The MTXαR method. The determination and use of “molecular” α values in molecular multiple scattering Xα calculations

A semiempirical approach is used to fix the α value for use in the extraatomic regions in multiple-scattering (MS Xα) calculations which retain the muffin-tin treatment of the potential. Such a “molecular” α value for an atom is determined by requiring the corresponding homonuclear diatomic molecule to have its minimum at the experimentally determined equilibrium separation; hence they are called α _R. Molecular α _R values are determined for the ground state Li₂ and F₂ molecules and are tested in a calculation of the ground state LiF potential curve. We find a binding energy at the calculated equilibrium separation to be within 1% of the experimental value. The LiF curve based entirely on the ordinary atomic α values is substantially inferior. The present MT Xα _R approach appears to be competitive with others which are intended to improve the muffin-tin version of MS Xα calculations.     

Manganese‐σ‐Borane Complexes from Dihaloboranes

The hydride complex K[(η⁵‐C₅H₅)Mn(CO)₂H] reacted with a range of dihalo(organyl)boranes X₂BR (X = Cl, Br; R = tBu,Mes, Ferrocenyl) to give the corresponding borane complexes[(η⁵‐C₅H₅)Mn(CO)₂(HB(X)R)]., The presence of a hydride in bridging position between manganese and boron was deduced from ¹¹B decoupled ¹H NMR spectra. Additionally, the structure of the tert‐butyl borane complex was confirmed by single‐crystal X‐ray diffraction.     

Phosphane Copper(I) Dicarboxylates: Synthesis and Their Potential Use as Precursors for the Spin‐coating Process in the Deposition of Copper

Dicopper dicarboxylates [(R₃P)_mCuXCu(PR₃)_m] ( 5a , X = O₂CCO₂, R = Ph, m = 2; 5b , X = O₂CCO₂, R = nBu, m = 3) were prepared by treatment of [Cu₂O] ( 1a ) with HO₂CCO₂H ( 2a ) in presence of PR₃ ( 4a , R = Ph; 4b , R = nBu). A further synthesis approach to mono‐ and dicopper dicarboxylates is given using an electrolysis cell equipped with Cu electrodes and charged with acids H₂X and phosphanes R₃P. Without addition of a base mononuclear [(nBu₃P)_mCuXH] ( 6a , m = 3, XH = O₂CCO₂H, 6b , m = 3, XH = O₂CCH₂CO₂H, 6c , m = 3, XH = O₂CCH₂CH₂CO₂H, 6d , m = 2, XH = O₂C‐2‐C₅H₄N‐6‐CO₂H) was formed, whereas in presence of NEt₃ ( 3 ), the dicopper systems [(R₃P)_mCuXCu(PR₃)_m] ( 5a , X = O₂CCO₂, R = Ph, m = 2; 5b , X = O₂CCO₂, R = nBu, m = 3; 5c , X = O₂CCH₂CO₂, R = nBu, m = 3; 5d , X = O₂CCH₂CH₂CO₂, R = nBu, m = 3; 5e , X = O₂C‐2‐C₅H₄N‐6‐CO₂, R = nBu, m = 3) were produced. When 6a reacted with [(tmeda)Zn(nBu)₂] ( 7 ), trimetallic [(tmeda)Zn((nBu₃P)₃CuO₂CCO₂)₂] ( 8 ) was accessible. In this heterobimetallic complex the Zn(tmeda) unit spans two CuO₂CCO₂ entities. The molecular structures of 5a , 6a and 6d in the solid state were determined by single X‐ray structure analysis. Complexes 5a and 6a are monomers, whereas 6d creates in the solid state a linear open chain coordination polymer by hydrogen bridge formation. Characteristic for 6d is the somewhat distorted trigonal bipyrimidal arrangement around the copper atom with the nBu₃P ligands in axial and the C₅H₃NCO₂H oxygen and nitrogen atoms in equatorial positions. In 5a the oxalate connectivity binds in a μ‐1,2,3,4 fashion being part of a planar Cu₂(oxalate) core. TG studies of several mono‐ and dicopper dicarboxylates were carried out. Release of the PR₃ ligands is recognized and the remaining Cu‐(di)carboxylate unit decomposes to afford elemental copper and CO₂. The deposition of copper onto pieces of PVD‐Cu oxidized silicon wafers by applying the spin‐coating process and using 5c and 5d as precursors is discussed.     

H/D isotope effect on charge‐inverted hydrogen‐bonded systems: Systematic classification of three different types in H3XH…YH3 (X = C,Si, or Ge,and Y = B,Al, or Ga) with multicomponent calculation

Three different H/D isotope effect in nine H₃XH(D)^…YH₃ (X = C, Si, or Ge, and Y = B, Al, or Ga) hydrogen‐bonded (HB) systems are classified using MP2 level of multicomponent molecular orbital method, which can take account of the nuclear quantum nature of proton and deuteron. First, in the case of H₃CH(D)^…YH₃ (Y = B, Al, or Ge) HB systems, the deuterium (D) substitution induces the usual H/D geometrical isotope effect such as the contraction of covalent R(C? H(D)) bonds and the elongation of intermolecular R(H(D)^…Y) and R(C^…Y) distances. Second, in the case of H₃XH(D)^…YH₃ (X = Si or Ge, and Y = Al or Ge) HB systems, where H atom is negatively charged called as charge‐inverted hydrogen‐bonded (CIHB) systems, the D substitution leads to the contraction of intermolecular R(H(D)^…Y) and R(X^…Y) distances. Finally, in the case of H₃XH(D)^…BH₃ (X = Si or Ge) HB systems, these intermolecular R(H(D)^…Y) and R(X^…Y) distances also contract with the D substitution, in which the origin of the contraction is not the same as that in CIHB systems. The H/D isotope effect on interaction energies and spatial distribution of nuclear wavefunctions are also analyzed. © 2015 Wiley Periodicals, Inc.     

Ein einfacher Weg zu α-substituierten (E)-3-Oxo-1-alkenylphosphonsäureestern

Zusammenfassung -Substituierte -Acylvinylphosphonate3 mitE-Konfiguration [R ²CO-CH=C(R ¹)-P(O)(OR)₂], werden in guten Ausbeuten durchWittig-Reaktion von Acylphosphonsäureestern1 [R ¹CO-P(O)(OR)₂,R ¹=Alkyl oder Aryl] mit (2-Oxoalkyliden)triphenylphosphoranen2 [R ²CO-CH=PPh ₃,R ²=Alkyl, O-Alkyl oder CH₂ X (X=Br, OMe, CO₂ Et)] erhalten.

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A convenient route to -substituted dialkyl (E)-3-oxo-1-alkenylphosphonates

-Substituted dialkyl (E)--acylvinylphosphonates [R ²CO-CH=C(R ¹)-P(O)(OR)₂,3], are easily obtained in good yields byWittig-reaction of dialkyl acylphosphonates1 [R ¹CO-P(O)(OR)₂,R ¹=alkyl or aryl) with 2-oxoalkylidene triphenylphosphoranes2 [R ²CO-CH=PPh ₃,R ²=alkyl, O-alkyl and CH₂ X (X=Br, OMe, CO₂ Et)].

     

A theoretical study of α-substituted cyclopropyl and isopropyl radicals

The structures of α-X-cyclopropyl and α-X-isopropyl radicals (X = H, CH₃, NH₂, OH, F, CN, and NC) are reported at the RHF 3-21G level of theory. The isopropyl radicals are pyramidal with out-of-plane angles varying from 12° (X = CN) to 39° (X = NH₂), and barriers to inversion ranging from 0.4 kcal/mol (X = H) to 4.0 kcal/mol (X = NH₂). The cyclopropyl radicals have larger out-of-plane angles, from 39.9° (X = CN) to 49.4° (X = NH₂), and their barriers to inversion, which increase with the inclusion of polarization functions, vary from 5.5 kcal/mol (X = H) to 16.7 kcal/mol (X = F). In both types of radicals the amino group is the most stabilizing substituent, while the α-fluoro has little effect. The β-fluoro group is weakly destabilizing in the cyclopropyl radical. The strain energies of the cyclopropyl radicals (36–43 kcal/mol) are compared with those of similarly substituted anions, cations, and cyclopropanes.     

Theoretical investigation on identical anionic halide‐exchange SN2 reaction processes on N‐haloammonium cation NH3X+ (X = F,Cl, Br,and I)

CCSD(T) calculations have been used for identically nucleophilic substitution reactions on N‐haloammonium cation, X^? + NH₃X⁺ (X = F, Cl, Br, and I), with comparison of classic anionic S_N2 reactions, X^? + CH₃X. The described S_N2 reactions are characterized to a double curve potential, and separated charged reactants proceed to form transition state through a stronger complexation and a charge neutralization process. For title reactions X^? + NH₃X⁺, charge distributions, geometries, energy barriers, and their correlations have been investigated. Central barriers ΔE for X^? + NH₃X⁺ are found to be lower and lie within a relatively narrow range, decreasing in the following order: Cl (21.1 kJ/mol) > F (19.7 kJ/mol) > Br (10.9 kJ/mol) > I (9.1 kJ/mol). The overall barriers ΔE relative to the reactants are negative for all halogens: ?626.0 kJ/mol (F), ?494.1 kJ/mol (Cl), ?484.9 kJ/mol (Br), and ?458.5 kJ/mol (I). Stability energies of the ion–ion complexes ΔE_comp decrease in the order F (645.6 kJ/mol) > Cl (515.2 kJ/mol) > Br (495.8 kJ/mol) > I (467.6 kJ/mol), and are found to correlate well with halogen Mulliken electronegativities (R² = 0.972) and proton affinity of halogen anions X^? (R² = 0.996). Based on polarizable continuum model, solvent effects have investigated, which indicates solvents, especially polar and protic solvents lower the complexation energy dramatically, due to dually solvated reactant ions, and even character of double well potential in reactions X^? + CH₃X has disappeared. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Linear relationships in α,β-unsaturated carbonyl compounds between the half-wave reduction potentials, the frontier orbital energies and the Hammett σp values

A linear relationship between the half-wave reduction potentials of α,β-unsaturated carbonyl compounds R–CHCH–COX and the Hammett σ_p values of R and X is proposed: E_1/2=−1.341σ_p(X)σ_p(R)+1.123σ_p(X)+1.746σ_p(R)−1.694. A linear relationship is also observed for the LUMO's energy values, the absolute chemical hardness η, the chemical potential μ, the electrophilicity power ω, or the polarisation of the ethylenic double bond with the Hammett σ_p values of R and X.     

“Short-bite” ligands in cluster synthesis

The short-bite ligands CH₂(PR ₂)₂ or CH(PR ₂)₃ (R = Me, Ph),RN(PX ₂)₂ (R=H, Me, Et;X = F, OR (R= Me, Et, i-Pr, Ph), Ph),RE(CH₂ ER₂)₂ (E = P, As;R = Me, Ph ), Ph₂ P(2-C₅H₄N) and related species are particularly versatile for the synthesis of di- and polynuclear complexes which frequently possess metal-metal bonds. In addition to homometallic products, these ligands often permit the directed synthesis of heterometallic complexes. Selected aspects of the chemistry of these complexes are also reviewed.     

Effect of organic anion adsorption on water permeability of microporous membranes

It was observed that adsorption of trace amounts of organic anions from aqueous permeants causes a logarithmic decrease in permeability of the microporous membrane until all of the available adsorption sites along the internal perimeters of the microcapillary inlets are filled. Thereafter, impedance appears to increase almost linearly with continued water flow reflecting the increase in depth of these perimeter areas saturated by uniform anion adsorption. The magnitude of this adsorption effect caused by anions of the homologous series H(CH₂)_nCO₂⁻ is proportional to n from n = 1 to n = 17, which is consistent with expectation on the basis of Traube's Rule. The total equivalent methylene impedance, X, caused by adsorption of other organic anions, such as R₁R₂CO₂⁻, is equal to the sum of its segments R₁ and R₂ linked in series to CO₂⁻, i.e., X_T = X₁ + X₂. This is not true, however, for molecules such as R₁AR₂CO₂⁻, where A is a nucleophilic atom or group of atoms that can serve as a second adsorption site. Apparently, the segment, R₂, is convoluted or held flat to the surface by the anchor points A and CO₂⁻, and only the segments R₁ extend full-length above the plane of anchor points, so that X_T is about equal to X₁.     

A Dimeric Gallium Hydrazide as an Active Lewis Pair – Complexation and Activation of Me2GaH and Various Heterocumulenes

Treatment of the dimeric gallium hydrazide [Me₂Ga‐N(2‐Ad)‐NC₅H₁₀]₂ ( 5 ) with Me₂GaH resulted in the formation of an adduct 6 by Ga–N bond cleavage and coordination of the metal hydride via a Ga–N and a 3c–2e Ga–H–Ga bond. This reaction reflects the typical behavior of frustrated Lewis pairs. Reactions with heterocumulenes R–N=C=X (R = Ph, CMe₃, Dipp, X = O; R = Ph, X = S) or X=C=X (X = O, S) resulted in the formation of the cyclic Ga–N insertion products Me₂Ga–N(R)C(O)N(2‐Ad)‐NC₅H₁₀ ( 7a – c ), Me₂GaS₂C‐N(2‐Ad)‐NC₅H₁₀ ( 8 ) or Me₂GaX₂C‐N(2‐Ad)‐NC₅H₁₀ [X = O ( 9 ); S ( 10 )] in moderate to good yields. Three different structural motifs were observed in the solid state: Five‐membered GaNCN₂ heterocycles with exocyclic C=O bonds for compounds 7a – c , four‐membered GaSCN or GaSCS heterocycles for compounds 8 and 9 (chelating coordination of the Ga atoms by SCN and CS₂ ligands) and an eight‐membered (GaOCO)₂ heterocycle for the dimeric CO₂ insertion product 10 . Treatment of 5 with PhCN or Ph₂CO resulted in a completely different reaction and afforded a dimeric Ga imide 11a or an alcoholate 11b . These reactions may start by retro‐hydrogallation with the formation of H₁₀C₅N–N=C(C₉H₁₄) and Me₂GaH and proceed by addition of the metal hydride to the polar multiple bonds of the nitrile or ketone.     

Microwave-assisted synthesis and antimicrobial activity of 5-trihalomethyl-3-arylisoxazoles

A series of twelve 5-trihalomethyl-3-arylisoxazoles was synthesized and screened for antibacterial and antifungal activities. The compounds were synthesized from the cyclondensation of 1,1,1-trihalo-4-alkoxy-3-alken-2-ones [CX ₃C(O)C(R ²)=C(R ¹)OR, where X = Cl and F; R=Me; R ²=H; R ¹=H, Me, F, Cl, Br, and NO₂] with hydroxylamine hydrochloride through a rapid one-pot reaction via microwave irradiation. Some of the 5-trihalomethyl-3-arylisoxazoles exhibited good in vitro anti-Cryptococcus activity. Correspondence: Marcos A. P. Martins, Núcleo de Química de Heterociclos (NUQUIMHE), Centro de Ciências Naturais e Exatas, Departamento de Química, Universidade Federal de Santa Maria, 97.105-900 Santa Maria, RS, Brazil.     

A New Structure Type for Rare-Earth-Metal Cluster Compounds stabilized by transition metals: KPr6I10Os,CsPr6I10Fe,CsLa6I10Fe,and CsLa6I10Mn

Reactions of KI, Pr, PrI₃, and Os in niobium tubes at 800° yielded black, air- and moisture-sensitive crystals of Kpr₆I₁₀Os which were characterized by single crystal X-ray diffraction (orthorhombic, Pnma, a = 15.362(3), b = 13.498(2), c = 14.128(3) Å, Z = 4, R(F)/R_w = 4.4/5.6%). Subsequent parallel experiments also gave, according to Guinier powder pattern data, the isostructural compounds CsPr₆I₁₀Fe (a = 15.312(2), b = 13.426(1), c = 14.154(1) Å), CsLa₆I₁₀Fe (a = 15.523(2), b = 13.646(2), c = 14.334(1) Å) and CsLa₆I₁₀Mn (a = 15.457(4), b = 13.737(2), c = 14.329(2) Å). The important structural feature is the presence of octahedral rare-earth-metal cluster units R₆ that are centered by a transition-metal atom Z and bridged and interconnected by halide atoms. The new compounds exhibit the same general pattern of halide connectivity (R₆Z)XXXX as do the triclinic compounds R₆X₁₀Z. However, the structural arrangement of the metal octahedra is significantly different; they are linked by I^i–i atoms into zigzag chains along [010] and these are interconnected into a three dimensional network by I^i–a atoms to form channels in which the alkali-metal atoms are located. The introduction of alkali-metal atoms into reactions leads to new quaternary compounds with discrete rare-earth-metal clusters centered by transition metals and more open structure frameworks. Measurements of the temperature dependencies of the magnetic susceptibilities for CsLa₆I₁₀Fe and CsLa₆I₁₀Mn are consistent with expectations for 17- and 16-electron cluster systems, respectively.     

Zur Reaktion von Halomethylphosphoniumhalogeniden, [R3PCYnX3–n]X,mit Phosphanen,R′3P

On the Reaction of Halomethylphosphonium Halides, [R₃PCY_nX_3–n]X, with Phosphanes, R′₃P The results of the reaction of 19 different halomethylphosphonium halides, [R₃PCY_nX_3–n]X (R = Ph, n-Bu, Me₂N, Et₂N; Y = H, F; X = Cl, Br, I; n = 0–2), with Ph₃P, n-Bu₃P, and (R₂N)₃P are presented. As reaction products bisphosphonium salts, [R₃P? CY_nX_2–n? PR′₃]X₂, and phosphoranylphosphonium salts, [R₃P=CY? PR′₃]X, or reduced (halo)methyl-phosphonium salts, [R₃PCHY_nX_2–n]X, are obtained. [Ph₃PCBrF₂]Br and [Bu₃PCBrF₂]Br react with R′₃P by trans-alkylation forming [R′₃PCBrF₂]Br. The factors influencing the course of the reaction are discussed.     

Compounds containing layers of composition [(SbF)XO4] (X = P, As). Crystal structures of Na(SbF)PO4 · 1.5H2O, Na(SbF)AsO4, NH4(SbF)PO4 · H2O, and NH4(SbF)AsO4 · 3H2O

The title compounds have been prepared in water by reaction of SbF₃ with dihydrogen phosphates or arsenates and characterized by single crystal X-ray work, IR, Raman, and Mössbauer spectroscopy. They have identical layer structures. Layers of composition [(SbF)XO₄]⁻ (X = P, As) were formed by sharing four corners between XO₄ tetrahedra and SbFO₄ pseudooctahedra. The lengths of the terminal Sb---F bond (with the lone pair in a trans-position) and the Sb---O bonds are 192 and 219 pm, respectively. The stacking of the layers and the interlayer distance depend on the cations and the number of intercalated water molecules. In Na(SbF)AsO₄ the Na⁺ ion is coordinated by only two oxygen atoms within 300 pm. Crystal data: Na(SbF)PO₄ · 5H₂O, monoclinic, P2₁/m, A = 656.2(5), B = 654.1(5), C = 867.9(3) pm, β = 92.43(1)°, 889 reflections, 81 parameters, R = 0.044, R_w = 0.046. NH₄(SbF)PO₄ · H₂O, tetragonal, I4/m, A = 656.6(3), C = 1439.8(5) pm, 680 reflections, 31 parameters, R = 0.023, R_w = 0.021. Na(SbF)AsO₄, tetragonal, P4/ncc, A = 671.8(1), C = 1756.4(4) pm, 1056 reflections, 28 parameters, R = 0.052, R_w = 0.065. NH₄(SbF)AsO₄ · 3H₂O, tetragonal, P4/ncc, A = 683.8(2), C = 1873.0(7) pm, 1194 reflections, 30 parameters, R = 0.042, R_w = 0.050.     

Structure and Bonding of the Mixed‐Valent Platinum Trihalides,PtCl3 and PtBr3

The isotypical crystal structures of the mixed valent trihalides PtCl₃ and PtBr₃ were redetermined by single crystal methods (space group R3¯; trigonal setting; PtCl₃: a = 21.213Å, c = 8.600Å, c/a = 0.4054; Z = 36; 1719 hkl; R = 0.035; PtBr₃: a = 22.318Å, c = 9.034Å; c/a = 0.4048; Z = 36; 1606 hkl; R = 0.027). A cubic closest packing of X^— anions forms the basis of an optimized arrangement of cuboctahedrally [Pt₆X₁₂] cluster molecules with Pt^II and enantiomers of helical chains of edge‐condensed [PtX₂X_4/2] octahedra with Pt^IV in cis‐Δ‐ and cis‐Λ‐configuration, respectively. The bond lengths vary with the function of the X^— ligands (d¯(Pt^II—X) = 2.315 and 2.445Å; d¯(Pt^II—Pt^II) = 3.336 and 3.492Å; d(Pt^IV—X) = 2.286 — 2.417Å and 2.437 — 2.563Å). The Pt^II atoms are shifted outwards the X₁₂ cuboctahedra by 0.045Å and 0.024Å, respectively. The symmetry governed Periodic Nodal Surface, PNS, perfectly separates the regions of different valencies. Quantum chemical calculations exclude the possible additional interactions between Pt^II and one of the exo‐ligands of Pt^IV.     

Optimization of ultrasonic‐assisted extraction of phenolic antioxidants from Malus baccata (Linn.) Borkh. using response surface methodology

In this study, the optimum extraction conditions for maximum recovery of the content of total phenolics (TPC) and total antioxidant abilities were analyzed for Malus baccata (Linn.) Borkh. using response surface methodology. The effects of ethanol percentage (X₁,%), ultrasonic power (X₂, W) and extraction temperature (X₃, °C) on the total phenolic content (Y₁) and antioxidant ability (Y₂) were evaluated. A second‐order polynomial model produced a satisfactory fitting of the experimental data with regard to total phenolic content (R² = 0.9942, P < 0.0001) and antioxidant ability (R² = 0.9966, P < 0.0001). The optimized conditions were ethanol concentration of 61.0%, ultrasonic power of 308.6 W, extraction temperature of 51.1°C for TPC and 60.5%, 311.4 W, 51.6°C for antioxidant ability, the predicted values agreed well with the experimental values. Results implied that the major phenolic compounds in obtained extracts as chlorogenic acid, quercetin‐3‐gal/glu, quercetin‐3‐xyl/ara, phloretin‐2‐xyloside, quercetin‐3‐ rhamnoside, and phloridzin.     

FAR IR SPECTRA AND STRUCTURES OF Zn(II) COMPLEXES OF 2-AMINOTHIAZOLES

Abstract

IR spectra and molecular structures of ZnL₂X₂ (L = 2-NH₂-4-R-thiazole, R = H (at), CH₃; 2-NH₂-6-R₁ -benzothiazole, R₁ = H (abt), CH₃, OCH₃, OC₂H₅ or 2-NH₂-tetrahydrobenzothiazole; X = Cl, Br, I) have been studied. It was found that the complex character of the far IR spectra and difficulties in v(NH₂) interpretation make conclusions regarding structure based only on IR data ambiguous, and in some cases discrepant. Single crystal X-ray data for the complexes with L = at, X = Br, I and L = abt, X = Br show that structures are built up of discrete tetrahedral ZnL₂X₂ molecules with monodentate ligands coordinated via endo-N atoms. It was found that in the coordination tetrahedra MN₂Cl₂ (M = Co²⁺, Zn²⁺) the central atom redistributes electron density between the thiazole ligands and the terminal Cl atoms.     

Optimized and validated high‐performance liquid chromatography method for the determination of deoxynivalenol and aflatoxins in cereals

A simple, sensitive and accurate analytical method was optimized and developed for the determination of deoxynivalenol and aflatoxins in cereals intended for human consumption using high‐performance liquid chromatography with diode array and fluorescence detection and a photochemical reactor for enhanced detection. A response surface methodology, using a fractional central composite design, was carried out for optimization of the water percentage at the beginning of the run (X1, 80–90%), the level of acetonitrile at the end of gradient system (X2, 10–20%) with the water percentage fixed at 60%, and the flow rate (X3, 0.8–1.2 mL/min). The studied responses were the chromatographic peak area, the resolution factor and the time of analysis. Optimal chromatographic conditions were: X1 = 80%, X2 = 10%, and X3 = 1 mL/min. Following a double sample extraction with water and a mixture of methanol/water, mycotoxins were rapidly purified by an optimized solid‐phase extraction protocol. The optimized method was further validated with respect to linearity (R²>0.9991), sensitivity, precision, and recovery (90–112%). The application to 23 commercial cereal samples from Greece showed contamination levels below the legally set limits, except for one maize sample. The main advantages of the developed method are the simplicity of operation and the low cost.