Kalyan V. Vasudevan

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.

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.

Boron di- and tri-cations

Previous work on boron di- and tri-cations is reviewed. The structural chemistry of representative examples of these classes of compound has been probed by determination of the single-crystal X-ray structures of [(4-Mepy)4B]Br3 and [py3BH]Br2. The electronic structures of the polycations [(py)3BH]2+, [(py)3BBr]2+, [(4-Mepy)3BH]2+, [(4-Mepy)4B]3+, [(Me3P)3BH]2+ and [(Me3P)4B]3+ have been examined by DFT methods. The atomic charges on these cations were evaluated by Mulliken, natural population analysis (NPA), Hirschfeld and Voronoi deformation density (VDD) methods.

Facile syntheses of thiophene-substituted 1,4-diazabutadiene (α-diimine) ligands and their conversion to phosphenium triiodide salts

Four novel N-aryl-2-thienyl substituted 1,4-diazabutadiene (alpha-diimine) ligands 5-8 have been prepared by cyanide ion-catalyzed intermolecular coupling of the appropriate aromatic aldimines. A ligand featuring a phenyl spacer moiety between a thiophene carbon atom and each imino nitrogen atom (12) has been prepared by a similar synthetic route. Ligands 5-8 and 12 were characterized on the basis of 1H and 13C NMR, IR and MS-CI spectroscopy. Upon treatment with PI3 in CH2Cl2 solution, ligands 5-8 undergo redox reactions to furnish the triiodide salts of the corresponding phosphenium cations 13-16 which were characterized by 1H, 13C and 31P NMR, and MS-CI spectroscopy. The phosphenium triiodide salt 15, and ligands 5-7 and 12 were also structurally authenticated.

An ionic liquid-mediated route to cerium(III) bromide solvates.

A novel synthetic route to a series of cerium bromide solvates is reported. The combination of bulk cerium bromide and the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide results in a precursor paste that enhances the solubility of the cerium(III)bromide moiety in a number of donor solvents. Crystallization from these solvents has resulted in the isolation and characterization of CeBr(3)(THF)(4) (2), CeBr(3)(2-Me-THF)(4) (3), and CeBr(3)(MeCN)(5)·MeCN (4). Additionally, 2 is shown to be an efficient precursor for the new species CeBr(3)(py)(4) (5) and CeBr(3)(bipy)(py)(3) (6).

Tetrakis(imino)pyracene Complexes Exhibiting Multielectron Redox Processes

The differences in redox behavior of the monofunctional bis(imino)acenaphthene (BIAN) and bifunctional tetrakis(imino)pyracene (TIP) ligands have been explored by treatment of the latter with PI(3), TeI(4), or BI(3). These reactions result in the formation of products involving the transfer of three or four electrons. Accompanying DFT calculations reveal that in each case the extent of electron transfer from each p-block element into the TIP ligand is dependent upon the element-TIP bonding interactions.

New bimetallic complexes supported by a tetrakis(imino)pyracene (TIP) ligand

The first examples of palladium dihalide and indium trihalide complexes supported by a tetrakis(imino)pyracene (TIP) ligand have been prepared and structurally characterized.

Facile routes to Alkyl-BIAN ligands

The Alkyl-BIAN ligands tert-Butyl-BIAN and 1-Adamantyl-BIAN have been synthesized and their structures have been determined by single-crystal X-ray diffraction along with that of the ZnCl2 complex of tert-Butyl-BIAN.

A Base Induced Transformation Of A 1,3-Dimethyl-1,3-Di-(1-Adamantyl)Formamidinium Salt Into Beta- Methyl-(1-Adamantyl)Amino Acrylonitriles In Aliphatic Nitriles

A novel 1,3-dimethyl-1,3-di-(1-adamantyl)formamidinium perchlorate has been prepared via the Vilsmeier-Haack reaction of N-methyl-N-(1-adamantyl)formamide and N-methyl- N-(1-adamantyl)amine in a mixture of phosphorus oxychloride and benzene. The new formamidinium salt was found to undergo addition-elimination reactions when treated with sodium hydride in acetonitrile or propionitrile solution, thereby forming the corresponding �-(methyl(1-adamantyl)amino)acrylonitriles and N-methyl-N-(1-adamantyl)amine. The 1 H and 13 C NMR spectra and the single-crystal X-ray structure of the new formamidinium salt have been determined along with those of the related compound 1,3-di-(1-adamantyl)-1- cyanoamidine and the corresponding �-(dialkylamino)acrylonitriles.