Excitonic Bands in the Spectra of Some Organic-Inorganic Hybrid Compounds Based on Metal Halide Units

Summary.  The optical absorption, photoluminescence, and photoconductivity spectra of some compounds of the formulas [R(CH₂) _n NH₃] _x M _y X _z , [R(CH₂) _n NH(CH₃)₂] _x M _y X _z , [R(CH₂) _n S(CH₃)₂] _x M _y X _z , [R(CH₂) _n SC(NH₂)₂] _x M _y X _z , and [R(CH₂) _n SeC(NH₂)₂] _x M _y X _z (R = organic residue; M = Bi(III), Pb(II), Sn(II), Cu(I), Ag(I) etc; X = I, Br, Cl; n, x, y, z = 0, 1, 2, 3, …) are briefly reviewed, and some new results are reported. The position, intensity, and shape of the excitonic bands depend on the dimensionality and size of the inorganic network as well as on the nature of the M, X, R, and onium moieties. Received June 23, 2000. Accepted August 1, 2000     

Etude des systemes CaHPO4−MHPO4−H2O (M=Sr,Ba) A 50°C

The systems CaHPO₄−MHPO₄−H₂O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca_1−xSr_xHPO₄ for 0.95<X<0.75 and Ca_xSr_1−xHPO₄ for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca₂Ba(HPO₄)₃ has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

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Zusammenfassung Bei 50°C wurde das System CaHPO₄−MHPO₄−H₂O (mitM=Sr, Ba) untersucht. FürM=Sr wurden Serien von Einzelphasen erhalten: Ca_1−xSr_xHPO₄ für 0.95<X< 0.75 und Ca_xSr_1−xHPO₄ für 0.4<X<1. Diese Mischkristalle wurden anhand ihrer Infrarotspektren und ihrer kristallographischen Elementarzellenparameter charakterisiert. FürM=Ba wurde die neue Phase Ca₂Ba(HPO₄)₃ ermittelt. Sie wurde mittels DRX, IR, ATD und chemischer Analyse charakterisiert.

     

Screening of variables in β-xylosidase recovery using cetyl trimethyl ammonium bromide reversed micelles

β-Xylosidase recovery by micelles using cetyl trimethyl ammonium bromide (CTAB) cationic surfactant was verified under different experimental conditions. A 2⁵⁻¹ fractional factorial design with center points was employed to verify the influence of the following factors on enzyme extraction: pH (x ₁), CTAB concentration (x ₂), electrical conductivity (x ₃), hexanol concentration (x ₄), and butanol concentration (x ₅). Statistical analysis of the results shows that of the fivevariables studied only hexanol and electrical conductivity did not have significant effects on the recovery of β-xylosidase. The other factors had significant effects in increasing order: (x ₁)>(x ₂)>(x ₅). The model predicts a recovery value of about 45%, which is similar to that obtained experimentally (43.5%).     

Structural study by X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy of the Na2Mn2(1 − x)Cd2xFe(PO4)3 (0 ≤ x ≤ 1) solid solution

Na₂Mn_{2(1 − x)}Cd_2xFe(PO₄)₃ (0 ≤ x ≤ 1) phosphates were prepared by solid state reaction and characterized by powder X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy. The X-ray diffraction patterns indicated the formation of a continuous solid solution which crystallizes in the alluaudite structural type characterized by the general formula X(2)X(1)M(1)M(2)₂(PO₄)₃. The cation distribution, deduced from a structure refinement of the x = 0, 0.5 and 1 compositions, is ordered in the X(2) sites and disordered in the remaining X(1), M(1) and M(2) sites. The magnetic susceptibility study revealed an antiferromagnetic behaviour of the studied compounds. The ⁵⁷Fe Mössbauer spectroscopy confirmed the structural results and proved the exclusive presence of Fe³⁺ ions.     

Density functional computation of 55Mn NMR parameters

Gradient-corrected (GGA) and hybrid variants of density functional theory are used to compute geometries and ⁵⁵Mn chemical shifts of MnO₄ ⁻, Mn(CO)₆ ⁺, Mn₂(CO)₁₀, Mn(CO)₅ X [X=H, Cl, C(O)Me], Mn(CO)₅ ⁻, Mn(NO)₃(CO), and Mn(C₅H₅)L _x [L _x =(CO)₃, C₆H₆, C₇H₈]. For this set of compounds, substituent effects on δ(⁵⁵Mn) are significantly underestimated with the pure GGA functional BPW91 and are well described with hybrid functionals such as mPW1PW91 and, in particular, B3LYP. The computed data provide evidence for solvent and counterion effects on δ(⁵⁵Mn) of MnO₄ ⁻ and Mn(CO)₆ ⁺, respectively. The latter, in the presence of Cl⁻, may be described as highly fluxional Mn(CO)₅C(O)Cl. Electric field gradients computed with the B3LYP functional can be used for a qualitative rationalization of observed trends in ⁵⁵Mn NMR line widths. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s002140020338x Received: 17 January 2002 / Accepted: 13 March 2002 / Published online: 3 June 2002     

Heat capacity of GdBaSr(Cu<Subscript>3−x</Subscript><Emphasis Type="Italic">M</Emphasis><Subscript>x</Subscript>)O<Subscript>7−δ</Subscript> superconductor (<Emphasis Type="Italic">M</Emphasis>=Zn and Ni)

In this study, GdBaSr(Cu_3−x M _x)O_7−δ bulk samples (M=Zn and Ni; 0≤x≤0.1) were prepared via solid-state reaction. Specific heat measurement (measured with thermal relaxation technique using PPMS) shows an obvious specific heat jump around the T _c for GdBaSrCu₃O_7−δ sample as observed in most of the high temperature superconductors. It shifts towards lower temperature with increasing of both Zn and Ni doping contents, whose tendency is similar to the decreasing of T _c. Debye temperature, Θ_D (derived from specific heat measurements) calculated at around 10 K is found to be directly proportional to the T _c.     

Excitonic Bands in the Spectra of Some Organic-Inorganic Hybrid Compounds Based on Metal Halide Units

 The optical absorption, photoluminescence, and photoconductivity spectra of some compounds of the formulas [R(CH₂) _n NH₃] _x M _y X _z , [R(CH₂) _n NH(CH₃)₂] _x M _y X _z , [R(CH₂) _n S(CH₃)₂] _x M _y X _z , [R(CH₂) _n SC(NH₂)₂] _x M _y X _z , and [R(CH₂) _n SeC(NH₂)₂] _x M _y X _z (R = organic residue; M = Bi(III), Pb(II), Sn(II), Cu(I), Ag(I) etc; X = I, Br, Cl; n, x, y, z = 0, 1, 2, 3, …) are briefly reviewed, and some new results are reported. The position, intensity, and shape of the excitonic bands depend on the dimensionality and size of the inorganic network as well as on the nature of the M, X, R, and onium moieties.     

A conjecture for some partial differential operators on L 2( R n)

OnX =L ²(R ⁿ), letQ = (Q ₁,Q ₂,…,Q _n) andP = (P ₁,P ₂, …,P _n) be the operators given by (Q _jf) (x) =x _jf(x),P _j = - i∂/∂x _j. For anyC ^∞ functionh:R ⁿ →R putH ₀ =h(P) andH =H ₀ + (1 +Q ²)^-δ, where δ > 1/2. By the method of scattering theory we prove thatH _ac, the absolutely continuous part ofH is unitarily equivalent toH ₀ when (a)n = 1 and (b) forn ≥ 2, whenh is in a large class of polynomials. It is conjectured that the results are true for any polynomialh. We use the techniques of Enss’ method and the idea of bound states for momentum.     

Synthesis, Structure, and Physical Studies of the New β-LiVOAsO4 Compound

Two new compounds of the A_xMOXO₄ family, β-LiVOAsO₄ and β-VOAsO₄, have been synthesized by solid state reaction and electrochemical lithium deintercalation from β-LiVOAsO₄, respectively. Both compounds are isostructural and are built like other β-VOXO₄ (X=S, P) by (VO₅)_∞ chains of distorted VO₆ octahedra connected via corner-shared AsO₄ tetrahedra. For β-LiVOAsO₄ the additional Li⁺ ions occupy chains of edge-shared octahedra running perpendicularly to the (VO₅)_∞ chains. The one-dimensional antiferromagnetic behavior suggested by the structure has been experimentaly confirmed. It is shown that lithium deintercalation occurs through a first-order transition at 4.02 V vs Li⁺/Li⁰. From chemical bond considerations it is shown why the redox potential of a given transition element M in a six-fold coordination involving (M=O)^m+ units lies between those observed in oxides and in M₂(XO₄)₃ compounds with (XO₄)ⁿ⁻ oxo anions (X=S, P, As).     

Liquid flow porous electrode: The effect of local variations in liquid-phase conductivity on its operation efficiency

For one-dimensional model of porous electrode (PE), an equation for the ideal ratio between the local conductivities of liquid phase κ_L(x) and solid phase κ_s(x), which provides uniform distributions of potential and current inside the PE, is obtained. It is shown that the principal possibilities of levering action of both phases are similar; however, the shapes of their ideal conductivity profiles are mirror-opposite. To gain a beneficial effect at the expense of conductivity of liquid phase, κ_L(x) should increase monotonically from the rear current lead to the frontal side of PE provided that the conductivities of phases are equal in the middle of PE. The effect of distortions of ideal κ_L(x) profile is analyzed. It is found that, with regard to the natural upper limit of solution conductivity, the best conditions for the levering action of ideal κ_L(x) profile should be expected in the porous matrices with low conductivity. It is shown that the formation of even few zones with opposite-shaped κ_L(x) profile inside PE (the solution conductivity decreases towards the frontal side of PE) leads to more nonuniform potential distribution and a decrease in the PE operation efficiency (especially at high total current density).     

Synthesis,spectroscopic characterization and redox reactivity of the copper(II) salicylaldiminates containing sterically hindered 2,6-diphenylphenol

New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X = H and 3,5-di-t-butyl substituents on the salicylaldehyde ring, L ^x H, and their copper(II) complexes, Cu(L ^x )₂, have been synthesized and characterized by i.r., u.v./vis., ¹H-n.m.r., ¹³C-n.m.r., e.s.r. spectroscopy and magnetic susceptibility measurements. E.s.r. study has shown that chemical oxidation of Cu(L ^x )₂ with PbO₂ produces ligand-centered Cu^II-phenoxyl radical species. The complexes are easily reduced with PPh₃ via intramolecular electron transfer from ligand to copper(II) to give unstable radical intermediates, which in time are converted to another stable secondary radical species. The analysis of e.s.r. spectra of Cu(L ^x )₂ and generated radical intermediates are presented.     

In situ X‐ray Diffraction Studies of Cation and Anion Inter­calation into Graphitic Carbons for Electrochemical Energy Storage Applications

Graphite is a redox‐amphoteric intercalation host and thus capable to incorporate various types of cations and anions between its planar graphene sheets to form so‐called donor‐type or acceptor‐type graphite intercalation compounds (GICs) by electrochemical intercalation at specific potentials. While the LiC_x/C_x donor‐type redox couple is the major active compound for state‐of‐the‐art negative electrodes in lithium‐ion batteries, acceptor‐type GICs were proposed for positive electrodes in the “dual‐ion” and “dual‐graphite” cell, another type of electrochemical energy storage system. In this contribution, we analyze the electrochemical intercalation of different anions, such as bis(trifluoromethanesulfonyl) imide or hexafluorophosphate, into graphitic carbons by means of in situ X‐ray diffraction (XRD). In general, the characterization of battery electrode materials by in situ XRD is an important technique to study structural and compositional changes upon insertion and de‐insertion processes during charge/discharge cycling. We discuss anion (X^–) and cation (M⁺) intercalation/de‐intercalation into graphites on a comparative basis with respect to the M_x⁺C_n^– and C_n⁺X_n^– stoichiometry, discharge capacity, the intercalant gallery height/gallery expansion and the M–M or X–X in‐plane distances.     

Voltammetric Determination of Phenoxybenzyl‐Type Insecticides at Chemically Modified Conducting Polymer‐Carbon Nanotubes Coated Electrodes

The electrochemical reduction of three common insecticides such as cypermethrin (CYP), deltamethrin (DEL) and fenvalerate (FEN) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNT‐GCE), polyaniline (herein called as modifier M₁) and polypyrrole (herein called as modifier M₂) deposited MWCNT/GCE using cyclic voltammetry. Influences of pH, scan rate, and concentration were studied. The surface morphology of the modified film was characterized by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD). A systematic study of the experimental parameters that affect differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived at. The calibration plots were linear over the insecticide's concentration range 0.1–100 mg L^?1 and 0.05–100 mg L^?1 for all the three insecticides at MWCNT‐GCE and MWCNT(M₁)‐GCE respectively. The MWCNT(M₂)‐GCE performed well among the three electrode systems and the determination range obtained was 0.01–100 mg L^?1 for CYP, DEL and FEN. The limit of detection (LOD) was 0.35 μg L^?1, 0.9 μg L^?1 and 0.1 μg L^?1 for CYP, DEL and FEN respectively on MWCNT(M₂)‐GCE modified system. Suitability of this method for the trace determination of insecticide in spiked soil sample was also determined.     

Low- and high-molecular-weight polyacetylenes: Synthesis,characterization, and thermal isomerization

Procedures for the synthesis of polyacetylene ([CH]_x) with M _n (number average molecular weight) from 400 to about 10⁶ have been developed. This probably represents the largest range of molecular weight (MW) obtainable for a given monomer by a single initiator system. The catalyst residue level in [CH]_x can be significantly reduced by acidic-methanol purification. The very low MW polymer L-[CH]_x (polyacetylenes with M _n 400–500), has the same cis crystal structure as the higher MW polymers but is less ordered along the c-axis. It is isomerized to the trans material with apparently a more compact unit cell than high MW polymers. There is annealing of crystallite which increases the longitudinal order during thermal isomerization. This process occurs more readily and with lower activation energy in L-[CH]_x than for polymers with higher MW. Isomerization of high MW polymers tends to trap cis units which can result in degradation as evidenced by the formation of sp³ carbon vibrations in IR spectra. This is true even for L-[CH]_x after prolonged heating. The results render credence to the proposal based on anamalous resonance Raman scattering profile that there can be very short trans segments in thermally isomerized trans-[CH]_x.     

Copolymerization of carbon dioxide and cyclohexene oxide with zinc/β‐ketoiminato complexes: Investigating the influence of the electron structure of zinc/β‐ketoiminato complexes on the catalytic activity and resultant copolymer properties

A series of LZnX zinc/β‐ketoiminato complexes [L = CH₃C(OH)?C(CH₂CH?CH₂)C(CH₃)?NAr ( L₁ ), CH₃C(OH)?C(CH₂CH₂CN)C(CH₃)?NAr ( L₂ ), CH₃C(OH)?C(CH₂C₆H₅)C(CH₃)?NAr ( L₃ ), or CH₃C(OH)?CHC(CH₃)?NAr ( L₄ ); Ar = 2,6‐ⁱPr₂C₆H₃; and initiation group X = alcoholate or acetate (for L₁ ) or alcoholate (for L₂ – L₄ )] were synthesized, and their activities toward the copolymerization of carbon dioxide with cyclohexene oxide were determined. The 3‐position substituents on the β‐ketoiminato ligand backbone of the zinc/β‐ketoiminato complexes played an important role not only in the catalytic activity but also in the intrinsic viscosity, chemical composition, and refined microstructure of the resultant copolymers. The order of the catalytic activity of L₁ ZnX with different initiation groups (X = OMe, OⁱPr, or OAc) was L₁ Zn (OⁱPr) > L₁ Zn (OMe) > L₁ Zn (OAc), being the opposite of the order of the leaving ability of the initiation groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6243–6251, 2006     

Operator technique for obtaining the recursion formulas of characteristic and matching polynomials as applied to polyhex graphs

A simple and efficient method, called an operator technique, for obtaining the recurrence relation of a given counting polynomial, e.g., characteristic P_G(x) or matching M_G(x) polynomial, for periodic networks is proposed. By using this technique the recurrence relations of the P_G(x) and M_G(x) polynomials for the linear zigzag-type and kinked polyacene graphs were obtained. For the lower members of these series of graphs, the coefficients of P_G(x) and M_G(x) polynomials are tabulated.     

N,S,O-Containing organic ligands based on salicylaldehyde and 2-thiosubstituted ethylamines and their complexes with CoII, NiII, and CuII

The reaction of 2,2′-di(2-hydroxybenzaliminoethyl) disulfide (H₂L¹) and 2-[(2-thioethyl)iminomethyl]phenol (H₂L²) with MCl₂·xH₂O (M = Co, Ni, Cu) afforded the [M₂(L¹)Cl₂] and [M(L²)]₂ complexes, respectively. Their structures were determined by the data of electronic and IR spectroscopy and PM3 quantum chemical calculations. The H₂L¹ ligand and the complexes were studied by electrochemistry (CV and using a rotating disk electrode). The primary electronic changes are localized on the ligand fragment upon the electrochemical oxidation and reduction of the complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1325–1330, July, 2007.     

On the determination of the average molecular weight,radius of gyration,and mass/length ratio of polydisperse solutions of polymerizing rod‐like macromolecular monomers by multi‐angle static light scattering

The angular dependence of the light scattered from polydisperse solutions of rod‐like or worm‐like linear polymers formed by the polymerization of rod‐like macromolecular monomers was studied with the aid of computer simulations. Except at very low conversion degrees, these ensembles are characterized by curved Zimm‐like plots. An appraisal of the use of polynomial fittings for the derivation of the weight‐average molecular weight (M_w) and of the z‐average square radius of gyration (<R_g²>_z) from such plots is presented and discussed. Depending on the average size and shape distribution, the use of polynomial fittings allows the applicability of the Zimm method well beyond the standard condition q²<R_g²>_z<<1, q being the scattering wavevector. In addition, the derivation of the w/z‐average mass/length ratio M_L of the polymers from only partially linear Casassa plots, from which large errors in the derived M_L values can be made, is analyzed. By combining the Casassa method with the complementary Holtzer plots, it is usually possible to assess the reliability of the results and give an estimate of their accuracy. However, it was also found that apparently linear Casassa plots, allowing a good estimate of the M_L value, may arise in particular situations even when the Holtzer plot would indicate otherwise.     

Phase diagram and metal distribution of the (CrxTi1−x)3Se4 system (0 ≤ x ≤ 1) with the Cr3S4-type structure

The phase diagram and metal distribution of the (Cr_xTi_1?x)₃Se₄ system were studied by X-ray, neutron diffraction, and DTA measurements. The metal distribution of M′M₂X₄ with the Cr₃S₄-type structure, which was estimated from the composition dependence of lattice parameters in the solid solution (M′_xM_1?x)₃X₄ system, was in good agreement with results from other measurements such as neutron diffraction and Mössbauer effect.