Design of donor–acceptor–donor (D–A–D) type small molecule donor materials with efficient photovoltaic parameters

Four Donor–Acceptor–Donor (D–A–D) type of donor molecules (M1‐M4) with triphenylamine (TPA) as donor moiety, thiophene as bridge, and thiazolothiazole as acceptor unit were designed and its photovoltaic parameters were equated with reference molecule “R.” DFT functional CAM‐B3LYP/6‐31G (d,p) was found best for geometry optimization and TD‐CAM‐B3LYP/6‐31G (d,p) was found suitable for excited state calculations. Among designed donor molecules, M4 manifests suitable lowest band gap of 4.73 eV, frontier molecular orbital energy levels as well as distinctive broad absorption of 455.3 nm due to the stronger electron withdrawing group. The electron‐withdrawing substituents contribute to red shifts of absorption spectra and better stabilities for designed molecules. The theoretically determined reorganization energies of designed donor molecules suggested excellent charge mobility property. The lower λ_e values in comparison with λ_h illustrated that these four donor materials would be ideal for electron transfer and M4 would be best amongst the investigated molecules with lowest λ_e of 0.0177. Furthermore, the calculated Voc of M4 is 2.04 V with respect to PC₆₀BM (phenyl‐C61‐butyric acid methyl ester). This study revealed that the designed donor materials are suitable and recommended for high performance organic solar cell devices.     

Solid Solution Formation between Vanadium(V) and ­Tungs­ten(V) Oxide Phosphate

The solid solutions (V_1–xW_x)OPO₄ with β‐VOPO₄ structure type (0.0 ≤ x ≤ 0.01) and α_II‐VOPO₄ structure type (0.04 ≤ x ≤ 0.26) were obtained from mixtures of V^VOPO₄ and W^VOPO₄ by conventional solid state reactions and by solution combustion synthesis. Single crystals of up to 3 mm edge length were obtained by chemical vapor transport (CVT) (800 → 700 °C, Cl₂ as a transporting agent). Single crystal structure refinements of crystals at x = 0.10 [a = 6.0503(2) Å, c = 4.3618(4) Å, R₁ = 0.021, wR₂ = 0.058, 21 parameters, 344 independent reflections] and x = 0.26 [a = 6.0979(2) Å, c = 4.2995(1) Å, R₁ = 0.030, wR₂ = 0.081, 21 parameters, 346 independent reflections] confirm the α_II‐VOPO₄ structure type (P4/n, Z = 2) with mixed occupancy V/W for the metal site. Due to the specific redox behavior of W⁵⁺ and V⁵⁺, solid solutions (V_1–xW_x)OPO₄ should be formulated as (V^IV_xV^V_1–2xW^VI_x)OPO₄. The valence states of vanadium and tungsten are confirmed by XPS measurements. V⁴⁺ with d¹ configuration was identified by EPR spectroscopy and magnetic measurements. Electronic spectra of the solid solutions show the IVCT(V⁴⁺ → V⁵⁺) and the LMCT(O^2– → V⁵⁺). (V_0.74W_0.26)OPO₄ powders exhibit semi‐conducting behavior (E_g = 0.7 eV).     

Multifunctionality in Bimetallic LnIII[WV(CN)8]3− (Ln=Gd,Nd) Coordination Helices: Optical Activity,Luminescence, and Magnetic Coupling

Two chiral luminescent derivatives of pyridine bis(oxazoline) (Pybox), (SS/RR)‐iPr‐Pybox (2,6‐bis[4‐isopropyl‐2‐oxazolin‐2‐yl]pyridine) and (SRSR/RSRS)‐Ind‐Pybox (2,6‐bis[8H‐indeno[1,2‐d]oxazolin‐2‐yl]pyridine), have been combined with lanthanide ions (Gd³⁺, Nd³⁺) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN^?‐bridged coordination chains: {[Ln^III(SS/RR‐iPr‐Pybox)(dmf)₄]₃[W^V(CN)₈]₃}_n ? dmf ? 4 H₂O (Ln=Gd, 1 ‐SS and 1 ‐RR; Ln=Nd, 2 ‐SS and 2 ‐RR) and {[Ln^III(SRSR/RSRS‐Ind‐Pybox)(dmf)₄][W^V(CN)₈]}_n ? 5 MeCN ? 4 MeOH (Ln=Gd, 3 ‐SRSR and 3 ‐RSRS; Ln=Nd, 4 ‐SRSR and 4 ‐RSRS). These materials display enantiopure structural helicity, which results in strong optical activity in the range 200–450 nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/Vis absorption spectra. Under irradiation with UV light, the Gd^III‐W^V chains show dominant ligand‐based red phosphorescence, with λ_max≈660 nm for 1 ‐(SS/RR) and 680 nm for 3 ‐(SRSR/RSRS). The Nd^III‐W^V chains, 2 ‐(SS/RR) and 4 ‐(SRSR/RSRS), exhibit near‐infrared luminescence with sharp lines at 986, 1066, and 1340 nm derived from intra‐f ⁴F_3/2→⁴I_{9/2,11/2,13/2} transitions of the Nd^III centers. This emission is realized through efficient ligand‐to‐metal energy transfer from the Pybox derivative to the lanthanide ion. Due to the presence of paramagnetic lanthanide(III) and [W^V(CN)₈]^3? moieties connected by cyanide bridges, 1 ‐(SS/RR) and 3 ‐(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between Gd^III (S_Gd=7/2) and W^V (S_W=1/2) centers with J _{1 ‐(SS)}=?0.96(1) cm^?1, J _{1 ‐(RR)}=?0.95(1) cm^?1, J _{3 ‐(SRSR)}=?0.91(1) cm^?1, and J _{3 ‐(RSRS)}=?0.94(1) cm^?1. 2 ‐(SS/RR) and 4 ‐(SRSR/RSRS) display ferromagnetic coupling within their Nd^III‐NC‐W^V linkages.     

Selenophene‐Flanked Diketopyrrolopyrrole Based Conjugated Polymers for Ambipolar Field‐Effect Transistors

The development of selenophene‐flanked DPP (SeDPP) based copolymers, especially for the ambipolar ones, lags behind other aromatic group flanked DPP‐based polymers. Herein, we report two new ambipolar SeDPP‐based conjugated polymers. One is the alternating polymer PSeDPPFT with normal SeDPP and 3,4‐difluorothiophene units. The other is PSeFDFT , in which the electron acceptor unit is replaced by a new SeDPP derivative, referred as to half‐fused SeDPP. The more planar structure of half‐fused SeDPP endows the backbone of PSeFDFT with good rigidity and planarity. Both polymers exhibit ambipolar transporting properties in air. The PSeFDFT based field‐effect transistors (FETs) display higher and more balanced ambipolar properties with μ_h^ave of 0.27 cm²·V^–1·s^–1, μ_e^ave of 0.18 cm²·V^–1·s^–1, and μ_h^ave/μ_e^ave of 1.5 than those of PSeDPPFT (μ_h^ave = 0.11 cm²·V^–1·s^–1, μ_e^ave = 0.042 cm²·V^–1·s^–1, and μ_h/μ_e = 2.6). This is attributed to the more planar structure, lower LUMO level, higher HOMO level, and better interchain packing orientations of PSeFDFT by comparing with PSeDPPFT . Therefore, a new molecular design strategy to modulate the hole and electron transporting properties is proposed for conjugated D‐A polymers.     

Mechanistic Features of the TiO2 Heterogeneous Photocatalysis of Arsenic and Uranyl Nitrate in Aqueous Suspensions Studied by the Stopped‐Flow Technique

The dynamics of the transfer of electrons stored in TiO₂ nanoparticles to As^III, As^V, and uranyl nitrate in water was investigated by using the stopped‐flow technique. Suspensions of TiO₂ nanoparticles with stored trapped electrons (e_trap^?) were mixed with solutions of acceptor species to evaluate the reactivity by following the temporal evolution of e_trap^? by the decrease in the absorbance at λ=600 nm. The results indicate that As^V and As^III cannot be reduced by e_trap^? under the reaction conditions. In addition, it was observed that the presence of As^V and As^III strongly modified the reaction rate between O₂ and e_trap^?: an increase in the rate was observed if As^V was present and a decrease in the rate was observed in the presence of As^III. In contrast with the As system, U^VI was observed to react easily with e_trap^? and U^IV formation was observed spectroscopically at λ=650 nm. The possible competence of U^VI and NO₃^? for their reduction by e_trap^? was analyzed. The inhibition of the U^VI photocatalytic reduction by O₂ could be attributed to the fast oxidation of U^V and/or U^IV.     

Theoretical studies on CuF+, CuF,CuF−, CuF2, and CuF2 −

Ab initio SCF studies were performed with Cu and F basis sets of near-Hartree-Fock (HF) limit quality to obtain accurate SCF results for the molecular ground state properties of CuF⁺, CuF, CuF^–, CuF₂, and CuF₂ ^–, as well as for the first two low-lying excited states of CuF₂. A study on the effects of electron correlation was carried out by Møller-Plesset (MP) and configuration interaction (Cl) calculations. The effect of relativity on the⁶³Cu nuclear quadrupole coupling in CuF was determined by use of a coupled HF procedure for a first-order spin-orbital-averaged Pauli operator. At the HF level the⁶³Cu coupling constant was found to be 35.8 MHz (in e²qQ h^–1), while allowing for relativity the value was reduced to 29.1 MHz, which is in better agreement with the experimental value of 22.0 MHz. The calculated molecular properties for CuF [r _e = 1.737 Å,D _e=4.38 eV, _e = 562 cm^–1 (MP4);r _e= 1.796 Å,D _e = 3.91 eV, _e=585 cm^–1 (CISD)] were in good agreement with experiment (r _e = 1.745 Å,D _e = 4.43 eV, _e=623 cm^–1). The adiabatic ground-state potential curve of CuF⁺ avoids crossing near the equilibrium distance between the two ionic potential curves Cu⁺-F and Cu²⁺-F^–. At the crossing point the Cu and F electric field gradients show a sharp discontinuity.     

Boron rings containing planar octacoordinate iron and cobalt

The boron rings containing planar octacoordinate transition metals, D _8h FeB₈ ²⁻, CoB₈ ⁻ and CoB₈ ³⁺, C _2v FeB₈, D _2h CoB₈ ⁺ and CoB₈, are optimized with all real vibrational frequencies at the B3LYP/6–311+G* level of the theory. The D _8h FeB₈ ²⁻ and CoB₈ ⁻ isomers are global minima, while D _8h CoB₈ ³⁺ is only local minimum. The electronic structure character of these systems is revealed by natural bond orbital (NBO) analysis, showing that the boron rings containing planar octacoordinate transition metals have stability and aromaticity with six π electrons. The aromaticity is confirmed by nucleus independent chemical shifts (NICS) calculations. Supported by the specialized research fund for the doctoral program of higher education (20060007030)     

A New Modified Pseudoequilibrium Calculation to Determine the Composition of Hydrogen and Nitrogen Plasmas at Atmospheric Pressure

This paper proposes a modified pseudoequilibrium calculation, which gives almost the same results as those of kinetic calculations to determine the composition of hydrogen and nitrogen plasmas at atmospheric pressure. The computing time is two to three orders of magnitude faster than that of the kinetic calculations. First, according to experimental results, a relationship between the electron temperature T_e and the heavy species one T_h has been proposed. The ratio T_e/T_h varies as a function of the logarithm of the ratio n_e/n _e ^max , _e ^max being the electron density in the plasma core for which equilibrium is achieved _e ^max ~ 10 ²³ ). The kinetic calculations have been performed assuming the microreversibility where the backward kinetic rate coefficient k_b is calculated by k_d/k_b=K_x, where k_d is the direct kinetic coefficient and K_x the molar fraction equilibrium constant. When electrons are involved in both direct and backward reactions, k_d and K_x are expressed as functions of T_e . However, when the direct reaction involves electrons while the backward one is due to collisions between heavy species (or the reverse), a temperature T* between T_e and T_h is introduced. T* is determined as a function of the ratio of the electron flux to that of neutral species in such a way that T*=T^e for n_e > 10²³ and T*=T_h for low values of n_e(n_e < 10¹⁵ m^–3). Compared to hydrogen, the nitrogen composition exhibits a very abrupt variation between 6000 and 6500 K, corresponding to a shift from the dissociation-dominated regime to that of ionization. It occurs because dissociation of nitrogen starts almost simultaneously with its ionization, which is not the case of H₂, for which dissociation is terminated long before ionization starts. If the charge transfer reaction, whose activation energy is low for both gases, is neglected, in both cases the electron density increases drastically below 9000 K. These results are quite similar to those obtained when calculating the composition with the multitemperature mass action law. The kinetic calculations are dominated by the reactions with a low activation energy: dissociation, dissociative recombination and charge transfer. Thus, a modified pseudoequilibrium calculation has been introduced, the plasma composition being calculated with the equilibrium constants corresponding to low activation energies[X₂ 2X, e+X ₂ ⁺ 2X, X ₂ ⁺ +X X⁺ + X₂ both for hydrogen (X=H) and nitrogen (X=N)] at the temperature T* between T_e and T_h. The results are in very good agreement with those of the kinetic calculations.     

Spectroscopic Investigation of the Europium(3+) Ion in a New ZnY4W3O16 Matrix

A new Zn and Eu tungstate was characterized by spectroscopic techniques. This tungstate, of the formula ZnEu₄W₃O₁₆, crystallized in the orthorhombic system and was synthesized by a solid‐state reaction. It melts incongruently at 1330°. The luminescent properties, including excitation and emission processes, luminescent dynamics, and local environments of the Eu³⁺ ions in ZnEu₄W₃O₁₆ and ZnY₄W₃O₁₆ : Eu³⁺ diluted phases (1, 5, and 10 mol‐% of Eu³⁺ ion) were studied basing on the f⁶‐intraconfigurational transitions in the 250–720 nm spectral range. The excitation spectra of this system (λ_em 615 and 470 nm) show broad bands with maxima at 265 and 315 nm related to the ligand‐to‐metal charge‐transfer (LMCT) states. The emission spectra under excitation at the O→W (265 nm) and O→Eu³⁺ (315 nm) LMCT states present the blue‐green emission bands. The emission of tungstate groups mainly originate from the charge‐transfer state of excited 2p orbitals of O^2? to the empty orbitals of the central W⁶⁺ ions. On the other hand, in the emission of the Eu³⁺ ions, both the charge transfer from O^2? to Eu³⁺ and the energy transfer from W⁶⁺ ions to Eu³⁺ are involved. The emission spectra under excitation at the ⁷F₀→⁵L₆ transition of the Eu³⁺ ion (394 nm) of ZnY₄W₃O₁₆ : Eu³⁺ diluted samples show narrow emission lines from the ⁵D₃, ⁵D₂, and ⁵D₁ emitting states. The effect of the active‐ion (Eu³⁺) concentration on the colorimetric characteristic of the emissions of the compound under investigation are presented.     

An <Emphasis Type="Italic">AB Initio</Emphasis> Study of the Electronic and Geometric Structure of BIS-of Dipivaloylmethane With Manganese,IRON, and Cobalt

An ab initio study of the structure of Mn(thd)₂, Fe(thd)₂, and Co(thd)₂ complexes in different electronic states is carried out. Quantum chemical calculations are performed using the PC GAMESS program with relativistic effective core pseudopotentials and Gaussian valence triple-zeta basis sets. Calculation methods: DFT/ROB3LYP and CASSCF followed by the inclusion of dynamic electron correlation through multiconfiguration quasi-degenerate second order perturbation theory (MCQDPT2). All three complexes are shown to have a low-spin electronic ground state with a planar structure of the bicyclic fragment at D _2h molecular symmetry. The M—O bond is mainly ionic, and M(thd)₂ molecules can be considered as an M²⁺ cation coordinated by two negatively charged bidentate ligands.     

过渡金属取代的钨铝杂多配合物的制备、表征和性质

用分步设计法合成了以铝为中心原子的过渡元素与钨的三元杂多配合物,经ICP、TG分析确定其化学式为K_4，6，7[AlM(OH₂)W₁₁O₃₉]·xH₂O(M=V⁵⁺、Cr³⁺、Mn²⁺、Fe³⁺、Co²⁺、Ni²⁺、Cu²⁺、Zn²⁺、Cd²⁺)。采用IR、UV、XRD、¹⁸³W和²⁷Al NMR等对配合物的结构进行了表征,表明配合物具有Keggin结构；循环伏安法对该系列配合物的氧化还原性质研究表明,其氧化还原过程为不可逆的两电子还原,配合物的磁化率测试均表现为顺磁性,还对其热稳定性进行了讨论。     

Theoretical study of spectroscopic and molecular properties of several low‐lying electronic states of CO molecule

The potential energy curves (PECs) of eight low‐lying electronic states (X¹Σ⁺, a³Π, a′³Σ⁺, d³Δ, e³Σ^?, A¹Π, I¹Σ^?, and D¹Δ) of the carbon monoxide molecule have been studied by an ab initio quantum chemical method. The calculations have been performed using the complete active space self‐consistent field method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation‐consistent aug‐cc‐pV5Z basis set. The effects on the PECs by the core‐valence correlation and relativistic corrections are included. The way to consider the relativistic corrections is to use the third‐order Douglas–Kroll Hamiltonian approximation at the level of a cc‐pV5Z basis set. Core‐valence correlation corrections are performed using the cc‐pCVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size‐extensivity errors by means of the Davidson modification (MRCI+Q). The spectroscopic parameters (D_e, T_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e, α_e, and γ_e) of these electronic states are calculated using these PECs. The spectroscopic parameters are compared with those reported in the literature. Using the Breit–Pauli operator, the spin–orbit coupling effect on the spectroscopic parameters is discussed for the a³Π electronic state. With the PECs obtained by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations, the complete vibrational states of each electronic state have been determined. The vibrational manifolds have been calculated for each vibrational state of each electronic state. The vibrational level G(ν), inertial rotation constant B_ν, and centrifugal distortion constant D_ν of the first 20 vibrational states when the rotational quantum number J equals zero are reported and compared with the experimental data. Comparison with the measurements demonstrates that the present spectroscopic parameters and molecular constants determined by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations are both reliable and accurate. © 2012 Wiley Periodicals, Inc.     

Synthesis,characterization, computational studies and biological activities of Co(II), Ni(II) and Cu(II) complexes of 2-Amino-1,3,4-thiadiazole derivatives

Abstract

Co(II), Ni(II), and Cu(II) complexes of 2-Amino-5-ethyl-1,3,4-thiadiazole (AET) and 2-Amino-5-(ethylthio)-1,3,4-thiadiazole (AEST) have been synthesized and characterized based on elemental analysis, magnetic susceptibility, infrared (4000–400 cm^?1), mass spectrometry (ESI and MALDI), UV–Vis (200–1100 nm) and thermal analysis (TGA/DTA). Molar conductance measurements proved that [M(L)₂(H₂O)₂]Cl₂·H₂O are electrolytic complexes where M represents Co, Ni, and Cu divalent metal ions. The geometrical isomerism of [M(L)₂(H₂O)₂]²⁺ ions were investigated by DFT-B3LYP calculations incorporated in Gaussian09 package; it favored the all trans isomers due to having the lowest energy points on the potential energy surface. The outcome of DFT-B3LYP quantum mechanical calculations using 6-31G(d) basis set favor six-coordinate sites via a bidentate ligand through exo amino and adjacent endo thiadiazole nitrogen (N₃) donors. These results were consistent with magnetic measurements combined with infrared and UV–Vis spectral interpretations. The predicted metal–ligand binding energies from B3LYP/6-31G(d) calculations follow the trend Cu²⁺>Ni²⁺>Co²⁺, in agreement with the Irving–Williams series. Both AET and AEST ligands and the synthesized complexes were screened for their antibacterial activity and the outcome was high antimicrobial activity of the complexes compared to the free ligands against one or more microbial species and in some cases (copper complexes) higher activity than standard drugs.     

DFT calculations of <Superscript>14</Superscript>N, <Superscript>17</Superscript>O,and <Superscript>2</Superscript>H NQR parameters: Investigation of hydrogen bond interactions in sulfapyridine crystalline structure

DFT calculations of electric field gradient (EFG) tensors at the sites of ¹⁴N, ¹⁷O, and ²H nuclei are carried out to characterize the hydrogen bond (HB) interactions in the sulfapyridine crystal structure. One-molecule (monomer) and hydrogen-bonded hexameric cluster models of sulfapyridine are constructed according to available X-ray coordinates where the proton positions are optimized. Then, EFG tensors are calculated for both monomer and target molecule in the hexameric cluster of sulfapyridine to show the effect of HB interactions on the tensors. The calculated EFG tensors are converted to the experimentally measurable nuclear quadrupole resonance (NQR) parameters: quadrupole coupling constant (C _Q ) and asymmetry parameter (η _Q ). The results reveal different contribution of various nuclei to N-H⋯N and N-H⋯O HB interactions in the cluster where the N2 and O1 have major contributions. The computations are performed with B3LYP and B3PW91 functionals DFT method and 6-311+G* and 6-311++G** standard basis sets using the Gaussian 98 package.     

A Heteroleptic Push–Pull Substituted Iron(II) Bis(tridentate) Complex with Low‐Energy Charge‐Transfer States

A heteroleptic iron(II) complex [Fe(dcpp)(ddpd)]²⁺ with a strongly electron‐withdrawing ligand (dcpp, 2,6‐bis(2‐carboxypyridyl)pyridine) and a strongly electron‐donating tridentate tripyridine ligand (ddpd, N,N′‐dimethyl‐N,N′‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine) is reported. Both ligands form six‐membered chelate rings with the iron center, inducing a strong ligand field. This results in a high‐energy, high‐spin state (⁵T₂, (t_2g)⁴(e_g*)²) and a low‐spin ground state (¹A₁, (t_2g)⁶(e_g*)⁰). The intermediate triplet spin state (³T₁, (t_2g)⁵(e_g*)¹) is suggested to be between these states on the basis of the rapid dynamics after photoexcitation. The low‐energy π^* orbitals of dcpp allow low‐energy MLCT absorption plus additional low‐energy LL′CT absorptions from ddpd to dcpp. The directional charge‐transfer character is probed by electrochemical and optical analyses, Mößbauer spectroscopy, and EPR spectroscopy of the adjacent redox states [Fe(dcpp)(ddpd)]³⁺ and [Fe(dcpp)(ddpd)]⁺, augmented by density functional calculations. The combined effect of push–pull substitution and the strong ligand field paves the way for long‐lived charge‐transfer states in iron(II) complexes.     

Diagrammatic perturbation theory: Potential curves for the ground state of the carbon monoxide molecule

Diagrammatic many-body perturbation theory is used to calculate the potential energy function for the X¹ σ+ state of the CO molecule near the equilibrium nuclear configuration. Spectroscopic constants are derived from a number of curves which are obtained from calculations taken through third order in the energy. By forming [2/1] Padé approximants to the constants we obtain: r_e = 1.125 Å (1.128 Å), B_e = 1.943 cm^?1 (1.9312 cm^?1), a^B_e = 0.0156 cm^?1 (0.0175 cm^?1), W_e = 2247 cm^?1 (2170 cm^?1), W_eX_e = 12.16 cm^?1 (13.29 cm^?1), where the experimental values are given in parenthesis.     

Diffusion Coefficients for Binary, Ternary, and Polydisperse Solutions from Peak-Width Analysis of Taylor Dispersion Profiles

Binary mutual diffusion coefficients D can be estimated from the width at half height W _1/2 of Taylor dispersion profiles using D=(ln 2)r ² t _R/(3W ² h) and values of the retention time t _R and dispersion tube radius r. The generalized expression D _h=−(ln h)r ² t _R/(3W ² _h ) is derived to evaluate diffusion coefficients from peak widths W _h measured at other fractional heights (e.g., (h = 0.1, 0.2,…,0.9). Tests show that averaging the D _h values from binary profiles gives mutual diffusion coefficients that are as accurate and precise as those obtained by more elaborate nonlinear least-squares analysis. Dispersion profiles for ternary solutions usually consist of two superimposed pseudo-binary profiles. Consequently, D _h values for ternary profiles generally vary with the fractional peak height h. Ternary profiles with constant D _h values can however be constructed by taking appropriate linear combinations of profiles generated using different initial concentration differences. The invariant D _h values and corresponding initial concentration differences give the eigenvalues and eigenvectors for the evaluation of the ternary diffusion coefficient matrix. Dispersion profiles for polymer samples of N i-mers consist of N superimposed pseudo-binary profiles. The edges of these profiles are enriched in the heavier polymers owing to the decrease in polymer diffusion coefficients with increasing polymer molecular weight. The resulting drop in D _h with decreasing fractional peak height provides a signature of the polymer molecular weight distribution. These features are illustrated by measuring the dispersion of mixed polyethylene glycols.     

Photochemical synthesis and ESR spectra of quintet meta-phenylenedinitrenes

Relationships between the molecular structures and zero-field splitting parameters of quintet m-phenylenedinitrenes formed during the photolysis of 1,3-diazidobenzenes in 2-methyltetrahydrofuran solutions frozen at 77 K were studied by ESR spectroscopy and B3LYP/6-31G* calculations. Simulations of the W₋₂/W₋₁, W₊₂/W₊₁, W₋₁/W₀, W₊₁/W₀, and W₊₂/W₀ (Δm _s = 2) transitions were performed for the first time and all signals in the ESR spectra of quintet m-phenylenedinitrenes were unambiguously assigned. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1085–1089, July, 2006.     

Acoustic Study of Solvent Coordination in the Hydration Shells of Potassium Iodide

The isentropic compressibilities of aqueous solutions of potassium iodide, from dilute to almost saturated, were determined at 288 to 308 K based on precise measurements of the speed of ultrasound. Using proper correlations, the hydration numbers (h) were calculated as well as the molar volume and compressibility parameters of the hydrated complexes (V _h , β _h V _h ) of water in the hydration shell (V _1h , β_1h V _1h), and of the cavity containing stochiometric mixtures of K⁺ and I⁻ ions (V _2h, β_2h V _2h). It is revealed that under the studied conditions, the obtained values of h and β _h V _h are independent of temperature whereas the molar compressibility of the hydration shell β _h V _h) is independent of concentration. The electrostatic field of the ions is shown to influence the temperature dependence of the molar volume of water in the hydration shell more substantially than a change of pressure alone influences the temperature dependence of the molar volume of pure water.     

Volume and compressibility effects in the formation of metal-EDTA complexes

We used precise measurements of ultrasonic velocity and density to study the complexation of ethylendiaminetetraacetic acid (EDTA) with Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ at 25‡C and pH 12. From these measurements we obtained the changes in the molar concentration increment of the ultrasonic velocity δA, the apparent molar adiabatic compressibility δK_sΦ, and the apparent molar volume δV_Φ of complex formation. The hydration contributions δ(AV_h) to the volume effect of binding range from 39.6 to 46.6 cm³-mol^-1 while the hydration contribution to the adiabatic compressibility change in the binding, δ(δK_h), ranges from 103.9X 10^-4 to 131.1 X 10^-4 cm³-mol^-1-bar^-1. These data are interpreted in terms of dehydration of interacting molecules,i.e., transfer of water molecules from the hydration shells of cations and EDTA into the bulk water. The ratio δ(δV_h)/ δ(δV_h) is in the range 0.35 to 0.38 bar, indicating a dominant contribution from the dehydration of charged atomic groups in the volume and the compressibility effects of complex formation.