Effects of the ligand structure and electronic properties of the central atom on the kinetics of complex formation of N-methyloctaethylporphyrine with solvate complexes in binary solvents

The reactivity of 3d-metal solvates [MX₂(S)₄] and [MX₂(S₁)_m(S₂)_4?m ] (where S, S₁, and S₂ are solvent molecules: pyridine, N,N-dimethylformamide, and dimethyl sulfoxide) toward porphyrins with different structures, N-methyloctaethylporphyrin and meso-tetraphenyltetrabenzoporphyrin, is discussed. A strong catalytic effect of solvents and ligands having π orbitals was found and rationalized in terms of trans effect in the coordination sphere of solvate salts. A probable activation mechanism of the trans effect was proposed, and its magnitude was shown to strongly depend on the metal nature.     

Thermal electronic properties of alkali clusters

We apply the finite-temperature Kohn-Sham method to alkali metal clusters, using the spherical jellium model and treating the valence electrons as a canonical system in the heat bath of the ions. We study the shell effects in the total free energyF(N) and the entropyS(N) for neutral clusters containingN atoms. Their strongest temperature dependence is due to the finite ground-state valueS ₀>0 of the electronic entropy for non-magic clusters. It leads to a decreasing amplitude and an increasing smear-out of the saw-tooth structure in the first difference Δ₁ F(N)=F(N?1)?F(N) with increasing temperatureT and cluster sizeN.     

Thermodynamics of undecanolactone,tridecanolactone, and pentadecanolactone from 0 to 340 K

The heat capacities C_p^o of undercanolactone, tridecanolactone, and pentadecanolactone have been measured between 10 and 370 K in a vacuum adiabatic calorimetric cryostat within about 0.2 per cent. The temperatures and enthalpies of physical transitions have been also estimated. The enthalpies of combustion of the compounds have been measured in an isothermal calorimeter with an accuracy of 0.05 per cent. From the results the functions {H (T) ? H (0)}, S^o(T), and {G^o(T) ? H^o(0)} have been calculated over the range 0 to 340 K, and the values of ΔH_f^o, ΔG_f^o and ΔS_f^o have been evaluated at T = 298.15 K.     

Reactivity of 3d-metal salt solvates in reactions with porphyrins: Influence of the trans effect

The reactivity of 3d-metal salt solvates [MX₂(S)₄] and [MX₂(S₁) _m (S₂)_4?m ] has been studied in reactions with different porphyrins: meso-tetraphenylporphine (H₂TPP), N-methyloctaethylporphine (H(N-Me)(β-Et)₈P), and meso-tetraphenyltetrabenzoporphine (H₂TBP(ms-Ph)₄). Solvents S, S₁, and S₂ are dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and pyridine (Py), respectively. The strong catalytic effect of the solvents and ligands with π orbitals on the reaction rates due to the trans influence in the coordination sphere of the salt solvates has been observed and explained. A possible activation mechanism of the trans influence was considered. A strong dependence of the trans effect on the nature of the metal and porphyrin was shown.     

Enthalpies of formation of solid cobalt-tellurium alloys

The enthalpies of formation of solid Co?Te alloys were determined at room temperature with an isoperibol solution calorimeter of the submarine type. Co?Te alloys and mechanical mixtures of the pure components were dissolved in separate experiments in a saturated hydrochloric acid (8.000n)—bromine mixture and the enthalpies of formation obtained by difference. For the NiAs-type β-phase ΔH _f ^o(N_Te)=(4.079–15.017N _Te) kcal·g-atom^?1 and for the marcasitetype γ-phase ΔH _f ^o(N _Te)=(3.787–14.400N _Te) kcal·g-atom^?1. Combining these results with data from the literature integral thermodynamic properties of solid Co—Te alloys were calculated at room temperature and at 600°C.     

Thermodynamic characteristics of triphenylantimony diacrylate

The heat capacity of triphenylantimony diacrylate Ph₃Sb(O₂CCH=CH₂)₂ was studied in an adiabatic vacuum calorimeter at 6?C350 K and differential scanning calorimeter at 330?C450 K. Melting was revealed at these temperatures; the melting point was estimated at 428.4 ± 0.5 K. It was accompanied by the partial decomposition of the substance. The low-temperature (20 K ?? T ?? 50 K) heat capacity was treated using the Debye theory of the heat capacity of solids and its multifractal model. The type of the structure topology was determined. The standard thermodynamic functions C _p ^o (T), H ^o(T) ? H ^o(0), S ^o(T), and G ^o(T) ? H ^o(0) of the compound in the crystal state were calculated from the obtained experimental data in the range from T ?? 0 to 428 K. The standard entropy of the formation of the crystalline compound Ph₃Sb(O₂CCH=CH₂)₂ at T = 298.15 K was determined.     

The heat capacity and thermodynamic functions of Ca0.5Zr2(PO4)3 crystalline phosphate from T → 0 to 650 K

The temperature dependence of the heat capacity C _p ^o = f(T) of crystalline calcium-zirconium phosphate was studied over the temperature range 7–650 K by precision adiabatic vacuum and dynamic scanning calorimetry. The experimental data were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o(T) ? H ^o(0), S ^o(T), and G ^o(T) ? H ^o(0) at temperatures from T → 0 to 650 K and the standard entropy of formation of Ca_0.5Zr₂(PO₄)₃ at T = 298.15 K. The data on low-temperature (30 K ≤ T ≤ 50 K) heat capacity were used to calculate fractal dimension D. Conclusions about the character of the topology of the structure of the phosphate were drawn.     

Kristallstruktur von Hexamincyclotriphosphazen,P3N3(NH2)6

Crystal Structure of Hexamine Cyclotriphosphazene, P₃N₃(NH₂)₆ In the presence of KNH₂ hexamine cyclotriphosphazene semi ammoniate (molar ratio 12:1) in NH₃ gives crystals of solvent free P₃N₃(NH₂)₆ within 5 d at 130°C and p(NH₃) = 110 bar. The structure was solved by X-rax methods: P₃N₃(NH₂)₆: P2₁/c, Z = 4, a = 10.889(6) Å, b = 5.9531(6) Å, c = 13.744(8) Å, β = 97.83(3)°, Z(F_o) = 1 721 with (F_o)² ≥ 3σ(F_o)², Z(var.) = 157, R/R_w = 0,036/0,041 The structure contains columns of molecules P₃N₃(NH₂)₆ all in the same orientation. The six-membered rings within one molecule have boat conformation. The columns are stacked together in a way that one is surrounded by four others shifted by half a lattice constant in direction [010]. Strong hydrogen bridge-bonds N? H…?N connect molecules within the columns and between them.     

Delayed fluorescence from the lowest 1B+3u state of anthracene,due to hetero-triplet—triplet annihilation of 3anthracene* and 3xanthone*

The P-type delayed fluorescence (DF) S_i→S_o of aromatic compounds results from the population of excited singlet states S_i by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T₁ : T₁ + T₁

S_i + S_o; S_i may be any excited singlet state whose excitation energy E(S_i ? 2 E(T₁). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(T_A¹) < E(T₁^B), hetero-TTA may lead to excited singlet states S_k^A which are not accessible by TTA of 2 T₁^A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state S_k^A which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h₁₀ or anthracene-d₁₀ or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. S_k^A is the lowest ¹B_3U⁺ state (B_b state) of anthracene.     

Dynamics of the photoinduced desorption of nitric oxide molecules from the surface of pure and modified platinum

The distribution of NO molecules desorbed from a Pt(111) surface due to valence electron excitation over rotational energy levels N(J) is analyzed using a simple impulse-induced model. A linear dependence is found between lnN(J) and (E_r)^1/2, where E_r is the rotational energy of the desorbed molecules. The lifetime of the excited state and the critical time of residence in the excited state estimated using this dependence are found to be close to one another (~10^?15 s). The frequency and amplitude of the tilting vibrations of the adsorbed molecules in the excited state are estimated.     

Schrödinger equation for a dirac bubble potential

The quantum-mechanical problem of a particle moving in a “Dirac bubble potential” U(r) = (λ/r_o)δ(r - r_o) is solved exactly for both bound and continuum states by making use of partial wave Green's functions G_l(r, r₀, k). Phase shifts are expressed in a compact form related to those for an impenetrable sphere.     

Ruthenium(III) complexes with modified nucleobases: N-Substituted adenines

New chlorido-dimethylsulfoxide-ruthenium(III) complexes with different N⁶-substituted adenines have been prepared and characterized. Three ruthenium complexes have been structurally characterized by X-ray diffraction crystallography: [Ru^IIICl₄(DMSO)[H-(N⁶-pentyladenine)]] (1), [Ru^IIICl₄(DMSO)[H-(N⁶-hexyladenine)]] (2) and [Ru^IIICl₄(DMSO)[H-(N⁶,N⁶-dibutyladenine)]] (3). In all cases ruthenium ion show octahedral geometry coordinated to four chlorido ligands and one S coordinated sulfoxide (DMSO). The coordination sphere is completed by an adenine moiety coordinated to Ru(III) via N(9) and protonated at N(3). Other similar complexes have been obtained with N⁶-propyladenine, [Ru^IIICl₄(DMSO)[H-(N⁶-propyladenine)]] · 0.5EtOH (4) and N⁶-benzylaminopurine (BAP) [Ru^IIICl₄(DMSO)[H-(BAP)]] · 0.5H₂O (5) which have been spectroscopically characterized. Otherwise, in different reaction conditions, we have obtained an out sphere complex of Ru(II), [H-(BAP)][Ru^IICl₃(DMSO)₃] (6), with identical complex unit than the structurally solved [H-(creat)][Ru^IICl₃(DMSO)₃] (7) which was included for comparison purposes. Preliminary electrophoretic mobility and atomic force microscopy (AFM) studies of the interaction between Ru(III) compounds and plasmidic DNA pBR322 have been performed. These results show different morphological changes in plasmidic DNA forms.     

The molecular mechanism of low-temperature decomposition of hydrogen sulfide under conjugated chemisorption-catalysis conditions

The molecular mechanism of interaction of two hydrogen sulfide molecules with the (Co^III-H_o)₂S₂(SH₂)₄ model active center containing occluded hydrogen was studied by the density functional theory method with the B3P86 hybrid exchange-correlation functional. The reaction was found to occur in the following elementary steps: molecular adsorption of hydrogen sulfide ? dissociative chemisorption ? S-S bond formation in the surface intermediate {2Co^III ? (μ-S₂) + 2H(ads)} with the release of the first hydrogen molecule into the gas phase H₂(g) ? the release of the second hydrogen molecule into the gas phase H₂(g) ? the formation of cyclooctasulfur in the reaction 4S₂(ads) → S₈(ads). The first three steps occur spontaneously at room temperature, the thermodynamic driving force of the process being the stoichiometric reaction of S-S bond formation at the stage of conjugated chemisorption of two hydrogen sulfide molecules on two adjacent metal ions with the release of the first hydrogen molecule into the gas phase. The catalytic cycle is terminated by the recombination of molecular sulfur S₂ into cyclooctasulfur S₈ in the adsorption layer and the release of the second hydrogen molecule into the gas phase.     

Thermodynamic properties of second generation poly(phenylene-pyridyl) dendrimer

The temperature dependence of heat capacity C _p ^o = f (T) of second generation hard poly(phenylene-pyridyl) dendrimer (G2-24Py) was measured by a adiabatic vacuum calorimeter over the temperature range 6–320 K for the first time. The experimental results were used to calculate the standard thermodynamic functions: heat capacity C _p ^o (T), enthalpy H ^o(T)–H ^o(0), entropy S ^o(T)–S ^o(0) and Gibbs function G ^o(T)–H ^o(0) over the range from T → 0 K to 320 K. The standard entropy of formation at T = 298.15 K of G2-24Py was calculated. The low-temperature heat capacity was analyzed based on Debye’s heat capacity theory of solids. Fractal treatment of the heat capacity was performed and the values of the temperature characteristics and fractal dimension D were determined. Some conclusions regarding structure topology are given.     

Preferential energy transfer from N2(A) to specific energy levels of Cu atoms

Emission spectra resulting from reaction of “clean” N₂(A³ Σ_u⁺) with copper atoms were studied using a flowing afterglow apparatus. The population distribution of the Cu states was calculated from the spectrum; it indicates that Cu atoms are excited by nearly resonant energy transfer processes. N₂(A,v') + Cu(²S_{$\text{1}\text{2}$}) → N₂(X, v) + Cu^* , and that the transfer is most efficient for N₂(A,v') → N₂(X,v) transitions with large Franck-Condon factors. The preferential energy transfer results in population inversion between some of the Cu states.     

System analysis of the thermodynamic properties of binary lanthanide hydrides

Systems analysis of available data on the thermodynamic properties of binary lanthanide hydrides is carried out. The standard thermodynamic characteristics of lanthanide dihydrides (Δ_f H ^o, S ^o, C _p ^o ) and their hypothetical trihydrides (Δ_f H ^o) are calculated. The calculations are performed using a semiempirical method that takes into account the effects of the number of f-shell electrons and the spin and orbital angular moments of ground states of the lanthanide ions on the thermodynamic properties of the compounds studied. It is established that the thermodynamic characteristics of the hydrides exhibit an antibatic behavior with respect to the atomic numbers of the natural series lanthanides. The tetrad effect was revealed for these series of compounds.     

Thermodynamics of the lanthanide halides I. Heat capacities and Schottky anomalies of LaCl3, PrCl3, and NdCl3 from 5 to 350 K

The heat capacities of LaCl₃, PrCl₃, and NdCl₃ have been measured from 5 to 350 K by adiabatic calorimetry. No co-operative thermal anomalies were seen in the temperature range investigated but substantial magnetic heat-capacity contributions of the non-cooperative (Schottky) type were found. Subtraction of the heat capacity of the diamagnetic and isostructural LaCl₃ from those of the paramagnetic members yields experimental Schottky heat-capacity contributions which are compared with heat capacities derived from spectroscopically determined energy levels. Small discrepancies between the calculated and experimental contributions are probably due to differences in lattice heat capacities between LaCl₃ and the others. The values of {(S^o(298.15 K) ? S^o(0)}/cal_th K^?1 mol^?1 are for LaCl₃ and NdCl₃, 32.88 and 36.67. Due to the possibility of a low-temperature phase transition, the entropy of PrCl₃ covers only the experimental range of this research and that of Colwell, Mangum, and Utton. {S^o(298.15 K) ? S^o(0.294 K)} for PrCl₃ is 36.64 cal_th K^?1 mol^?1.     

Modelling of an Atmospheric Pressure Nitrogen Glow Discharge Operating in High-Gas Temperature Regimes

A model of an atmospheric pressure nitrogen glow discharge in high-gas temperature regimes is developed. The model considers a fairly complete set of chemical reactions, including several processes with the participation of electronically exited nitrogen atoms describing the energy balance and charged particles kinetic processes in the discharge. It is shown that the thermal dissociation of vibrationally excited molecules plays an essential role in the production of N(⁴ S) atoms. The dominant ion within the investigated current range (52–187 mA) is the molecular N₂ ⁺ with an increasing proportion of atomic N⁺ towards high-current values. The process of production of electrons within the almost whole current range is controlled predominantly by associative ionization in atomic collisions N(² P) + N(² P) → N₂ ⁺ + e; being the N(² P) atoms mainly produced via quenching of N₂(A ³∑ _u ⁺ ) electronically excited molecules by N(⁴ S) atoms. The results of calculations are compared with the available experimental data and a good agreement is found.     

The use of positron lifetime measurements in a study of electron scavenging by a range of radiosensitizer compounds

Positron lifetime measurements were made in aqueous solutions of a number of radiosensitizer compounds in order to measure the o-Ps inhibition and quenching constants. By making measurements in the presence and in the absence of perchloric acid, the inhibiting effects on the o-Ps yield due to epithermal and trapped electrons could be determined on the basis of the spur model. Inhibition constants relating to the scavenging by the sensitizer molecule of epithermal electrons. (K₁) and traped electrons, (K₂) were found for eight basic nitroimidazoles. The results are also discussed in terms of electron trap depth which is here taken to be equivalent to the one-electron redox potential, E¹₇. It is concluded that o-Ps lifetime measurements alone are not capable of determining the finer details of these spur reactions. Estimates of the respective yields of RS^- and OH^. species in oxygen and R—NO₂ compounds show that these are not able to explain the large differences in sensitizing efficiency.     

Base and catalyst-free synthesis of nitrobenzodiazepines via a cascade N-nitroallylation-intramolecular aza-Michael addition involving o-phenylenediamines and nitroallylic acetates

A [4+3] annulation of o-phenylenediamines with primary nitroallylic acetates affords nitrobenzodiazepines (NBDZs) in good to excellent yield. The reaction which proceeds in MeOH at room temperature in the absence of any base or catalyst involves a cascade S_N2 N-nitroallylation-intramolecular aza-Michael addition sequence. In the case of mono-N-arylated o-phenylenediamines and o-aminobenzamides, the reaction stops at the S_N2 stage affording nitroallylic amines. On the other hand, reaction of o-aminobenzamides with secondary nitroallylic acetates delivers S_N2′ products. Formation of stable S_N2 and S_N2′ products provides insights into the reactivity of primary and secondary nitroallylic acetates and also the mechanism of formation of nitrobenzodiazepines.