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Wing-Tak Wong

Publications and source records attributed to Wing-Tak Wong.

At least 19 recordsLinked to original sources
PubMed2006

Nanostructure PtRu/MWNTs as anode catalysts prepared in a vacuum for direct methanol oxidation.

Platinum and ruthenium nanoparticles that are uniformly dispersed on multiwalled carbon nanotubes (MWNTs) were synthesized by vacuum pyrolysis using Pt(acac)2 and Ru(acac)3 as the metal precursors. The resulting nanocomposites were characterized by transmission electron microscopy and X-ray diffraction. The Pt, Pt45Ru55, and Ru nanoparticles had mean diameters of 3.0 +/- 0.6, 2.7 +/- 0.6, and 2.5 +/- 0.4 nm and the same mole number as their metal precursors at 500 degrees C. The electrocatalytic activity of the Pt/MWNTs and PtRu/MWNTs was investigated at room temperature by cyclic voltammetry and chronoamperometry. All of the electrochemical results showed that the PtRu/MWNTs exhibited a high level of catalytic activity for methanol oxidation as a result of the large surface area of the supporting carbon nanotubes and the wide dispersion of the Pt and Ru nanoparticles. Compared with the Pt/MWNTs, the onset potential for methanol oxidation of the PtRu/MWNTs was significantly lower, and the ratio of the forward anodic peak current to the reverse anodic peak current during methanol oxidation was somewhat higher. The Pt45Ru55/MWNTs displayed the best electrocatalytic activity of all of the carbon-nanotube-supported Pt and PtRu catalysts.

Journal Article↗
PubMed2006

2D LnIII RuIII 2 compounds constructed from trans-[Ru(acac)2(CN)2]-. Syntheses, structures, and magnetic properties.

A series of cyano-bridged Ln(III)Ru(III)2 coordination polymers, Ph4P{Ln(NO3)2[Ru(acac)2(CN)2]2} [Ln = Tb (1), Dy (2), Er (3), Gd (4); Hacac = acetylacetone] have been synthesized by the reaction of Ln(NO3)3 with trans-Ph4P[Ru(acac)2(CN)2] in methanol. X-ray crystallographic determination reveals that these compounds are isostructural and have a wavy (4,4) layer structure with the Ln3+ ions bridged by trans-[Ru(acac)2(CN)2]-. Magnetic studies shows that the magnetic coupling between the Ln(III) and Ru(III) ions through the cyano bridges in 1-4 is negligibly weak.

Journal Article↗
PubMed2006

NMR studies of lysozyme surface accessibility by using different paramagnetic relaxation probes.

Paramagnetic probes, whose approach to proteins can be monitored by nuclear magnetic resonance (NMR) studies, have been found to be of primary relevance for investigating protein surfaces' accessibility. Here, a Gd(III) neutral complex which contains two metal ions, [Gd2(L7)(H2O)2], is suggested as a paramagnetic probe particularly suited for systematic NMR investigation of protein surface accessibility, due to an expected high relaxivity and to the lack of electric charge which could favor specific interactions. Hen egg white lysozyme has been used as a model system to verify the absence of preferential approaches of this paramagnetic probe to specific protein moieties by comparing paramagnetic perturbation profiles of 1H-13C HSQC signals obtained in the presence of TEMPOL and [Gd2(L7)(H2O)2]. From the similarity of the measured paramagnetic perturbation profiles induced by the two different probes, specific interactions of [Gd2(L7)(H2O)2] with the enzyme could be ruled out. The large size of the latter probe is suggested to be responsible for the strong paramagnetic perturbations observed for CalphaH groups which are located in convex surface-exposed regions. The combined use of the two probes reveals fine details of the dynamics controlling their approach toward the protein surface.

Electron Spin Resonance Spectroscopy↗
PubMed2005

Heterometallic MIIRuIII2 compounds constructed from trans-[Ru(Salen)(CN)2]- and trans-[Ru(Acac)2(CN)2]-. Synthesis, structures, magnetic properties, and density functional theoretical study.

The synthesis, structures, and magnetic properties of four cyano-bridged M(II)Ru(III)2 compounds prepared from the paramagnetic Ru(III) building blocks, trans-[Ru(salen)(CN)2]- 1 [H2salen = N,N'-ethylenebis(salicylideneimine)] and trans-[Ru(acac)2(CN)2]- (Hacac = acetylacetone), are described. Compound 2, {Mn(CH3OH)4[Ru(salen)(CN)2]2}.6CH3OH.2H2O, is a trinuclear complex that exhibits antiferromagnetic coupling between Mn(II) and Ru(III) centers. Compound 3, {Mn(H2O)2[Ru(salen)(CN)2]2.H2O}n, has a 2-D sheetlike structure that exhibits antiferromagnetic coupling between Mn and Ru, leading to ferrimagnetic-like behavior. Compound 4, {Ni(cyclam)[Ru(acac)2(CN)2]2}.2CH3OH.2H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane), is a trinuclear complex that exhibits ferromagnetic coupling. Compound 5, {Co[Ru(acac)2(CN)2]2}n, has a 3-D diamond-like interpenetrating network that exhibits ferromagnetic ordering below 4.6 K. The density functional theory (DFT) method was used to calculate the molecular magnetic orbitals and the magnetic exchange interaction between Ru(III) and M(II) (Mn(II), Ni(II)) ions.

Journal Article↗
PubMed2005

Structure and spectroscopy of Tb[Au(CN)2]3.3H2O.

The compound Tb[Au(CN)2]3.3H(2)O crystallizes in a layered structure in the hexagonal space group P6(3)/mcm with the 9-coordinate environment of Tb3+ comprising six (CN)- and three OH2 in a tricapped trigonal prism. The shortest Au...Au distance is 3.31 angstroms. The vibrational spectra show that the series Ln[Au(CN)2]3.3H2O (Ln = Y, Pr, Sm, Eu, Tb) are isostructural. The electronic spectra of Eu[Au(CN)2]3.3H2O clearly show that Eu3+ occupies one site of spectroscopic site symmetry D3h, in agreement with the crystallographic data. The electronic emission and absorption spectra of Tb[Au(CN)2]3.3H2O have been recorded at temperatures down to 1.5 K, and the f-f pure electronic transitions are interpreted in detail as arising from the lowest electronic states (in D3h symmetry) (7F6)E' in absorption and (5D4)E'' in emission. At low energy, further bands are assigned to the vibronic structure of the CN stretching and water stretching modes, with the latter more predominant. Although the CN stretching vibrations show exclusive infrared or Raman activity in Tb[Au(CN)2]3.3H2O, both of these infrared and Raman active modes are observed in the two-center vibronic transitions. The reasons for this are discussed.

Journal Article↗
PubMed2005

Carbon-bridged bis(phenolato)lanthanide alkoxides: syntheses, structures, and their application in the controlled polymerization of epsilon-caprolactone.

A convenient method for the synthesis of lanthanide alkoxo complexes supported by a carbon-bridged bis(phenolate) ligand 2,2'-methylenebis(6-tert-butyl-4-methylphenoxo) (MBMP2-) is described. The reaction of (C5H5)3Nd with MBMPH2 in a 1:1 molar ratio in THF gave the bis(phenolato)lanthanide complex (C5H5)Nd(MBMP)(THF)2 (1) in a nearly quantitative yield. Complex 1 further reacted with 1 equiv of 2-propanol in THF to yield the bis(phenolato)lanthanide isopropoxide [(MBMP)2Nd(mu-OPr(i))(THF)2]2 (2) in high yield. Complex 2 can also be synthesized by the direct reaction of (C5H5)3Nd with MBMPH2 in a 1:1 molar ratio and then with 1 equiv of 2-propanol in situ in THF. Thus, the analogue bis(phenolato)lanthanide alkoxides [(MBMP)2Ln(mu-OR)(THF)2]2 [R = Pr(i), Ln = Yb (3); R = Me, Ln = Nd (4), Yb (5); R = CH2Ph, Ln = Nd (6), Yb (7)] were obtained by the reactions of (C5H5)3Ln (Ln = Nd, Yb) with MBMPH2 and then with 2-propanol, methanol, or benzyl alcohol, respectively. The ytterbium complex {[(MBMP)2Yb(THF)2]2(mu-OCH2Ph)(mu-OH)} (8) was also isolated as a byproduct. The single-crystal structural analyses of complexes 1-3 and 8 revealed that the coordination geometry around lanthanide metal can be best described as a distorted tetrahedron in complex 1 and as a distorted octahedron in complexes 2, 3, and 8. A O-H...Yb agostic interaction was observed in complex 8. Complexes 2-7 were shown to be efficient catalysts for the controlled polymerization of epsilon-caprolactone.

Journal Article↗
PubMed2005

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.

Journal Article↗
PubMed2004

Luminescent Tb3+ complex with pendant crown ether showing dual-component recognition of H+ and K+ at multiple pH windows.

[structure: see text] A lanthanide luminescent probe that was functionalized with quinoline-alkylated diaza-18-crown-6 showed dual-component recognition of concentrations of H+ and K+ at four independent pH ranges, including in the physiological pH window. Moreover, it exhibited pH- and [K+]-independent long-lived lanthanide luminescent lifetimes in aqueous solution.

Crown Ethers↗
PubMed2004

Syntheses, structures, photoluminescence, and theoretical studies of d(10) metal complexes of 2,2'-dihydroxy-[1,1']binaphthalenyl-3,3'-dicarboxylate.

The free solvated ligand, H(2)bna.CH(3)OH.H(2)O (1), and its dimeric complex, [Cd(2)(bna)(2)(H(2)O)(6)] (2) (bna = 2,2'-dihydroxy-[1,1']-binaphthalene-3,3'-dicarboxylate), were obtained by evaporation of the solutions, while two new d(10) metal-hydroxy cluster-based coordination polymers, namely [Cd(8)(OH)(4)(H(2)O)(10)(bna)(6)].17H(2)O (3) and [Hpy](2)[Zn(4)(OH)(2)(H(2)O)(2)(bna)(4)].2H(2)O.2CH(3)CN (4), were obtained by a hydrothermal route. All the compounds have been characterized by X-ray crystallography and photoluminescence measurements. Compound 1 consists of a three-dimensional, hydrogen-bonded supramolecular array, 2 exhibits a dimeric molecule featuring a square motif organized by two Cd(II) atoms and two bna ligands each at the corner, and 3 contains unprecedented [Cd(8)(micro(3)-OH)(2)(micro-OH)(2)(micro-H(2)O)(2)](12+) octanuclear metallacrown cores which are interlinked through bna to afford a two-dimensional structure, while 4 features layers with butterfly-shaped [Zn(4)(micro(3)-OH)(2)](6+) clusters. All the complexes display photoluminescent properties in the blue/green range. The manifestation of photoluminescence, as probed by molecular orbital calculations performed on the complexes and also on hypothetical multinuclear complexes, is attributed to a ligand-to-metal charge-transfer mechanism. In addition to presenting a new approach for the study of the photoluminescent properties of metal-cluster-based coordination polymers by using simple model compounds, the study also reveals the dominant role of the structure of the ligand over that of the d(10) metal-hydroxy (or oxy) cluster and the presence of the cluster significantly increasing the emission lifetime.

Journal Article↗
PubMed2004

Highly electrophilic (salen)ruthenium(VI) nitrido complexes.

A series of cationic ruthenium(VI) nitrido species containing the cyclohexyl-bridged salen ligand (L) and its derivatives, [RuVI(N)(L)]+, have been prepared by treatment of [NBun4][RuVI(N)Cl4] with H2L in methanol. The structure of [RuVI(N)(L)](ClO4) (1a) has been determined by X-ray crystallography, d(RuN) = 1.592 A. In solvents such as DMF or DMSO, [RuVI(N)(L)]+ undergoes a facile N...N coupling reaction at room temperature to produce N2 and [RuIII(L)(S)2]+ (S = solvent). 1a reacts rapidly with secondary amines to produce diamagnetic RuIV-hydrazido(1-) species, [RuIV(N(H)NR2)(L)(HNR2)]+. The reaction with morpholine is first order in RuVI and second order in morpholine with k(CH3CN, 25 degrees C) = 2.08 x 106 M-2 s-1. This rate constant is over 4 orders of magnitude larger than that of the corresponding reaction of the electrophilic osmium nitride, trans-[OsVI(N)(tpy)(Cl)2]+, with morpholine. The structure of [Ru(NHNC4H8)(L)(NHC4H8)](PF6)2 has been determined by X-ray crystallography, the Ru-N(hydrazido) distance is 1.940 A, and the Ru-N-N angle is 129.4 degrees .

Journal Article↗
PubMed2004

Novel gadolinium(III) polyaminocarboxylate macrocyclic complexes as potential magnetic resonance imaging contrast agents.

Two novel Gd(III) complexes with functionalised polyaminocarboxylate macrocycles, 1,4,7-tris(carboxymethyl)-9,24-dioxo-14,19-dioxa-1,4,7,10,23- pentaazacyclododecane (L(1)) and 1,4,7-tris(carboxymethyl)-9,25-dioxo-14,17,20-trioxa-1,4,7,10,23- pentaazacyclotridecane (L(2)), were prepared in good yield. Their potential use as magnetic resonance imaging (MRI) contrast agents (CAs) was evaluated by investigating their relaxation behaviour as a function of pH, temperature and magnetic field strength. The 1/T(1) proton relaxivities at 20 MHz and 25 degrees C of GdL(1) (5.87 mM(-1) s(-1)) and GdL(2) (6.14 mM(-1) s(-1)) were found to be significantly higher than the clinically used Gd 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Gd(DOTA)(-)) and Gd diethylenetriaminepentaethanoic acid (Gd(DTPA)(2-)). The complexes possess one water molecule in the inner coordination sphere whose mean residence lifetime was estimated to be 1.1 and 1.5 micros at 25 degrees C by variable temperature (VT) (17)O NMR spectroscopy.

Contrast Media↗
PubMed2003

Syntheses, structures, photoluminescence, and theoretical studies of a novel class of d10 metal complexes of 1H-[1,10]phenanthrolin-2-one.

A novel asymmetric monosubstituted 1,10-phenanthroline, Hophen.0.5 H(2)O (1, Hophen=1H-[1,10]phenanthrolin-2-one), was generated by a facile route, and a novel class of crystalline, d(10)-metal, monomeric or oligomeric complexes of this ligand, namely [Hg(ophen)(2)].4 H(2)O.CH(2)Cl(2) (2), [Cd(3)Cl(ophen)(5)].1.5 H(2)O.2 CH(2)Cl(2) (3), and [Zn(4)O(ophen)(4)(OAc)(2)].4H(2)O.2 CH(2)Cl(2) (4), were obtained by means of liquid diffusion, and were characterized by X-ray crystallography and photoluminescence studies. Complex 1 exhibits a hydrogen-bonded dimeric structure, 2 is a neutral monomeric complex, 3 has a trinuclear structure with the ophen ligand acting as a bridge through the ketone groups, and 4 features a tetranuclear Zn(4)O core that is consolidated further by bridging ophen and acetate ligands. All the complexes display photoluminescent properties in the blue/green region. The photoluminescent mechanisms were investigated by means of molecular orbital calculations, which showed that the photoluminescent properties are ligand-based and can be tuned upon ligation to different metal ions.

Aldose-Ketose Isomerases↗
PubMed2003

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.

Journal Article↗