Bis(diphenylphosphino)methane trimethylphosphine alkyl and η-cyclopentadienyl compounds of rhodium(I); P{H} two dimensional δ/J resolved and Overhauser effect nuclear magnetic resonance spectroscopy

Neutral mononuclear tertiary phosphine rhodium(I) complexes of the formula RhX(PMe₃)(dppm), X = Cl, CH₂SiMe₃, CH₂CMe₃, CH₂CMe₂Ph, η⁵-C₅H₅, DPPM = bis(diphenylphosphino)methane, RhCl(PPh₃)(dppm), RhX(dppm)₂, X = Cl, Me and Rh(η⁵-C₅H₅(dppm) have been synthesised. In Rh(η⁵-C₅H₅)(PMe₃)(dppm), the dppm ligand is unidentate according to ³¹P{¹H} NMR and X-ray data.The ³¹P{¹H} NMR spectral parameters of RhX(PR₃)(dppm) have been determined by a combination of two dimensional δ/J resolved spectroscopy and heteronuclear nuclear Overhauser effect difference spectroscopy (NOEDS) in conjunction with iterative analysis of the one dimensional spectra.     

A Jahn–Teller analysis of K3 and Rb3 in the electronic states 1E′ and 1E″

The potential energy surfaces (PES) of the Jahn–Teller distorted doublet 1²E′ (1B₂/1A₁) ground state and 1²E″ (2B₁/1A₂) excited state of alkali metal trimers (K₃, Rb₃) are studied with three high-level computational chemistry methods whose results are compared: single-reference coupled cluster, equation-of-motion coupled cluster and multi-reference second-order Rayleigh–Schrödinger perturbation theory. The doubly degenerate E electronic state interacts with the twofold degenerate vibrational e mode. We use the E ⊗ e Jahn–Teller effect theory to analyze in detail one- and two-dimensional cuts of the PES as a function of the symmetry-adapted internal coordinates Q_s, Q_x and Q_y and we extract the associated Jahn–Teller parameters. Spin-orbit coupling is accounted for by means of the Effective-Core-Potential-LS technique and spin-orbit splitting constants are extracted. We also provide the geometries, the binding energies and tentative vibronic spectra for the 1²E″ ← 1²E′ transitions.     

Electron spin resonance spectra of α-sulfonyl iminoxy radicals

Syn- andanti-α-sulfonyl iminoxy radicals have been generatedin situ by lead tetra-acetate oxidation of α-oximino sulfones. The ESR spectra of the geometrical isomers have been assigned and the¹⁴N and¹H hyperfine splitting constants are discussed in terms of the proposed structures.     

Synthesis, structure and DNA binding studies of mononuclear copper(II) complexes with mixed donor macroacyclic ligands, 2,6-bis({N-[2&3-(phenylselenato)alkyl]}benzimidoyl)-4-methylphenol

Two new phenol based macroacyclic Schiff base ligands, 2,6-bis({N-[2-(phenylselenato)ethyl]}benzimidoyl)-4-methylphenol (bpebmpH, 1) and 2,6-bis({N-[3-(phenylselenato)propyl]}benzimidoyl)-4-methylphenol (bppbmpH, 2) of the Se₂N₂O type have been prepared by the condensation of 4-methyl-2,6-dibenzoylphenol (mdbpH) with the appropriate (for specific reactions) phenylselenato(alkyl)amine. These ligands with Cu(II) acetate monohydrate in a 2:1 molar ratio in methanol form complexes of the composition [(C₆H₂(O)(CH₃){(C₆H₅)CN(CH₂)_nSe(C₆H₅)}{(C₆H₅)CO}₂Cu] (3 (n = 2), 4 (n = 3)) with the loss of phenylselenato(alkyl)amine and acetic acid. In both these complexes, one arm of the ligand molecule undergoes hydrolysis, and links with Cu(II) in a bidentate (NO) fashion, as confirmed by single crystal X-ray crystallography of complex 3. The selenium atoms do not form part of the copper(II) distorted square planar coordination sphere which has a trans-CuN₂O₂ core. The average Cu–N and Cu–O distances are, respectively, 1.973(3) and 1.898(2) Å. The N–Cu–N and O–Cu–O angles are, respectively, 167.4(11)° and 164.5(12)°. The compounds 1–4 have been characterized by elemental analysis, conductivity measurements, mass spectrometry, IR, electronic, ¹H and ⁷⁷Se{¹H} NMR spectroscopy and cyclic voltammetry. The interaction of complex 3 with calf thymus DNA has been investigated by a spectrophotometric method and cyclic voltammetry.     

Dynamic 1H NMR spectroscopy of η2-ethylene transition metal complexes

The low-temperature ¹H NMR spectra of bis(ethylene)trimethylphosphinenickel (1), η⁵-cyclopentadienyl(ethylene)methylnickel (2a), bis(ethylene)-η⁵-cyclopentadienylcobalt (2b), [bis(1-ethyl-2,4,6-triphenylphosphorinyl)nickel]P,P′-nickel(ethylene) (3) and η⁵-cyclopentadienyl(ethylene)hydrido(triphenylphosphine)ruthenium (4) exhibit {AA′B′B} (1) {ABB′A} (2a and 2b), {ABA′B′} (3) or {ABCD} (4) spin patterns, respectively, for the complexed ethylene. A full line shape analysis including all the proton couplings was performed for the ethylene rotation in 1, 2a and 2b. In addition to olefin rotation, a reversible intramolecular β-H-elimination was confirmed for 4 by magnetization transfer experiments.     

The use of selenophenyl galactopyranosides for the synthesis of α and β-(1→4)-C-disaccharides

Methyl α-C-lactoside {β-D-Gilp-C-(1→4)-α-D-Glcp-OMe} and its α anomer were expeditiously synthesized by radical coupling of various selenophenyl galactopyranosides onto methyl 2,3-di-O-benzyl-4-deoxy-4-C-methylene-α-D-xylo-hexopyranoside, which aretemporarily connected through a silaketal tether.     

New series of platinum group metal complexes bearing η- and η-cyclichydrocarbons and Schiff base derived from 2-acetylthiazole: Syntheses and structural studies

The mononuclear complexes [(η⁶-arene)Ru(ata)Cl]PF₆ {ata = 2-acetylthiazole azine; arene = C₆H₆ [(1)PF₆]; p-ⁱPrC₆H₄Me [(2)PF₆]; C₆Me₆ [(3)PF₆]}, [(η⁵-C₅Me₅)M(ata)]PF₆ {M = Rh [(4)PF₆]; Ir [(5)PF₆]} and [(η⁵-Cp)Ru(PPh₃)₂Cl] {η⁵-Cp = η⁵-C₅H₅ [(6)PF₆]; η⁵-C₅Me₅ (Cp^*) [(7)PF₆]; η⁵-C₉H₇ (indenyl); [(8)PF₆]} have been synthesised from the reaction of 2-acetylthiazole azine (ata) and the corresponding dimers [(η⁶-arene)Ru(μ-Cl)Cl]₂, [(η⁵-C₅Me₅)M(μ-Cl)Cl]₂, and [(η⁵-Cp)Ru(PPh₃)₂Cl], respectively. In addition to these complexes a hydrolysed product (9)PF₆, was isolated from complex (4)PF₆ in the process of crystallization. All these complexes are isolated as hexafluorophosphate salts and characterized by IR, NMR, mass spectrometry and UV–Vis spectroscopy. The molecular structures of [2]PF₆ and [9]PF₆ have been established by single-crystal X-ray structure analyses.     

Pressure Dependence of the Lattice Distortion in Perovskite La0.5−xBixCa0.5MnO3 (x=0.1, 0.15, 0.2)

The in situ behavior of distorted perovskite La_0.5−xBi_xCa_0.5MnO₃ (x=0.1, 0.15, 0.2) under high pressure has been studied by energy-dispersive X-ray diffraction in a diamond anvil cell. An abnormal change of the 202–040 d-spacing ascribed to the disappearance of the distortion mode Q₂ in the MnO₆ octahedra is observed at 1.2, 1.4, and 1.6 GPa, respectively, and it results in a reduction of the Jahn–Teller distortion commonly existing in the manganites. Effect of the unique 6s² long-pair character of the Bi³⁺ ion on the pressure dependence of the lattice distortion is discussed.     

The O–H···O, O–H···N and C–H···O hydrogen bonds in 1,4-dimethylpiperazine mono-betaine monohydrate

1,4-Dimethylpiperazine mono-betaine (1-carboxymethyl-1,4-dimethylpiperazinium inner salt, MBPZ) crystallizes as monohydrate. The crystals are orthorhombic, space group Pccn. Two MBPZ molecules and two water molecules form a cyclic oligomer, (MBPZ·H₂O)₂. The O–H···O and O–H···N hydrogen bonds are of 2.769(1) and 2.902(1) Å, respectively. The dimers interact with the neighboring molecules through the C–H···O hydrogen bonds of 3.234(1) Å. The piperazine ring assumes a chair conformation with the N(4)–CH₃ and N⁺(1)–CH₂COO⁻ groups in the equatorial position and the N⁺(1)–CH₃ group in the axial one. The FTIR spectrum is compared with that calculated by the B3LYP/6-31G(d,p) level of theory.     

Magnetic {Mo72Fe30}-embedded hybrid nanocapsules

Magnetic nanocapsules were constructed by fabricating nanometer scaled C₆₀-like “Keplerate” type {Mo₇₂Fe₃₀} with molecular formula [Mo₇₂^VIFe₃₀^IIIO₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁]ca.150H₂O into nanocapsule shells using the LbL technique. The morphology of the obtained hybrid nanocapsules was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Shell thickness of the {Mo₇₂Fe₃₀}-embedded nanocapsules can be tailored at the nanometer level more precisely than other nanoparticle-embedded capsules due to the homogeneous diameter and surface charges of {Mo₇₂Fe₃₀}. Interestingly, the {Mo₇₂Fe₃₀}-embedded nanocapsules could be separated and aligned under a circumstance of magnetic field, though {Mo₇₂Fe₃₀} is a paramagnetic molecule. This is the first time to fabricate hybrid magnetic materials containing {Mo₇₂Fe₃₀} using LbL technique. The obtained nanocapsules can be a good candidate for bioseparation as well as targeted delivery.     

A simple method to prepare single isomer tetrasubstituted olefins by successive Suzuki–Miyaura cross-couplings of E-β-chloro-α-iodo-α,β-unsaturated esters

A convenient method of synthesizing tetrasubstituted olefins as single isomers is described. E-β-Chloro-α-iodo-α,β-unsaturated esters are first converted into the corresponding E-β-chloro-α,β-unsaturated esters using Suzuki–Miyaura coupling reactions with arylboronic acids and alkenylboronic acids. These transformations gave complete selectivity, and proceeded with substitution at the more activated α-iodide position. These compounds, isolated as single isomers, were then transformed into tetrasubstituted olefins by Suzuki–Miyaura couplings with arylboronic acids, alkenylboronic acids, and alkyl boranes to afford the corresponding tetrasubstituted olefins as single isomers. During this coupling process, it was discovered that the use of small ligands, such as PMe₃ or PEt₃, was critical for efficient coupling. The stereochemistry and regiochemistry of the products were unequivocally established using NMR methods.     

Strength of the [Z–I···Hal]− and [Z–Hal···I]− Halogen Bonds: Electron Density Properties and Halogen Bond Length as Estimators of Interaction Energy

Bond energy is the main characteristic of chemical bonds in general and of non-covalent interactions in particular. Simple methods of express estimates of the interaction energy, E_int, using relationships between E_int and a property which is easily accessible from experiment is of great importance for the characterization of non-covalent interactions. In this work, practically important relationships between E_int and electron density, its Laplacian, curvature, potential, kinetic, and total energy densities at the bond critical point as well as bond length were derived for the structures of the [Z–I···Hal]⁻ and [Z–Hal···I]⁻ types bearing halogen bonds and involving iodine as interacting atom(s) (totally 412 structures). The mean absolute deviations for the correlations found were 2.06–4.76 kcal/mol.     

A study of the growth and CO electrooxidation behaviour of PtRh alloys on Pt{1 0 0} single crystals

The formation of quasi-crystalline PtRh two dimensional films supported on Pt{1 0 0} is described. For the first time, the voltammetry of PtRh{1 0 0} single crystal alloys covering the whole range of alloy composition is reported. Synthesis follows a similar procedure to that described previously for the formation of PtPd alloys supported on Pt{h k l} but with some important provisos concerning the final annealing step. CO electrooxidation was used as a probe reaction and for certain PtRh{1 0 0} surface alloys, unusually high electrocatalytic activity was observed relative to monometallic Pt and Rh electrodes. The flame annealing of a “PtRhPt sandwich” precursor structure was found to be the best method of forming the PtRh alloy surfaces. For PtRh films annealed under nitrogen, significant phase separation was observed in agreement with previous surface science studies of PtRh adlayers on Pt{1 0 0} annealed in the absence of oxygen. In addition, an excess of Rh in the “sandwich structure” from which the alloy was formed tended to preclude good alloy formation. It is suggested that the protocols for thin film formation described may prove useful in many other important electrocatalytic systems.     

Voltammetric studies on the α-tocopherol anion and α-tocopheroxyl (Vitamin E) radical in acetonitrile

The α-tocopheroxyl radical was generated voltammetrically by one-electron oxidation of the α-tocopherol anion (E ^r_1/2=−0.73 V versus Ag|Ag⁺) that was prepared by reacting α-tocopherol with Et₄NOH in acetonitrile (with Bu₄NPF₆ as the supporting electrolyte). Cyclic voltammograms recorded at variable scan rates (0.05–10 V s⁻¹), temperatures (−20 to 20°C) and concentrations (0.5–10 mM) were modelled using digital simulation techniques to determine the rate of bimolecular self-reaction of α-tocopheroxyl radicals. The k values were calculated to be 3×10³ l mol⁻¹ s⁻¹ at 20°C, 2×10³ l mol⁻¹ s⁻¹ at 0°C and 1.2×10³ l mol⁻¹ s⁻¹ at −20°C. In situ electrochemical-EPR experiments performed at a channel electrode confirmed the existence of the α-tocopheroxyl radical.     

Theoretical study of [Hg3(o-C6F4)3]n · {benzene} (n = 1, 2) complexes

The electronic structure and spectroscopic properties of [Hg₃(o-C₆F₄)₃]_n · {benzene} (n = 1, 2) were studied at the HF, MP2 and PBE levels. The interaction between [Hg₃(o-C₆F₄)₃] and benzene at the HF and MP2 levels was analyzed. Secondary π-interactions (Hg–benzene) were found to be the main contribution short-range stability in the [Hg₃(o-C₆F₄)₃] · {benzene} complex. At the MP2 and PBE levels equilibrium Hg–C distances of 338.4 and 361.4 pm; and interaction energies of 46.6 and 29.2 kJ/mol were found, respectively. The absorption spectra of these complexes were calculated by the single excitation time-dependent method at PBE level.     

Studies on kinetics of complexation of lanthanide α-hydroxycarboxylates with 1,10-phenanthroline

Kinetics of the coordination reaction of lanthanide (La^III, Eu^III) α-hydroxycarboxylates [LnL₃(H₂O)₂] with 1,10-phenanthroline (phen) in methanol-water (v/v, 3:2) were studied at 25°C by calorimetric titration. A one-step reaction process in accordance with the rate law has been suggested. The reaction is found to be first order for both lanthanide α-hydroxycarboxylates and phen. We have evaluated rate constants of the reactions. It is found that a linear free energy relationship exists between the stability constants of the lanthanide-α-hydroxycarboxylate-phen ternary complex and the rate constants. It is also found that a linear free energy relationship exists between the rate constants of La-hydroxycarboxylate with phen and the acid strength of α-hydroxy-acid as primary ligand, but the linear free energy relationship does not exist in the Eu-α-hydroxycarboxylate-phen ternary complex. The influence of other factors upon the reaction rate constants was also discussed.     

Tetraarylester der μ-Imidodiphosphorsäure und ihre Thioderivate — Strukturuntersuchungen

Tetraarylesters of μ-Imido-Diphosphoric Acid and its Thio Derivatives — Structure Investigations New O,O′,O″,O?-tetratolyl- and ditolyl-diphenylesters of the μ-imido-diphosphoric acid and its mono and dithio derivatives were synthesized, compared with the corresponding tetraphenylesters and investigated by ¹H, ¹³C, and ³¹P NMR spectroscopy and X-ray crystal structure analysis. Structures of the O,O′,O″,O?-tetrakis-(2-methyl-phenyl)-μ-imidodiphosphate, 1b , as well as of the corresponding ortho-, meta- and para-tolylesters of the μ-imido-monothiodiphosphoric acid ( 2a , 2b , 2c ) were determined. All the compounds form dimers via N? H…?O hydrogen bonds in the crystal as well as in nonpolar solvents. The distances around the phosphorus atoms rise with decreasing electronegativity of the phosphorus substituents. Signs of the ²J_{P? N? P} coupling constants were determined by ¹³C{¹H, ³¹P} triple resonance experiments for some compounds. These constants become more negative owing to substitution of a phosphoryl by a thiophosphoryl group.     

Unusual stabilization of cationic “M(η-allyl) (M = Pt, Pd) units by a dianionic cis-{Pt(C6F5)2(CCSiMe3)2} fragment

Chloride abstraction from [{M(η³ --- C₃H₅)Cl}_n] (M = Pt, n = 4 or M = Pd, n = 2) by (NBu₄)₂[cis-Pt(C₆F₅)₂(CCSiMe₃)₂] (1) gives rise to novel homo- and hetero-dinuclear zwitterionic derivatives (NBu₄) [{cis-Pt(C₆F₅)₂(CCSiMe₃)₂}M(η³-C₃H₅)] (M = Pt 2; M = Pd 3) which are formed by a M(η³-allyl)⁺ unit attached to both alkynyl ligands of the {cis-Pt(C₆F₅)₂(CCSiMe₃)₂}²⁻ fragment. The structure of 3 has been established by X-ray diffraction.     

Adsorption mechanism of Cu from aqueous solution by chitosan-coated magnetic nanoparticles modified with α-ketoglutaric acid

In order to better understand the adsorption mechanism of chitosan-coated magnetic nanoparticles modified with α-ketoglutaric acid (α-KA-CCMNPs), the removal of Cu²⁺ by α-KA-CCMNPs from aqueous solution was investigated in a batch system at 18, 35 and 50 °C. Different experimental approaches were applied to show mechanistic aspects, such as adsorption isotherms, kinetics and thermodynamics studies. Adsorption equilibrium studies showed that Cu²⁺ adsorption followed Langmuir model. The kinetics of the interactions was best described by pseudo-second-order mechanism. The thermodynamic parameters (ΔG°, ΔH° and ΔS°) analysis predicted that the adsorption process was strongly dependent on temperature of medium, and spontaneous and endothermic process. The XPS combined with FT-IR spectra revealed that N atom of –NH– group and O atom of carboxyl group in α-KA-CCMNPs coordinated with Cu²⁺. Experimental results from this study provide data that would be required if this heavy metal adsorption system was to be “scaled up” for industrial application.     

15N NMR of 1,4‐dihydropyridine derivatives

In this article, we describe the characteristic ¹⁵N and ¹H_N NMR chemical shifts and ¹J(¹⁵N–¹H) coupling constants of various symmetrically and unsymmetrically substituted 1,4‐dihydropyridine derivatives. The NMR chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as character and position of the substituent in heterocycle, N‐alkyl substitution, nitrogen lone pair delocalization within the conjugated system, and steric effects. Copyright © 2013 John Wiley & Sons, Ltd.