Chemistry of dihydrogen complexes containing only phosphorus co-ligands

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2) (dppm = Ph2PCH2PPh2; L = phosphite) have been prepared by protonating the precursor hydride complexes cis-[(dPPM)(2)Ru(H)(L)][BF4] using HBF4.Et2O. The precursor hydride complexes have been obtained from trans-[(dppm)(2)Ru(H)(L)][BF4][(L = phospfiite) via a rare acid-catalysed isomerization reaction in six coordinate species. The trans-[(dppm)(2)Ru(H)(L)][BF4] complexes (L = phosphine) upon protonation gave the isomerized derivatives, however, further addition of acid resulted in a five-coordinate species, [(dppm)(2)RuCl](+) presumably via an intermediate phosphine dihydrogen complex. The electronic as well as the steric properties of the co-ligands seem to strongly influence the structure-reactivity behaviour of this series of complexes.

Dendritic encapsulation of amino acid-metal complexes. Synthesis and studies of dendron-functionalized L-tyrosine-metal (Zn-II, Co-II) complexes

This paper describes the synthesis, characterization and studies of dendrimers possessing an amino acid-metal complex as the core. Using Frechet-type polyaryl ether dendrons, L-tyrosine-metal (Zn-II and Co-II) complex cored dendrimers of 0-4 generations were synthesized. The metal complexation of the tyrosine unit at the focal point of these dendrons took place smoothly, in excellent yields, even though the sizes of the dendrons increase as the generations advance. Spectrophotometric titrations with CoII metal ion confirmed the formation of a 2 : 1 dendritic ligand to metal complex and the existence of a pseudotetrahedral geometry at the metal centre is also inferred. Cyclic voltammetric studies of dendrimer-Co-II complexes showed that while the electron transfer of Co-II to Co-I was facile for generations 0-2, such a process was difficult with generations 3 and 4, indicating a rigid encapsulation of the metal ion centre by proximal dendron groups. Further reduction of Co-I to Co-0 and the corresponding oxidation processes appear to be limited by adsorption at the surfaces of the electrodes.

Effect of molecular association and reactivity on substitution in chromium(III)-salprn complexes

A new chromium(III)-Schiff base complex, [Cr(5-chlorosalprn)(H2O)(2)]ClO4, where salprn=N,N'-propylenebis(salicylideneimine) has been prepared and characterized by electrospray ionization mass spectrometric (ESIMS) analysis and other spectroscopic techniques. Single crystal X-ray data reveal that the complex assumes a trans-diaquo structure, [Cr(C17H18Cl2N2O4)]ClO4.H2O. The effect of phenyl ring substituents on the rate of formation of [O=Cr-V Schiff base](+) has been investigated. The bimolecular rate constant for the formation of O=Cr-V species by the [Cr(Schiff base)(H2O)(2)]ClO4, where the Schiff base=salprn, (1) and 5-chlorosalprn, (2) with PhOI was compared. In the case of (2) the rate was found to be faster by an order of magnitude at pH=4 compared to (1). The introduction of a chloro-substituent on the phenyl ring not only influences the rate of redox reactivity but also the pKa values of aquo ligands of the complexes, indicating the difference in the electronic environment around the metal ion in both (1) and (2).

Half-sandwich (eta(6)-arene)ruthenium(II) chiral Schiff base complexes: Analysis of the diastereomeric mixtures in solution by 2D-NMR spectroscopy

2D NMR spectroscopy has been used to determine the metal configuration in solution of three complexes, viz. [(eta(6)-p-cymene)Ru(L*)Cl] (1) and [(eta(6)-p-cymene)Ru(L*)(L')] (ClO4) (L' = H2O, 2; PPh3, 3), where L* is the anion of (S)-(1-phenylethyl)salicylaldimine. The complexes exist in two diastereomeric forms in solution. Both the (R-Ru,S-C)- and (S-Ru,S-C)-diastereomers display the presence of attractive, CH/pi interaction involving the phenyl group attached to the chiral carbon and the cymene ring hydrogens. This interaction restricts the rotation of the C*-N single bond and, as a result, two structural types with either the hydrogen atom attached to the chiral carbon (C*) or the methyl group attached to C* in close proximity of the cymene ring protons get stabilized. Using 2D NMR spectroscopy as a tool, the spatial interaction involving these protons are studied in order to obtain the metal configuration(s) of the diastereomeric complexes in solution. This technique has enabled us to determine the metal configuration as (R-Ru,S-C) for the major isomers of 1-3 in solution.

Organometallic chemistry of diphosphazanes. Part 15. Half-sandwich cyclopentadienyl ruthenium complexes of achiral and chiral diphosphazanes

Reaction of [CpRu(PPh3)(2)Cl] (1) {Cp = eta(5)-(C5H5)} with X2PN(CHMe2) PYY' {X = Y = Y' = Ph (L-1); X = Y = Ph, Y' = OC6H4Me-4 (L-4); X = Y = Ph, Y' = OC6H3Me2- 3,5 (L-5); X = Y = Ph, Y' = N2C3HMe2 (L-6)} yields the cationic chelate complexes, [CpRu(eta(2)-(X2PN(CHMe2) PYY')) PPh3] Cl. On the other hand, the reaction of 1 with X2PN(CHMe2)PYY' {X = Ph, YY' = O2C6H4(L-3)} gives the complex, [CpRu(eta(1)-L-2)(2)PPh3] Cl. Both types of complexes are formed with X2PN(CHMe2) PYY' {X = Ph, YY' = O2C6H4 (L-3)}. The reaction of 1 with (R),(S)-(H12C20O2) PN(CHMe2) PPh2 (L-7) yields both cationic and neutral complexes, [CpRu{eta(2)-(L-7)} PPh3] Cl and [CpRu{eta(1)-(L-7)}(2)PPh3] Cl and [CpRu{eta(2)-(L-7)}Cl]. The reactions of optically pure diphosphazane, Ph2PN(*CHMePh) PPhY (Y = Ph (L-8); Y = N2C3HMe2-3,5 (L-9)) with 1 give the neutral and cationic ruthenium complexes, [CpRu{eta(2)-(Ph2PN(R) PPhY)} Cl] and [CpRu{eta(2)-(Ph2PN(R)PPhY)} PPh3] Cl. "Chiral-at-metal" ruthenium complexes of diphosphazanes have been synthesized with high diastereoselectivity. The absolute configuration of a novel ruthenium complex, (SCSPRRu)-[(eta(5)-C5H5) Ru*{eta(2)-(Ph2PN(*CHMePh)P*Ph( N2C3HMe2-3,5))} Cl] possessing three chiral centers, is established by X-ray crystallography. The reactions of [CpRu{eta(2)-(L-8)} Cl] with mono or diphosphanes in the presence of NH4PF6 yield the cationic complexes, [CpRu{eta(2)-(L-8)}{eta(1)-(P)}] PF6 {P = P(OMe)(3), PPh3, Ph2P(CH2)(n)PPh2 (n = 1 or 2)}.

Systematic trends in structural and thermodynamic properties of ternary oxides in the systems Ln-Pd-O (Ln = lanthanide element)

Isothermal sections of the phase diagrams for the systems Ln-Pd-O (Ln = lanthanide element) at 1223 K indicate the presence of two inter-oxide compounds Ln(4)PdO(7) and Ln(2)Pd(2)O(5) for Ln = La, Pr, Nd, Sm, three compounds Ln(4)PdO(7), Ln(2)PdO(4) and Ln(2)Pd(2)O(5) for Ln = Eu, Gd and only one compound of Ln(2)Pd(2)O(5) for Ln = Tb to Ho. The lattice parameters of the compounds Ln(4)PdO(7), Ln(2)PdO(4) and Ln(2)Pd(2)O(5) show systematic nonlinear variation with atomic number. The unit cell volumes decrease with increasing atomic number. The standard Gibbs energies, enthalpies and entropies of formation of the ternary oxides from their component binary oxides (Ln(2)O(3) and PdO) have been measured recently using an advanced version of the solid-state electrochemical cell. The Gibbs energies and enthalpies of formation become less negative with increasing atomic number of Ln. For all the three compounds, the variation in Gibbs energy and enthalpy of formation with atomic number is markedly non-linear. The decrease in stability with atomic number is most pronounced for Ln(2)Pd(2)O(5), followed by Ln(4)PdO(7) and Ln(2)PdO(4). This is probably related to the repulsion between Pd2+ ions on the opposite phases Of O-8 cubes in Ln(2)Pd(2)O(5), and the presence of Ln-filled O-8 cubes that share three faces with each other in Ln4PdO7. The values for entropy of formation of all the ternary oxides from their component binary oxides are relatively small. Although the entropies of formation show some scatter, the average value for Ln = La, Pr, Nd is more negative than the average value for the other lanthanide elements. From this difference, an average value for the structure transformation entropy of Ln(2)O(3) from C-type to A-type is estimated as 0.87 J.mol(-1).K-1. The standard Gibbs energies of formation of these ternary oxides from elements at 1223 K are presented as a function of lanthanide atomic number. By invoking the Neumann-Kopp rule for heat capacity, thermodynamic properties of the inter-oxide compounds at 298.15 K are estimated. (C) 2002 Elsevier Science Ltd. All rights reserved.

System Dy-Fe-O: thermodynamic properties of ternary oxides using Calvet calorimetry and solid-state electrochemical cell

The enthalpy increments and the standard molar Gibbs energies of formation-of DyFeO3(s) and Dy3Fe5O12(s) have been measured using a Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. A co-operative phase transition, related to anti-ferromagnetic to paramagnetic transformation, is apparent. from the heat capacity data for DyFeO3 at similar to 648 K. A similar type of phase transition has been observed for Dy3Fe5O12 at similar to 560 K which is related to ferrimagnetic to paramagnetic transformation. Enthalpy increment data for DyFeO3(s) and Dy3Fe5O12(s), except in the vicinity of the second-order transition, can be represented by the following polynomial expressions:{H(0)m(T) - H(0)m(298.15 K)) (Jmol(-1)) (+/-1.1%) = -52754 + 142.9 x (T (K)) + 2.48 x 10(-3) x (T (K))(2) + 2.951 x 10(6) x (T (K))(-1); (298.15 less than or equal to T (K) less than or equal to 1000) for DyFeO3(s), and {H(0)m(T) - H(0)m(298.15 K)} (Jmol(-1)) (+/-1.2%) = -191048 + 545.0 x (T - (K)) + 2.0 x 10(-5) x (T (K))(2) + 8.513 x 10(6) x (T (K))(-1); (208.15 less than or equal to T (K) less than or equal to 1000)for Dy3Fe5O12(s). The reversible emfs of the solid-state electrochemical cells: (-)Pt/{DyFeO3(s) + Dy2O3(s) + Fe(s)}/YDT/CSZ//{Fe(s) + Fe0.95O(s)}/Pt(+) and (-)Pt/{Fe(s) + Fe0.95O(s)}//CSZ//{DyFeO3(s) + Dy3Fe5O12(s) + Fe3O4(s)}/Pt(+), were measured in the temperature range from 1021 to 1250 K and 1035 to 1250 K, respectively. The standard Gibbs energies of formation of solid DyFeO3 and Dy3Fe5O12 calculated by the least squares regression analysis of the data obtained in the present study, and data for Fe0.95O and Dy2O3 from the literature, are given by Delta(f)G(0)m(DyFeO3,s)(kJmol(-1))(+/-3.2)= -1339.9 + 0.2473 x (T(K)); (1021 less than or equal to T (K) less than or equal to 1548)and D(f)G(0)m(Dy3Fe5O12,s) (kJmol(-1)) (+/-3.5) = -4850.4 + 0.9846 x (T (K)); (1035 less than or equal to T (K) less than or equal to 1250) The uncertainty estimates for Delta(f)G(0)m include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagram and chemical potential diagrams for the system Dy-Fe-O were developed at 1250 K. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

The first bis(phosphine) monoxide (BPMO) complexes of copper(I)

Copper(l) complexes of bis(phosphine) monoxide ligands, bis(diphenylphosphino)ethane monoxide (dppeo) and bis(diphenylphosphino)methane monoxide (dppmo) have been prepared and characterized. One of the complexes with dppeo was characterized by X-ray crystal structure analysis confirming Cu(I) coordination to hard and soft donors. The stability of these complexes in solution was probed via spectroscopic and electrochemical studies. Copper(I) is more readily oxidized in the presence of the hard 0 donor ligands. In solution, they readily exchange the hard donor O, for soft ligands. Although copper(l) prefers soft ligands and is more stable towards oxidation in their presence, it coordinates to hard donors when there is electrostatic or an entropy driven advantage. (C) 2002 Elsevier Science Ltd. All rights reserved.

Synthesis, crystal structure and catalytic properties of (p-cymene)ruthenium(II) azophenol complexes: azophenyl to azophenol conversion by oxygen insertion to a ruthenium---carbon bond

Azophenol complexes of formulation [(η6-p-cymene)RuCl(Ln)] (1–6, n=1–6) were prepared by two synthetic methods involving either an oxygen insertion to the Ru---C bond in cycloruthenated precursors forming complexes 1 and 2 or from the reaction of [{(η6-p-cymene)RuCl}2(μ-Cl)2] with azophenol ligands (HL3–HL6) in the presence of sodium carbonate in CH2Cl2. The molecular structure of the 1-(phenylazo)-2-naphthol complex has been determined by X-ray crystallography. The complex has a η6-p-cymene group, a chloride and a bidentate N,O-donor azophenol ligand. The complexes have been characterized from NMR spectral data. The catalytic activity of the complexes has been studied for the conversion of acetophenone to the corresponding alcohol in the presence of KOH and isopropanol. Complexes 4 and 6 having a methoxy group attached to the ortho-position of the phenylazo moiety and 2 with a methyl group in the meta-position of the phenolic moiety show high percentage conversion (>84%).

Propensity of formation of zipper architecture vs. Lincoln log arrangement in solvated molecular complexes of melamine with hydroxybenzoic acids

Molecular complexes of melamine with hydroxy and dihydroxybenzoic acids have been analyzed to assess the collective role of the hydroxyl (OH) and carboxyl (COOH) functionalities in the recognition process. In most cases, solvents of crystallization do play a major role in self-assembly and structure stabilization. Hydrated compounds generate linear chains of melamine molecules with acid molecules pendant resulting in a zipper architecture. However, anhydrous and solvated compounds generate tetrameric units consisting of melamine dimers together with acid molecules. These tetramers in turn interweave to form a Lincoln log arrangement in the crystal. The salt/co-crystal formation in these complexes cannot be predicted apriori on the basis of Delta pK(a) values as there exists a salt-to-co-crystal continuum.

A study of phase separation in ternary alloys

We have studied the evolution of microstructure when a disordered ternary alloy is quenched into a ternary miscibility gap. We have used computer simulations based on multicomponent Cahn-Hilliard (CH) equations for c(A) and c(B), the compositions (in mole fraction) of A and B, respectively. In this work, we present our results on the effect of relative interfacial energies on the temporal evolution of morphologies during spinodal phase separation of an alloy with average composition, c(A) = 1/4, c(B) = 1/4 and c(C) = 1/2. Interfacial energies between the 'A' rich, 'B' rich and 'C' rich phases are varied by changing the gradient energy coefficients. The phases associated with a higher interfacial energy are found to be more rounded than those with lower energy. Further, the kinetic paths (i.e. the history of A-rich, B-rich and C-rich regions in the microstructure) are also affected significantly by the relative interfacial energies of the three phases.

Nanocrystallisation and Nanoquasicrystallisation in (Ti/Hf)-Zr-(Ni/Cu) Ternary Alloys

The applicability of the confusion principle and size factor in glass formation has been explored by following different combinations of isoelectronic Ti, Zr and Hf metals. Four alloys of nominal composition Zr41.5Ti41.5Ni17, Zr41.5Hf41.5Ni17, Zr25Ti25Cu50 and Zr34Ti16Cu50 have been rapidly solidified to obtain an amorphous phase and their crystallisation behaviour has been studied. The Ti-Zr-Ni alloy crystallises in three steps. Initially this alloy precipitates icosahedral quasicrystalline phase, which on further heat treatment precipitates cF96 Zr2Ni phase. The Zr-Hf-Ni alloy can not be amorphised under the same experimental conditions. The amorphous Zr-Ti-Cu alloys at the initial stages of crystallisation phase-separateinto two amorphous phases and then on further heat treatment cF24 Cu5Zr and oC68 Cu10Zr7 phase are precipitated. The lower glass-forming abilityof Zr-Hf-Ni alloy and the crystallisation behaviour of the above alloys has been studied. The rationale behind nanoquasicrystallisation and the formation of other intermetallic phases has been explained.

Surfactant-mediated Synthesis of Functional Metal Oxide Nanostructures via Microwave Irradiation-assisted Chemical Synthesis

Nanostructured materials have attracted considerable interest in recent years due to their properties which differ strongly from their bulk phase and potential applications in nanoscale electronic and optoelectronic devices. Metal oxide nanostructures can be synthesized by variety of different synthesis techniques developed in recent years such as thermal decomposition, sol-gel technique, chemical coprecipitation, hydrothermal process, solvothermal process, spray pyrolysis, polyol process etc. All the above processes go through a tedious synthesis procedure followed by prolonged heat treatment at elevated temperature and are time consuming. In the present work we describe a rapid microwave irradiation-assisted chemical synthesis technique for the growth of nanoparticles, nanorods, and nanotubes of a variety of metal oxides in the presence of an appropriate surfactant, without the use of any templates The method is simple, inexpensive, and helps one to prepare nanostructures in a very simple way, and in a very short time, measured in minutes. The synthesis procedure employs high quality metalorganic complexes (typically -diketonates) featuring a direct metal-to-oxygen bond in its molecular structure. The complex is dissolved in a suitable solvent, often with a surfactant added, and the solution then subjected to microwave irradiation in a domestic microwave oven operating at 2.45 GHz frequency with power varying from 160-800 W, from a few seconds to a few minutes, leading to the formation of corresponding metal oxides. This method has been used successfully to synthesize nanostructures of a variety of binary and ternary metal oxides such as ZnO, CdO, Fe2O3, CuO, Ga2O3, Gd2O3, ZnFe2O4, etc. There is an observed variation in the morphology of the nanostructures with the change of different parameters such as microwave power, irradiation time, appropriate solvent, surfactant type and concentration. Cationic, anionic, nonionic and polymeric surfactants have been used to generate a variety of nanostructures. Even so, to remove the surfactant, there is either no need of heat treatment or a very brief exposure to heat suffices, to yield highly pure and crystalline oxide materials as prepared. By adducting the metal complexes, the shape of the nanostructures can be controlled further. In this manner, very well formed, single-crystalline, hexagonal nanorods and nanotubes of ZnO have been formed. Adducting the zinc complex leads to the formation of tapered ZnO nanorods with a very fine tip, suitable for electron emission applications. Particle size and their monodispersity can be controlled by a suitable choice of a precursor complex, the surfactant, and its concentration. The resulting metal oxide nanostructures have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, FTIR spectroscopy, photoluminescence, and electron emission measurements.

Efficient visible light induced nuclease activity of a ternary mono-1,10-phenanthroline copper(II) complex containing 2-(methylthio)ethylsalicylaidimine

Ternary Schiff base copper(II) complex [CuL(phen)](ClO4), where HL is 2-(methylthio)ethylsalicylaldimine and phen is 1,10-phenanthroline, has been prepared and structurally characterized by X-ray crystallography. The complex shows a CuN3OS coordination in a square-pyramidal (4 + 1) geometry with the sulfur as an equatorial ligand. The complex is an avid binder to double-stranded DNA in the minor groove and exhibits both photonuclease and chemical nuclease activity. When exposed to UV light of 312 nm (96 W) or visible light of 532 nm (125 W) under aerobic conditions, the complex causes significant cleavage of supercoiled pUC19 DNA in the absence of any externally added reducing agent or H2O2.