Some aspects of metal-support strong interactions in Rh/Al2O3 catalyst under oxidising and reducing conditions

The aim of the Letter is to elucidate the nature of metal-support interaction in the 2 wt% Rh/Al₂O₃ catalyst obtained by annealing Rh–O–Al xerogel at 1113 K in air.XPS, HRTEM, and XRD results reveal that during the Rh–O–Al xerogel annealing in air, rhodium incorporates into forming alumina, which results mostly in Rh⁴⁺/δ-Al₂O₃ solid solution formation.However, in the course of the catalyst reduction at 773 with H₂ and at 823 K with CH₄ the Rh⁴⁺/δ-Al₂O₃ solid solution transforms into Rh–Al alloy. The islands of rhodium form on the surface of the Rh–Al alloy nanocrystallites if the reduction is slow enough.     

In situ complexation of rhodium(II) tetracarboxylates with some derivatives of cysteine and related ligands studied by 1H and 13C nuclear magnetic resonance spectroscopy

The complexation of N-phthaloyl, N-formyl, and N,N-dimethyl derivatives of S-methylcysteine methyl ester (both racemic and optically pure) with three dimeric rhodium(II) salts, acetate Rh₂AcO₄, trifluoroacetate Rh₂TFA₄, and (R)-(+)-α-methoxy-α-trifluoromethylphenylacetate Rh₂Mosh₄ was investigated by nuclear magnetic resonance spectroscopy (NMR) at room and lower temperatures. The complexation was carried out in situ, in CDCl₃ solution using titration procedure; the results were examined by the analysis of ¹H and ¹³C NMR chemical shift change (Δδ). The complexation of free S-methyl cysteine and hydrochloride salt of its methyl ester was performed in D₂O solution. For comparison, complexation of some derivatives of leucine, phenylalanine, and proline was examined.

N-phthaloyl and N-formyl derivatives of cysteine formed 1 : 1 and 1 : 2 axial complexes with all dirhodium salts. Rhodium substrates were bonded via sulfur. In one case, the complexation of Rh₂TFA₄ by both sulfur and N-formyl oxygen was noted. Similar complexation of Rh₂TFA₄, via CHO group, was found for N-formyl derivatives of leucine, phenylalanine, and proline. For N,N-dimethyl derivative of cysteine, both N and S atoms were involved in bonding. At room temperature, in all cases, ligand exchange was fast on the NMR timescale.     

FICA,a new chiral derivatizing agent for determining the absolute configuration of secondary alcohols by 19F and 1H NMR spectroscopies

Optically active 1-fluoroindan-1-carboxylic acid (FICA) was designed and prepared as its methyl ester for determining the absolute configuration of chiral molecules by both ¹H and ¹⁹F NMR spectroscopies. Enantiomerically pure isomers of FICA methyl esters (FICA Me esters) were obtained by chromatographic separation using HPLC with a Daicel Chiralcel OJ-H column. The absolute configuration of the (+)-FICA Me ester was deduced to be (S) by X-ray crystallographic analysis of the (+)-FICA amide of (R)-α-phenethylamine. Both enantiomers were derived to the diastereomeric esters of chiral secondary alcohols by an ester exchange reaction. In the ¹H NMR spectra, the signs of Δδ_H (δ_R ? δ_S) were consistent on each side of the FICA molecular plane. Therefore, the concept of the modified Mosher’s method could be successfully applied to the FICA-based procedure. Moreover, the consistency in the signs of Δδ_F (δ_R ? δ_S) values suggests that the FICA method would be reliable in assigning the absolute configurations of secondary alcohols based on ¹⁹F NMR spectroscopy.     

Redox behavior and transport properties of La0.5−2xCexSr0.5+xFeO3−δ and La0.5−2ySr0.5+2yFe1−yNbyO3−δ perovskites

The effects of doping the mixed-conducting (La,Sr)FeO_3−δ system with Ce and Nb have been examined for the solid-solution series, La_0.5−2xCe_xSr_0.5+xFeO_3−δ (x = 0–0.20) and La_0.5−2ySr_0.5+2yFe_1−yNb_yO_3−δ (y = 0.05–0.10). Mössbauer spectroscopy at 4.1 and 297 K showed that Ce⁴⁺ and Nb⁵⁺ incorporation suppresses delocalization of p-type electronic charge carriers, whilst oxygen nonstoichiometry of the Ce-containing materials increases. Similar behavior was observed for La_0.3Sr_0.7Fe_0.90Nb_0.10O_3−δ at 923–1223 K by coulometric titration and thermogravimetry. High-temperature transport properties were studied with Faradaic efficiency (FE), oxygen-permeation, thermopower and total-conductivity measurements in the oxygen partial pressure range 10⁻⁵–0.5 atm. The hole conductivity is lower for the Ce- and Nb-containing perovskites, primarily as a result of the lower Fe⁴⁺ concentration. Both dopants decrease oxide-ion conductivity but the effect of Nb-doping on ionic transport is moderate and ion-transference numbers are higher with respect to the Nb-free parent phase, 2.2 × 10⁻³ for La_0.3Sr_0.7Fe_0.9Nb_0.1O_3−δ cf. 1.3 × 10⁻³ for La_0.5Sr_0.5FeO_3−δ at 1223 K and atmospheric oxygen pressure. The average thermal expansion coefficients calculated from dilatometric data decrease on doping, varying in the range (19.0–21.2) × 10⁻⁶ K⁻¹ at 780–1080 K.     

Separation performance of polyimide composite membrane prepared by dip coating process

The effects of the preparation conditions in a dip coating process on polyimide composite membranes have been investigated. Polyimide precursor obtained from pyromellitic dianhidride (PMDA) and 4,4′-oxydianiline (ODA) was mixed with triethylamine and poly(amic acid)tri-ethylamine salt (PAA salt) was made. An asymmetric polyimide membrane (PI-2080) as a supporting membrane was dipped in a PAA salt (concentration 0–5 wt.%) methanol solution. The coating layers of PAA salt were converted to these of polyimide by annealing at 200°C for 3 h in an ordinary vacuum oven.The performance of the polyimide composite membrane was evaluated by gas permeation (N₂, O₂, CO₂, at 1 kg/cm²) and pervaporation (feed: a 95 vol.% ethanol aqueous solution at 30–60°C). The composite membranes prepared using a coating solution of 5 wt.% PAA salt showed the CO₂/N₂ selectivity of over 25 on gas permeation, and separation factor α (H₂O/EtOH) of over 800 with a total flux of 0.21 kg/m² h on pervaporation.     

Electrochemical characterisation of MBaCo3ZnO7+δ (M = Y,Er, Tb) as SOFC cathode material with low thermal expansion coefficient

The electrochemical oxygen activation at high temperature was studied on a new class of oxygen-store material based on the system YBaCo₄O_7+δ. Three different porous layers made of YBaCo₃ZnO_7+δ, ErBaCo₃ZnO_7+δ and TbBaCo₃ZnO_7+δ were electrochemically tested as oxygen activation coatings and showed a very promising activity. The envisaged applications for these materials are principally as SOFC cathodes and as catalytic layer on oxygen membranes. The electrochemical performance followed the order Tb ? Y > Er at any tested temperature. Area specific resistance for the best performing material (TbBaCo₃ZnO_7+δ) ranges from 30 mΩ cm² at 850 °C to 0.46 Ω cm² at 650 °C. High temperature XRD showed that the thermal expansion coefficient (25–900 °C) in air of TbBaCo₃ZnO₇ is 9.45 × 10^?6 K^?1, which evidences the good thermochemical compatibility of this cobalt-rich electrocatalyst with YSZ/GDC electrolytes.     

Novel amphiphilic triblock copolymer based on PPDO,PCL, and PEG: Synthesis,characterization, and aqueous dispersion

Amphiphilic triblock copolymer, poly(p-dioxanone-co-caprolactone)-block-poly(ethylene oxide)-block-poly(p-dioxanone-co-caprolactone) (PPDO-co-PCL-b-PEO-b-PPDO-co-PCL) was synthesized by ring opening polymerization (ROP) of p-dioxanone and ɛ-caprolactone initiated through the hydroxyl end of poly(ethylene glycol) (PEG) in the presence of stannous 2-ethyl hexanoate [Sn(oct)₂] as a catalyst. Polymerization and structural features of the polymers were analyzed by different physicochemical techniques (GPC, ¹H NMR, ¹³C NMR, FT-IR, DSC and TGA). The splitting of ¹H NMR resonance at δ 2.3 and δ 4.1 ppm reveals the random copolymerization. Polymeric nanoparticles were prepared in phosphate buffer (pH 7.4) by co-solvent evaporation technique at room temperature (25 °C). Existence of hydrophobic domains as cores of the micelles were characterized by ¹H NMR spectroscopy and further confirmed with fluorescence technique using pyrene as a probe. Critical micelle concentration (CMC) of the polymer in phosphate buffer (pH. 7.4) was decreased from 2.3 × 10⁻³ to 7.6 × 10⁻⁴ g/L with the fraction of PCL. Polymeric nanoparticles observed by atomic force microscopy (AFM) were uniform and spherical, with smooth textured of around 50–30 nm diameter. Dynamic light scattering (DLS) and electrophoretic light scattering (ELS) measurements showed a monodisperse size distribution of around 113–90 nm hydrodynamic diameters and negative zeta (ζ) potential (−4 to −14 mV), respectively. The investigations for the polymeric nanoparticles in aqueous medium showed that the composition of the hydrophobic segment of amphiphilic block copolymer makes a significant influence on its physicochemical characteristics.     

Pyridine-containing chiral macrocycles for the enantioselective recognition of amino acid derivatives and their molecular dynamics simulations

Two novel C₂-symmetric optically active pyridine-15-crown-5 type ligands containing lipophilic chains at the stereogenic centres, macrocycles 5 and 6, were prepared from (S)-1,2-propanediol and (S)-3-aryloxy-1,2-propanediol for the enantiomeric recognition of amino acid ester derivatives. These novel macrocycles have been shown to be strong complexing agents for primary organic ammonium salts (with K values of up to 1363.5 M^?1, ΔG^o of up to 17.86 kJ mol^?1 and a selectivity ratio of 80:20) by ¹H NMR titration method. These macrocyclic host exhibited enantioselective binding towards the l-enantiomer of phenylalanine methyl ester hydrochloride with K_L/K_D up to 8.57 in CDCl₃ containing 0.25% CD₃OD. Experimental results have been detailed with molecular dynamic calculations at atomic level concerning the molecular recognition and discrimination properties of a chiral pyridino-15-crown-5. The binding free energies were calculated as ～?25 kJ mol^?1. The results indicated that the host binds and discriminates valine salts better than phenylalanine salts. The molecular dynamics, MM/PBSA calculations are consistent with the ¹H NMR results.     

Perovskite-type oxides for high-temperature oxygen separation membranes

Oxygen permeation through dense ceramic membranes of perovskite-like SrCo_0.9−xFe_0.1Cr_xO_3−δ (x = 0.01–0.05), Sr_1−x−yLn_xCoO_3−δ(Ln = La, Nd, Sm, Gd; x = 0.30–0.35; y = 0–0.10), SrCo_1−xTi_xO_3−δ (x = 0.05–0.20) and LaM_1−xNi_xO_3−δ (M = Ga, Co, Fe; x = 0–0.6) was studied. The SrCoO_3−δ-based solid solutions with cubic perovskite structure were found to exhibit highest permeation fluxes compared to other membranes. However, high thermal expansion coefficients and interaction with gas species such as carbon dioxide may complicate the employment of SrCoO_3−δ membranes for oxygen separation membranes. Alternatively, the LaGa_1−xNi_xO_3−δ (x = 0.2–0.5) perovskites, having significant permeation fluxes as well as thermal expansion coefficients in the range of (10.8–11.6) × 10⁻⁶ K⁻¹, were demonstrated to be suitable as membrane materials at oxygen pressures from 1 × 10⁻² to 2 × 10⁴ Pa. Testing oxygen permeation at oxygen partial pressures of 1–60 atm showed that only oxides with a high oxygen deficiency such as SrCo_0.85Ti_0.15F_3−δ possess sufficient oxygen permeation fluxes. The oxygen permeability of perovskites on the basis of LaGaO₃ and LaCoO_3−δ was found to be negligible at oxygen pressures above 15 atm, caused by low oxygen vacancy concentration and ionic conductivity of such ceramic materials.     

Gas phase synthesis and X-ray crystal structures of supramolecular networks with bromocorannulene: Similarities and differences with their corannulene analogs

The reactivity of bowl-shaped mono-bromocorannulene (C₂₀H₉Br) has been examined and compared with that of corannulene (C₂₀H₁₀). Although bromination of corannulene was shown to flatten the bowl and change its electronic properties, it has not affected the outcome of coordination reactions toward the avid Lewis acidic [Rh₂(O₂CCF₃)₄] complex. Two new products have the same composition [{Rh₂(O₂CCF₃)₄}_m · (C₂₀H₉Br)_n] where m:n = 1:1 (1) and 3:2 (2), as the corresponding corannulene-based analogs. The X-ray diffraction studies of 1 and 2 revealed 1D chain and 2D layered structures built on η²-coordination of rhodium(II) to rim carbon sites of the C₂₀H₉Br-bowl, similar to those of C₂₀H₁₀. While no essential difference is found in 2D structures, the local coordination environments of the [Rh₂(O₂CCF₃)₄] unit differ in their 1D complexes.     

Magnetic properties of nitric oxide adsorbed within channel crystals

The crystalline one-dimensional compounds, [M₂(bza)₄(pyz)]_n (bza = benzoate; pyz = pyrazine; M = Cu^II (1)) and [M₂(bza)₄(2-mpyz)]_n (2-mpyz = 2-methylpyrazine; M = Rh^II (2), Cu^II (3)), demonstrate gas absorbency of NO. The amounts of adsorbed NO gas are 0.61 for 1, 0.30 for 2, and 0.23 for 3 per M₂ unit at 195 K (800 Torr). The crystals of 1 adsorbed more NO molecules than did those of 2 and 3. The magnetic susceptibilities of the NO-inclusion crystals indicate that included NO molecules interact antiferromagnetically with neighboring guests without dimerization to N₂O₂. Magnetic behaviors indicated NO aggregation in the narrow 1D channels of 1–3 under unsaturated adsorption conditions.     

Synthesis and crystal structure of the first chain-type nitridosilicates RE5Si3N9 (RE = La,Ce)

The novel branched chain-type nitridosilicates Ce₅Si₃N₉ and La₅Si₃N₉ have been synthesized in a radio-frequency furnace starting from the respective metals and silicon diimide Si(NH)₂ at 1625 °C for La₅Si₃N₉ and 1650 °C for Ce₅Si₃N₉, respectively. The structure of Ce₅Si₃N₉ has been determined by single-crystal X-ray diffraction (Ce₅Si₃N₉, Cmca (no. 64), a = 10.567(2) Å, b = 11.329(2) Å, c = 15.865(3) Å, V = 1899.3 Å³, Z = 8, R₁ = 0.0391, 1480 independent reflections, 90 refined parameters). The structure of isotypic La₅Si₃N₉ has been refined by the Rietveld method, starting from single-crystal data of Ce₅Si₃N₉ (La₅Si₃N₉, Cmca (no. 64), a = 10.647(4) Å, b = 11.414(4) Å, c = 16.030(5) Å, V = 1948.1 Å³, Z = 8, R_P = 0.0348, R_F² = 0.0533). Both compounds are built up of alternating Q²- and Q³-type corner sharing SiN₄ tetrahedra with additional corner sharing Q¹-units attached to the Q³-tetrahedra pointing alternately in opposing directions. These zipper-like chains are intertwined in both directions perpendicular to the chain itself to form a three-dimensionally interlocked structure with the rare-earth ions situated between the chains. Magnetic measurements resulted in a ferromagnetic ground state with a magnetic moment in agreement with Ce³⁺.     

Organo-aluminum,zinc and magnesium derivatives of the imidotris(amido)phosphate Me3SiNP(NHtBu)3

Reactions of (^tBuHN)₃PNSiMe₃ (1) with the alkyl-metal reagents dimethylzinc, trimethylaluminum and di-n-butylmagnesium yield the monodeprotonated complexes [MeZn{(N^tBu)(NSiMe₃)P(NH^tBu)₂}] (2), [Me₂Al{(N^tBu)(NSiMe₃)P(NH^tBu)₂}] (3) and [Mg{(N^tBu)(NSiMe₃)P(NH^tBu)₂}₂] (4), respectively. Attempts to further deprotonate complex 2 with n-butyllithium or di-n-butylmagnesium result in nucleophilic displacement of the methylzinc fragment by lithium or magnesium. The two remaining amino protons of 3 are removed by reaction with di-n-butylmagnesium to give a heterobimetallic complex in which the coordination sphere of magnesium is completed by two molecules of THF (5 · 2THF) or one molecule of TMEDA (5 · TMEDA). Reaction of complex 3 with 1 equiv. of n-butyllithium followed by treatment of the product with di-n-butylmagnesium yields the complex {Me₂Al[(N^tBu)(NSiMe₃)P(N^tBu)₂]MgBu} Li · 4THF (6 · 4THF), the first example of a triply deprotonated complex of 1 containing three different metals. Reaction of complex 5 with iodine results in cleavage of an Al–Me group to give {MeIAl[(N^tBu)(NSiMe₃)P(N^tBu)₂Mg]} (7). Complexes 5 · 2THF, 5 · TMEDA, 6 · 4THF and 7 have been characterized in solution by multinuclear (¹H, ¹³C, ³¹P and ⁷Li) NMR spectroscopy, while the solid-state structures of 2, 4 and 5 · 2THF have been determined by X-ray crystallography.     

A general method for the synthesis of enantiopure aliphatic chain alcohols with established absolute configurations. Part 1. Application of the MαNP acid method to acetylene alcohols

A method using (S)-(+)-2-methoxy-2-(1-naphthyl)propionic acid 1 (MαNP acid) has been applied to acetylene alcohols 4–14 to determine their absolute configurations by ¹H NMR anisotropy and/or X-ray crystallography. Diastereomeric MαNP esters prepared from racemic acetylene alcohols and (S)-(+)-MαNP acid 1 were easily separable by HPLC on silica gel. From the ¹H NMR anisotropy Δδ data of separated diastereomeric MαNP esters {Δδ = δ (R,X) − δ(S,X) = δ(2nd fr.) − δ(1st fr.)}, the absolute configurations of the first eluted esters were determined. This MαNP acid method has been successfully applied to various acetylene alcohols 4–12 and 14. In the case of MαNP esters 21b, 24a, and 26a, their absolute configurations were unambiguously determined by X-ray crystallography, which confirmed the absolute configuration assignments performed by ¹H NMR anisotropy. These acetylene alcohol MαNP esters can serve as key intermediates for the synthesis of enantiopure aliphatic chain alcohols with established absolute configurations as described in Part 2 of this series.     

Enhancement of electrochemical performance and thermal compatibility of GdBaCo2/3Fe2/3Cu2/3O5+δ cathode on Ce1.9Gd0.1O1.95 electrolyte for IT-SOFCs

Transition-metal doped double-perovskite structure oxides GdBaCo_2/3Fe_2/3Ni_2/3O_5+δ (FN-GBCO), GdBaCo_2/3Fe_2/3Cu_2/3O_5+δ (FC-GBCO), GdBaCoCuO_5+δ (C-GBCO) and pristine GdBaCo₂O_5+δ (GBCO) were synthesized via a citrate combustion method. The thermal-expansion coefficient (TEC) and electrochemical performance of the oxides were investigated as potential cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The TEC exhibited by the FC-GBCO cathode up to 900 °C is 14.6 × 10^?6 °C^?1, which is lower than the value of GBCO (19.9 × 10^?6 °C^?1). Area specific resistances (ASR) of 0.165 Ω cm² at 700 °C and 0.048 Ω cm² at 750 °C were achieved for the FC-GBCO cathode on a Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte. An electrolyte supported (300 μm thick) single-cell configuration of FC-GBCO/CGO/Ni-CGO attained a maximum power density of 435 mW cm^?2 at 700 °C. The unique composition of GBCO co-doped with Fe and Cu ions in the Co sites exhibited reduced TEC and enhancement of electrochemical performance and good chemical compatibility with CGO, and this composition is proving to be a potential cathode for IT-SOFCs.     

Uranium(VI) bis(imido) disulfonamide and dihalide complexes: Synthesis density functional theory analysis

Novel cis- and trans-bis(imido) uranium disulfonamide derivatives have been prepared from iodide metathesis reactions between two equivalents of K[N(Me)(SO₂Ar’)] (Ar’ = 4-Me-C₆H₄) and U(N^tBu)₂(I)₂(L)_x (L = OPPh₃, x = 2; Me₂bpy, x = 1; Me₂bpy = 4,4’-dimethyl-2,2’-bipyridyl). These bis(amide) derivatives serve as useful precursors for the synthesis of the trans-diphenolate complex U(N^tBu)₂(O-2-^tBuC₆H₄)₂(OPPh₃)₂ (5), cis- and trans-dithiolate complexes U(N^tBu)₂(SPh)₂(L)_x (L = OPPh₃ (6); Me₂bpy (7)), and cis- and trans-dihalide complexes with the general formulas U(N^tBu)₂(X)₂(L)_x (X = Cl, L = OPPh₃ (8), L = Me₂bpy (10); X = Br, L = OPPh₃ (9), L = Me₂bpy (11)). DFT calculations performed on the trans-dihalide series U(N^tBu)₂(X)₂(L)₂ and the UO₂²⁺ analogues UO₂X₂(OPPh₃)₂ suggest that the uranium centers in the [U(N^tBu)₂]²⁺ ions possess more covalent character than analogous UO₂²⁺ derivatives but that the U-X bonds in the U(N^tBu)₂X₂L₂ complexes possess a more ionic nature.     

Multi-functional zwitterionic compounds as additives for lithium battery electrolytes

A series of multi-functional zwitterionic compounds having both ester and sulfonate groups were synthesized and their electrochemical properties were investigated. The effect of added zwitterionic compounds on the cycling performance of the cell containing 1 M LiPF₆ in EC, DMC, and EMC (1/1/1 by vol.) was also examined. The cell capacity was not varied much at 1/5 C up to 50 cycles with the addition of either 2.25 wt% N-methylpyrrolidinium-N-(propyl sulfonate) (MePyS) or N-methylpiperidinium-N-(propyl sulfonate) (MePipS) as an additive, but dropped significantly at higher C rate of 1 C. Such a sharp decrease of the performance at higher C rate was not observed when MePyS or MePipS was replaced by N-(2-acetoxyethyl) pyrrolidinium-N-(propyl sulfonate) (EsPyS) or N-(2-acetoxyethyl) piperidinium-N-(propyl sulfonate) (EsPipS), implying the positive role of the ester functional group.FT-IR study clearly demonstrates that ester-containing zwitterionic compounds are able to interact with Li⁺ ions through both sulfonate and ester functional groups.     

Structure elucidation of BaSi2O2N2 – A host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs

BaSi₂O₂N₂ is a promising host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs. Applying a combined approach, its orthorhombic average structure (space group Cmcm (no. 63), a = 14.3902(3) Å, b = 5.3433(1) Å, c = 4.83256(7) Å and V = 371.58(2) Å³, Z = 4) has been elucidated by electron diffraction and structure solution from X-ray and neutron powder diffraction data with subsequent Rietveld refinement (wRp = 0.0491 for X-ray data). The structure contains layers of highly condensed SiON₃ tetrahedra with O terminally bound to Si. The Ba²⁺ ions are situated between the layers and are surrounded by a cuboid of O atoms capped by two N atoms. In the structure, there is only one Ba site and one Si site, respectively, which is in accordance with a single sharp ²⁹Si NMR signal observed at ?52.8 ppm typical for SiON₃ tetrahedra in MSi₂O₂N₂ type oxonitridosilicates. Lattice energy calculations support the results of the structure determination.     

Formation of chiral ionic liquids and imidazol-2-ylidene metal complexes from the proteinogenic aminoacid l-histidine

Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(n-propyl)₂-OMe⁺Br⁻]. It features a melting point of 39 °C and may serve as a useful readily available optically active ionic liquid. Its subsequent treatment with silver oxide gave the corresponding l-histidine derived chiral N-heterocyclic carbene complex [“(carbene)₂Ag · AgBr₂”]. Transmetallation by treatment with Pd(CH₃CN)₂Cl₂ or [Rh(cod)Cl]₂ led to the formation of the respective chiral late metal imidazol-2-ylidene complexes [“(carbene)₂PdCl₂”] and [“(carbene)RhCl(cod)”], respectively. Four diastereomers of the square planar palladium system were observed. Due to the additional chirality center in the l-histidine-derived “Arduengo-carbene ligand” two diastereomers of the rhodium carbene complex were formed.     

Isopiestic determination of the osmotic and activity coefficients of dilute aqueous solutions of symmetrical and unsymmetrical quaternary ammonium bromides with a new isopiestic cell at 298.15 K

The osmotic coefficients of Bu₄NBr, sec-Bu₄NBr, iso-Bu₄NBr, Bu₂Et₂NBr and Bu₃EtNBr were determined by isopiestic method at 298.15 K in dilute aqueous solutions. A branched isopiestic cell was used. The osmotic coefficients of tetra-alkyl-ammonium solutions were analyzed comparing these with the Debye–Hückel limiting law. The order of the osmotic coefficient variation is Bu²Et₂N⁺ > BuEt₃N⁺ > sec-Bu₄N⁺ > iso-Bu₄N⁺ > n-Bu₄N⁺. The results were fitted to the Pitzer equation and the parameters β₀ and β₁ were calculated. The results are discussed.