Recent progress in the studies of endohedral metallofullerenes

This overview presents the recent progress in the area of endohedral metallofullerenes in the past several years. The important results have been summarized as follows: (1) Many metals including Group 3 metals, most of the lanthanide series elements, and Group 2 metals have been encapsulated into a fullerene cage to form mono-, di-, and trimetallofullerenes by using the arc-evaporation technique. (2) Some endohedral metallofullerenes such as Group 3 metals, most of the lanthanide series elements, Group 2 metals, and some of their isomers have been successfully isolated and purified by a two-step or several-step HPLC technique. By using high-temperature and high-pressure extraction with pyridine, Ln@C-80, Ln@C-82, and Ln2@C-80 for most rare-earth metals have been selectively extracted in high yield (about 1% of the saw soot) from fullerenes and other size metallofullerenes. (3) The endohedral nature of metallofullerenes such as Y@C-82, Sc2@C-84, and Sc@C-82 has been finally confirmed by synchrotron X-ray powder diffraction. The symmetries and the structures of metallofullerenes such as Ca@C-82(III), La-2@C-80(I-h), Sc-2@C-84(D-2d), and Sc-2@C-84(C-s) have been confirmed by NMR measurements. (Lb) The information on the electronic structures and properties of endohedral metallofullerenes has been obtained by various spectrometric means Such as EPR, W-vis-MR, XPS, CV. It is generally accepted that three-electron transfer is favorable when M = Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Lu but Sc, Eu, Sm, Yb, Tm, Ca, Sr, Ba prefer to donate two electrons to the fullerene cages. (5) Several chemical reactions of endohedral metallofullerenes have been reported in which reagents are disilacyclopropane, digermacyclopropane, diphenyldiazomethane, and trifluoroacetic acid. (6) Mass spectrometry provided the crucial evidence that led to the discovery of metallofullerenes in 1985 and has always played a key role in their identification and characterization, Ion-mobility measurements of gas-phase ions have obtained the information of structures and the formation mechanism of endohedral metallofullerenes. till Theoretical calculations on the endohedral metallofullerenes have made an important contribution to the studies on the symmetry of the cage, the position of metal atom(s) inside the cage, the number of electronic transfer between metal atom(s) and fullerene cage, etc. (C) 2000 Elsevier Science S.A. All rights reserved.

Synthesis, electrochemistry and fluorescence of four new Ru(phen)(3)(2+) derivatives

Four typical LB monolayer film materials, Ru(phen)(3)(2+) complexes with one ligand attached to different long chain alkyl amides, were designed and synthesized. Their chemical structures were identified by the techniques of FT-IR, H-1 NMR and ESI-MS. Also, UV-Vis, electrochemistry and fluorescence of these complexes are reported.

Reaction of halfsandwich iridium polychalcogenide complexes with dimethyl acetylenedicarboxylate. Molecular structure of Cp*Ir[S2C2(COOMe)(2)]

The pentamethylcyclopentadienyl iridium complexes Cp*Ir(PMe3)(E-n) (E = S, n = 4, 5 or 6; E = Se, n = 2 or 4 E = Te, n = 2) react with dimethyl acetylenedicarboxylate to give Cp*Ir(PMe3)[E2C2(COOMe)(2)] compounds which tend to lose the trimethylphosphine ligand; the molecular structure of the dithiolene derivative, Cp*Ir[S2C2(COOMe)(2)], has been determined.

Studies on preparation of iron phenanthroline and 8-hydroxyquinoline complexes/Y zeolite, characterization and catalytic hydroxylation of phenol

Iron phenanthroline - and 8 - hydroxyquinoline complexes /Y zeolite, denoted a FePhen/Y and FeOx/Y respectively, were prepared; The formation of the metal complexes mentioned above within the cages of Y zeolite and their crystal structures were determined by elemental analyses, diffuse reflectance UV-Vis,SEM,BET,and XRD methods; The influence of experimental parameters upon phenol conversion and product selectivities were investigated as well.

Studies on preparation, characterization of cobalt(II) phenanthroline and 8-hydroxyquinoline complexes/Y zeolite, and catalytic hydroxylation of phenol

Cobalt(II) phenanthroline and 8-hydroxyquinoline complexes/Y zeolite, denoted as CoPhen/Y and CoOx/Y respectively, were prepared, The formation of the metal complexes mentioned above within the cages of Y zeolite and their crystal structures were determined by elementary analyses, TG-DTA, diffuse reflectance UV-Vis, SEM, BET and XRD methods. The influence of experimental parameters upon phenol conversion and product selectivities was investigated as well.

STRUCTURE OF CIS-DIAQUABIS(1,10-PHENANTHROLINE)ZINC SULFATE HEXAHYDRATE

[Zn(C12H8N2)2(H2O)2]SO4.6H2O, M(r) = 665.98, triclinic, P1BAR, a = 10.070 (4), b = 12.280 (3), c = 13.358 (2) angstrom, alpha = 109.12 (2), beta = 92.58 (2), gamma = 110.85 (2)-degrees, V = 1433.9 (7) angstrom 3, Z = 2, D(x) = 1.54 g cm-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 10.1 cm-1, F(000) = 692, T = 293 K, R = 0.044 for 3985 observed reflections. The Zn atom is coordinated in a distorted octahedral geometry by four N atoms from two 1,10-phenanthroline (phen) ligands and two water molecules. The intermolecular ring-stacking interactions between the phen ligands occur in two forms: infinite chains and discrete dimers. Hydrogen bonds further stabilize the structure.

SYNTHESIS OF ALKALI-METAL HYDRIDES USING LANTHANIDE TRICHLORIDE-NAPHTHALENE AS CATALYST UNDER MILD CONDITIONS

The hydrogenation of alkali metals using lanthanide trichloride and naphthalene as catalyst has been studied. LnCl3(Ln = La, Nd, Sm, Dy, Yb) and naphthalene can catalyze the hydrogenation of sodium under atmospheric pressure and 40-degrees-C to form sodium hydride. The activities of lanthanide trichlorides are in the following order: LaCl3 > NdCl3 > SmCl3 > DyCl3 > YbCl3. Although lithium proceeds in the same catalytic reaction, the kinetic curve of the lithium hydrogenation is different from that of sodium. Lanthanide trichlorides display no catalytic effect on the hydrogenation of potassium in presence of naphthalene. The mechanism of this reaction has been studied and it is suggested that the anion-radical of alkali metal naphthalene complexes may be the intermediate for the hydrogenation of alkali metals and the function of LnCl3 is to catalyze the hydrogenation of the intermediate. The products are porous solids with high specific surface area (83 m2/g for NaH) and pyrophoric in air. They are far more active than the commercial alkali metal hydrides. The combination of these hydrides with some transition metal complexes exhibits high catalytic activity for the hydrogenation of olefins.

Precursor chemistry for oxide related materials

This thesis describes modelling, synthesis, spectroscopic and physical characterisation, as well as application of Magnesium, Calcium and Copper β-diketonate, β-ketoiminate, β-diiminate, Schiff base, amide and fluorenyl compounds. The selected compounds could potentially find application in materials deposition using Atomic Layer Deposition (ALD), MOCVD, CVD and Sol-Gel techniques. Quantum chemical modelling was used as a tool to perform the comprehensive and rapid study of magnesium and calcium precursor molecules in order to predict which of them would be more successful in ALD of metal oxides. Precursor chemistry plays a key role in ALD, since precursors must be volatile, thermally stable, chemisorb on the surface and react rapidly with existing surface groups. This Thesis describes one aspect of this, surface reactivity between ligands and hydroxyl groups, via a gas-phase model with energetics computed at the level of Density Functional Theory (DFT). A number of different synthetic strategies, both aerobic and anaerobic, were investigated for the synthesis of the described metal complexes. These included the use of different metal starting reagents such as, anhydrous and hydrated inorganic metal salts, metal alkyls and Grignard reagents. Some of previously unreported metal complexes of homoleptic and heteroleptic magnesium, calcium and copper β-diketonates, β-ketoiminates, β-diiminates, amides and Schiff base type were synthesised and characterised: [Mg(hfpd)2(DipPa)], [Mg(hfpd)2(MapH)2], [Mg(hf-ebp)(THF)2], [Mg(tf-Pap)Cl(THF)2], [Ca(PhNacnac)2], [Cu(tf-Pap)2], [Cu(PhNacnac)2], [Cu(hf-ebp)], [Cu(DipPa)] and [Cu(DipPa)2(4,4’-bypy)]. A comprehensive study on the thermal properties of magnesium, calcium and copper β-diketonates, β-ketoiminates, β-diiminates, Schiff base, amide and fluorenyl complexes was performed using TGA and sublimation of selected compounds. Atomic Layer Deposition of MgO using magnesium β-ketoiminate – [bis{(4-N-phenyl)-2-pentonato} magnesium] and β-diketonate - [bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)(THF)magnesium hydrate] was performed on Si(100) substrates at 180°C and 0.2 Torr using O2 plasma.

Imidazo[4,5-f]-1,10-phenanthrolines: Versatile ligands for the design of metallomesogens

2-Aryl-substituted imidazo[4,5-f]-1,10-phenanthrolines were used as building blocks for metal-containing liquid crystals (metallomesogens). Imidazo[4,5-f]-1,10-phenanthrolines are versatile ligands because they can form stable complexes with various d-block transition metals, including platinum(II) and rhenium(I), as well as with lanthanide(III) and uranyl ions and they can easily be structurally modified by a judicious choice of benzaldehyde precursor. None of the ligands designed for this study were liquid-crystalline. However, mesomorphism could be induced by their coordination to various metallic fragments. The thermal behavior of the metal complexes depended on the metal-to-ligand ratio and the substitution pattern of the coordinating ligands. Complexes with a metal-to-ligand ratio of 1:1 [ML, with M = Pt(II), Re(I)] were not liquid-crystal line. The lanthanide(III) complexes with a metal-to-ligand ratio of 1:2 [ML2 with M = Ln(III)] formed an enantiotropic cubic mesophase or were not liquid-crystalline, depending on the nature of the lanthanide(III) ion and the substitution pattern of the ligands. A 1:3 uranyl complex of the type [ML3](2+) exhibited a hexagonal columnar mesophase over a broad temperature range. Self-assembled monolayers of a europium(III) complex were investigated by scanning tunneling microscopy, which revealed that the complex formed well-ordered structures over long distances at the 1-octanoic acid-graphite interface. The rhenium(I) complexes and the europium(III) complexes with 2-thenoyl-trifluoroacetonate or dibenzoylmethanate and imidazo[4,5-f]-1,10-phenanthroline showed good luminescence properties.

Rare-earth quinolinates: Infrared-emitting molecular materials with a rich structural chemistry

Near-infrared-emitting rare-earth chelates based on 8-hydroxyquinoline have appeared frequently in recent literature, because they are promising candidates for active components in near-infrared-luminescent optical devices, such as optical amplifiers, organic light-emitting diodes, .... Unfortunately, the absence of a full structural investigation of these rare-earth quinolinates is hampering the further development of rare-earth quinolinate based materials, because the luminescence output cannot be related to the structural properties. After an elaborate structural elucidation of the rare-earth quinolinate chemistry we can conclude that basically three types of structures can be formed, depending on the reaction conditions: tris complexes, corresponding to a 1:3 metal-to-ligand ratio, tetrakis complexes, corresponding to a 1:4 metal-to-ligand ratio, and trimeric complexes, with a 3:8 metal-to-ligand ratio. The intensity of the emitted near-infrared luminescence of the erbium(Ill) complexes is highest for the tetrakis complexes of the dihalogenated 8-hydroxyquinolinates.

Application Of the Michaelis-Arbuzov Reaction to the Synthesis Of Internucleoside 3'-S-Phosphorothiolate Linkages

The 5'-O-monomethoxytrityl-3'-S-(aryldisulfanyl)-3'-deoxythymidines 7 and 8 have been prepared by the reaction of 5'-O-monomethoxytrityl-3'-thiothymidine with the appropriate arenesulfenyl chloride. These disulfides undergo a Michaelis–Arbusov reaction with simple trialkyl phosphites to yield 5'-O-monomethoxytrityl-3'-thiothymidin-3'-yl O,O-dialkyl phosphorothiolates. More interestingly, 3'-deoxy-3'-S-(2, 4-dinitrophenylsulfanyl)-5'-O-monomethoxytritylthymidine 8 reacts with a variety of thymidin-5'-yl dialkyl phosphites to give dithymidine phosphorothiolate triesters with the phosphorothiolate group protected with either a methyl or a 2-cyanoethyl group. 3'-O-(tert-Butyldimethylsilyl)thymidin-5'-yl triethylammoniumphosphonate 17 is converted into the corresponding bis-(O-trimethylsilyl) phosphite by treatment with bis(trimethylsilyl)trifluoroacetamide. in situ Reaction of this phosphate with disulfide 8 gives, after work-up, the dithymidine phosphorothiolate diester directly. Methylation of compound 17 with methyl chloromethanoate, followed by silylation and subsequent reaction with disulfide 8, gives the methyl-protected dithymidine phosphorothiolate triester.

Resonance Raman probing of the interaction between dipyridophenazine complexes of Ru(II) and DNA

Resonance Raman (RR) spectroscopy has been used to probe the interaction between dipyridophenazine (dppz) complexes of ruthenium(II), [Ru(L)(2)(dppz)](2+) (L = 1,10-phenanthroline (1) and 2,2-bipyridyl (2)), and calf-thymus DNA. Ground electronic state RR spectra at selected probe wavelengths reveal enhancement patterns which reflect perturbation of the dppz-centered electronic transitions in the UV-vis spectra in the presence of DNA. Comparison of the RR spectra recorded of the short-lived MLCT excited states of both complexes in aqueous solution with those of the longer-lived states of the complexes in the DNA environment reveals changes to excited state modes, suggesting perturbation of electronic transitions of the dppz ligand in the excited state as a result of intercalation. The most prominent feature, at 1526 cm(-1), appears in the spectra of both 1 and 2 and is a convenient marker band for intercalation. For 1, the excited state studies have been extended to the A and A enantiomers. The marker band appears at the same frequency for both but with different relative intensities. This is interpreted as reflecting the distinctive response of the enantiomers to the chiral environment of the DNA binding sites. The results, together with some analogous data for other potentially intercalating complexes, are considered in relation to the more general application of time-resolved RR spectroscopy for investigation of intercalative interactions of photoexcited metal complexes with DNA.

RAMAN-SCATTERING AND SCANNING ELECTRON-TUNNELING STUDIES OF METAL LIQUID-LIKE FILMS PRODUCED FROM SILVER AND GOLD SOLS

Surface-enhanced Raman scattering (SERS) excited at several visible wavelengths and recorded using a cooled charged-coupled device detector is reported from the mobile, interfacial, liquid-like metal films (MELLFs) formed when solutions of metal complexes or pyridine in chlorocarbon solvents are mixed with aqueous sols of silver or gold. MELLF formation has not previously been reported for gold sols or for pyridine as stabilizer. Comparison of the spectra for the MELLFs formed from individual metal complexes and from 50:50 mixtures show that the spectral patterns observed for the latter are distinctive and are not generally equivalent to the sum of the spectra associated with the individual complexes, in contrast to the situation observed for sols where the individual spectra do appear to be additive. Raman scattering from both gold and silver MELLFs is readily observed at excitation wavelengths in the red, around 750 nm, but at 514 nm only that from silver films is detectable. These findings are considered in terms of particle size and absorption band intensities. A preliminary study of the film surface topography and particle size was carried out by scanning tunnelling electron microscopy (STM) of Ag MELLFs deposited on gold-coated mica substrates. Computer-processed images of the STM data show the presence on the film surface of finger-like bars, 200-400 nm long with approximately square cross-section, 40-60 nm side, together with other smaller cuboid features. The implications of these findings in relation to SERS are briefly considered.

The Use of Electrospray Mass Spectrometry to Determine Speciation in a Dynamic Combinatorial Library for Anion Recognition

The composition of a dynamic mixture of similar 2,2'-bipyridine complexes of iron(II) bearing either an amide (5-benzylamido-2,2'-bipyridine and 5-(2-methoxyethane)amido-2,2'-bipyridine) or an ester (2,2'-bipyridine-5-carboxylic acid benzylester and 2,2'-bipyridine-5-carboxylic acid 2-methoxyethane ester) side chain have been evaluated by electrospray mass spectroscopy in acetonitrile. The time taken for the complexes to come to equilibrium appears to be dependent on the counteranion, with chloride causing a rapid redistribution of two preformed heteroleptic complexes (of the order of 1 hour), whereas the time it takes in the presence of tetrafluoroborate salts is in excess of 24^^h. Similarly the final distribution of products is dependent on the anion present, with the presence of chloride, and to a lesser extent bromide, preferring three amide-functionalized ligands, and a slight preference for an appended benzyl over a methoxyethyl group. Furthermore, for the first time, this study shows that the distribution of a dynamic library of metal complexes monitored by ESI-MS can adapt following the introduction of a different anion, in this case tetrabutylammonium chloride to give the most favoured heteroleptic complex despite the increasing ionic strength of the solution.