THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) I. N,N'-Bis-(acetylacetone) ethylenediimine and N,N'-Bis-(1,1,1-trifluoroacetylacetone) ethylenediimine

Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)₂], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)₂], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)₂], g_z =2.183 ± 0.003, g_x =2.047 ± 0.004, g_y =2.048 ± 0.004, A_z =204.8 × 10^?4cm^?1, A_x =31.5 × 10^?4cm^?1, A_y =27.1 × 10^?4 cm^?1, A_zN= 12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.3 × 10^?4 cm^?1: Cu[en(tfacac)₂], g_z =2.192 ± 0.002, g_x =2.048 ± 0.004, g_y =2.046 ± 0.004, A_z =200.8 × 10^?4 cm^?1, A_x =31.1 × 10^?4 cm^?1, A_y =28.3 × 10^?4 cm^?1, A_zN =12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.6 × 10^?4 cm^?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp².     

Hybrid Polyoxotungstates as Functional Comonomers in New Cross‐Linked Catalytic Polymers for Sustainable Oxidation with Hydrogen Peroxide

Anchoring terminal octenyl tails on molecular polyoxotungstates yield polymerizable organic–inorganic monomers with formula [{CH₂?CH(CH₂)₆Si}_xO_ySiW_wO_z]^4? [x=2, w=11, y=1, z=39 ( 1 ); x=2, w=10, y=1, z=36 ( 2 ); and x=4, w=9, y=3, z=34 ( 3 )]. These molecular hybrids can use aqueous hydrogen peroxide to catalyze the selective oxidation of organic sulfides in CH₃CN. Copolymerization of 1 – 3 with methyl methacrylate and ethylene glycol dimethacrylate leads to porous materials with a homogeneous distribution of the functional monomers, as indicated by converging evidence from FTIR spectroscopy and electronic microscopy. The catalytic polymers activate hydrogen peroxide for oxygen transfer, as demonstrated by the quantitative and selective oxidation of methyl p‐tolyl sulfide, which was screened as model substrate. The hybrid material containing monomer 2 was also tested in n‐octane to evaluate its potential for the oxidation and removal of dibenzothiophene, a well‐known gasoline contaminant.     

Observation of Slow Relaxation and Single‐Molecule Toroidal Behavior in a Family of Butterfly‐Shaped Ln4 Complexes

A family of five isostructural butterfly complexes with a tetranuclear [Ln₄] core of the general formula [Ln₄(LH)₂(μ₂‐η¹η¹Piv)(η²‐Piv)(μ₃‐OH)₂]?x H₂O?y MeOH?z CHCl₃ ( 1 : Ln=Dy^III, x=2, y=2, z=0; 2 : Ln=Tb^III, x=0, y=0, z=6; 3 : Ln=Er^III, x=2, y=2, z=0; 4 : Ln=Ho^III, x=2, y=2, z=0; 5 : Ln=Yb^III, x=2, y=2, z=0; LH₄=6‐{[bis(2‐hydroxyethyl)amino]methyl}‐N′‐(2‐hydroxy‐3‐methoxybenzylidene)picolinohydrazide; PivH=pivalic acid) was isolated and characterized both structurally and magnetically. Complexes 1 – 5 were probed by direct and alternating current (dc and ac) magnetic susceptibility measurements and, except for 1 , they did not display single‐molecule magnetism (SMM) behavior. The ac magnetic susceptibility measurements show frequency‐dependent out‐of‐phase signals with one relaxation process for complex 1 and the estimated effective energy barrier for the relaxation process was found to be 49 K. We have carried out extensive ab initio (CASSCF+RASSI‐SO+SINGLE_ANISO+POLY_ANISO) calculations on all the five complexes to gain deeper insights into the nature of magnetic anisotropy and the presence and absence of slow relaxation in these complexes. Our calculations yield three different exchange coupling for these Ln₄ complexes and all the extracted J values are found to be weakly ferro/antiferromagentic in nature (J₁=+2.35, J₂=?0.58, and J₃=?0.29 cm^?1 for 1 ; J₁=+0.45, J₂=?0.68, and J₃=?0.29 cm^?1 for 2 ; J₁=+0.03, J₂=?0.98, and J₃=?0.19 cm^?1 for 3 ; J₁=+4.15, J₂=?0.23, and J₃=?0.54 cm^?1 for 4 and J₁=+0.15, J₂=?0.28, and J₃=?1.18 cm^?1 for 5 ). Our calculations reveal the presence of very large mixed toroidal moment in complex 1 and this is essentially due to the specific exchange topology present in this cluster. Our calculations also suggest presence of single‐molecule toroics (SMTs) in complex 2 . For complexes 3 – 5 on the other hand, the transverse anisotropy was computed to be large, leading to the absence of slow relaxation of magnetization. As the magnetic field produced by SMTs decays faster than the normal spin moments, the concept of SMTs can be exploited to build qubits in which less interference and dense packing are possible. Our systematic study on these series of Ln₄ complexes suggest how the ligand design can help to bring forth such SMT characteristics in lanthanide complexes.     

THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) II. N,N'-bis(salicylidene)ethylenediimine and 7-methyl-N,N'-bis (salicylidene)ethylenediimine

Abstract

The EPR spectra of single crystals of ⁶³Cu(II) doped N, N'-bis(salicylidene)ethylenediimine Ni(II), [Ni(sal)₂en] and 7-methyl-N, N'-bis(salicylidene)ethylenediimine Ni(II), [Ni(7-me sal)₂en] have been studied. The usual doublet spin-Hamiltonian parameters for the complexes have been found to be: Cu(II)[(sal)₂en]; g _z =2.192 ± 0.002; g _x =2.046 ± 0.004; g _y =2.049 ± 0.004; A _z =201.0 × 10^?4 cm^?1; A _x =29.3 × 10^?4 cm^?1; A _y =31.3 × 10^?4 cm^?1; A^N _z =12.6 × 10^?4 cm^?1; A ^N _x =14.5 × 10^?4 cm^?1; A ^N _y =15.7 × 10^?4 cm^?1; A ^H _z =6.3 × 10^?4 cm^?1; A ^H _x =7.3 × 10^?4 cm^?1; A ^H _y =7.9 × 10^?4 cm^?1; Cu(II)[(7-me sal)₂en]; g _z =2.189 ± 0.002; g _x =2.037 ± 0.004; g _y =2.046 ± 0.004; A _z =203.0 × 10^?4 cm^?1; A _x =36.9 × 10^?4 cm^?1; A _y =22.7 × 10^?4 cm^?1; A ^N _z =12.6 × 10^?4 cm^?1; A ^N _x =13.3 × 10^?4 cm^?1; A ^N _y =14.0 × 10^?4 cm^?1. Values of molecular orbital coefficients calculated for these complexes show that their bonding properties are similar to those of other compounds of this type. There is considerable covalency in the metal-ligand [sgrave]-bonds, and significant in-plane pi-bonding is present.     

2D l‐Di‐toluoyl‐tartaric acid Lanthanide Coordination Polymers: Toward Single‐component White‐Light and NIR Luminescent Materials

A series of five l ‐di‐p‐toluoyl‐tartaric acid (l ‐DTTA) lanthanide coordination polymers, namely {[Ln₄K⁴ L₆(H₂O)_x]?yH₂O}_n, [Ln=Dy ( 1 ), x=24, y=12; Ln=Ho ( 2 ), x=23, y=12; Ln=Er ( 3 ), x=24, y=12; Ln=Yb ( 4 ), x=24, y=11; Ln=Lu ( 5 ), x=24, y=12] have been isolated by simple reactions of H₂L (H₂L= L ‐DTTA) with LnCl₃?6 H₂O at ambient temperature. X‐ray crystallographic analysis reveals that complexes 1 – 5 feature two‐dimensional (2D) network structures in which the Ln³⁺ ions are bridged by carboxylate groups of ligands in two unique coordinated modes. Luminescent spectra demonstrate that complex 1 realizes single‐component white‐light emission, while complexes 2 – 4 exhibit a characteristic near‐infrared (NIR) luminescence in the solid state at room temperature.     

Structural studies on 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazan chelates with cerium(III), thorium(IV) and uranium(VI)

Summary Solid complexes of 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazans were prepared and characterized by elemental analysis, IR, NMR, TGA and DTA analyses. Based on these studies, the suggested general formula for the complexes is [M(HL) _m (OH^–) _n or (NO ₃ ^– or Cl^–) _x ·(H₂O) _y or (C₂H₅OH orDMSO) _z , where HL=formazanM=Ce³⁺, Th⁴⁺, and UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 andz=0–3. The metal ions are expected to have coordination numbers 6–8.

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Strukturuntersuchungen an 3-Acetyl-1,5-diaryl- und 3-Cyan-1,5-diaryl-formazan-Chelaten mit Cer(III), Thorium(IV) und Uran(VI)

Zusammenfassung Die hergestellten Chelate wurden mittels Elementaranalyse, IR, NMR, TGA und DTA charakterisiert. Darauf basierend wird die generelle Formel [M(HL) _m (OH^–) _n bzw. (NO ₃ ^– oder Cl^–) _x ·(H₂O) _y oder (C₂H₅OH bzw.DMSO) _z ] vorgeschlagen, wobei HL=Formazan,M=Ce³⁺, Th⁴⁺ oder UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 undz=0–3. Die Metallionen haben Koordinationszahlen von 6–8.

     

Xanthone. I. optical detection of an extremely large sublevel splitting the lowest triplet state

The phosphorescence spectrum of xanthone in n-hexane is resolved into three components, one of which is due to thermally activated emission from a n_π* origin. The other two emissions originate from extremely widely split sublevels of the lowest triplet state, which is of ³ππ* origin. higher energy of T_Lx, and T_1y, and thus below 4K there is thermal depletion of T_1z which has the largest radiative strength. Th consequence of spin-orbit coupling between the T_x and T_y sublevels of the-two very close-lying, lowest triplet states. There are signif mixing of orbital character, a mixing which is governed by spin-orbit coupling rather than vibronic coupling.     

Excellent Performance of Few‐Layer Borocarbonitrides as Anode Materials in Lithium‐Ion Batteries

Borocarbonitrides (B_xC_yN_z) with a graphene‐like structure exhibit a remarkable high lithium cyclability and current rate capability. The electrochemical performance of the B_xC_yN_z materials, synthesized by using a simple solid‐state synthesis route based on urea, was strongly dependent on the composition and surface area. Among the three compositions studied, the carbon‐rich compound B_0.15C_0.73N_0.12 with the highest surface area showed an exceptional stability (over 100 cycles) and rate capability over widely varying current density values (0.05–1 A g^?1). B_0.15C_0.73N_0.12 has a very high specific capacity of 710 mA h g^?1 at 0.05 A g^?1. With the inclusion of a suitable additive in the electrolyte, the specific capacity improved drastically, recording an impressive value of nearly 900 mA h g^?1 at 0.05 A g^?1. It is believed that the solid–electrolyte interphase (SEI) layer at the interface of B_xC_yN_z and electrolyte also plays a crucial role in the performance of the B_xC_yN_z .     

Paramagnetic resonance of interstitial mo5+ in a tio2 lattice

Paramagnetic absorption of Mo⁵⁺ has been studied in a polycrystalline TiO₂ rutile lattice, The g tensor (g_x = 1.897, g_y = 1.920, g_z = 1.857) and the hyperfine tensor (A_x = 32.7, (A_y = 51.2, (A_z = 58.5 (in 10^?4 cm^?1)) are in agreement with those expected for an nd¹ ion in an interstitial position.     

Structural studies of Rh4(CO)12 derivatives in solution and in the solid state

The crystal structures of Rh₄(CO)₁₀(PPh₃)₂ and Rh₄(CO)₉P(OPh)₃₃ are reported. ³¹P-¹H NMR studies on Rh₄(CO)₁₂-_x {P(OPh)₃}_x(X  1, 2 and 3) show that each derivative exists as only one isomer in solution whereas the analogous triphenylphosphine derivatives can exist as different isomers. A quantitative redistribution of triphenylphosphites occurs on mixing Rh_4-(CO)₁₂-_xL_x with Rh₄(CO)₁₂-_yL_y (L  P(OPh)₃; x  0, 1, 2, y  x + 2; x  0, y  x + 4) to give Rh₄(CO)₁₂-_zL_z[z $\text{1}\text{2}$(x + y)]; a related rapid intermolecular randomisation of carbonyls occurs on mixing Rh₄(¹²CO)₁₂ with Rh₄(¹³CO)₁₂.     

Matrix effects on the fast atom bombardment mass spectra of palladium complexes

In an attempt to identify and characterize the intermediates involved in multi-step palladium catalyzed coupling reactions, under fast atom bombardment (FAB) conditions, the selection of a matrix to enhance ion formation without degrading the palladium complex is critical. In general, it is observed that the analysis of tetrakis(triphenylphosphine)palladiurn(0) using glycerol, m-nitrobenzyl alcohol or o-nitrophenyl octyl ether as the FAB matrix compound produces several ions which correspond to complexes of the type Pd_xL_yO_z⁺ (L = PPh₃; x = 1-4; y = 1-4; z = 0-2), in addition to clusters containing one or more matrix molecules. FAB mass spectra generated using triethanolamine- or tetramethylene sulfone (sulfolane) are observed to contain ions related to the palladium(0) complex with little or no interference from ions related to the oxidation or reduction processes.     

The Liquid Junction Potential in Potentiometric Titrations. IX. The Calculation of Potentials Across Liquid Junctions of the Type, AY|AY+BY z(B)+HY+ A y L, for Emf Cells where Strong or Weak Complexes are Formed, Respectively, at [Y−] = C mol⋅L−1, Constant and −log 10[H+]≤ 7

In the present part, potential functions are derived for the calculation of the total potential anomalies, Δ E _B and Δ E _H, for Emf cells where strong or weak complexes are formed, respectively. A weak or strong electrolyte is considered to be used as complexing agent (A _y L), respectively, at the experimental condition, [Y^?] = C mol?L^?1, constant. The cells have indicator electrodes reversible to B ^z(B)+ (cell B) and H⁺ ions (cell H), respectively. The system, HY–BY _z(B)-A _Y L-AY and the protolysis of the acids HL and H₂L in the ionic medium (A⁺, Y^?) are studied. Here, y = |z _L |. Moreover, some useful Emf titrations are suggested for the experimental determination of the slope functions SL(H, L^?), SL (H, L^2?) and SL(H, HL^?). The usefulness of the derived potential functions is established using the H⁺-acetate^? (CH₃COO^?) system as an example.     

Application of the inner product technique to double-well potentials in three-dimensional quantum systems by expanding the potential functions around their minima

Energy eigenvalues of double-well potentials for three-dimensional systems are calculated by means of an expansion of the potential function V(x,y,z;Z²,λ,a_IJ)=-Z²[x²+y²+z²] +λ{x⁴+y⁴+z⁴+2a_IJ[x²y²+x²z²+y²z²]} around its minimum, using the inner product technique, for various values of perturbation parameters Z²,λ and a_IJ. Some of the results calculated by this technique are compared with results obtained by other methods. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxygen barrier,free volume,and blending properties of polyamide 12/poly (vinyl alcohol) blends

Oxygen permeation rates, average volumes of free‐volume‐cavities (V_f), and fractional free volumes (F_v) of polyamide 12 (PA12)/poly(vinyl alcohol) (PVA) (ie, PA12_xPVA⁰⁵_y, PA12_xPVA⁰⁸_y, and PA12_xPVA¹⁴_y) blend films with varying PVA degrees of polymerization reduced to a minimum value when their PVA contents reached a corresponding optimal value, respectively. The minimum oxygen permeation rates, V_f, and F_v values obtained for the optimal PA12_xPVA^z_y blown films were reduced considerably with decreasing PVA degrees of polymerization. Experimental findings from dynamic mechanical analysis, differential scanning calorimetry, wide angle X‐ray diffraction, and Fourier transform infrared spectroscopy of the PA12_xPVA^z_y blend series suggest that PA12 and PVA in PA12_xPVA^z_y are miscible to some extent at the molecular level when their PVA contents are near and less than the corresponding critical values. The considerably enhanced oxygen barrier properties of the PA12_xPVA^z_y blend films with optimized compositions are attributed to the significantly reduced local free volume characteristics.     

Determination of the population,depopulation and the anisotropic spin lattice relaxation rates in the photoexcited triplet state of phenazine. A light modulation-EPR study

The photoexcited triplet state of phenazine in toluene glasses at 35 K is investigated by light modulation-EPR spectroscopy. From the transient EPR spectra and the kinetics in the three canonical orientations (p = x, y, z) the rate parameters are determined. Thus, the depopulation rate constants k_p, the anisotropic spin lattice relaxation rate constants W_p, and the ratios between the population constants A_p are calculated: k_x = (2.2 ± 0.3) × 10² s^?1, k_y = (0.21 ± 0.04) × 10² s^?1, k_z = (0.06 ± 0.03) × 10² s^?1, W_x = (8.6 ± 0.9) × 10³ s^?1, W_y = (11.0 ± 1.0) × 10³ s^?1, W_z = (14.0 ± 1.4) × 10³ s^?1, and A_x: _Ay:A_z ≈ 1:0.04:0.02. It is concluded therefore that the in-plane spin state |τ_x > is the active one.     

Bioluminescent Enzymatic Assay as a Tool for Studying Antioxidant Activity and Toxicity of Bioactive Compounds

A bioluminescent assay based on a system of coupled enzymatic reactions catalyzed by bacterial luciferase and NADH:FMN‐oxidoreductase was developed to monitor toxicity and antioxidant activity of bioactive compounds. The assay enables studying toxic effects at the level of biomolecules and physicochemical processes, as well as determining the toxicity of general and oxidative types. Toxic and detoxifying effects of bioactive compounds were studied. Fullerenols, perspective pharmaceutical agents, nanosized particles, water‐soluble polyhydroxylated fullerene‐60 derivatives were chosen as bioactive compounds. Two homologous fullerenols with different number and type of substituents, C₆₀O_2–4(OH)_20–24 and Fe_0.5C₆₀(OH) _xO_y (x + y = 40–42), were used. They suppressed bioluminescent intensity at concentrations >0.01 g L^?1 and >0.001 g L^?1 for C₆₀O_2–4(OH)_20‐24 and Fe_0.5C₆₀(OH)_xO_y, respectively; hence, a lower toxicity of C₆₀O_2–4(OH)_20–24 was demonstrated. Antioxidant activity of fullerenols was studied in model solutions of organic and inorganic oxidizers; changes in toxicities of general and oxidative type were determined; detoxification coefficients were calculated. Fullerenol C₆₀O_2–4(OH)_20–24 revealed higher antioxidant ability at concentrations 10^?17?10^?5 g L^?1. The difference in the toxicity and antioxidant activity of fullerenols was explained through their electron donor/acceptor properties and different catalytic activity. Principles of bioluminescent enzyme assay application for evaluating the toxic effect and antioxidant activity of bioactive compounds were summarized and the procedure steps were described.     

Enhanced lithium-ion intercalation and conduction of transparent tantalum oxide films by lithium addition with an atmospheric pressure plasma jet

An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO _y C _z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC₂H₅)₅] and lithium tert-butoxide [(CH₃)₃COLi] precursors. Transparent organo-lithiated tantalum oxide (Li _x TaO _y C _z ) films expose noteworthy Li⁺ ion intercalation and conduction performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li⁺ ionic diffusion coefficient and conductivity of 6.2?×?10^?10 cm²/s and 6.0?×?10^?11 S/cm for TaO _y C _z films are greatly progressed of up to 9.6?×?10^?10 cm²/s and 7.8?×?10^?9 S/cm for Li _x TaO _y C _z films by co-synthesis with an APPJ.     

First-principles calculation of temperature-dependent electronic transitions mechanism in V or Nb substituted BiFeO3

Here, we present a simulation study of temperature-dependent electronic transitions in BiVO₃ (BVO) and BiNbO₃ (BNO) using density functional theory (DFT) together with generalized gradient approximation (GGA) and two-dimensional correlation analysis (2D-CA). The results indicate that heat accumulation can accelerate the degeneracy of V-3d orbital in BVO and the splitting of Nb-4d orbital in BNO at 750 K. We found changes in the type of d–p hybrid orbital as follows, for BVO: V-d_x²_+y² + d_Z²-O-2p_z → V-d_x²_+y²-O-2p_z; and for BNO: Nb-d_x²_+y²-O-2p_z → Nb-d_x²_+y² + d_Z²-O-2p_z. Furthermore, we found changes in the type of hybrid orbital leading to the following electron–electron interactions, for BVO: t_2g (V-d_Z²-O-2p_z) + e_g (V-d_x²_+y²-O-2p_z) → t_2g (V-d_x²_+y²-O-2p_z); and for BNO: t_2g + e_g (Nb-d_x²_+y² + d_Z²-O-2p_z) → t_2g (Nb-d_x²_+y²-O-2p_z) + e_g (Nb-d_z²-O-2p_z). The electronic transitions are determined by a charge-transfer from the occupied O-2p⁴ orbitals to the unoccupied V-3d³ (or Nb-4d³) and Bi-6p³ orbitals. Due to the temperature-dependent electronic structure closely related to these electronic transitions, this study provides a new perspective for the design and improvement of BFO-based temperature-sensitive devices.     

Spectroscopic and magnetic studies on electrogenerated mixed-valence ruthenium complexes

Electrochemical synthesis has enabled several sequences of triple chloride bridged diruthenium complexes of general type [L_3?xCl_xRuCl₃RuCl_yL_3?y]^z/z+1/z+2 (L = soft neutral ligand) to be generated. The intervalence charge transfer bands in the optical spectra of the mixed-valence Ru^II,III₂ compounds and variable temperature magnetic measurements for the corresponding Ru^III.III₂ complexes reveal that the degree of metal—metal interaction in these confacial bioctahedral systems decreases as the molecular asymmetry (y?x) increases.     

A model for transitional plane Couette flow

A simplified model of plane Couette flow is derived by means of a cross-stream (y) Galerkin expansion in terms of trigonometric functions appropriate for idealized stress-free boundary conditions at the plates. A set of partial differential equations is obtained, governing the in-plane (x–z) space-dependence of a velocity field taken in the form: u=U₀(x,z,t)+[1+U₁(x,z,t)]sin(πy/2), v=V₁(x,z,t)cos(πy/2), w=W₀(x,z,t)+W₁(x,z,t)sin(πy/2). Beyond Lorenz-like Waleffe's modeling (Waleffe 1997), this Swift–Hohenberg type of approach is expected to give an access to the microscopic mechanism of spatiotemporal intermittency typical of the transition to turbulence in plane Couette flow (Pomeau 1986, Bergé et al. 1998).