Electroviscous effect of moderately concentrated colloidal suspensions: Stern-layer influence

A previous model for the viscosity of moderately concentrated suspensions has been extended. The influence of a dynamic Stern layer (DSL), which produces an additional surface conductance at the electrolyte-particle interface, is included. The theoretical treatment is based on Happel's cell model with Simha's boundary conditions for the interparticle hydrodynamic interactions and on a dynamic Stern-layer model for ionic conduction on the particle surface according to Mangelsdorf and White (ref 39). The results are valid for arbitrary zeta potentials and double-layer thickness. Extensive theoretical predictions are shown and interesting new behaviors are found. The comparison with the results in the absence of additional surface conductance shows a great influence of this mechanism in the energy dissipation during the laminar flow of these suspensions. We conclude that the inclusion of a dynamic Stern layer will be required to match the predictions with the experimental results.     

Synthesis and catalytic properties of N -functionalised carbene complexes of rhodium(I)

Reaction of [RhCl(COD)]₂, with 1,3-dialkylimidazolinylidene (1) or 1,3-dialkylbenzimidazolinylidene (2) resulted in the formation of rhodium(I) 1,3-dialkylimidazolin-2-ylidene (3a-c) and 1,3-dialkylbenzimidazolin-2-ylidene (4a,b) complexes. Triethylsilane reacts with acetophenone derivatives in the presence of catalytic amounts of RhCl(COD)(1,3-dialkylimidazolin-2-ylidene) or RhCl(COD)(1,3-dialkylbenzimidazolin-2-ylidene) to give the corresponding silylethers in good yield (57–98%).     

Synthesis and photophysicochemical properties of novel mononuclear rhodium(III) phthalocyanines

Chloro axially-substituted octa(4-isopropylphenoxy)rhodium(III)phthalocyanine, (R)₈PcRhCl (3), was reacted with the nitrogenous bases pyridine (Py) and pyrazine (Pyz) to give the axially-disubstituted octa(4-isopropylphenoxy)rhodium(III)phthalocyanines [(R)₈PcRhCl(L)] (4) and (5), L = (Py) and (Pyz), respectively. In this study, the fluorescence quantum yield (Φ_F), the phosphorescence quantum yield (Φ_phos) and the photodegradation quantum yield (Φ_pd) values for the newly synthesized rhodium phthalocyanine complexes (RhPcs) 4 and 5 are reported. The complexes have also been fully characterized by elemental analysis, FD mass spectrometry, FT-IR and ¹H NMR spectroscopy.     

Aggregation in colloidal suspensions and its influence on the suspension viscosity

Influence of aggregate formation on rheological properties of concentrated suspensions is discussed and reviewed. Methods of Stokesian and Brownian dynamic simulations of aggregation are discussed and the results of simulations for both Brownian and non-Brownian particles are presented.     

Some physico-chemical and catalytic properties of nickel(II) oxide promoted with gadolinium(III) oxide

Chemical and phase compositions of NiO–Gd₂O₃ catalysts have been studied. It has been found that the Gd₂O₃ dopant retards the sintering of NiO and increases its deviation from stoichiometry. Catalytic activity for CO oxidation does not change monotonically with an increase in Gd₂O₃ content in the catalysts.

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NiO–Gd₂O₃ . , Gd₂O₃ NiO - . Gd₂O₃ .

     

Mesoporous MgO: Synthesis,physico-chemical,and catalytic properties

Mesoporous MgO was obtained via the hydrothermal synthesis using both ionogenic and non-ionogenic surfactants as structure-directing templates. The materials prepared were characterized by SEM, BET-N₂, XRD, and TG-DTA techniques. MgO particles are spherical 20-μm aggregates of primary oxide particles well shaped as rectangular parallelepipeds. Magnesium oxide samples have the specific surface area of 290–400 m²/g and pore sizes of 3.3–4.1 nm. Their mesoporous structure remained unchanged after calcination up to 350°C. Catalytic activity of mesoporous MgO was studied in acetone condensation reaction.     

Synthesis and catalytic properties of rhodium(I) complexes with anionic chelate nitrogen-oxygen ligands

Summary Dicarbonyl complexes of rhodium(I) [Rh(CO)₂(LL)], where LL = salicylaldoximate, 8-oxyquinolinate, glycinate, leucinate, aminophenolate or pyridine carboxylate and [Rh(COD)(LL)], where COD = 1,5-cyclooctadiene, were prepared and characterized by elemental analysis, and i.r. and n.m.r. spectra. Their activity to catalytic hydroformylation of styrene has been evaluated at atmospheric pressure of COH₂(11).     

Synthesis and catalytic properties of cationic palladium(II) and rhodium(I) complexes bearing diphosphinidinecyclobutene ligands

Cationic palladium(II) and rhodium(I) complexes bearing 1,2-diaryl-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene ligands (DPCB–Y) were prepared and their structures and catalytic activity were examined (aryl = phenyl (DPCB), 4-methoxyphenyl (DPCB–OMe), 4-(trifluoromethyl)phenyl (DPCB–CF₃)). The palladium complexes [Pd(MeCN)₂(DPCB–Y)]X₂ (X = OTf, BF₄, BAr₄ (Ar = 3,5-bis(trifluoromethyl)phenyl)) were prepared by the reactions of DPCB–Y with [Pd(MeCN)₄]X₂, which were generated from Pd(OAc)₂ and HX in MeCN. On the other hand, the rhodium complexes [Rh(MeCN)₂(DPCB–Y)]OTf were prepared by the treatment of [Rh(μ-Cl)(cyclooctene)₂]₂ with DPCB–Y in CH₂Cl₂, followed by treatment with AgOTf in the presence of MeCN. The cationic complexes catalyzed conjugate addition of benzyl carbamate to α,β-unsaturated ketones.     

Influence of poly(ethylene oxide) brushes on the rheological properties of MgO colloidal suspensions in water

A combined experimental and multiscale simulation study of the influence of polymer brush modification on interactions of colloidal particles and rheological properties of dense colloidal suspensions has been conducted. Our colloidal suspension is comprised of polydisperse MgO colloidal particles modified with poly(ethylene oxide) (PEO) brushes in water. The shear stress as a function of shear rate was determined experimentally and from multiscale simulations for a suspension of 0.48 volume fraction colloids at room temperature for both bare and PEO-modified MgO colloids. Bare MgO particles exhibited strong shear thinning behavior and a yield stress on the order of several Pascals in both experiments and simulations. In contrast, simulations of PEO-modified colloids revealed no significant yielding or shear thinning and viscosity only a few times larger than solvent viscosity. This behavior is inconsistent with results obtained from experiments where modification of colloids with PEO brushes formed by adsorption of PEO-based comb-branched chains resulted in relatively little change in suspension rheology compared to bare colloids over the range of concentration of comb-branch additives investigated. We attribute this discrepancy in rheological properties between simulation and experiment for PEO-modified colloidal suspensions to heterogeneous adsorption of the comb-branch polymers.     

Some novel manganese(III) porphyrins with catalytic properties

Abstract

A series of manganese(III) porphyrins with 4-methylimidazole have been prepared. These are high-spin complexes having general formula [Mn^III(THMPP)X(4-MeIm)], where THMP?=?5,10,15,20-tetra(4-hydroxy-3-methoxyphenyl)porphine ligand, X?=?Cl^?, Br^?, NCS^?, or N₃^? and 4-MeIm?=?4-methylimidazole. All the complexes have been characterized by UV-visible, FT-IR, ESI-MS spectra, elemental analyses and magnetic susceptibility measurements. These manganese(III) porphyrins oxidize aromatic alcohols to aldehydes. The oxidation reactions have been carried out at room temperature in the presence of oxidants such as NaIO₄, H₂O₂, and NaOCl. The comparative studies proved that NaIO₄ behaves as the most efficient oxidant in these oxidative transformation reactions.     

Cytotoxic half-sandwich rhodium(III) complexes: Polypyridyl ligand influence on their DNA binding properties and cellular uptake

The DNA binding of polypyridyl (pp) (η⁵-C₅Me₅)Rh^III complexes of the types [(η⁵-C₅Me₅)RhCl(pp)](CF₃SO₃) (2-6) (pp = bpy, phen, dpq, dppz, dppn), [(η⁵-C₅Me₅)Rh{(Me₂N)₂CS}(pp)](CF₃SO₃)₂ (7-9) (pp = dpq, dppz, dppn) and [(η⁵-C₅Me₅)Rh(L)(pp)](CF₃SO₃) (10) (L = C₆H₅S⁻) and (11) (L = C₁₀H₇S⁻) has been studied by UV/Vis spectroscopy, circular dichroismus and viscosity measurements. Complexes 3-11 are cytotoxic towards the human MCF-7 breast and HT-29 colon cancer cell lines and exhibit IC₅₀ values in the range 0.56-10.7 μM. Stable intercalative binding into CT-DNA is indicated for the dpq and dppz complexes by large increases ΔT_m of 6-12 °C in the DNA thermal denaturation temperature for r = [complex]/[DNA] = 0.1 and by induced CD bands and large viscosity increases. In contrast, significant DNA lengthening is not observed after incubation of the biopolymer with the dppn complexes 2 and 9 at molar ratios of r < 0.08. Pronounced hypochromic shifts for the π-π^∗ transitions of the dppn ligands in the range 320-425 nm indicate the possible presence of surface stacking. The in vitro cytotoxicities of the chloro complexes 4-6 and the (Me₂N)₂CS complexes 7-9 are dependent on the size of the polypyridyl ligand with IC₅₀ values decreasing in the order dpq > dppz > dppn. For instance, IC₅₀ values of 5.3, 1.5 and 0.91 μM were determined for 7-9 against MCF-7 cells. Rapid Cl⁻/H₂O exchange leads the formation of aqua dications for 4-6, whose levels of cellular uptake and cytotoxicities are similar to those established for 7-9. Intramolecular interactions between the aromatic thiolate and dppz ligands of 10 and 11 prevent significant DNA intercalation. X-ray structural determinations have been performed for 2-7 and 11.     

Silsesquioxyl rhodium(I) complexes--synthesis, structure and catalytic activity

The first bi- and mononuclear rhodium(I) complexes [{Rh(μ-OSi(8)O(12)(i-Bu)(7))(cod)}(2)] (5), [Rh(cod)(PCy(3))(OSi(8)O(12)(i-Bu)(7))] (6) with a hindered hepta(iso-butyl)silsesquioxyl ligand bonded to the rhodium(I) center through Rh-O-Si bonds have been synthesized and their structures have been solved by spectroscopic methods and X-ray analysis. Their exemplary catalytic properties in silylative coupling of vinylsilanes with styrene are also presented.     

Ligating properties of thionitrosoamines: III. Carbonyl complexes of rhodium(I) and rhodium(III) containing N-thionitrosodimethylamine

Me₂NNS reacts with [Rh(CO)₂Cl]₂ to produce the complex cis-Rh(SNNMe₂)(CO)₂Cl (1). The latter undergoes reversible CO substitution by Me₂NNS to give the complex trans-Rh(SNNMe₂)₂(CO)Cl (2a). Complexes 1 and 2a, in solution lose CO and Me₂NSS, respectively, to give the complex trans-(μ-Cl)₂[Rh(SNNMe₂)(CO)]₂ (3). Complex 1 can also be prepared by bubbling CO through a CH₂Cl₂ solution of Rh(SNNMe₂)(diene)Cl (diene = 1,5-cyclooctadiene (4a), norbornadiene (4b)) obtained by a bridge-splitting reaction of Me₂NNS with [Rh(diene)Cl]₂. 1 and 2a react with EPh₃ (E = P, As, Sb) to give the complexes trans-Rh(EPh₃)₂(CO)Cl. The complexes trans-Rh(E′Ph₃)₂(CO)X (X = Cl, E′ = As, Sb; X = Br, NCS, E′ = As) undergo reversible E′Ph₃ displacement upon treatment with Me₂NNS to give the complexes trans-Rh(SNNMe₂)₂(CO)X (X = Cl (2a), Br (2b), NCS (2c)). Oxidative additions of Br₂, I₂, or HgCl₂ to 2a produce stable adducts, while the reaction of 2a with CH₃I gives an inseparable mixture of the adduct Rh(SNNMe₂)₂(CO)(CH₃)ClI and the acetyl derivative Rh(SNNMe₂)₂(CH₃CO)ClI. A mixture of the acetyl derivative (μ-Cl)₂[Rh(SNNMe₂)(CH₃CO)I]₂ and the adduct (μ-Cl)₂[Rh(SNNMe₂)(CO)(CH₃)I]₂ is obtained by treating 1 with CH₃I. The IR spectra of all the compounds are consistent with S-coordination of Me₂NNS. Because of the restricted rotation around the NN bond, the ¹H NMR spectra of the new compounds exhibit two quadruplets in the range 3.5–4.3δ when ⁴J(HH) = 0.7–0.5 Hz. When ⁴J(HH) < 0.5 Hz, the perturbing effect of the quadrupolar relaxation of the ¹⁴N nucleus obscures the spin-spin coupling and two broad signals are observed in the range 3.6–4δ.     

Ion size effects on the dielectric and electrokinetic properties in aqueous colloidal suspensions

One of the main assumptions of the classical theory most widely used to characterize electrokinetic phenomena is that ions behave as point-like entities. While the realization of the importance of the finite ion size goes back to Stern, 1924, it was Bikerman who presented in 1942 the first expression for the steric interactions among ions. Even now, this is the most often used expression, mainly due to its analytic simplicity. However, once ions are considered to have a finite size, other consequences besides the steric interactions have to be considered. For example, the finite closest approach distance of ions to the interface, the dielectrophoretic force acting on ions in a non-uniform electric field, the variation of the electrolyte solution permittivity with the local ion concentration, and the corresponding Born force acting on the ions, have to be taken into account. In this work, we examine these items in detail and discuss the main contributions made in this field. They show that even for the relatively low surface charge and electrolyte concentration values encountered in colloidal suspension studies, corrections to the classical theory due to ion size effects are far from negligible.     

Thermal properties of rhodium(III) chloride

Thermal decomposition of rhodium(III) chloride under inert, oxidative and reductive gas atmospheres was investigated in order to determine its thermal properties. Stoichiometries of the reactions occurring during heating are described. it is suggested that the chemical formula of soluble rhodium(III) chloride should be presented as RhCl₃·HCL·xH₂O. Cold crystallisation of anhydrous rhodium(III) chloride at a temperature of about 500°C was established. The procedure for quantitative determination of volatile matter (water and hydrochloric acid) content and rhodium content by thermogravimetry is given and discussed. The repeatability and reproducibility of the method are estimated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis, structure, and catalytic properties of polymer-immobilized rhodium clusters

Immobilized Rh₆ clusters (cyclohexene hydrogenation catalysts) were prepared by the polymer-analogous transformations or copolymerization of cluster-containing monomers and characterized. Intermediates formed in the course of a catalytic reaction were studied using IR spectroscopy, XPS, and atomic force microscopy. It was found that the relative intensity of a low-energy line in the Rh3d _5/2 spectrum of the initial polymer-immobilized cluster in the XPS spectrum of Rh₆ increased in the course of hydrogenation. The catalytic activity of the immobilized complex changed symbatically with both the number of Rh atoms bound to the H(CO) group and the number of Rh atoms, the charge on which was greater than that in the parent cluster. Some experimental evidence was obtained in favor of the hypothesis of cluster fragmentation in the course of hydrogenation with the formation of highly active, most likely, nanosized particles, which are true catalysts, in low concentrations. The surface of macrocomplex particles after hydrogenation became more homogeneous and hydrophilic; this fact is also indicative of an increase in the concentration of polar functional groups in surface layers. This was likely due to Rh-Rh bond cleavage in the polymer-immobilized cluster.     

1,4-dicyanobutene-bridged binuclear rhodium(I) complexes and their catalytic activities

Reactions of Rh(ClO₄)(CO)(PPh₃)₂ with dicyano olefins, cis-NCCHCH-CH₂CH₂CN (c-DC1B), rans-NCCHCHCH₂CH₂CN (t-DC1B), trans-NCCH₂CHCHCH₂CN (t-DC2B), and NCCH₂CH₂CH₂CN (DCB) produce the binuclear dicationic rhodium(I) complexes, [(CO)(PPh₃)₂RhNCACNRh-(PPh₃)₂(CO)](ClO₄)₂ (NCACN = c-DC1B 1), t-DC1B (2), t-DC2B (3), DCB (4). Complexes 1 and 2 are catalytically active for the hydrognation of c-DC1B and t-DC1B, respectively, to give DCB, while complex 3 catalyze the isomerization of t-DC2B to give c-DC1B and t-DC1B, and the hydrogenation of t-DC2B to DCB at 100°C.     

Synthesis and structural properties of a series of pentacoordinate rhodium nitrosyl complexes: Crystal and molecular structures of cis-dibromonitrosylbis(methoxydiphenylphosphine)rhodium and trans-dibromonitrosylbis(iso-propoxydiphenylphosphine)rhodium

The pentacoordinate rhodium nitrosyl complexes [RhBr₂(NO)L₂ [L = P(OPh)₂Ph, P(OMe)Ph₂ or P(OPrⁱ)Ph₂] have been synthesized and the structures of [RhBr₂(NO){P(OMe)Ph₂}₂] and [RhBr₂(NO){P(OPrⁱ)Ph₂}₂] have been determined X-ray crystallographically. Both of these latter compounds are tetragonal pyramidal with the nitrosyl group apical. The methoxydiphenylphosphine ligands in [RhBr₂(NO){P(OMe)Ph₂}₂] are cis-disposed whereas the larger cis-propoxydiphenylphosphine ligands in [RhBr₂(NO){P(OPrⁱ)Ph₂}₂] are mutually trans. The nitrosyl group in trans-[RhBr₂(NO){P(OPrⁱ)Ph₂}₂] eclipses an Rh-P axis but in cis-[RhBr₂(NO){P(OMe)Ph₂}₂] it is staggered with respect to the P-Rh-P linkage. The isomeric behaviour of nitrosyl complexes of type [RhX₂(NO)L₂] (X = halogen, L = phosphorus donor ligand) is rationalized in terms of the size of the ligand L.