Nondestructive multi-element determination of air particulates in Hong Kong

Nondestructive neutron activation analysis employing reactor neutrons and a Ge(Li) gamma-spectrometer has been used to determine the trace element level of air particulates in various areas of Hong Kong. Comparison of the average concentrations of the trace elements of air particulates was made among industrial, heavy-traffic and residential areas. It was found that industrial areas have higher concentrations of Co, Cr, Hg, Mn and Zn, while heavy-traffic areas have very high concentrations of Br. Comparison of the pollution level of Hong Kong with other cities was also made. The average concentrations of Co, Cr, Hg, Zn and Br of air particulates in Hong Kong were found to have higher values than those of other cities. Finally, daily variation of the trace element level in a special area (Hung Hom) had been studied, but no significant variation was found.     

A novel,highly electrical conducting,single-component molecular material: [Ag2(ophen)2] (Hophen = 1H-[1,10]phenanthrolin-2-one)

This communication describes a highly conducting, single-component molecular material [Ag2(ophen)2] (Hophen = 1H-[1,10]phenanthrolin-2-one) based on very strong off-set pi-pi stacking interactions with an unusually short ring-to-ring distance of ca. 3.15 A between adjacent molecules and silver(I)-pi interactions with the Ag...C contact of 3.082 A between adjacent molecules. The title compound, having a room-temperature conductivity of 14 S cm-1, is structurally different from both the known conducting single-component molecular materials of transition-metal complexes with sulfur-containing pi-delocalized dithiolene ligands and the known conducting multicomponent organosilver(I) materials.     

HPLC analysis of an amino bisphosphonate in pharmaceutical formulations using postcolumn derivatization and fluorescence detection

Monosodium 4-amino-1-hydroxybutane-1, 1-diphosphonic acid (MK-217) is a bone resorption inhibitor implicated in the treatment of malignant hypercalcemia. This compound is very water soluble and has five ionizable groups with pKa values over the entire pH range. As a result, it is difficult to maintain a single species in solution for chromatographic separation. Since there is no chromophore in the molecular structure, UV detection is ineffective. The compound and its potential degradation products are separated by ion-pair chromatography using 0.01 M cetyltrimethylammonium bromide as the ion-pairing agent and a polymeric stationary phase. Detection is by fluorescence detection after postcolumn derivatization of the primary amine with ophthalaldehyde and mercaptoethanol (OPA-MERC). Optimization of the chromatographic separation and the postcolumn reaction has been carried out, and the method has been applied to the analysis of MK-217 in intravenous solutions and tablet formulations.     

Coupling reactions of CO2 with neat epoxides catalyzed by PPN salts to yield cyclic carbonates

The off-the-shelf reagent PPN+Cl- and PPN-manganese carbonylates [PPN]+[Mn(CO)4L]- (L = CO, PPh3) are good catalysts for the coupling reactions of CO2 with neat epoxides without the use of organic solvents to afford cyclic carbonates. PPN salts with weak nucleophilic anions such as PPN+BF4- and PPN+OTf- are, however, inactive for the coupling reactions.     

Synthesis and structural characterization of a series of high-hydride content osmium-rhodium carbonyl complexes by the hydrogenation of arene-coordinated clusters

The reaction of [Os3Rh(mu-H)3(CO)12] with an excess amount of 4-vinylphenol (as hydride acceptor) in refluxing m-xylene, chlorobenzene or benzene yielded the three new clusters [Os5Rh2(mu-CO){eta6-C6H4(CH3)2}(CO)16] 1, [Os5Rh2(mu-CO)(eta6-C6H5Cl)(CO)16] 2 and [Os5Rh2(mu-CO)(eta6-C6H6)(CO)16] 3. The treatment of [Os3Rh(mu-H)3(CO)12] 4 in refluxing toluene with an excess amount of 4-vinylphenol afforded a new complex, [Os4Rh(mu-H)(eta6-C6H5CH3)(CO)12], which was isolated as a brown complex in 20% yield together with two known compounds, [Os5Rh2(eta6-C6H5CH3)(mu-CO)(CO)16] in 10% yield and [Os3Rh4(mu3-eta1:eta1:eta1-C6H5CH3)(CO)13] in 5% yield. Complexes 1-4 were fully characterized by IR, 1H NMR spectroscopy, mass spectroscopy, elemental analysis and X-ray crystallography. The molecular structures of compounds 1-3 are isomorphous, and only differ in the arene-derivatives that attach to the same metal core. Their metal cores can be viewed as a monocapped octahedral, in which an osmium atom caps one of the Os-Os-Os triangular faces of the Os4Rh2 metal framework. Complex 4 has a trigonal-bipyramidal metal core with a C6H5Me ligand that is terminally bound to the Rh atom that lies in the trigonal plane of the metal core. The hydrogenation of [Os5Rh2(eta6-C6H5CH3)(mu-CO)(CO)16] with [Os3(mu-H)2(CO)10] in chloroform under reflux resulted in two hydrogen-rich compounds: [Os7Rh3(mu-H)11(CO)23] 5 and [Os5Rh3Cl(mu-H)8(CO)18] 6, both in moderate yields. The reaction of [Os5Rh2(eta6-C6H5CH3)(mu-CO)(CO)16] with hydrogen in refluxing chloroform yielded a new cluster compound, [Os5Rh(mu-H)5(CO)18] 7, in 20% yield, together with a known osmium-rhodium cluster, [Os6Rh(mu-H)7(mu-CO)(CO)18], as a major compound. Clusters 5, 6, and 7 have been fully characterized by both spectroscopic and crystallographic methods. Additionally, a deuterium-exchange experiment was performed on [Os7Rh3(mu-H)11(CO)23] 5 and [Os5Rh3Cl(mu-H)8(CO)18] 6. Both the compounds proved to be able to exchange the H atom with D in the presence of D2SO4, and the absence of the hydride signal in the 1H NMR spectrum is consistent with this. Therefore, clusters 5 and 6 may serve as appropriate new hydrogen storage models.     

Hydrocarbon oxidation by beta-halogenated dioxoruthenium(VI) porphyrin complexes: effect of reduction potential (RuVI/V) and C-H bond-dissociation energy on rate constants

beta-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru(VI)(F(28)-tpp)O(2)] [F(28)-tpp=2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(VI)(beta-Br(8)-tmp)O(2)] [beta-Br(8)-tmp=2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(2,4,6-trimethylphenyl)porphyrinato(2-)] were prepared from reactions of [Ru(II)(por)(CO)] [por=porphyrinato(2-)] with m-chloroperoxybenzoic acid in CH(2)Cl(2). Reactions of [Ru(VI)(por)O(2)] with excess PPh(3) in CH(2)Cl(2) gave [Ru(II)(F(20)-tpp)(PPh(3))(2)] [F(20)-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(II)(F(28)-tpp)(PPh(3))(2)]. The structures of [Ru(II)(por)(CO)(H(2)O)] and [Ru(II)(por)(PPh(3))(2)] (por=F(20)-tpp, F(28)-tpp) were determined by X-ray crystallography, revealing the effect of beta-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru(VI)(F(20)-tpp)O(2)] shows a Ru=O bond length of 1.718(3) A. Electrochemical reduction of [Ru(VI)(por)O(2)] (Ru(VI) to Ru(V)) is irreversible or quasi-reversible, with the E(p,c)(Ru(VI/V)) spanning -0.31 to -1.15 V versus Cp(2)Fe(+/0). Kinetic studies were performed for the reactions of various [Ru(VI)(por)O(2)], including [Ru(VI)(F(28)-tpp)O(2)] and [Ru(VI)(beta-Br(8)-tmp)O(2)], with para-substituted styrenes p-X-C(6)H(4)CH=CH(2) (X=H, F, Cl, Me, MeO), cis- and trans-beta-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k(2)) obtained for the hydrocarbon oxidations by [Ru(VI)(F(28)-tpp)O(2)] are up to 28-fold larger than by [Ru(VI)(F(20)-tpp)O(2)]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru(VI)(F(28)-tpp)O(2)] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k(2) values for the oxidation of styrene and ethylbenzene by [Ru(VI)(por)O(2)] increase with E(p,c)(Ru(VI/V)), and there is a linear correlation between log k(2) and E(p,c)(Ru(VI/V)). The small slope (approximately 2 V(-1)) of the log k(2) versus E(p,c)(Ru(VI/V)) plot suggests that the extent of charge transfer is small in the rate-determining step of the hydrocarbon oxidations. The rate constants correlate well with the C-H bond dissociation energies, in favor of a hydrogen-atom abstraction mechanism.     

Synthesis and characterization of phosphorescent cyclometalated iridium complexes

The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several different cyclometalated ligands are reported. IrCl3.nH2O cleanly cyclometalates a number of different compounds (i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole, and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, CwedgeN2Ir(mu-Cl)2IrCwedgeN2 (CwedgeNis a cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric CwedgeN2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by the nature of the cyclometalating ligand, leading to lambda(max) values from 510 to 606 nm for the complexes reported here. The strong spin-orbit coupling of iridium mixes the formally forbidden 3MLCT and 3pi-pi* transitions with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1-0.4) and room temperature lifetimes in the microsecond regime. The emission spectra of the CwedgeN2Ir(LX) complexes are surprisingly similar to the fac-IrCwedgeN3 complex of the same ligand, even though the structures of the two complexes are markedly different. The crystal structures of two of the CwedgeN2Ir(acac) complexes (i.e., CwedgeN = ppy and tpy) have been determined. Both complexes show cis-C,C', trans-N,N' disposition of the two cyclometalated ligands, similar to the structures reported for other complexes with a "CwedgeN2Ir" fragment. NMR data (1H and 13C) support a similar structure for all of the CwedgeN2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and (tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes relative to their solution spectra.     

Synthesis and copolymerization reaction of a triosmium alkylidyne carbonyl cluster [Os3(μ-H)2(CO)9(μ3-CNC5H4-CH=CH2)]

A neutral triosmium alkylidyne carbonyl cluster containing the 4-vinylpyridine (4vpy) moiety [Os₃(µ-H)₂(CO)₉(µ₃-CNC₅H₄-CH=CH₂)] (1) has been prepared as red crystalline solids in good yield. Monomer (1) was copolymerized with styrene in the presence of ,'-azobis(isobutyronitrile) (AIBN) in chloroform at 60°C and a polymer-immobilized alkylidyne cluster of osmium was obtained. To compare the spectroscopic properties with the copolymers, a structurally similar repeating unit of the copolymers, [Os₃(µ-H)₂(CO)₉(µ-₃-CNC₅H₄-CH₂CH₃)I](2), has also been synthesized and characterized.     

Oxidative addition of 2,2′-dithiosalicylic acid to the cluster [Os3(CO)10)(CH3CN)2]

The reaction of 2,2'-dithiosalicylic acid with two equivalents of [Os₃(CO)₁₀ (CH₃CN)] in THF at –78°C yields yellow crystals of [{Os₃(CO)₁₀(-H)}₂ (O₂CC₆H₄S)₂] 1 in moderate yield. Hydrogenetaion of 1 in refluxing CHCl₃ affords [Os₃(CO)₁(-H)(O₂CC₆H₅)] 2 in good yield. Structures of 1 and 2 have been established by single crystal X-ray structure analysis.