Showing papers by "Alan H. Cowley published in 2010"

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.

Abstract: A novel efficient antenna complex of Eu3+ [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 Eu3+ 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 ...

Synthesis, crystal structure, and photoluminescence of homodinuclear lanthanide 4-(dibenzylamino)benzoate complexes

Abstract: Three new binuclear lanthanide complexes of general formula [Ln2(L)6(H2O)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 P1, 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 η2-chelating benzoates, two μ-η1:η1-carboxylate interactions from the bridging benzoates, and two water molecules. By contrast, in complex 2, the Eu3+ ion coordination environment is best described as a distorted tricapped-trigonal prism, each europium ion being coordinated to three η2-chelating...

Synthesis and Crystal Structures of Lanthanide 4-Benzyloxy Benzoates: Influence of Electron-Withdrawing and Electron-Donating Groups On Luminescent Properties

Abstract: Three new 4-benzyloxy benzoic acid derivatives [4-benzyloxy benzoic acid = HL1; 3-methoxy-4-benzyloxy benzoic acid = HL2; 3-nitro-4-benzyloxy benzoic acid = HL3] have been employed as ligands for the support of six lanthanide coordination compounds [Tb3+ = 1–3; Eu3+ = 4–6] with the aim of testing the influence of electron releasing (-OMe) or electron withdrawing (-NO2) substituents on the photophysical properties. The new complexes have been characterized by a variety of spectroscopic techniques and two of the Tb3+ complexes [1 and 2] have been structurally authenticated by single-crystal X-ray diffraction. Compounds 1 and 2 crystallize in the monoclinic space group P21/n and their molecular structures consist of homodinuclear species that are bridged by two oxygen atoms from two benzoate ligands. In the case of 1, the carboxylate ligands coordinate to the central Tb3+ ion in bidentate chelating and bidentate bridging modes. By contrast, three different coordination modes (bidentate chelating, bidentate bridging and monodentate) are observed in the case of compound 2. Examination of the packing diagrams for 1 and 2 revealed the presence of a one-dimensional molecular array that is held together by intermolecular hydrogen-bonding interactions. The incorporation of an electron-releasing substituent on position 3 of 4-benzyloxy benzoic acid increases the electron density of the ligand and consequently improves the photoluminescence of the Tb3+ complexes. On the other hand, the presence of an electron-withdrawing group at this position dramatically decreases the overall sensitization efficiency of the Tb3+-centered luminescence due to dissipation of the excitation energy by means of a π*-n transition of the NO2 substituent along with the participation of the ILCT bands. The weaker photoluminescence of the Eu3+ complexes is attributable to the poor match of the triplet energy levels of the 4-benzyloxy benzoic acid derivatives with that of the emitting level of the central metal ion.

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

Abstract: 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.

Synthesis and coordination compounds of a bis(imino)acenaphthene (BIAN)-supported N-heterocyclic carbene

Abstract: The bis(imino)acenaphthene-supported N-heterocyclic carbene IPr(BIAN) has been prepared by deprotonation of the precursor imidazolium chloride. Treatment of IPr(BIAN) imidazolium chloride with Ag2O afforded the silver complex [IPr(BIAN)]AgCl which can be converted into the corresponding gold complex [IPr(BIAN)]AuCl by reaction with (tht)AuCl (tht = tetrahydrothiophene). The iridium complex [IPr(BIAN)]Ir(COD)Cl was prepared by reaction of the imidazolium chloride with KOtBu and [Ir(COD)Cl]2 and subsequently converted to the carbonyl complex [IPr(BIAN)]Ir(CO)2Cl by exposure to an atmosphere of CO. All new compounds were characterized by single-crystal X-ray diffraction, multinuclear NMR, MS and HRMS data.

Synthesis, study, and applications of polymeric n-heterocyclic carbenes

Abstract: A brief review of our work on orthogonally-positioned NHC metallopolymers is highlighted herein. Some pertinent literature is presented, followed by the synthetic strategy employed as well as comprehensive electrochemical analyses. Derivatization of a suitable diimine into a electropolymerizable gold (I) NHC complex resulted in the first orthogonally-positioned NHC metallopolymer. Extension of this methodology to prepare analogous group 11, iridium and sulfur-substituted metallopolymers generated thin films with electrochromic activity that could be tuned by proper selection of the metal center.

Pentacarbonyl(trimethylamine)chromium and Pentacarbonyl(trimethylamine)Molybdenum

Abstract: Pentacarbonyl(trimethylamine)chromium (1) and pentacarbonyl(trimethylamine)molybdenum (2) are isomorphous and crystallize in the space group P21/n, a = 6.8267(14) A, b = 11.269(2) A, c = 14.692(3) A, β = 102.89(3)°, V = 1,101.8(4) A3, Z = 4 for 1 and a = 6.949(5) A, b = 11.362(5) A, c = 14.927(5) A, β = 102.639(5)°, V = 1,150.0(10) A3, Z = 4 for 2; both compounds possess distorted octahedral molecular geometries that result from the steric influence of the coordinated amine ligand. The title compounds are isomorphous and crystallize in the space group P21/n with a distorted octahedral geometry.

Growth and Characterization of GaAs Films from Tris(di-tert- butylarsino)gallane.

Abstract: We report the use of tris(di-tert-butylarsino)gallane [Ga(As(t-Bu){sub 2}){sup 3}], a nonstoichiometric, single-source precursor, for the growth of GaAs films. Epitaxial films were grown between 415 and 590 {degrees}C in a chemical beam epitaxy reactor operating at 8x10{sup {minus}6} Torr. The growth rate and surface smoothness were found to decrease with increasing temperature. Growth rates ranged from 0.1 to 0.042 {mu}m/h. The Ga:As ratio in the deposited films was studied by energy-dispersive spectroscopy, and they were not found to contain any nonstoichiometric Ga or As. Secondary ion mass spectrometry analysis of the films indicated high levels of Si, O, and C, which are impurities in the precursor. 26 refs., 4 figs., 2 tabs.