Seik Weng Ng's research while affiliated with UCSI University and other places

The acidic triangular copper(I) 4-nitro-3,5-bis-(trifluoromethyl)pyrazolate (Cu 3 pz 3) and its adducts with thiophenic compounds were prepared and structurally characterized by X-ray diffraction. Except Cu 3 pz 3 ·DMDBT-L, the adducts, namely, Cu 3 pz 3 ·DBT, Cu 3 pz 3 ·DBT· 0.5C 7 H 8 , Cu 3 pz 3 ·2DBT, Cu 3 pz 3 ·DMDBT-S, and Cu 3 pz 3 ·2DMT, feature a short intermolecular Cu I −S thienyl contact, ranging from 2.544 to 2.327 Å (DBT = dibenzothiophene, DMDBT = 4,6-dimethyldibenzothiophene, DMT = 2,5-dimethylthiophene). Two kinds of crystals (colorless and yellow) can be differentiated by the Cu−S distance in the crystal structures of Cu 3 pz 3 · DMDBT-L/S. By comparison of the structures reported here and those simulated for adsorption of thiophenic compounds over Cu(I)-containing adsorbents by theoretical calculations, it is suggested that Cu 3 pz 3 could be used as an efficient model compound of adsorbent to investigate the metal-promoted adsorptive desulfurization. A preliminary investigation has demonstrated that dibenzothiophene (DBT) can be effectively adsorbed by Cu 3 pz 3 from model oils. ■ INTRODUCTION Adsorptive removal of heterocyclic aromatic S-containing organics (HASC, mainly thiophene-derivatives) from liquid fuels, commonly called adsorptive desulfurization (ADS), is a promising complementary or alternative measure for currently widely used hydrodesulfurization (HDS), the latter of which has proven less effective for the removal of thiophenic compounds. 1−3 In order to improve the performance of ADS, transition metals (such as Cu + , Ag + , Ni 2+ , etc.) and rare earth metals (such as Ce 4+ , La 3+ , etc.) have been grafted into the structures of adsorbents like zeolites, activated carbon, and MOFs, taking advantage of the "π-complexation" and "direct S−M interaction" endowed by metals. 4−6 Although much effort has been devoted to improving the adsorption performance, practical application of ADS remains a huge challenge due to poor adsorption selectivity and low adsorption capacity. The detailed mechanisms are needed to better understand the adsorption process and design more efficient adsorbents for ADS. Unfortunately, studies of the adsorption mechanism were, to some extent, hampered by the complexity of the adsorption system. As a result, theoretical simulations were frequently used to get insights into the interactions governing adsorption. 7,8 An improved understanding of the structure−function relationship is desired for the purpose of discovering high-performing adsorbents. Investigation of model compounds can provide simplified yet effective information on complex systems. We recently proposed that a type of triangular coinage metal pyrazolates (M 3 pz 3) with coordinatively unsaturated metal sites may be utilized as model compounds simulating metal-functionalized adsorbents (Scheme 1). 9−12 X-ray analyses of the M 3 pz 3 adducts with thiophenic compounds have demonstrated the significant contributions of intermo-lecular M···S and M···C interactions in the adsorption of HASC from oils. Our study also shows that enhancement of the Lewis acidity (or π acidity) of M 3 pz 3 (e.g., by incorporation of electron-withdrawing groups on pyrazolyl ring) can greatly improve the adsorption performance. For example, 4-nitro-3,5-bis(trifluoromethyl)pyrazole (nbtfmpzH) is strongly acidic due to the presence of −CF 3 and −NO 2 substituents. Its silver(I) complex (Ag 3 pz 3) exhibits a strong π-acidity and has a much higher adsorptive affinity for HASC presented in iso-octane, 11 in comparison with the structurally similar [Ag(denpz)] 3 (denpz − = 3,5-diethyl-4-nitropyrazolato anion). 10 Considering the abundance and metal prices as well as the similarity of coinage metals, copper may be a suitable substitute for silver for our ongoing research. An investigation has therefore been conducted on the preparation and crystal structure determination of the HASC adducts of copper(I) 4-nitro-3,5-bis(trifluoromethyl)pyrazolate (abbreviated as Cu 3 pz 3 hereafter). It is hoped that studying the model compounds may provide critical structural parameters for the interaction of metal ions with HASC molecules, which are essential to establish the mechanism of metal-promoted

The first coordination‐saturated buckyball with a C60 molecule totally encased in an icosidodecahedral Cu30 in a (μ30‐(η²)30)‐fashion, namely C60@Cu30@Cl36N12, has been successfully realized by a C60‐templated assembly. The 48 outmost coordinating atoms (36Cl+12N) comprise a new simple polyhedron that is described by a ccf topology. Charge transfer from (CuI, Cl) to C60 explains the expansion of the light absorption up to 700 nm, and accounts for an ultrafast photophysical process that underpins its high photothermal conversion efficiency. This work makes a giant step forward in exohedral metallofullerene (ExMF) chemistry.

The first coordination‐saturated buckyball with C60 molecule totally encased in an icosidodecahedral Cu30 in a (μ30‐(η2)30)‐fashion, namely C60@Cu30@Cl36N12, has been successfully realized via a C60‐templated assembly. The 48 outmost coordinating atoms (36Cl + 12N) comprise a new simplicial polyhedron that is described by a ccf topology. Charge transfer from (CuI, Cl) to C60 explains the expansion of light absorption up to 700 nm, and accounts for an ultrafast photophysical process that underpins its high photothermal conversion efficiency. This work puts a giant step forward in exohedral metallofullerene (ExMF) chemistry.

Two metallofullerene frameworks (MFFs) constructed from a penta‐shell Keplerate cuprofullerene chloride, C 60 @Cu 24 @Cl 44 @Cu 12 @Cl 12 , have been successfully prepared via a C 60 ‐templated symmetry‐driven strategy. The icosahedral cuprofullerene chloride is assembled on a C 60 molecule through [η ² ‐(C=C)]−Cu I and Cu I −Cl coordination bonds, resulting in the penta‐shell Keplerate with the C 60 core canopied by 24 Cu, 44 Cl, 12 Cu and 12 Cl atoms that fulfill the tic @ rco @ oae @ ico @ ico penta‐shell polyhedral configuration. By sharing the outmost‐shell Cl atoms, the cuprofullerene chlorides are connected into 2D or 3D ( snf net) frameworks. TD‐DFT calculations reveal that the charge transfer from the outmost Cu I and Cl to C 60 core is responsible for their light absorption expansion to near‐infrared region, implying anionic halogenation may be an effective strategy to tune the light absorption properties of metallofullerene materials.

Two 2D coordination sheets with pure Cu I and mixed Cu I /Cu II centers based on tetranuclear cuprofullerene pentafluorobenzoate were afforded under solvothermal conditions. They are constructed with linear (μ 2 -η ² :η ² ) 2 -C 60 connecting Cu I /Cu II pentafluorobenzoate...

A novel multi-functional Co(II)-organic framework {[Co2(SBTB)(BDBM)2(H2O)]·3H2O}n (Co-MOF 1) was successfully synthesized through the assembly between Co2+ and 5-sulfo-1, 2, 4-benzoic acid (H4SBTB) in the presence of the auxiliary flexible ligand,...

Tris(diethyldithiocarbamato-κ S )antimony(III), [Sb(C 5 H 10 NS 2 ) 3 ], is tentatively presumed to comprise a triclinic and a monoclinic polymorph intergrown into each other. The geometry in the triclinic phase is a ψ-capped octahedron and that in the monoclinic phase is a ψ-pentagonal bipyramid. The study also identifies the polyhedral symbols for a reported pair of polymorphs of another Sb III coordination compound, as well as for those of published polymorphic modifications of other Bi III and Pb II coordination compounds; the symbols in the pair differ in most of these examples. When differentiating related structures of such classes of coordination compounds, lone-pair stereochemistry may be another informative variable, as stereochemical activity is not always apparent from bond distances and angles only.

The salts {[Ln2Ln*(Hhmq)3(OAc)3(hfac)2]⁺ [Ln*(hfac)3(OAc)(MeOH)]⁻} (Hhmq=2‐methanolquinolin‐8‐oxide, hfac=hexafluoroacetylacetonate; Ln, Ln*=Er, Gd, Yb) feature a discrete heteronuclear cation consisting of two types of lanthanide atoms. The quinolinoxy O‐atom serves as a μ2‐bridge to two Ln atoms and as a μ3‐bridge to all three atoms, with metal⋅⋅⋅metal distances being around 3.7 Å. For 1 ([Yb2Er]⁺), near‐infrared downshifted luminescence is switched to competitive upconversion luminescence upon irradiation by a 980 nm laser under an extremely low excitation power (0.288 W cm⁻²) through introduction of fluoride ions. The stability of 1 after addition of fluoride was confirmed by powder X‐ray diffraction and multistage mass spectrometry, associated with the ¹H NMR of 6 ([La2Eu]⁺). More importantly, the at least 20‐fold enhancement of the quantum yield in non‐deuterated solvents at room temperature under low power densities (2 W cm⁻²) is the highest among the few molecular examples reported.

The performance of discrete heteropolynuclear Yb/Er salts is switched from a Yb/Er doublet to competitive upconversion luminescence exploiting fluoride association. A more than 20-fold enhancement of the relative quantum yield ϕUC under low power densities in non-deuterated solvents at room temperature was recorded. Abstract The salts {[Ln2Ln*(Hhmq)3(OAc)3(hfac)2]⁺ [Ln*(hfac)3(OAc)(MeOH)]⁻} (Hhmq=2-methanolquinolin-8-oxide, hfac=hexafluoroacetylacetonate; Ln, Ln*=Er, Gd, Yb) feature a discrete heteronuclear cation consisting of two types of lanthanide atoms. The quinolinoxy O-atom serves as a μ2-bridge to two Ln atoms and as a μ3-bridge to all three atoms, with metal⋅⋅⋅metal distances being around 3.7 Å. For 1 ([Yb2Er]⁺), near-infrared downshifted luminescence is switched to competitive upconversion luminescence upon irradiation by a 980 nm laser under an extremely low excitation power (0.288 W cm⁻²) through introduction of fluoride ions. The stability of 1 after addition of fluoride was confirmed by powder X-ray diffraction and multistage mass spectrometry, associated with the ¹H NMR of 6 ([La2Eu]⁺). More importantly, the at least 20-fold enhancement of the quantum yield in non-deuterated solvents at room temperature under low power densities (2 W cm⁻²) is the highest among the few molecular examples reported.