Structure of cyano-bridged Eu(III)—Co(III) bimetallic assembly and its application to photophysical verification of photomagnetic phenomenon

New crystal structure of Eu(DMF)₄(H₂O)₃Co(CN)₆·H₂O (DMF = N,N′-dimethylformamide) (Eu-Co) has been determined to be monoclinic, P2(1)/n, a = 19.796(12) Å, b = 8.862(11) Å, c = 17.525(10) Å, β = 96.26(5)°, V = 3056(5) ų, Z = 4. The Eu(III) ion adopts an antiprismatic eight-coordination and forms a cyano bridge with r(Eu-N) = 2.496(7) Å and Θ(Eu-N-C) = 165.7(7)° to the Co(III) ion. The complex exhibits some common features with the Eu-Fe complex. Diffuse reflectance electronic spectra and magnetic susceptibility of Eu-Cr, Eu-Mn, Eu-Fe, and Eu-Co complexes were compared. By substituting the metal ions, both electronic and structural features affected the charge transfer bands and superexchange interactions concerning cyanide ligands. In addition, only Eu-Co exhibited ⁵ D ₀ → ⁷ F ₂ and ⁵ D ₀ → ⁷ F ₁ luminescence bands at 16300 cm^?1 and 16900 cm^?1, respectively at 298 K (λ_ex = 360 nm (27000 cm^?1)), because quenching by cyano-bridged ions did not prevent Eu(III) ion from exhibiting emission. Thus, only Eu-Co may be suitable for verification of an assumption of mechanism concerning drastic photoinduced magnetic changes for Nd-Fe. Merely small decrease of magnetization was observed for Eu-Co after UV light irradiation at 2.0 K. This result was attributed to slight structural changes around cyano bridges without transitions of spin states.     

Theoretical prediction of the new high-density lithium boride LiB<Subscript>11</Subscript> with polymorphism and pseudoplasticity

We predict the possibility of existence of the new lithium boride LiB₁₁ with polymorphism. For energy reasons, the preferred type is α′-LiB₁₁ (trigonal space group R3m, a _h = 0.4982 nm, c _h = 1.1123 nm, z _h = 3, ρ = 2.63 g/cm³), with a framework built of tetrahedra and one-capped octahedra. α′-LiB₁₁ is pseudoplastic because of twinning via the high-symmetry state of α-LiB₁₁ (cubic space group \(F\bar 43m\), a = 0.6810 nm, z = 4, ρ = 2.65 g/cm³) and a bipolaron semiconductor. α → α′ transition is accompanied by the 0.0627-nm displacement of 1/11 B atoms. The β′ polymorph (tetragonal space group \(I\bar 4m2\), a = 0.4404 nm, c = 0.7708 nm, ρ = 2.80 g/cm³) is transformation hardened because of the transition to the α′ phase. We infer that LiB₁₁ formation is possible under high pressure.     

Nickel(II) complex with 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane

A nickel(II) complex, [Ni(taetacn)](ClO₄)₂ ? H₂O, where taetacn = 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane was synthesized. The crystal structure was determined by the single-crystal X-ray diffraction method at 293 K. The complex crystallizes in the orthorhombic space group Pna2₁ with a = 16.004(2) Å, b = 10.186(1) Å, c = 13.937(2) Å, V = 2271.9(5) ų, D_x = 1.56 g cm^?3, D_m = 1.59 g cm^?3 (floatation method), and Z = 4. The R₁ [I > 2σ(I)] and wR₂ (all data) values are 0.0636 and 0.1672, respectively, for all 4845 independent reflections. The compound is composed of octahedral nickel(II) cation with three 2-aminoethyl pendant groups of taetacn, tetrahedral ClO ₄ ^? anion, and a water molecule of crystallization. Electronic spectra are consistent with the octahedral geometry. Temperature dependence of the magnetic susceptibility (4.5–300 K) can be interpreted considering the zero-field splitting of the nickel(II) ion (g = 2.14, D = 3.72 cm^?1, and Nα = 300 × 10^?6 cm³ mol^?1). Cyclic voltammetry in DMF showed quasi-reversible and irreversible oxidation waves (E_pa = 0.54 V, E_pc = 0.45 V; E_pa = 1.16 V, E_pc = 0.71 V vs. Ag/Ag⁺).     

Analysis of the Vibrational Structure of the <Emphasis Type="Italic">n</Emphasis>–π* Transition in the High-Resolution UV Absorption Spectrum of Methacryloyl Fluoride in the Gas Phase

The UV absorption spectrum of methacryloyl fluoride molecule in the gas phase is obtained in the wavenumber range of 32300–35900 cm^?1. The resolved vibrational structure of this spectrum consists of 153 absorption bands. The assignment of all bands has been made for the first time. Values ν_00trans = 35670.0 сm^?1 and ν_00cis = 35371.1 cm^?1 are determined. The fundamental frequencies for isomers in the S₀ and S₁ states are found. Several Deslandres Tables (DTs) are constructed for the torsional vibration of the s-trans- and s-cis-isomers of the investigated molecule using the NONIUS program. The origins in these DTs correspond to bands attributed to ν₀₀, and to the fundamental frequencies of each isomer in states S₀ and S₁. These DTs are used to determine harmonic frequencies ω_e, anharmonicity coefficients х₁₁, and the frequencies of torsional vibration 0–v transitions up to high values of vibrational quantum number v for s-trans- and s-cis-isomers in both electronic states. The frequencies of torsional vibrations for the s-trans-isomer and the s-cis-isomer in the S₀ state are ν″₁ = 80.9 сm^?1 and ν″₁ = 59.8 сm^?1, respectively. The frequencies for the s-trans- isomer and the s-cis-isomer in the S₁ state are ν′₁ = 134.1 сm^?1 and ν′₁ = 103.6 cm^?1, respectively.     

The assignment of signals in the EPR spectra of axially symmetrical quintet dinitrenes

Fine structure levels in an external magnetic field and angular dependences of resonance magnetic fields on the direction of an external magnetic field were calculated for two axially symmetrical quintet dinitrenes with the zero-field splitting parameters D _q = 0.260 cm^?1, E _q = 0.000 and D _q = 0.243 cm^?1, E _q = 0.003 cm^?1. The EPR spectra of such dinitrenes contained lines of only three xy transitions (xy ₁, xy ₂, and xy ₄), two Δm _s = ±2 transition lines between the W _?2 and W ₀ sublevels, and three additional lines from noncanonically oriented molecules whose magnetic axis Z made an angle of 12°–16° or 52°–54° with an external magnetic field.     

Europium,terbium, and ytterbium 3-(3′-triethoxysilylpropyl)pentane-2,4-dionates. Synthesis and the formation of luminescent sol-gel films

3-(3′-Triethoxysilylpropyl)pentane-2,4-dione, (EtO)₃SiCH₂CH₂CH₂C[-C(O)CH₃]₂ (I), was synthesized from 3-allylpentane-2,4-dione, CH₂ = CH-CH₂-C[-C(O)CH₃]₂, and triethoxysilane, (EtO)₃SiH, in the presence of Speier’s catalyst. The silylation occurred mainly at the terminal C atom of the allyl group. The corresponding europium(III), terbium(III), and ytterbium(III) β-diketonates were synthesized from compound I and appropriate metal isopropoxides and used to obtain transparent sol-gel films containing Eu³⁺, Tb³⁺, and Yb³⁺ cations. The film formation was studied by IR spectroscopy. It was found that moisture causes not only the hydrolysis and condensation of triethoxysilyl groups but also the hydration of the cation of the rare-earth metal. When the terbium complex was excited at the wavelength of one of the two peaks (230 and 308 nm) in the excitation spectrum, the cation fluoresced intensely at 491, 547, 585, and 623 nm due to the transitions ⁵ D ₄ → ⁷ F ₆, ⁵ D ₄ → ⁷ F ₅, ⁵ D ₄ → ⁷ F ₄, and ⁵ D ₄ → ⁷ F ₃, respectively. All these bands were narrow, the band at 547 nm being most intense. No emission from the organosilicon matrix at 440 nm was observed. The emission spectra of Eu³⁺-containing films showed, along with the bands at 593, 618, 667, and 700 nm due to the emission from the cation (⁵ D ₀ → ⁷ F ₁, ⁵ D ₀ → ⁷ F ₂, ⁵ D ₀ → ⁷ F ₃, and ⁵ D ₀ → ⁷ F ₄ transitions, respectively), an intense band at 491 nm due to the emission from the matrix.     

Electronic absorption spectra of solutions of molecular chlorine in molten alkali metal chlorides

Electronic reflection absorption spectroscopy has been used for measuring the electronic spectra of chlorine solutions in molten alkali metal chlorides 2CsCl-NaCl, KCl-NaCl, and CsCl in the range 240–400 nm. Absorption bands of chloride melts are interpreted as electronic transitions in the molecular group Cl₂ and in the triatomic linear group Cl ₃ ^? of symmetry D _∞h and C _∞V .     

Dynamics of radiationless transitions in large molecules: 3. Decay of vibration-phonon states

The statistical operator of the ensemble of high-frequency intramolecular vibrations associated with the phonon reservoir depends on the phonon occupation numbers under thermal equilibrium conditions. The eigenvalues of energy of statistically averaged vibration-phonon (VP) states are complex quantities. In the case of weak VP coupling, only one- and two-phonon transitions are taken into consideration for calculating the decay rate constant, in which the difference of phonon energies compensates for the difference in energy between the initial and final intramolecular states. Although the fast evolution of amplitudes of VP states is due to intramolecular redistribution of energy and is not reduced to exponential decay of the initial state, the imaginary components of the eigenvalues coincide with those predicted by Fermi’s golden rule. The relative contribution of two-phonon (combination) transitions compared with one-phonon transitions increases with an increase in the density of intramolecular states and temperature, becoming prevalent for large molecules at T ≥ D ? Δ₀ (D = 100–200 K (70–140 cm^?1) is the Debye temperature and Δ₀～10 cm^?1 is the spacing between neighboring intramolecular vibration levels). When T ≥ D, the decay rate constant is K ∝ T ².     

Laser flash photolysis of aqueous acetaminophen solutions

The N-acetyl-4-aminophenoxyl radical, a supposed intermediate of the enzymatic oxidation of acetaminophen in living organisms, was prepared and studied by means of nanosecond laser flash photolysis. A number of important spectral-kinetic parameters of this species were determined, namely, the absorption coefficient at 440 nm ((4.2±0.2)×10³ l mol^?1cm^?1), the quantum yield of acetaminophen photoionization at 266 nm (φ= 0.03), and the rate constants for recombination (2k= (2.4±0.3))×10⁹ l mol^?1s^?1) and the reaction with the superoxide radical (k= (9±2))×10⁹ l mol^?1s^?1).     

<Emphasis Type="Italic">Ab initio</Emphasis> study of scandium fluoride molecules: ScF,ScF<Subscript>2</Subscript>, AND ScF<Subscript>3</Subscript>

Equilibrium geometric parameters, normal mode frequencies and intensities in IR spectra, atomization enthalpy, and relative energies of low-lying electronic states of scandium fluoride molecules (ScF, ScF₂, and ScF₃) are calculated by the coupled-cluster method (CCSD(T)) in triple-, quadruple, and quintuple-zeta basis sets with the subsequent extrapolation of the calculation results to the complete basis set limit. The ScF molecule is also studied by the CCSDT technique. The error in the approximate calculation of triple excitations in the CCSD(T) method does not exceed 0.002 Å for the equilibrium internuclear distance R _e, 4 cm^?1 for the vibrational frequency, and 0.2 kcal/mol for the dissociation energy of the molecule. In the ground electronic state \(\tilde X^2 \) A ₁(C _2ν ) of ScF₂ molecules, R _e(Sc-F) = 1.827 Å and α_e(F-Sc-F) = 124.2°; the energy barrier to bending (linearization) h = E _min(D _g8h ) ? E _min(C_2ν) = 1652 cm^?1. The relative energies of Ã²Δ _g and \(\tilde B^2 \)Π _g electronic states are 3522 cm^?1 and 14633 cm^?1 respectively. The bond distance in the ScF₃ molecule (\(\tilde X^1 \) A′₁, D _3h ) is refined: R _e(Sc-F) = 1.842 Å. The atomization enthalpies Δ_at H ₂₉₈ ⁰ of ScF _k molecules are 139.9 kcal/mol, 289.0 kcal/mol, and 444.8 kcal/mol for k = 1, 2, 3 respectively.     

Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi₃GeO₄ crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, g _xx = g _yy = 1.915, g _zz = 1.932. The EPR spectrum is dictated by Cr⁴⁺ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 μm is also caused by transitions of Cr⁴⁺ with tetrahedral surroundings to germanium sites. Original Russian Text Copyright ? 2005 N. V. Chernei, V. A. Nadolinnyi, N. V. Ivannikova, V. A. Gusev, I. N. Kupriyanov, V. N. Shlegel, and Ya. V. Vasiliev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 444–450, May–June, 2005.     

Electronic and crystal structure of (N-CH<Subscript>3</Subscript>-2,2′-bipyridinium)(dodecahydro-dicarba-<Emphasis Type="Italic">nido</Emphasis>-undecaborate)

The compound [N-Me-2,2′-Bipy]⁺[C₂B₉H₁₂]^?-(N-CH₃-2,2′-bipyridinium)(dodecahydro-dicarba-nidoundecaborate) has been synthesized, and its structure has been determined. The compound was defined by IR, ¹¹B and ¹⁴N NMR, and X-ray photoelectron spectroscopy. Crystal data: C₁₃H₂₃B₉N₂, M = 304.62, monoclinic crystals, space group P2₁/c, a = 11.840(4) Å, b = 10.051(3) Å, c = 15.573(6) Å, β = 102.43(3)°, V = 1809.8(10) ų, Z = 4, d _calc = 1.118 g/cm³, R = 0.0607.     

Enhanced performance of field-effect transistors based on C<Subscript>60</Subscript> single crystals with conjugated polyelectrolyte

Contact resistance at the interface between metal electrodes and semiconductors can significantly limit the performance of organic field-effect transistors, leading to a distinct voltage drop at the interface. Here, we demonstrate enhanced performance of n-channel field-effect transistors based on solution-grown C₆₀ single-crystalline ribbons by introducing an interlayer of a conjugated polyelectrolyte (CPE) composed of poly[(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFN⁺Br^?). The PFN⁺Br^? interlayer greatly improves the charge injection. Consequently, the electron mobility is promoted up to 5.60 cm² V^?1 s^?1 and the threshold voltage decreased dramatically with the minimum of 4.90 V.     

Copper(II) trinuclear complex with trimesic acid salicylidene hydrazone: Synthesis,structure, and magnetic properties

A trinuclear copper(II) complex of trimesic acid salicylidene hydrazone (H₆L) having the composition [Cu₃L · 4Py] · CH₃OH was synthesized and characterized. By X-ray crystallography, the crystals are triclinic: a = 11.7940(4) Å, b = 13.7241(5) Å, c = 15.8993(6) Å, α = 107.4120(10)°, β = 94.2900(10)°, γ = 105.5650(10)°, space group \(P\bar 1\), Z = 2. The number of symmetrically unique reflections having I > 2σ(I) is 7636, R = 0.0465, and R _w = 0.1198. The newly prepared complex contains, in its unit cell, two [Cu₃L · 4Py] molecules which are linked to form a dimer on account of phenoxo bridges (the Cu-O bond length is 2.555 the Cu…Cu distance is 3.348 Separations between them are 9.414, 9.371, and 9.667 of temperature is satisfactorily fitted in terms of a triangular cluster model (?2J = 2.2 cm^?1) with extra intermolecular interactions (zJ′ = 0.4 cm^?1). EPR spectra of solutions at 360–380 K feature a poorly resolved HFS, whose modeling gives a satisfactory result with allowance for the interaction of unpaired electrons with three equivalent copper nuclei (g = 2.098; a _Cu = 25.8 × 10^?4 cm^?1).     

Bis(1,10-phenanthroline)lithium perchlorate: Crystal structure and dissociation in acetone

The composition of the solid phase formed in acetone at a 1,10-phenanthroline (phen):LiClO₄ concentration ratio close to 2:1 was found. According to X-ray diffraction data, the molecular structure of bis(1,10-phenanthroline)lithium perchlorate is as follows: space group Pnna, a 7.191(2), b 39.929(9), c 14.494(3) Å, Z 8, and D _x 1,490 g cm^?3. The IR spectra data show that the complex Li(phen)₂ClO₄ dissociates in acetone into a 1:1 complex and a phen molecule in the solution equilibrium with the solid phase.     

Copper(II) complex with salicylaldehyde <Emphasis Type="Italic">N</Emphasis>-(2-salicylideneiminoglutaryl)hydrazone: Synthesis and structure

A copper(II) complex with salicylaldehyde N-(2-salicylideneiminoglutaryl)hydrazone (H₄L) of the formula [Cu₂L · 2Py]₂ · 8H₂O (I) was obtained and characterized by X-ray diffraction. The crystals are monoclinic, space group P2₁, a = 13.0663 Å, b = 16.5553 Å, c = 17.7650 Å, β = 97.9420°; Z = 4. The complex is tetranuclear with a “dimer-of-dimers” structure in which the copper cations of two binuclear subunits are linked by phenoxy bridges. The EPR spectra of solutions of complex I show a superposition of two signals of four HFS lines (g ₁ = 2.111, a ₁ = 56.8 × 10^?4 cm^?1 and g ₂ = 2.183, a ₂ = 71.0 × 10^?4 cm^?1).     

Stepwise magnetic behavior of the liquid crystal iron(III) complex

EPR and Mössbauer spectroscopy is used to study a new liquid crystal complex of iron(III) with a Schiff base: 4,4′-dodecyloxybenzoyloxybenzoyl-4-oxysalicylidene-2-aminopyridine with a PF ₆ ^? counterion. It is shown that Fe(III) ions exist only in the high-spin (HS, S = 5/2) state. It is found that under the influence of temperature the system demonstrates the stepwise behavior of the product of the integrated intensity of EPR lines (I) and temperature (proportional to χ T, where χ is the magnetic susceptibility) with an inflection point at ～80 K. Above 80 K a new EPR spectrum is detected due to the excited S = 2 state and the formation of dimeric molecules (through oxygen bridges) with a strong intramolecular antiferromagnetic exchange interaction J ₁ = 162.1 cm^?1. Below 80 K iron(III) complexes are organized in 1D chains where the exchange value J ₂ = 2.1 cm^?1. At 80 K there is a structural phase transition in the system: the transition from a 1D chain organization of HS Fe(III) centers to dimeric molecules. Based on quantum chemical calculations a model of the binuclear iron(III) complex is proposed.     

The sol–gel chromium-modified V<Subscript>6</Subscript>O<Subscript>13</Subscript> as a cathodic material for lithium batteries

A new V₆O₁₃-based material has been synthesized via the sol–gel route. This sol–gel mixed oxide has been obtained from an appropriate heat treatment of the chromium-exchanged V₂O₅ xerogel performed under reducing atmosphere. This new compound, with the chemical formula Cr_0.36V₆O_13.50, exhibits a monoclinic structure (C2/m) with the following unit cell parameters, a=11.89 Å, b=3.68 Å, c=10.14 Å, β=101.18°. The electrochemical characterization of this compound has been performed using galvanostatic discharge–charge experiments in the potential range 4–1.5 V and completed by ac impedance spectroscopy measurements. It exhibits a specific capacity of about 370 mAh g^?1, which makes the compound Cr_0.36V₆O_13.50 the best one in the V₆O₁₃-based system: 85% of the initial capacity (315 mAh g^?1) after the 35th cycle is still available at C/25 without any polarization. From impedance spectroscopy, a high kinetics of Li transport (D _Li=1.8×10^?9 cm² s^?1) is found at mid-discharge.     

Effects of conjugated systems on UV-visible light-sensitive D-<Emphasis Type="Italic">π</Emphasis>-A type sulfonium salt photoacid generators

A series of D-π-A type sulfonium salt photoacid generators with different π-conjugated structures, such as triphenyl, phenylstilbene, styryl-biphenyl, and stilbene, were designed to determine the effect of molecular structures on the photochemical and photophysical properties. The mechanisms of photochemical generation of H⁺ were studied by UV-Vis spectroscopy, theoretical calculations, and fluorescence spectroscopy. It is found that the frontier orbits determine the absorption, the molar extinction coefficients, and the quantum yields of photoacid generation. Triphenyl systems connected with sulfonium are beneficial to increase the quantum yields of acid generation. The photoreactivity of four sulfonium salts was further evaluated through the polymerizations of various epoxide monomers at different irradiation wavelengths (365–425 nm) by using the real-time infrared spectroscopy with light-emitting diodes. The high quantum yields for acid generation (Φ _H ⁺ = ~0.32 to 0.58) and the high molar extinction coefficients (ε = ~23500 L?mol^?1?cm^?1 to 31000 L?mol^?1?cm^?1) of the sulfonium salts lead to high conversion rates (over 50%–80%). Hence, these photoinitiators exhibit potential for the photocuring applications.     

Mononuclear cobalt (III) complexes with <Emphasis Type="Italic">N</Emphasis>-salicylidene-2-hydroxy-5-bromobenzylamine and <Emphasis Type="Italic">N</Emphasis>-salicylidene-2-hydroxy-5-chlorobenzylamine

Cobalt (III) complexes with N-salicylidene-2-hydroxy-5-bromobenzylamine (H₂sbba) and N-salicylidene-2-hydroxy-5-chlorobenzylamine (H₂scba), [n-(C₄H₉)₄N][Co(sbba)₂] (I) and [n-(C₄H₉)₄N][Co(scba)₂] (II), were synthesized. The crystal structure of II was determined by the single-crystal X-ray diffraction method at 90 K confirming its crystallization in the monoclinic space group P2₁/n with a = 11.729(2) Å, b = 16.901(3) Å, c = 21.483(4) Å, β = 98.840(4)°, V = 4208.2(14) ų, D_x = 1.295 g cm^?3, and Z = 4. The R1 [I > 2σ(I)] and wR2 (all data) values of 0.0664 and 0.1920, respectively, for all 9521 independent reflections. The compound is composed of a tetra(n-butyl)ammonium cation and an octahedral cobalt(III) complex anion with two scba^2? ligands in a meridional fashion. The electronic spectral features of I and II are consistent with the octahedral cobalt(III) ion with an N₂O₄ donor set.