trans-Dichloro-bis-(arylazoimidazole)palladium(II): Synthesis, Structure, Photoisomerization, and DFT Calculation

Reaction between PdCl2 and 1-alkyl-2-(arylazo)imidazole (RaaiR') or 1-alkyl-2-(naphthyl-alpha/beta-azo)imidazole (alpha/beta-NaiR') under reflux in ethanol has isolated complexes of compositions Pd(RaaiR')(2)Cl-2 (5, 6) and Pd(alpha/beta-NaiR')(2)Cl-2 (7, 8). The X-ray structure determination of one of the molecules, Pd(alpha-NaiBz)(2)Cl-2 (7c), has reported a trans-PdCl2 configuration, and alpha-NaiBz acts as monodentate N(imidazole) donor ligand. The spectral (IR, UV-vis, H-1 NMR) data support the structure. UV light irradiation (light source: Perkin-Elmer LS 55 spectrofluorimeter, Xenon discharge lamp, lambda = 360-396 nm) in a MeCN solution of the complexes shows E-to-Z isomerization of the coordinated azoimidazole unit. The reverse transformation, Z-to-E, is very slow with visible light irradiation. Quantum yields (phi(E-Z)) of E-to-Z isomerization are calculated, and phi is lower than that of the free ligand but comparable with those of Cd(II) and Hg(II) complexes of the same ligand. The Z-to-E isomerization is a thermally induced process. The activation energy (E-a) of Z-to-E isomerization is calculated by controlled-temperature experimentation. cis-Pd(azoimidazole)Cl-2 complexes (azomidazole acts as N(imidazole) and N(azo) Chelating ligand) do not respond upon light irradiation, which supports the idea that the presence of noncoordinated azo-N to make free azo (-N=N-) function is important to reveal photochromic activity. DFT calculation of Pd(alpha-NaiBz)(2)Cl-2 (7c) has suggested that the HOMO of the molecule is constituted of Pd (32%) and Cl (66%), and hence photo excitation may use the energy of Pd and Cl instead of that of the photofunctional -N=N-Ar motif; thus, the rate of photoisomerization and quantum yield decrease versus the free ligand values.

Late Transition Metal and Aluminum Complexes for the Polymerization of Ethene and Acrylates

Polyethene, polyacrylates and polymethyl acrylates are versatile materials that find wide variety of applications in several areas. Therefore, polymerization of ethene, acrylates and methacrylates has achieved a lot attention during past years. Numbers of metal catalysts have been introduced in order to control the polymerization and to produce tailored polymer structures. Herein an overview on the possible polymerization pathways for ethene, acrylates and methacrylates is presented. In this thesis iron(II) and cobalt(II) complexes bearing tri- and tetradentate nitrogen ligands were synthesized and studied in the polymerization of tertbutyl acrylate (tBA) and methyl methacrylate (MMA). Complexes are activated with methylaluminoxane (MAO) before they form active combinations for polymerization reactions. The effect of reaction conditions, i.e. monomer concentration, reaction time, temperature, MAO to metal ratio, on activity and polymer properties were investigated. The described polymerization system enables mild reaction conditions, the possibility to tailor molar mass of the produced polymers and provides good control over the polymerization. Moreover, the polymerization of MMA in the presence of iron(II) complex with tetradentate nitrogen ligands under conditions of atom transfer radical polymerization (ATRP) was studied. Several manganese(II) complexes were studied in the ethene polymerization with combinatorial methods and new active catalysts were found. These complexes were also studied in acrylate and methacrylate polymerizations after MAO activation and converted into the corresponding alkyl (methyl or benzyl) derivatives. Combinatorial methods were introduced to discover aluminum alkyl complexes for the polymerization of acrylates and methacrylates. Various combinations of aluminum alkyls and ligands, including phosphines, salicylaldimines and nitrogen donor ligands, were prepared in situ and utilized to initiate the polymerization of tBA. Phosphine ligands were found to be the most active and the polymerization MMA was studied with these active combinations. In addition, a plausible polymerization mechanism for MMA based on ESI-MS, 1H and 13C NMR is proposed.

Schiff Base Complexes and their Assemblies on Surfaces

Schiff bases and their transition metal complexes are of significant current interest even though they have been prepared for decades. They have been used in various applications such as catalysis, corrosion protection, and molecular sensors. In this study, N-aryl Schiff base ketimine ligands as well as numerous new, differently substituted salen and salophen-type ligands and their cobalt(II), copper(II), iron(II), manganese(II), and nickel(II) complexes were synthesised. New solid state structures of the above compounds and the dioxygen coordination properties of cobalt(II) complexes and catalytic properties of three synthesised binuclear complexes were examined. The prepared complexes were applied in the formation of self-assembled layers on a polycrystalline gold surface and liquid-graphite interface. The effect of metal ion and ligand structure on the as-formed patterns was studied. When studying gold surfaces, a unique thiol-assisted dissolution of elemental gold was observed and a new thin gold foil preparation method was introduced. In the summary, synthesis, structures, and properties of Schiff base ligands and their transition metal complexes are described in detail and the applications of these reviewed. Assemblies of other complexes on a liquid-graphite interface and on a gold surface are also presented, and the surface characterisation methods and surfaces employed are described.

Polymer supported metal complexes as catalysts for oxidation of thiosalts by molecular oxygen IV. Quaternised poly(4-vinyl pyridine) complexes with Cu2+ as template

Copper(II) complexes of quaternised poly(4-vinylpyridine) (PVP) of different degrees of quaternisation and copper content have been prepared by crosslinking the polymer with 1,2-dibromoethane in the presence of Cu2+ ion as template. The stability constant of the PVP---Cu(II) complexes is found to increase with the degree of crosslinking quaternisation of the resin, but the rate at which Cu2+ is adsorbed by the resin decreases. An optimum combination of both stability and rate can be achieved with a moderate degree (31%) of crosslinking. A kinetic study reveals that quaternisation increases significantly the catalytic activity of the complex for the oxidation of S2O2−3 by O2 compared with PVP----Cu(II) without quaternisation, but it deactivates the complex for the oxidation of both S3O2−6 and S4O2−6. The batch reactor oxidation kinetics at pH 2.16, where the rate is observed to be maximum, is well explained by the Langmuir—Hinshelwood model assuming the coordination of both O2 and thioanion to Cu(II) as a precursor to the oxidation reaction.

Monothiobiurst complexes of some bivalent metal chlorides

The complexes of monothiobiuret with Co(II), Ni(II), Cd(II) and Hg(II) chlorides are investigated. The ligand is suggested to be unidentate bonding through sulfur in Co(II) and Hg(II) complexes and bidentate bonding through both sulfur and oxygen atoms in the other two complexes.

Adducts of bis(acetylacetonato)zinc(II) with 1,10-phenanthroline and 2,2'-bipyridine

In each of the zinc(II) complexes bis(acetylacetonato-kappa(2)O,O')(1,10-phenanthroline-kappa(2)N,N')zinc(II), [Zn(C(5)H(7)O(2))(2)(C(12)H(8)N(2))], (I), and bis(acetylacetonato-kappa(2)O,O')(2,2'-bipyridine-kappa(2)N,N')zinc(II), [Zn(C(5)H(7)O(2))(2)(C(10)H(8)N(2))], (II), the metal center has a distorted octahedral coordination geometry. Compound (I) has crystallographically imposed twofold symmetry, with Z' = 0.5. The presence of a rigid phenanthroline group precludes intramolecular hydrogen bonding, whereas the rather flexible bipyridyl ligand is twisted to form an intramolecular C-H...O interaction [the chelated bipyridyl ligand is nonplanar, with the pyridyl rings inclined at an angle of 13.4 (1) degrees]. The two metal complexes are linked by dissimilar C-H...O interactions into one-dimensional chains. The present study demonstrates the distinct effects of two commonly used ligands, viz. 1,10-phenanthroline and 2,2'-bipyridine, on the structures of metal complexes and their assembly.

Crystal structure of 3-acetylcoumarin-o-aminobenzoylhydrazone and synthesis, spectral and thermal studies of its transition metal complexes

Transition metal [Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)] complexes of a new Schiff base, 3-acetylcoumarin-o-aminobenzoylhydrazone were synthesized and characterized by elemental analyses, magnetic moments, conductivity measurements, spectral [Electronic, IR, H-1 and C-13 NMR, EPR] and thermal studies. The ligand crystallizes in the monoclinic system, space group P2(1)/n with a = 9.201(5), b = 16.596( 9), c = 11.517(6) angstrom, beta= 101.388(9)degrees, V = 1724.2 (17) angstrom(3) and Z = 4. Conductivity measurements indicated Mn(II) and Co(II) complexes to be 1 : 1 electrolytes whereas Ni(II), Cu(II), Zn(II) and Cd(II) complexes are non-electrolytes. Electronic spectra reveal that all the complexes possess four-coordinate geometry around the metal.

Synthesis and structural characterization of a new ruthenium hydride ethylene complex

A ruthenium(II) ethylene complex, trans-[Ru(H)(C2H4)- (dppm)(2)][BF4], hearing two 1,1-bis(diphenylphosphino) methane (dppm) ligands has been synthesized and structurally characterized using X-ray crystallography. In the molecular structure, the Ru-II center shows a distorted octahedral coordination geometry formed by four P atoms of the two chelating dppm ligands, a hydride, and an ethylene ligands. The four dppm P atoms are almost co-planar with the hydride and the ethylene ligands perpendicular to this plane. The C-C bond distance of the bound ethylene is 1.375(6) angstrom, which is elongated by 0.042 angstrom as compared to free ethylene (1.333(2) angstrom). The packing diagram of the complex shows two voids or channels, which are occupied by BF4- counterion and water molecules.

Some sulphoxide complexes of iron

Diphenyl sulphoxide(DPSO) and dimethyl sulphoxide(DMSO) complexes of iron(II) having the composition [Fe(DPSO)6](ClO4)2, Fe(DPSO)2Cl2, Fe(DPSO)3Br2, Fe(DPSO)4I2, [Fe (DMSO)3Cl2]. DMSO and [Fe(DMSO)3Br2]. DMSO and DPSO complexes of iron(III), Fe(DPSO)2 Cl3 have been prepared and their physico-chemical properties studied. Their magnetic moments at room temperature show them to be spin-free complexes. The i.r. spectra reveal that oxygen is the donor atom in all the complexes. The electronic spectra of iron(II) complexes indicate octahedral coordination for the metal ion. A salt like structure [Fe(DPSO)4Cl2][FeCl4], is suggested for the iron (III) complex, where the cationic species has distorted octahedral structure while the anionic species has tetrahedral structure.

Reactions of coordinated bivalent tetradentate schiff-base chelates of nickel (II) and palladium (II)

Reactions of N,N′-n-propylene-bis(acetylacetoneimino) metal (II), M[n-P-(AI)2], where M=Ni(II) or Pd(II), with nitrosating reagents have been investigated. Mono- and di-nitrosated complexes were obtained selectively, depending upon the concentration of the nitrosating reagents and the reaction time. In both the cases, the γ-CH group is transformed to an ambidentate isonitroso group (>C=NOH), which coordinates to the metal ion by dislodging the already coordinated carbonyl group. The factors influencing the mode of binding of the isonitroso group have been discussed. The bromination reactions of the mono-nitrosated products of M[n-P-(AI)2] and Pd (II) complexes, Pd [E/i-P-(AI)2], where E/i-P-(AI)2 is a dianion of ethylene/i-propylene-bis (acetylacetoneimine), are also reported. The reaction products have been characterized by elemental analyses, electrical conductivity molecular weight determination, and ir, pmr and electronic spectral data.

Amino acid-lanthanide interactions, Part 2. The X-ray crystal structures of lanthanide and calcium complexes of 1-amino-cyclohexane-1-carboxylic acid (Acc6)

The structures of [Nd-2(Acc(6))(H2O)(6)](ClO4)(6) .(H2O)(6) (1) [Er-2(Acc(6))(4)(H2O)(8)](ClO4)(6) .(H2O)(11) (2) and [Ca-5(Acc(6))(12)(H2O)(6)](ClO4)(10).(H2O)(4) (3) (Acc(6) = 1-aminocyclohexane-1-carboxylic acid) have been determined by X-ray crystallography. The lanthanide complexes 1 and 2 are dimeric in which two lanthanide cations are bridged by four carboxylato groups of Acc(6) molecules. In addition, the neodymium complex (1) features the unidentate coordination of the carboxyl group of an Acc(6) molecule in place of a water molecule in the erbium complex (2). The coordination number in both 1 and 2 is eight. The calcium Acc(6) complex (3) is polymeric; three different calcium environments are observed in the asymmetric unit. Two calcium ions are hexa-coordinated and one is hepta-coordinated. Considerable differences are observed between the solid state structures of Ln(III) and Ca-II complexes of Acc(6

Photo-activated cytotoxicity of a pyrenyl-terpyridine copper(II) complex in HeLa cells

Terpyridine copper(II) complexes Cu(L)(2)](NO3)(2) where L is (4'-phenyl)-2 2' 6' 2 `'-terpyridine (ph-tpy in 1) and 4-(1 pyrenyl)]-2 2' 6' 2'-terpyridine (py-tpy in 2) are prepared characterized and their photocytotoxic activity studied The crystal structure of complex 1 shows distorted octahedral CuN6 coordination geometry The 1 2 electrolytic and one-electron paramagnetic complexes show a visible band near 650 nm in DMF-H2O The complexes show emission band at 352 nm for 1 and 425 nm for 2 when excited at 283 and 346 nm respectively The Cu(II)-Cu(I) redox couple is observed near -0 2 V versus SCE in DMF-0 1 m TBAP The complexes are avid partial-intercalative binders to calf thymus DNA giving binding constant (K-b) values of similar to 10(6) M-1 Complex 2 with its photoactive pyrenyl moiety exhibits significant photocleavage of pUC19 DNA in red light via singlet oxygen pathway Complex 2 also exhibits significant photo-activated cytotoxicity in HeLa cancer cells in visible light giving IC50 value of 11 9 mu M while being non-toxic in dark with an IC50 value of 130 5 mu M (C) 2010 Elsevier Ltd All rights reserved

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.

Time-resolved fluorescence studies on covalently linked porphyrin�nitroarene complexes. Conformational control of photoinduced electron transfer reactions

Time-resolved fluorescence studies were carried out on a series of free-base and zinc(II) derivatives of meso-tetraphenylporphyrins covalently linked to either 1,3-dinitrobenzene (DNB) or 1,3,5-trinitrobenzene (TNB) acceptor units. These acceptor units were linked at different sites (at the ortho, meta or para positions of one of the phenyl groups of meso-tetraphenylporphyrin) to the donor porphyrins such that the resulting isomeric intramolecular donor-acceptor complexes exhibit different centre-to-centre (ctc) distances and relative orientations. Biexponential fluorescence decay profiles observed for several of these covalently linked complexes were rationalized in terms of the presence of ''closed'' and ''extended'' conformers. Detailed analyses of the fluorescence decay data have provided a comprehensive understanding of the photoinduced electron transfer (PET) reactions occurring in systems containing zinc(II) porphyrin donors. It is observed that although DNB-linked zinc(II) complexes follow the trends predicted for the efficiency of PET with respect to donor-acceptor distance, the TNB-linked zinc(II) porphyrins exhibit a behaviour which is dictated by steric effects. Similarly, although the thermodynamic criteria predict a greater efficiency of charge separation in TNB-linked complexes compared with DNB-linked complexes, the reverse trend observed has been attributed to orientational effects. In the complexes containing free-base porphyrin donors, PET is expected to be less efficient from a thermodynamic viewpoint. In a few of these cases, fluorescence quenching seems to occur by parallel mechanisms other than PET.

DNA cleavage by intercalatable cobalt-bispicolylamine complexes activated by visible light

Two intercalatable Co-II-complexes of anthryl or anthraquinone attached bispicolylamine derivatives cleave plasmid pTZ19R DNA spontaneously upon exposure to visible light under ambient conditions.