Alan H. Cowley

Highly luminescent poly(methyl methacrylate)-incorporated europium complex supported by a carbazole-based fluorinated β-diketonate ligand and a 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene oxide co-ligand.

A novel efficient antenna complex of Eu(3+) [Eu(CPFHP)(3)(DDXPO)] supported by a highly fluorinated carbazole-substituted β-diketonate ligand, namely, 1-(9H-carbazol-2-yl)-4,4,5,5,5-pentafluoro-3-hydroxypent-2-en-1-one (CPFHP) and the 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene oxide (DDXPO) ancillary ligand, has been synthesized, structurally characterized, and its photoluminescent behavior examined. The single-crystal X-ray diffraction analysis of Eu(CPFHP)(3)(DDXPO) revealed that this complex is mononuclear, and that the central Eu(3+) ion is surrounded by eight oxygen atoms, six of which are provided by the three bidentate β-diketonate ligands. The remaining two oxygen atoms are furnished by the chelating phosphine oxide ligand. The coordination polyhedron is best described as that of a distorted square antiprism. The photophysical properties of Eu(CPFHP)(3)(DDXPO) benefit from adequate protection of the metal by the ligands with respect to non-radiative deactivation as well as an efficient ligand-to-metal energy transfer process which exceeds 66% in chloroform solution with a quantum yield of 47%. As an integral part of this work, the synthesis, characterization, and luminescent properties of poly(methyl methacrylate) (PMMA) polymer films doped with Eu(CPFHP)(3)(DDXPO) are also reported. The luminescent efficiencies of the doped films (photoluminescence quantum yields 79-84%) are dramatically enhanced in comparison with that of the precursor complex. The new luminescent PMMA-doped Eu(CPFHP)(3)(DDXPO) complex therefore shows considerable promise for polymer light-emitting diode and active polymer optical fiber applications.

Copper(I) and nickel(II) complexes with 1 : 1 vs. 1 : 2 coordination of ferrocenyl hydrazone ligands: Do the geometry and composition of complexes affect DNA binding/cleavage, protein binding, antioxidant and cytotoxic activities?

A new series of geometrically different complexes containing ferrocenyl hydrazone ligands were synthesised by reacting suitable precursor complex [MCl(2)(PPh(3))(2)] with the ligands HL(1) or HL(2) (where M = Cu(II) or Ni(II); HL(1) = [Cp(2)Fe(CH=N-NH-CO-C(6)H(5))] (1) and HL(2) = [Cp(2)Fe(CH=N-NH-CO-C(5)H(4)N)]) (2). The new complexes of the composition [Cu(L(1))(PPh(3))(2)], (3) [Cu(L(2))(PPh(3))(2)] (4), [Ni(L(1))(2)] (5) and [Ni(L(2))(2)] (6) were characterised by various spectral studies. Among them, complexes 3 and 5 characterised by single crystal X-ray diffraction showed a distorted tetrahedral structure for the former with 1:1 metal-ligand stoichiometry, but a distorted square planar geometry with 1:2 metal-ligand stoichiometry in the case of the latter. Systematic biological investigations like DNA binding, DNA cleavage, protein binding, free radical scavenging and cytotoxicity activities were carried out using all the synthesised compounds and the results obtained were explained on the basis of structure-activity relationships. The binding constant (K(b)) values of the synthesised compounds are found to be in the order of magnitude 10(3)-10(5) M(-1) and also they exhibit significant cleavage of supercoiled (SC) pUC19 DNA in the presence of H(2)O(2) as co-oxidant. The conformational changes of bovine serum albumin (BSA) upon binding with the above complexes were also studied. In addition, concentration dependent free radical scavenging potential of all the synthesised compounds (1-6) was also carried out under in vitro conditions. Assays on the cytotoxicity of the above complexes against HeLa and A431 tumor cells and NIH 3T3 normal cells were also carried out.

Synthesis, Crystal Structure, and Photoluminescence of Homodinuclear Lanthanide 4-(Dibenzylamino)benzoate Complexes

Three new binuclear lanthanide complexes of general formula [Ln(2)(L)(6)(H(2)O)(4)] (Ln = Tb (1), Eu (2), and Gd (3)) supported by the novel aromatic carboxylate ligand 4-(dibenzylamino)benzoic acid (HL) have been synthesized. Complexes 1 and 2 were structurally characterized by single-crystal X-ray diffraction. Both 1 and 2 crystallize in the triclinic space group P(1), and their molecular structures consist of homodinuclear species that are bridged by two oxygen atoms from two carboxylate ligands via different coordination modes. The discrete bridged dimer of 1 is centrosymmetric and features 8-coordinate terbium atoms, each of which adopts a distorted square-antiprismatic geometry. Both coordination spheres comprise two eta(2)-chelating benzoates, two mu-eta(1):eta(1)-carboxylate interactions from the bridging benzoates, and two water molecules. By contrast, in complex 2, the Eu(3+) ion coordination environment is best described as a distorted tricapped-trigonal prism, each europium ion being coordinated to three eta(2)-chelating benzoate ligands and two water molecules. One of the eta(2)-carboxylate ligands is involved in a further interaction with an adjacent metal, thus rendering the overall binding mode bridging tridentate, mu-eta(2):eta(1). Scrutiny of the packing diagrams for 1 and 2 revealed the existence of a one-dimensional molecular array that is held together by intermolecular hydrogen-bonding interactions. The Tb(3+) complex 1 exhibits high green luminescence efficiency in the solid state with a quantum yield of 82%. On the other hand, poor luminescence efficiency has been noted for the Eu(3+)-4-(dibenzylamino)benzoate complex.

Effect of substitution and planarity of the ligand on DNA/BSA interaction, free radical scavenging and cytotoxicity of diamagnetic Ni(II) complexes: a systematic investigation.

Four new bivalent nickel hydrazone complexes have been synthesised from the reactions of [NiCl(2)(PPh(3))(2)] with H(2)L {L = dianion of the hydrazones derived from the condensation of salicylaldehyde or o-hydroxy acetophenone with p-toluic acid hydrazide (H(2)L(1)) (1), (H(2)L(2)) (2) and o-hydroxy acetophenone or o-hydroxy naphthaldehyde with benzhydrazide (H(2)L(3)) (3) and (H(2)L(4)) (4)} and formulated as [Ni(L(1))(PPh(3))] (5), [Ni(L(2))(PPh(3))] (6), [Ni(L(3))(PPh(3))] (7) and [Ni(L(4))(PPh(3))] (8). Structural characterization of complexes 5-8 were accomplished by using various physico-chemical techniques. In order to study the influence of substitution in the ligand and its planarity on the biological activity of complexes 5-8 containing them, suitable hydrazone ligands 1-4 have been selected in this study. Single crystal diffraction data of complexes 5, 7 and 8 proved the geometry of the complexes to be distorted square planar with a 1 : 1 ratio between the metal ion and the coordinated hydrazones. To provide more insight on the mode of action of complexes 5-8 under biological conditions, additional experiments involving their interaction with calf thymus DNA (CT DNA) and bovine serum albumin (BSA) were monitored by UV-visible and fluorescence titrations respectively. Further, the ligands 1-4 and corresponding nickel(ii) chelates 5-8 have been tested for their scavenging effect towards OH and O(2)(-) radicals. The effect of complexes 5-8 to arrest the growth of HeLa and Hep-2 tumour cell lines has been studied along with the cell viability against the non-cancerous NIH 3T3 cells under in vitro conditions.

Design, Synthesis, and Study of Main Chain Poly(N-Heterocyclic Carbene) Complexes: Applications in Electrochromic Devices

A series of poly(N-heterocyclic carbene) complexes in which the carbene functionalities are orthogonally connected to the main chains of the respective polymers have been synthesized via oxidative electropolymerization of various bis(bithiophene)-substituted monomers with appended transition metal or main group entities (M = Ir, Au, Ag, or S). The polymers were characterized using a range of electrochemical, X-ray photoelectron spectroscopy, UV-vis spectroscopy, profilometry, and four-point probe conductivity measurements. Most of the polymers exhibited an intense absorbance wave at 700 nm under oxidative conditions which was attributable to the formation of polarons along the main chains. The iridium-containing thin film poly(8) was found to possess a significant NIR absorbance at 1100 nm in which the metal moiety effectively functioned as an electron sink. Electrochemical analyses of the polymer thin films revealed that they exhibited highly reversible electrochromic phenomena.

3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped into poly-β-hydroxybutyrate matrix as a promising light-conversion molecular device

A novel class of efficient antenna complexes of Tb3+ based on the use of 3-phenyl-4-acyl-5-isoxazolone ligands has been designed, synthesized, characterized and their photophysical properties evaluated . The new heterocyclic β-diketonate complexes of Tb3+ exhibit high green luminescence efficiency in the solid state with quantum yields between 59–72%. Furthermore in this work, the synthesis, characterization and luminescent properties of poly-β-hydroxybutyrate (PHB) polymer films doped with Tb3+-3-phenyl-4-acyl-5-isoxazolonate complexes at 5, 10, 15 and 20% (mass) are reported. The fact that the luminescent efficiency of doped films is enhanced (quantum yields between 74–86%) compared with precursor samples revealed that the polymer matrix acts as a co-sensitizer for Tb3+centers. The luminescence intensity decreases, however, with increasing precursor concentration in the doped PHB to greater than 15% where a saturation effect is observed, indicating that changes in the polymer matrix improve the absorption properties of the film, consequently quenching the luminescent effect. Synthesized luminescent polymers containing Tb3+-hetrocyclic β-diketonate complexes showed promising photoluminescence efficiency for applications to polymer light-emitting diodes and active polymer optical fibers.

The reactions of stable nucleophilic carbenes with main group compounds

Publisher Summary This chapter discusses various reactions of stable nucleophilic carbenes with main group compounds. Special interest is associated with carbenes that feature the attachment of donor groups to the carbenic carbon as they behave as nucleophiles and, in some instances, can be isolated. Stable nucleophilic carbenes that are capable of forming isolable complexes with a variety of main group species in oxidation states ranging from +1 to +6. The majority of the complexes that have been reported thus far possess 1:1 stoichiometry; however, there are several instances of 2:1 complexation and one example of a 3:1 complex. Although, in principle, it is possible to write double-bonded (carbene)CuEXn canonical forms to describe the interactions between carbenes and main group entities (EXn), in the stable nucleophilic carbene complexes the bonding is predominantly of the donor–acceptor type—namely (carbene)C→EX n . As such, the chemistry of these two-electron donor carbenes bears a strong-resemblance to that of electron-rich phosphines.

Lanthanide-Based Coordination Polymers Assembled from Derivatives of 3,5-Dihydroxy Benzoates: Syntheses, Crystal Structures, and Photophysical Properties

Two new aromatic carboxylic acids, namely, 3,5-bis(benzyloxy)benzoic acid (HL1) and 3,5-bis(pyridine-2-ylmethoxy)benzoic acid (HL2), have been prepared by replacing the hydroxyl hydrogens of 3,5-dihydroxy benzoic acid with benzyl and pyridyl moieties, respectively. The anions derived from HL1 and HL2 have been used for the support of a series of lanthanide coordination compounds [Eu(3+) = 1-2; Tb(3+) = 3-4; Gd(3+) = 5-6]. The new lanthanide complexes have been characterized on the basis of a variety of spectroscopic techniques in conjunction with an assessment of their photophysical properties. Lanthanide complexes 2, 4, and 6, which were synthesized from 3,5-bis(pyridine-2-ylmethoxy)benzoic acid, were structurally authenticated by single-crystal X-ray diffraction. All three complexes were found to exist as infinite one-dimensional (1-D) coordination polymers with the general formula {[Ln(L2)(3)(H(2)O)(2)]·xH(2)O}(n). Scrutiny of the packing diagrams for 2, 4, and 6 revealed the existence of interesting two-dimensional molecular arrays held together by intermolecular hydrogen-bonding interactions. Furthermore, the coordinated benzoate ligands serve as efficient light harvesting chromophores. In the cases of 1-4, the lowest energy maxima fall in the range 280-340 nm [molar absorption coefficient (ε) = (0.39-1.01) × 10(4) M(-1) cm(-1)]. Moreover, the Tb(3+) complexes 3 and 4 exhibit bright green luminescence efficiencies in the solid state (Φ(overall) = 60% for 3; 27% for 4) and possess longer excited state lifetimes than the other complexes (τ = 1.16 ms for 3; 1.38 ms for 4). In contrast to the foregoing, the Eu(3+) complexes 1 and 2 feature poor luminescence efficiencies.

An alkyl-substituted indium(I) tetramer

Abstract The first indium(I) alkyl, [InC(SiMe3)3]4 (1), has been prepared by treatment of InCl with LiC(SiMe3)3·2 THF in Et2O solution. Compound 1 crystallizes in the space group Pnma with a=30.465(2), b=13.855(2), c=17.824(2)A, and Z=4. Individual molecules of 1 feature a tetrahedral In4 core with an average indium-indium distance of 3.09(2)A.

Organometallic chemical vapor deposition of III/V compound semiconductors with novel organometallic precursors.

Compound semiconductors such as gallium arsenide (GaAs) and indium phosphide (InP) are important materials used in the fabrication of microelectronic and optoelectronic devices. Several techniques have been employed for the preparation of thin films of these materials, including organometallic chemical vapor deposition (OMCVD) and molecular beam epitaxy (MBE). Apart from the potential environmental, safety, and health hazards of handling pyrophoric and toxic reagents under these conditions, the conventional OMCVD methodology also suffers from stoichiometry control problems, impurity incorporation (particularly carbon), and unwanted side reactions. The ideal chemical solution to the problem is to cause the III-V bond to be as strong as, or stronger than, the other bonds in the molecule such that under film growth conditions the bonds between the group III and group V elements remain intact while the other bonds are broken. The obvious way to strengthen the III-V interaction is to replace the donor-acceptor linkage by a two-center, two-electron bond. The authors initial studies have therefore focussed on the design and synthesis of organometallic molecules which feature /sigma/ bonding between the group III and group V elements. A further objective was to lower the deposition temperature by employing substituents that undergo facile hydrocarbon elimination.