.027(9)°, V = 1968.4(4) ų, Z = 1, D _c = 1.726 g/cm³, F(000) = 1045, μ(MoK _α) = 1.154 mm^–1, T = 133(2) K, the final R = 0.0316 and wR = 0.0692 for 7032 observed reflections with I > 2σ(I). The coordination polymer is built of a pentanuclear Co(II) cluster, four dnbpdc ligands, two hydroxyl groups, six coordination water and sixteen crystal water molecules. Ligand oxygen atoms exhibit three types of coordination modes (monodentate, syn-syn bridging bidentate and bridging tridentate). Moreover, the infinite three-dimensional supramolecular network is generated by coordination and hydrogen bonds. The thermal stability of complex 1 is evaluated by differential scanning calorimetry and thermogravimetric analysis.     

The thermodynamic characteristics of formation of organic molecule complexes with the magnesium ion in water: The results of quantum-chemical modeling

The Gibbs energy ΔG _b of formation of organic molecule complexes with the Mg²⁺ ion in water was calculated on the basis of a two-stage scheme for the complex formation reaction. The first stage is ligand transfer from infinity into the second coordination sphere of the Mg²⁺ ion, and the second stage is the dissociation of bonds between water molecules and the Mg²⁺ ion and the formation of bonds between the ligand and Mg²⁺. The contribution of the first reaction stage to ΔG _b was calculated on the assumption that the ligand was a solid body with a charge or dipole moment (if the ligand was neutral). The contribution of the second stage to ΔG _b was calculated using quantum-chemical modeling. The major contribution to ΔG _b was made by a change in the internal energy of the complex as a result of the dissociation/formation of coordination bonds and a change in the electric component of the Gibbs energy of interaction between the magnesium ion and molecule with water when they formed a complex. The contribution of the nonpolar component of complex interaction with water was comparatively small. Accurate calculations of the contribution of vibrational degrees of freedom to ΔG _b were also of importance.     

Synthesis,crystal structure,and electrochemical properties of the complex [Ni(imidazole)<Subscript>6</Subscript>](DBSH)<Subscript>2</Subscript> · 2DMF

The title complex [Ni(Im)₆](DBSH)₂ · 2DMF(H₂DBSH = 3,5-dibromosalicylaldehyde, Im = imidazole, DMF = N,N-dimethylformamide) has been prepared and characterized by X-ray diffraction analysis. It crystallizes in the monoclinic system, space group P2₁/c with a = 14.7271(13), b = 9.0221(8), c = 18.1143(16) Å, β = 100.408(2)°, V = 2367.2(4) ų, Z = 2, M _r = 1171.22, F(000) = 1172, ρ _c = 1.643 g/cm³ and μ(MoK _α) = 3.844 mm^?1. The structure was refined to R = 0.0425 and wR = 0.1052 for 3646 observed reflections. The X-ray crystal structure analysis revealed that the center nickel(II) cation is bonded to six nitrogen atoms from six imidazole to form a six-coordinated elongated octahedron. The complex includes a DBSH^2? anion and two DMF solvates. The intramolecular and intermolecular hydrogen bonds in the crystal structure play remarkably important role in the thermostability of the title complex. The electrochemical properties were studied in DMF with an electrochemical analyzer.     

Cathodic Stripping Voltammetry of 2-Mercapto-5-Methyl-1,3,4-Thiadiazol and 2,5-Dimercapto-1,3,4-Thiadiazol at a Controlled-Growth Mercury Drop Electrode

2-Mercapto-5-methyl-1,3,4-thiadiazol (MMTD) and 2,5-dimercapto-1,3,4-thiadiazol (DMTD) were studied by differential pulse cathodic stripping voltammetry (DPCSV). The influence of buffer, pH, accumulation potential (E_acc), and accumulation time (t_acc) was investigated. It was stated that the concentration of the buffer affects the height of DPCSV peaks. The best analytical signals were recorded in acetate buffer at pH 4.3 and a buffer concentration of 0.01 mol/L for MMTD and 0.02 mol/L for DMTD, E_acc = 0.2 V, and t_acc = 120 s for MMTD and 180 s for DMTD. A linear dependence was found from 1 to 8 × 10^?8 mol/L for MMTD and from 1 × 10^?8 to 1 × 10^?7 mol/L for DMTD. The influence of cations [Cu(II), Co(II)] was also considered.     

Variation of the Intersection Point of the Potential Surface Crossing Induced by the Laser Phase Along the Reaction Path in Ion-Molecule Reactions: Application To Li<Superscript>+</Superscript> + CH<Subscript>4</Subscript>

A laser ion-molecule reaction interaction through both polarizability and dipole moment contribution leads to variation in the intersection point in potential energy surface crossings along the reaction path; the polarizability is maximum and the dipole changes its sign at s = 4 a.u., defining a virtual transition state. Using the gauge representation (electric field gauge) for a wave length λ = 20.6 μm, intensity I = 5×10¹² W/cm², I = 1×10¹³ W/cm², I = 3×10¹³ W/cm², we show here that we can create a laser-induced potential energy surface crossing along the reaction path (s = 7-8 a.u.). We illustrate such effects for the Li H + CH ₃ ⁺ ? Li⁺ + CH₄ reaction which takes the form of inverted Morse (without a barrier) using ab initio methods for calculating the reaction path and electric properties of the ion-molecule reaction.     

Structure and charge-transport properties of LnBaCuCoO<Subscript>5 + δ</Subscript> (Ln = Y,Dy) cuprocobaltites

LnBaCuCoO_{5 + δ} (Ln = Y, Dy) cuprocobaltites were prepared. Their unit cell parameters were determined and their thermal expansion, electrical conductivity (σ), and Seebeck coefficient (S) were studied in air in the range 300–1100 K. The compounds have tetragonal structures (space group P4/mmm). Their unit cell parameters are a = 0.3867(2) nm, c = 0.7550(7) nm, V = 112.9(2) × 10^?3 nm³ for YBaCuCoO_4.98; and a = 0.3872(2) nm, c = 0.7562(7) nm, V = 113.4(2) × 10^?3 nm³ for DyBaCuCoO_5.01. They are p-type semiconductors. The electrical conductivity of DyBaCuCoO_{5 + δ} is slightly lower and its Seebeck coefficient is 1.5–2 times higher than the respective values for YBaCuCoO_{5 + δ} apparently because of different electronic configurations of the rare-earth cations in LnBaCuCoO_{5 + δ} (4d ⁰ for Y³⁺ and 4f ⁹ for Dy³⁺). Dilatometric measurements show that the LnBaCuCoO_{5 + δ} phases in the range 300–1100 K do not experience structural phase transitions, and their linear thermal expansion coefficients (LTEC) are 14.3 × 10^?6 K^?1 for Ln = Y and 14.7 × 10^?6 K^?1 for Ln = Dy.     

Tetrakis(isothiocyanato)manganese(II) bis[aqua(18-crown-6)potassium] (18-crown-6)(thiocyanato)potassium

A new complex compound, i.e., tetrakis(isothiocyanato)manganese(II) bis[aqua(18-crown-6)potassium] (18-crown-6)(thiocyanato)potassium, was synthesized and its crystal structure was studied by X-ray diffraction (space group P2₁/m, a = 13.377, b = 14.690, c = 17.499 Å, β = 108.96°, Z = 2) and refined by the least-squares method in anisotropic approximation to R = 0.060 for 4715 independent reflections (CAD-4 automated diffractometer, λMoK _α). In the crystal, infinite chains are formed through the coordination bonds between its components. The monomer fragment of a chain [Mn(NCS)₅K₃(18-crown-6)₃(H₂O)₂] lies in plane m; three of the five SCN^? ligands and one of the two water molecules behave as bridges. The [Mn(NCS)₄]^2? anion has the tetrahedral structure. The coordination polyhedron of each of the three K⁺ cations is a distorted hexagonal bipyramid with six O atom of the corresponding crown ligand in a base. Three 18-crown-6 ligands have standard crown conformation.     

Complexation of Chlorodiethylenetriaminegold(III) with Chloride Ions in Aqueous Solutions

The reaction of Au(Dien)Cl²⁺ (Dien is diethylenetriamine) with the chloride ion was studied spectrophotometrically in an aqueous solution at I = 1.0 mol/l and T = 20°C. The formation constant of pentacoordinated Au(Dien)Cl ₂ ⁺ was determined and its spectrum was calculated.     

Tetraaquatetrakis(ɛ-caprolactam)lutetium(III) hexaisothiocyanatochromate(III) sesquihydrate

The ionic complex [Lu(?-C₆H₁₁NO)₄(H₂O)₄][Cr(NCS)₆] · 1.5H₂O, the first example of coordination of ?-caprolactam to the lutetium atom, was synthesized by the reaction of Lu(NO₃)₃, K₃[Cr(NCS)₆], and ?-caprolactam in an aqueous solution. The structure of the complex was established by IR spectroscopy and X-ray crystallography. The crystals are triclinic, space group P \(\bar 1\) T = 100 K, a = 11.9604(3) Å, b = 12.3640(3) Å, c = 18.3506(5) Å, α = 91.3200(10)°, β = 108.6640(10)°, γ = 112.4460(10)°, V = 2343.45(10) ų, Z = 2, ρ_calcd = 1.597 g/cm³, R = 0.0299 for 9839 reflections with F _hkl ≥4σ(F). The coordination polyhedron of the lutetium atom is a distorted square antiprism with broken square faces with the oxygen atoms of the organic ligands and water at the vertices. There are weak intramolecular hydrogen bonds N-H…O(H₂) in the cation. The coordination polyhedron of the chromium atom is a somewhat distorted octahedron. The thermal stability of the compound was studied in an inert atmosphere and in air.     

Renium(V) complexation with <Emphasis Type="Italic">N</Emphasis>-ethylthiourea

The stepwise complexation of rhenium(V) with N-ethylthiourea has been studied by the potentiometric method in 6 mol/L HCI at 298 K. It has been found that rhenium(V) forms five complex species with this ligand of the following compositions: [ReOLCl₄]^?, [ReOL₂Cl₃], [ReOL₃Cl₂]⁺, [ReOL₄Cl]²⁺, and [ReOL₅]³⁺. The calculated logarithms of stepwise formation constants of the complexes are the following: logK₁ = 4.10 ± 0.05, logK₂ = 3.16 ± 0.02, logK₃ = 2.61 ± 0.02, logK₄ = 2.26 ± 0.02, and logK₅ = 1.80 ± 0.02. It has been shown that the introduction of the ethyl radical into the thiourea molecule leads to an increase in the stability of rhenium(V) complexes.     

Synthesis,Crystal Structure,Luminescence Sensing,and Photocatalytic Properties of a 2D Cobalt(II) Coordination Polymer Containing Bis(benzimidazole) Moieties

A new cobalt(II) coordination polymer, namely [Co(L)(Ndc)] _n (I), where L = 1,5-bis(5,6- dimethylbenzimidazole)pentane, H₂Ndc = 2,6-naphthalenedicarboxylic acid, was synthesized and characterized by elemental analysis, IR spectra, powder X-ray diffraction and single-crystal X-ray diffraction (CIF file CCDC no. 1548044). Complex I displays a 2D (4,4) layer which further extended into a 3D supramolecular framework via weak C–H···O hydrogen bondings. The luminescence explorations demonstrated that I exhibits highly selective and sensitive sensing for Cr₂O ₇ ^2? with high quenching efficiency K_sv value of 9.87 × 10³ L mol^?1 and low detection limit (0.24 μM (S/N = 3)). Meanwhile I also exhibits highly selective and sensitive sensing for Fe³⁺ with quenching efficiency K_sv = 3.6 × 10⁴ L mol^–1 and low detection limit (0.32 μM (S/N = 3)). Complex I exhibits higher photocatalytic activities for the degradation of methylene blue under UV irradiation. Additionally, the thermal behavior and electrochemical properties of the compound are also presented.     

<Emphasis Type="Italic">Ab initio</Emphasis> quantum-chemical study of vinylation of pyrrole and 2-phenylazopyrrole with acetylene in a KOH/DMSO system

Interaction between pyrrole and its 2-vinyl, 2-azo, and 2-phenylazo derivatives with acetylene in the gas phase and DMSO was studied using the MP2/6-311++G**//MP2/6-31G* ab initio approach and including the solvation effects within the framework of the continuum model. Possible reasons are considered for the hindered character of direct vinylation of azopyrroles with acetylene in superbasic media. The introduction of the azo group in the 2 position of the pyrrole ring leads to the increased stability of the pyrrole anion and increased acidity from pK _a = 22.1 for pyrrole and pK _a = 20.5 for vinylpyrrole to pK _a = 16.6 and 16.4 for 2-azopyrrole and 2-phenylazopyrrole, respectively. The binding energy between the pyrrole anion and the acetylene molecule decreases concurrently. The heat of formation of the pyrrole anion adducts with acetylene changes from ΔH = 4.8 kcal/mol for pyrrole to ΔH = 22.4 kcal/mol for 2-phenylazopyrrole. For all anion adducts under study, preferable isomers are Z isomers formed by the interaction of pyrrole anions with the cis-distorted acetylene molecule, but the formation of the E isomers corresponds to a lower activation barrier, which explains known Z stereoselectivity of the nucleophilic addition to monosubstituted acetylenes. When an azo group is introduced, the reaction becomes more endothermal, and the energy barriers to the formation of both Z and E isomers increase. Among other reasons for lowering of the activity of 2-arylazopyrroles during vinylation we consider possible reaction of acetylene addition at the most remote nitrogen atom of the azo group and participation of the anion center in cation chelation (K⁺ in the calculation).     

Crystal and molecular structure of the potassium salt of 2,4-di-<Emphasis Type="Italic">iso</Emphasis>-propoxy-6-dinitromethyl-1,3,5-triazine

An X-ray diffraction study of the potassium salt of 2,4-di-iso-propoxy-6-dinitromethyl-1,3,5-triazine was performed. Monoclinic crystals, C₁₀H₁₄N₅O ₆ ^? ·K⁺; M = 339.36; a = 9.645(2) Å, b = 8.803(2) Å, c = 17.686(3) Å; β = 92.50(2)°; V = 1500.2(5) Å ³, d _c = 1.50 g/cm³, Z = 4, space group P2₁/a. The 2,4-di-iso-propoxy-6-dinitromethyl-1,3,5-triazine anion is nonplanar. The 1,3,5-triazine heterocycle is planar; the angle between the ring and the dinitromethyl fragment is 87.9(5)°. The potassium cation is in the general position; its coordination number is 7. The cation is bonded to four 2,4-di-iso-propoxy-6-dinitromethyl-1,3,5-triazine molecules. Infinite layers are formed due to the coordination bonds in crystal.     

Synthesis and crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis[dichloro(thiocyanato)copper(II)]

A new complex salt [4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis[dichloro(thiocyanato)copper(II)], [H₂(Crypt-222)][CuCl₂(SCN)]₂, is synthesized and studied by X-ray diffraction analysis. The crystals are monoclinic (space group C2/c, a = 14.603 Å, b = 8.330 Å, c = 25.091 Å, β = 100.76°, Z = 4). The structure is solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.047 for 2943 independent reflections (CAD-4 automated diffractometer, λMoK _α radiation). The Cu²⁺ cations and Cl^? and SCN^? anions form infinite polymeric chains of spiro-conjugated alternating centrosymmetric four-membered CuCl₂Cu cycles and eight-membered Cu(SCN)₂Cu cycles through coordination bonds. The coordination polyhedron of the Cu²⁺ cation is a distorted trigonal bipyramid. The [H₂(Crypt-222)]²⁺ dication contains trifurcate N⁺-(…O)₃ bonds on axis 2.