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Central Metal Ion (central + metal_ion)
Selected AbstractsPalladium-Catalyzed meso-Amination and Amidation of Porphyrins: Marked Acceleration with the Ni(II) Central Metal Ion.CHEMINFORM, Issue 1 2004Toshikatsu Takanami Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and Structural Characterisation of Copper(II) 15-Metallacrown-5 Complexes with PbII, HgII, AgI, NaI and YIII Central Metal IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Sabry Hamed Seda Abstract The new copper(II) 15-metallacrown-5 complexes with the central metal ions PbII, HgII, AgI, NaI and YIII, with the formula [MCu5L5]Xn {H2L is 2-picolinehydroxamic acid or (S)-phenylalaninehydroxamic acid and X, is NO3, or Cl,}, have been synthesised and characterised by NMR and UV/Vis spectroscopy, electrospray mass spectrometry and elemental analysis. The PbII - and HgII 15-metallacrown-5 complexes were obtained in the crystalline form as pyridine adducts [PbCu5(picha)5(py)6](NO3)2·3(py) and [HgCu5(picha)5(py)7](NO3)2·2(py) and their X-ray crystal structures were determined. In both complexes, each peripheral CuII ion of the metallacrown is coordinated by one pyridine molecule bonded in the axial position. In the case of the PbII derivative, one additional axial pyridine molecule is bound to the central metal ion, while in the case of the HgII derivative, two axial pyridine ligands are bound to the central HgII ion. The relative stability of the copper(II) 15-metallacrown-5 complexes with various central metal ions was determined on the basis of competition reactions. The relative preference of the 15-metallacrown-5 system for the central metal ion follows the series NaI, AgI < lanthanide(III), HgII < PbII.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Model Systems for Fluorescence and Singlet Oxygen Quenching by MetalloporphyrinsCHEMMEDCHEM, Issue 3 2007Jason Abstract Next-generation photodynamic therapy agents will minimize extraneous phototoxicity by being active only at the target site. To this end, we have developed a model system to systematically investigate the excited-state quenching ability of a number of metalloporphyrins. Central metal ions that prefer four-coordinate, square planar orientations (AgII, CuII, NiII, PdII, and ZnII) were used. Porphyrin dimers based on 5-(4-aminophenyl)-10,15,20-triphenylporphyrin and comprising both a free base porphyrin and a metalloporphyrin covalently linked through a five-carbon alkyl chain were synthesized. The fluorescence and singlet oxygen quantum yields for the dimers were probed at 630 and 650,nm, respectively, resulting in the excitation of only the free base porphyrin and allowing a comparison of the quenching efficacy of each central metal ion. These results demonstrate that metalloporphyrins can serve as efficient quenchers, and may be useful in the design of novel light-activated therapeutic agents. [source] Investigation of the stereodynamics of tris-(, -diimine),transition metal complexes by enantioselective dynamic MEKCELECTROPHORESIS, Issue 2 2009Sabrina Bremer Abstract Enantiomerization of octahedral tris(, -diimine),transition metal complexes was investigated by enantioselective dynamic MEKC. Varying both the transition metal ion (Fe2+, Fe3+, and Ni2+) and the bidentate diimine ligand (1,10-phenanthroline and 2,2,-bipyridyl), the enantiomer separations were performed either in a 100,mM sodium tetraborate buffer (pH 9.3) or in a 100,mM sodium tetraborate/sodium dihydrogenphosphate buffer (pH 8.0) both containing sodium cholate as chiral surfactant. The unified equation of dynamic chromatography was employed to determine apparent reaction rate constants from the electropherograms showing distinct plateau formation. Apparent activation parameters ,H, and ,S, were calculated from temperature-dependent measurements between 10.0 and 35.0°C in 2.5,K steps. It was found that the nature of the central metal ion and the ligand strongly influence the enantiomerization barrier. Surprisingly, complexes containing the 2,2,-bipyridyl ligand show highly negative activation entropies between ,103 and ,116,J (K,mol),1 while the activation entropy of tris(1,10-phenanthroline) complexes is positive indicating a different mechanism of interconversion. Furthermore, it was found that the Ni2+ complexes are stereostable under the conditions investigated here making them a lucent target as enantioselective catalysts. [source] Synthesis and Structural Characterisation of Copper(II) 15-Metallacrown-5 Complexes with PbII, HgII, AgI, NaI and YIII Central Metal IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Sabry Hamed Seda Abstract The new copper(II) 15-metallacrown-5 complexes with the central metal ions PbII, HgII, AgI, NaI and YIII, with the formula [MCu5L5]Xn {H2L is 2-picolinehydroxamic acid or (S)-phenylalaninehydroxamic acid and X, is NO3, or Cl,}, have been synthesised and characterised by NMR and UV/Vis spectroscopy, electrospray mass spectrometry and elemental analysis. The PbII - and HgII 15-metallacrown-5 complexes were obtained in the crystalline form as pyridine adducts [PbCu5(picha)5(py)6](NO3)2·3(py) and [HgCu5(picha)5(py)7](NO3)2·2(py) and their X-ray crystal structures were determined. In both complexes, each peripheral CuII ion of the metallacrown is coordinated by one pyridine molecule bonded in the axial position. In the case of the PbII derivative, one additional axial pyridine molecule is bound to the central metal ion, while in the case of the HgII derivative, two axial pyridine ligands are bound to the central HgII ion. The relative stability of the copper(II) 15-metallacrown-5 complexes with various central metal ions was determined on the basis of competition reactions. The relative preference of the 15-metallacrown-5 system for the central metal ion follows the series NaI, AgI < lanthanide(III), HgII < PbII.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Oxidation of ,4 - and ,5 -Steroids with Hydrogen Peroxide Catalyzed by Porphyrin Complexes of MnIII and FeIIIEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2004Susana L. H. Rebelo Abstract In this paper we describe a new environmentally friendly method to promote the stereoselective epoxidation of ,4 - and ,5 -steroids. Metalloporphyrins efficiently catalyze the epoxidation reactions of 17,-acetoxy-4-androstene (1), 4-cholestene (2) and 3,-acetoxy-5-cholestene (3) in the presence of H2O2 as oxygen donor. Modeling the molecular structure of the porphyrin as well as the central metal allows the control of the preferential formation of ,- or ,-epoxides. Porphyrins with bulky, electron-withdrawing groups in the ortho positions of the meso phenyls and with MnIII as the central metal ion, such as [Mn(TDCPP)Cl], gave preferentially the ,-epoxide of ,4 - and ,5 -steroids. [Fe(TPFPP)Cl] catalyzes preferentially the ,-epoxidation of ,4 -steroids and also increases the stereoselectivity for the ,-epoxide in ,5 -steroids, similar to the results obtained with m -CPBA (m -chloroperbenzoic acid) as oxidant. The substrate structure strongly influences the chemoselectivity of the reactions. The X-ray structures of two main products were determined, and two-dimensional NMR techniques allowed the full assignment of 1H and 13C NMR resonances as well as the stereochemistry of these products. A mechanistic proposal involving oxo species for the ,-approach and peroxy species for the ,-approach is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis, characterization, and thermal and antimicrobial studies of newly developed transition metal,polychelates derived from polymeric Schiff baseJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009Nahid Nishat Abstract Monomeric Schiff base derived from salicylaldehyde and 1,3-diaminopropane was subjected to polycondensation reaction with formaldehyde and piperazine in basic medium. The resin was found to form polychelates readily with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) metal ions. The materials were characterized by elemental analysis, spectral studies (IR, 1H-NMR, 13C-NMR, and UV,visible), magnetic moment measurements, and thermal analysis. The electronic spectra and magnetic moment measurements of the synthesized polychelates confirmed the geometry of the central metal ion. Metal,resin bonds were registered in the IR spectra of the polychelates. The thermogravimetric analysis data indicated that the polychelates were more stable than the corresponding polymeric Schiff base. All the synthesized metal,polychelates showed excellent antibacterial activities against the selected bacteria. The antimicrobial activities were determined by using the shaking flask method, where 25 mg/mL concentrations of each compound were tested against 105 CFU/mL bacteria solutions. The number of viable bacteria was calculated by using the spread-plate method, where 100 ,L of the incubated antimicrobial agent in bacteria solutions were spread on agar plates, and the number of bacteria was counted after 24 h of incubation period at 37°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Studies on the Synthesis and Activity of Three Tripalladium Complexes Containing Planaramine LigandsCHEMMEDCHEM, Issue 11 2009Mohammad Farhad Abstract The present study deals with the synthesis, characterization and activity against human cancer cell lines: A2780, A2780cisR and A2780ZD0473R of three tripalladium complexes, MH3, MH4 and MH5, that each have two planaramine ligands bound to the central metal ion. Cellular uptake levels, extent of DNA binding, and nature of interaction with salmon sperm and pBR322 plasmid DNA were determined for each complex. Palladium compounds are much more reactive than their corresponding platinum derivatives, which makes them therapeutically inactive but toxic. However, the results of the present study suggest that significant antitumour activity can be introduced in palladium complexes by lessening their reactivity by the introduction of sterically hindered ligands such as 2-hydroxypyridine, 3-hydroxypyridine and 4-hydroxypyridine. When bound to the central palladium ion, 4-hydroxypyridine appears to be more activating than 2-hydroxypyridine and 3-hydroxypyridine, suggesting that noncovalent interactions, such as hydrogen bonding, may also be key determinants of antitumour activity in addition to the steric effect. While cisplatin binds with DNA to form intrastrand GG adducts that causes local bending of a DNA strand, these planaramine-derived palladium complexes are expected to bind with DNA and form a number of long-range interstrand GG adducts that would cause a global change in DNA conformation, provided the tripalladium cations in MH3, MH4 and MH5 persist under physiological conditions. [source] Model Systems for Fluorescence and Singlet Oxygen Quenching by MetalloporphyrinsCHEMMEDCHEM, Issue 3 2007Jason Abstract Next-generation photodynamic therapy agents will minimize extraneous phototoxicity by being active only at the target site. To this end, we have developed a model system to systematically investigate the excited-state quenching ability of a number of metalloporphyrins. Central metal ions that prefer four-coordinate, square planar orientations (AgII, CuII, NiII, PdII, and ZnII) were used. Porphyrin dimers based on 5-(4-aminophenyl)-10,15,20-triphenylporphyrin and comprising both a free base porphyrin and a metalloporphyrin covalently linked through a five-carbon alkyl chain were synthesized. The fluorescence and singlet oxygen quantum yields for the dimers were probed at 630 and 650,nm, respectively, resulting in the excitation of only the free base porphyrin and allowing a comparison of the quenching efficacy of each central metal ion. These results demonstrate that metalloporphyrins can serve as efficient quenchers, and may be useful in the design of novel light-activated therapeutic agents. [source] Inclusion Complexes for Use in Room-Temperature Gas-Sensor DesignEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2007Liwei Mi Abstract The inclusion complex [{Co(bpy)(H2O)4}·(fcds)]n (1), which has been constructed using the guest molecule ferrocene-1,1,-disulfonate (fcds), the bridging ligand 4,4,-bipyridine (bpy) and d7 Co2+, contains an infinite zigzag chain formed by the central CoII ion and the bridging bpy ligand. Guest fcds molecules lie between two adjacent zigzag chains. The highly conjugated structure of complex 1 means that it can be used as a metal-organic semiconductor, and it also shows a high response to liquefied petroleum gas (LPG) and ethanol/petroleum ether (EP) at room temperature. The inclusion complexes [{Co(bpp)2(H2O)2}·(fcds)·4H2O]n [2; bpp = 1,3-bis(4-pyridyl)propane] and [{Zn(bpy)(H2O)4}·(fcds)]n (3), on the other hand, cannot be employed as room-temperature gas sensors because they are insulators. The electrical resistivity of inclusion complex [{Ni(bpy)(H2O)4}·(fcds)]n (4) is 621 M,, whereas that of [{Co(bpy)(H2O)4}SO4·(4-abaH)2·3H2O]n (5) (4-abaH = 4-aminobenzoic acid) is only 137 M,. This means that the semi-conducting properties of such inclusion complexes depend on both the conjugated structure and the central metal ions. Furthermore, conjugated inclusion complexes with an odd number of electrons could be useful for the design of highly selective room-temperature gas sensors.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis and Structural Characterisation of Copper(II) 15-Metallacrown-5 Complexes with PbII, HgII, AgI, NaI and YIII Central Metal IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Sabry Hamed Seda Abstract The new copper(II) 15-metallacrown-5 complexes with the central metal ions PbII, HgII, AgI, NaI and YIII, with the formula [MCu5L5]Xn {H2L is 2-picolinehydroxamic acid or (S)-phenylalaninehydroxamic acid and X, is NO3, or Cl,}, have been synthesised and characterised by NMR and UV/Vis spectroscopy, electrospray mass spectrometry and elemental analysis. The PbII - and HgII 15-metallacrown-5 complexes were obtained in the crystalline form as pyridine adducts [PbCu5(picha)5(py)6](NO3)2·3(py) and [HgCu5(picha)5(py)7](NO3)2·2(py) and their X-ray crystal structures were determined. In both complexes, each peripheral CuII ion of the metallacrown is coordinated by one pyridine molecule bonded in the axial position. In the case of the PbII derivative, one additional axial pyridine molecule is bound to the central metal ion, while in the case of the HgII derivative, two axial pyridine ligands are bound to the central HgII ion. The relative stability of the copper(II) 15-metallacrown-5 complexes with various central metal ions was determined on the basis of competition reactions. The relative preference of the 15-metallacrown-5 system for the central metal ion follows the series NaI, AgI < lanthanide(III), HgII < PbII.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Description of the Ground-State Covalencies of the Bis(dithiolato) Transition-Metal Complexes from X-ray Absorption Spectroscopy and Time-Dependent Density-Functional CalculationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2007Kallol Ray Dr. Abstract The electronic structures of [M(LBu)2], (LBu=3,5-di- tert -butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(,) forms. The extent of electron transfer strongly depends on the effective nuclear charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(LBu)2], (M=Ni, Pd, Pt) and [Au(LBu)2] are best described as delocalized class,III mixed-valence ligand radicals bound to low-spin d8 central metal ions while [M(LBu)2], (M=Cu, Au) and [M(LBu)2]2, (M=Ni, Pd, Pt) contain completely reduced dithiolato(2,) ligands. The case of [Co(LBu)2], remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S1s,valence-, versus S1s,valence-, transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal,sulfur bonds from ligand K-edge absorption spectroscopy. [source] Ytterbium Coordination Polymer with Four Different Coordination Numbers: The First Structural Characterization of Lanthanide Phthalate ComplexCHINESE JOURNAL OF CHEMISTRY, Issue 9 2002Yong-Hong Wan Abstract The novel ytterbium coordination polymer is a two-dimensional framework in which the central metal ions have four different coordination numbers and form four kinds of coordination polyhedra. The four kinds of coordination polyhedra connect into infinite chains by sharing oxygen atoms. [source] | |||||||||||||||||||