Organometallic chemistry of diphosphazanes. Part 7. Platinum(II), palladium-(o), -(I) and -(II) complexes of RN[P(OPh)2]2(R = Me or Ph)

The reactions of [MCl2(cod)](M = Pd or Pt, cod = cycloocta-1,5-diene) with RN[P(OPh)2]2[R = Me (L1) or Ph (L2)] afford the chelate complexes [MCl2L1] and [MCl2L2]. The dinuclear palladium(O) complex, [Pd2L13] has been synthesized by starting from [Pd2(dba)3](dba = dibenzylideneacetone). Redox condensation of [Pd2(dba)3] and [PdCl2(PhCN)2] in the presence of the diphosphazane ligands gives the dinuclear palladium(I) complexes [Pd2Cl2L12] and [Pd2Cl2L22]. The structures of the complexes have been deduced from 1H and 31P NMR spectroscopic data. Single-crystal X-ray diffraction studies confirm the structures of [Pd2L13] and [Pd2Cl2L22].

Palladium(II) chloride complexes of bis(pyrazolyl)cyclotriphosphazenes

Reactions of the bis(3,5-dimethylpyrazolyl)cyclotriphosphazene derivatives gem-N3P3(MeNCH(2)CH(2)O)(2)(dmp)(2) (1) and nongeminal cis-N3P3(OPh)(4)(dmp)(2) (2) with PdCl2 afford complexes of the type [PdCl2.(L)] (L = 1 or 2). In these complexes, the phosphazenes act as bidentate NN-donor ligands with the two pyrazolyl pyridinic nitrogen atoms bonded to the metal, thus forming a six- and an eight-membered chelate ring, respectively. The structures of 2 and [PdCl2.(2)] (4) have been confirmed by single-crystal X-ray diffraction. Crystal data for 2: a = 16.759(2) Angstrom, b = 10.788(3) Angstrom, c = 19.635(9) Angstrom, beta = 101.61(3)degrees, P2(1/c), Z = 4, R = 0.038 for 4688 reflections with F > 5 sigma(F). Crystal data for 4: a = 9.701(3) Angstrom, b = 24.853(4) Angstrom, c = 15.794(4) Angstrom, beta = 101.46(2)degrees, P2(1/n), Z = 4, R = 0.030 for 5416 reflections with F > 5 sigma(F).

Protonation of polyaniline and its polyelectrolyte complexes at different ionic strength: contribution of Donnan effect

UV-visible spectra of polyaniline and its polyelectrolyte complexes show evidence for different degree of protonation when equilibrated with different ionic strength at a particular pH, due to the Donnan effect. For pure polyaniline, when the fixed charge on the film is positive, protonation is higher ionic strength whereas, when the polyaniline is doped with a polyelectrolyte resulting in a net negative fixed charge on the film, the protonation is less at higher ionic strength.

Reaction of spironaphthalenones with hydroxylamine: Part III. A novel mechanism for the formation of products and trapping of an intermediate.

A mechanism involving the intermediacy of nitrene 5, formed from the oxime of spironaphthalenone 1 by acid catalysed dehydration, has been proposed to explain the formation of pyrrolotropones/pyrrolo esters from spironaphthalenones. The initially formed nitrene rearranges to the isopyrrole 6, which either undergoes sigmatropic migration to the pyrrolotropone 2 or adds alcohol to form the pyrrolo ester depending on substitution at 1′ position. The isopyrrole intermediate 6 has been trapped as a Diels-Alder adduct 8.

Reactions of copper(I) aryloxides with phenyl isothiocyanate: steric and ligand control in the oligomerization of [N-phenylimino(aryloxy)methanethiolato]copper(I) complexes

The preparation of five different copper(I) complexes [CuSC(=NPh)(OAr)}L(n)]m (1-5) formed by the insertion of PhNCS into the Cu-OAr bond and the crystal structure analyses of three of them have been carried out. A monomeric species 1 (OAr = 2,6-dimethylphenoxide) is formed in the presence of excess PPh3 (n = 2, m = 1) and crystallizes as triclinic crystals with a = 12.419(4) angstrom, b = 13.298(7) angstrom, c = 15.936(3) angstrom, alpha = 67.09(3)-degrees, beta = 81.63(2)-degrees, gamma = 66.54(3)-degrees, V = 2224(2) angstrom3, and Z = 2. The structure was refined by the least-squares method to final R and R(w) values of 0.038 and 0.044, respectively, for 7186 unique reflections. Copper(I) 2,5-di-tert-butyl-4-methylphenoxide results in the formation of a dimeric species 2 in the presence of P(OMe)3 (n = 1, m = 2), where the coordination around Cu is trigonal. Crystals of 2 were found to be orthorhombic with a = 15.691(2) angstrom, b = 18.216(3) angstrom, c = 39.198(5) angstrom, v = 11204(3) angstrom3, and Z = 8. Least-squares refinement gave final residuals of R = 0.05 and R(w) = 0.057 with 6866 unique reflections. A tetrameric species 3 results when PPh3 is replaced by P(OMe)3 in the coordination sphere of copper(I) 2,6-dimethylphenoxide. It crystallizes in the space group P1BAR with a = 11.681 (1) angstrom, b = 13.373(2) angstrom, c = 20.127(1) angstrom, a = 88.55(l)-degrees, beta = 89.65(l)-degrees, gamma = 69.28(1)-degrees, V = 2940(l) angstrom3, and Z = 2. Least-squares refinement of the structure gave final values of 0.043 and 0.05 for R and R(w) respectively using 12214 unique reflections. In addition, a dimeric species 4 is formed when 1 equiv of PPh3 is added to the copper(I) 4-methylphenoxide, while with an excess of PPh3 a monomeric species 5 is isolated. Some interconversions among these complexes are also reported.

Swellability properties of polyelectrolyte complexes of polyaniline

Polyelectrolyte complexes of polyaniline with both strong and weak anionic polyelectrolytes have been prepared. It has been found that the swellability of the complexes depends on the charge content of polyaniline, i.e., on the intercrosslinking between polyaniline (which is a polyacation) and polyanions. It has also been observed that polyaniline in the polyaniline-polystresulfonic acid complex exists in the conducting state when equilibrated with basic pH in aqueous media of moderately high ionic strength.

The effects of charge density and concentration on the composition of polyelectrolyte complexes

Polyelectrolyte complex formation involving carboxymethylcellulose and quaternized poly(vinylpyridine) as the polyions has been studied using viscosity and u.v. spectroscopic methods. The influence of charge density and molecular weight of two polycations on the composition of the complex has been investigated at two different concentrations. The charge density of the polycation is found to have different influences on the composition at different concentrations. The molecular weight of the polycation and the location of the ionic site on the polycation do not show any effect on the composition. A drastic increase in the viscosity of the polyion mixture containing quaternized poly(2-vinylpyridine) in the non-stoichiometric ratio shows evidence for the existence of the soluble polyelectrolyte complex. The results are analysed on the basis of the relative extension of the polyelectrolyte chains.

The Exchange Processes in Zinc-Complexes of o-Vanillin Salicyloylhydrazone as studied by 2-Dimensional NMR

Zinc forms two types of complexes with o-vanillin salicyloylhydrazone. The H-1 and C-13 nmr studies suggest that it coordinates with azomethine nitrogen, the carbonyl oxygen and with one or both of the phenolic oxygens. The H-1-H-1 and H-1 decoupled C-13-C-13 two-dimensional nuclear Overhauser and exchange spectra show that there is an exchange between the two types of complexes.

(Ba3MTiMO9)-Ti-III-O-V (M-III = Fe, Ga, Y, Lu, M-V = Nb, Ta, Sb) perovskite oxides Synthesis, structure and dielectric properties

We describe the synthesis structures and dielectric properties of new perovskite oxides of the formula (Ba3MTiMO9)-Ti-III-O-V for M-III = Fe Ga Y Lu and M-V = Nb Ta Sb While M-V = Nb and Ta oxides adopt disordered/partially ordered 3C perovskite structures where M-III/Ti/M-V metal-oxygen octahedra are corner connected the M-V = Sb oxides show a distinct preference for the 6H structure where Sb-V/Ti-IV metal-oxygen octahedra share a common face forming (Sb Ti)O-9 dimers that are corner-connected to the (MO6)-O-III octahedra The preference of antimony oxides (Sb-V 4d(10)) for the 6H structure which arises from a special Sb-V-O chemical bonding that tends to avoid linear Sb-O-Sb linkages unlike Nb-V/Ta-V d(0) atoms which prefer similar to 180 degrees Nb/Ta-O-Nb/Ta linkages - is consistent with the crystal chemistry of M-V-O oxides in general The dielectric properties reveal a significant difference among Mill members All the oxides with the 3C structure excepting those with Mill = Fe show a normal low loss dielectric behaviour with epsilon = 20-60 in the temperature range 50-400 degrees C the M-III = Fe members with this structure (M-V = Nb Ta) display a relaxor-like ferroelectric behaviour with large E values at frequencies <= 1 MHz (50-500 degrees C) (C) 2010 Elsevier Masson SAS All rights reserved

Geometry and quadratic nonlinearity of charge transfer complexes in solution using depolarized hyper-Rayleigh scattering

We report large quadratic nonlinearity in a series of 1:1 molecular complexes between methyl substituted benzene donors and quinone acceptors in solution. The first hyperpolarizability, beta(HRS), which is very small for the individual components, becomes large by intermolecular charge transfer (CT) interaction between the donor and the acceptor in the complex. In addition, we have investigated the geometry of these CT complexes in solution using polarization resolved hyper-Rayleigh scattering (HRS). Using linearly (electric field vector along X direction) and circularly polarized incident light, respectively, we have measured two macroscopic depolarization ratios D = I-2 omega,I-X,I-X/I-2 omega,I-Z,I-X and D' = I-2 omega,I-X,I-C/I-2 omega,I-Z,I-C in the laboratory fixed XYZ frame by detecting the second harmonic scattered light in a polarization resolved fashion. The experimentally obtained first hyperpolarizability, beta(HRS), and the value of macroscopic depolarization ratios, D and D', are then matched with the theoretically deduced values from single and double configuration interaction calculations performed using the Zerner's intermediate neglect of differential overlap self-consistent reaction field technique. In solution, since several geometries are possible, we have carried out calculations by rotating the acceptor moiety around three different axes keeping the donor molecule fixed at an optimized geometry. These rotations give us the theoretical beta(HRS), D and D' values as a function of the geometry of the complex. The calculated beta(HRS), D, and D' values that closely match with the experimental values, give the dominant equilibrium geometry in solution. All the CT complexes between methyl benzenes and chloranil or 1,2-dichloro-4,5-dicyano-p-benzoquinone investigated here are found to have a slipped parallel stacking of the donors and the acceptors. Furthermore, the geometries are staggered and in some pairs, a twist angle as high as 30 degrees is observed. Thus, we have demonstrated in this paper that the polarization resolved HRS technique along with theoretical calculations can unravel the geometry of CT complexes in solution. (C) 2011 American Institute of Physics. doi:10.1063/1.3514922]

Geometry and quadratic nonlinearity of charge transfer complexes in solution: A theoretical study

In this paper, we have computed the quadratic nonlinear optical (NLO) properties of a class of weak charge transfer (CT) complexes. These weak complexes are formed when the methyl substituted benzenes (donors) are added to strong acceptors like chloranil (CHL) or di-chloro-di-cyano benzoquinone (DDQ) in chloroform or in dichloromethane. The formation of such complexes is manifested by the presence of a broad absorption maximum in the visible range of the spectrum where neither the donor nor the acceptor absorbs. The appearance of this visible band is due to CT interactions, which result in strong NLO responses. We have employed the semiempirical intermediate neglect of differential overlap (INDO/S) Hamiltonian to calculate the energy levels of these CT complexes using single and double configuration interaction (SDCI). The solvent effects are taken into account by using the self-consistent reaction field (SCRF) scheme. The geometry of the complex is obtained by exploring different relative molecular geometries by rotating the acceptor with respect to the fixed donor about three different axes. The theoretical geometry that best fits the experimental energy gaps, beta(HRS) and macroscopic depolarization ratios is taken to be the most probable geometry of the complex. Our studies show that the most probable geometry of these complexes in solution is the parallel displaced structure with a significant twist in some cases. (C) 2011 American Institute of Physics. doi:10.1063/1.3526748]

Ab initio molecular orbital calculations on ion pair-water complexes of metal halides and oxides

Ab initio MO calculations are performed on a series of ion-molecular and ion pair-molecular complexes of H2O + MX (MX = LiF, LiCl, NaCl, BeO and MgO) systems. BSSE-corrected stabilization energies, optimized geometrical parameters, internal force constants and harmonic vibrational frequencies have been evaluated for all the structures of interest. The trends observed in the geometrical parameters and other properties calculated for the mono-hydrated contact ion pair complexes parallel those computed for the complexes of the individual ions. The bifurcated structures are found to be saddle points with an imaginary frequency corresponding to the rocking mode of water molecules. The solvent-shared ion pair complexes have high interaction energies. Trends in the internal force constant and harmonic frequency values are discussed in terms of ion-molecular and ion-pair molecular interactions.

Bioinorganic and medicinal chemistry: aspects of gold(I)-protein complexes

Gold(I)-based drugs have been used successfully for the treatment of rheumatoid arthritis (RA) for several years. Although the exact mechanism of action of these gold(I) drugs for RA has not been clearly established, the interaction of these compounds with mammalian enzymes has been extensively studied. In this paper, we describe the interaction of therapeutic gold(I) compounds with mammalian proteins that contain cysteine (Cys) and selenocysteine (Sec) residues. Owing to the higher affinity of gold(I) towards sulfur and selenium, gold(I) drugs rapidly react with the activated cysteine or selenocysteine residues of the enzymes to form protein-gold(I)-thiolate or protein-gold(I)-selenolate complexes. The formation of stable gold(I)-thiolate/selenolate complexes generally lead to inhibition of the enzyme activity. The gold-thiolate/selenolate complexes undergo extensive ligand exchange reactions with other nucleophiles and such ligand exchange reactions alter the inhibitory effects of gold(I) complexes. Therefore, the effect of gold(I) compounds on the enzymatic activity of cysteine-or selenocysteine-containing proteins may play important roles in RA. The interaction of gold(I) compounds with different enzymes and the biochemical mechanism underlying the inhibition of enzymatic activities may have broad medicinal implications for the treatment of RA.

Calcium ionophore, A23187 and its amino acid complexes: spectroscopic and molecular modeling studies.

The circular dichroism, fluorescence, Nuclear Magnetic Resonance and BLM conductance studies indicate that A23187 forms a stable complex with amino acids at low ionophore concentrations (<10(-4)M). However, A23187 prefers to be in a dimeric structure with no significant binding to amino acids, at concentrations higher than 10(-4)M. It was also observed that at lower concentrations, at which the amino acids bind to the ionophore, the affinity for calcium ions was several orders of magnitude lower than that at higher ionophore concentrations. We have also conducted molecular modeling studies to examine the structure of the A23187 dimer and its amino acid complexes. The results of these modeling studies strongly support our experimental results and validate the formation of a hydrogen bonded and energetically stable A23187 dimer and its amino acid complexes.

Copper( 11) Complexes of Novel Tripodal Ligands containing Phenolate and Benzimidazole/Pyridine Pendants: Synthesis, Structure, Spectra and Electrochemical Behaviour

Mononuclear copper(II) complexes of tri- and tetra-dentate tripodal ligands containing phenolic hydroxyl and benzimidazole or pyridine groups have been isolated. They are of the type (CuL(X)].nH2O, [CuL(H2O)]X.nH2O or [CuL].nH2O where X = Cl-, ClO4-, N3- or NCS- and n = 0-4. The electronic spectra of all the complexes exhibit a broad absorption band around 14000 cm-1 and the polycrystalline as well as the frozen-solution EPR spectra are axial, indicating square-based geometries. The crystal structure of [CuL(Cl)] [HL = (2-hydroxy-5-nitrobenzyl)bis(2-pyridyl-methyl)amine] revealed a square-pyramidal geometry around Cu(II). The mononuclear complex crystallises in the triclinic space group P1BAR with a = 6.938(1), b = 11.782(6), c = 12.678(3) angstrom and alpha = 114.56(3), beta = 92.70(2), gamma = 95.36(2)-degrees. The co-ordination plane is comprised of one tertiary amine and two pyridine nitrogens and a chloride ion. The phenolate ion unusually occupies the axial site, possibly due to the electron-withdrawing p-nitro group. The enhanced pi delocalisation involving the p-nitrophenolate donor elevates the E1/2 values. The spectral and electrochemical results suggest the order of donor strength as nitrophenolate < pyridine < benzimidazole in the tridentate and nitrophenolate < benzimidazole < pyridine in the tetradentate ligand complexes.