Lip Lin Koh

Copper(II) complexes of the antitumour-related ligand salicylaldehyde acetylhydrazone (H2L) and the single-crystal X-ray structures of [{Cu(HL)H2O}2] · 2(NO3) and [{Cu(HL) (pyridine) (NO3)}2]

Binary and ternary copper(II) complexes of the ligand salicylaldehyde acetylhydrazone (H2L) have been prepared. In acid or neutral media monoanionic HL complexes separate. Addition of the Lewis bases pyridine (py) and thiourea (tu) to [{Cu(HL)H2O}2] · 2(NO3) results in the monoanionic ternary ligand adducts [{Cu(HL) (py) (NO3)}2] and [Cu(HL) (tu) (NO3)], respectively. With base, the le soluble dianionic complex [{CuL}2] was isolated. Addition of py to [{CuL}2]afforded the dianionic ternary complex [CuL(py)]·12H2O. The complexes have been characterized by a range of physicochemical techniques and the crystal and molecular structures of [{Cu(HL)H2O}2] · 2(NO3) and [{Cu(HL) (py) (NO3)}2] determined. Crystals of [{Cu(HL)H2O}2] · 2 (NO3), C18H22Cu2N6O12, are monoclinic, with space group P21/c, a=7.217(4), b=11.758(8), c=13.764(8) A, β=95.47(4)° and Z=4. [{Cu(HL)H2O}2] · 2 (NO3) is a centrosymmetric (planar) dimer, the monomeric units being bridged through the phenoxy oxygen. The copper atom has a square-pyramidal geometry with the basal donor atoms coming from the tridentate ligand (ONO) and the symmetry-related phenolate (O). The more weakly bound apical donor oxygen is supplied by a coordinated water molecule. The nitrate is not bound. Crystals of [{Cu(HL)(py) (NO3)}2], C28H28Cu2N8O10, are monoclinic, with space group P21/c, a=10.642(3), b=11.796(3), c=13.137(2) A, β=111.03(2)° and Z=4. [{Cu(HL) (py) (NO3)}2] is a weakly interacting centrosymmetric (stacked) dimer, the monomeric units being bridged axially through the phenoxy oxygen. The copper atom has a tetragonal geometry with the equatorial donor atoms coming from the tridentate ligand (ONO) and the pyridine (N). The more weakly bound nitrato anion provides the other axial donor (O). Several of the complexes exhibit interesting magnetic properties.

Solid‐State Structural Transformations from 2D Interdigitated Layers to 3D Interpenetrated Structures

ndc) in the presence 4-spy. The 4-spy unit in both theproducts undergoes photodimerization reaction under UVlight. The structural transformation of one of these com-pounds is accompanied by single-crystal-to-single-crystal(SCSC) manner which helps to confirm the formation three-fold interpenetrated 3D structure (Scheme 1).Light yellow block-shaped crystals of [Zn

Substituent-dependent structures and catalysis of benzimidazole-tethered N-heterocyclic carbene complexes of Ag(I), Ni(II) and Pd(II)

Homoleptic cationic benzimidazole-imidazolin-2-ylidene N-heterocyclic carbene (NHC = L) complexes of Ni(II) and Pd(II) have been prepared directly from the ligand precursor in salt form [H.L]Cl and from the transmetallation route via Ag(I). The N-tether of the imidazolinylidene ring imposes a significant influence on the nuclearity of the intermediate Ag(I)-NHC complexes and the geometric isomer outcome of the d(8) products. Use of a benzyl-substituted NHC gives [Ag(4)(L(Bn))(2)Cl(4)], 2a (from [HL(Bn)]Cl, 1a, and Ag(2)O) (Bn = benzyl), which shows an alignment of four silver atoms bridged by the difunctional C-N ligands and chlorides. Its transmetallation with NiCl(2)(PPh(3))(4) and PdCl(2)(MeCN)(2) results in double-metal salts 2[M(L(Bn))(2)](2+)[Ag(4)Cl(8)](4-) (M = Ni (3a) and Pd (4a)). The nuclearity of the Ag(4) aggregate is maintained in the transmetallation process. Their Ag-free forms [M(L(Bn))(2)]Cl(2) (M = Ni (5) and Pd (6)) were prepared by direct deprotonation of 1a with M(OAc)(2). The two carbenic carbon donor are cis- to each other in both 3a and 4a, thus imposing the weaker sigma-benzimidazole nitrogen donor to be trans to them. A sterically demanding mesityl pendant however gives the dinuclear dissymmetic [Ag(2)(L(Mes))(2)Cl(2)], 2b (Mes = mesityl) that shows a 12-membered metallomacrocyclic ring with a 2-coordinated [Ag(I)(NHC)(2)] and 4-coordinated [Ag(I)(Imd)(2)Cl(2)] (Imd = imidazole). Transmetallation of the latter, or direct metallation from [HL(Mes)]Cl, 1b, gives [M(L(Mes))(2)]Cl(2) (M = Ni (3b) and Pd (4b)) with the two carbonic carbon trans to each other. The catalytic potential of 3b and 4b, which are more effective than 5 and 6, has been demonstrated by their high activities in Ni-catalyzed Kumada at room temperature and Pd-catalyzed Heck couplings of aryl and/or heteroaryl halides, respectively.

Structures of copper complexes of the hybrid [SNS] ligand of bis(2-(benzylthio)ethyl)amine and facile catalytic formation of 1-benzyl-4-phenyl-1H-1,2,3-triazole through click reaction

A hybrid ligand, bis(2-(benzylthio)ethyl)amine (SNS), with an amine and two thioether donors reacts with Cu(II) to give mononuclear [CuCl(2)(SNS)] (1), [CuBr(2)(SNS)] (2), [Cu(OTf)(2)(SNS)(OH(2))] (3), and an one-dimensional Cu(I) coordination polymer [Cu(2)I(2)(SNS)](n) (4). All complexes have been characterized by single-crystal X-ray diffraction analysis, and 1-3 were studied by EPR analysis at room temperature. Complexes 1 and 2 are penta-coordinated with a distorted square pyramidal metal supported by a tridentate SNS ligand on the basal plane. Complex 3 shows a tetragonally distorted octahedral sphere with two trans and weakly bonding monodentate triflates. A 12-membered ring in the solid lattice is formed by intermolecular H-bonding among the coordinated triflate and aqua ligands from four neighboring molecules. Complex 4, the only Cu(I) in this series, shows a coordination polymer chain [Cu(4)I(4)](n) comprising tetrahedral Cu(I) centers stitched by the SNS ligand in a unique bridge-chelate mode in the form of a helix. All four complexes are catalytically active at room temperature in a copper-catalyzed azide-alkyne cycloaddition (CuAAA) three-component click reaction of benzyl chloride, sodium azide, and phenylacetylene in an aqueous MeCN mixture to give good isolated yields of 1-benzyl-4-phenyl-1H-1,2,3-triazole, without the use of a base or reducing agent.

Functionalized 1,2,3-Triazoles as Building Blocks for Photoluminescent POLOs (Polymers of Oligomers) of Copper(I)

Two 3-D and one 2-D metal-organic frameworks [Cu(8)I(8)(L1)(4)](n) (1), [Cu(8)I(8)(L2)(4)](n) (2) and [Cu(4)I(4)(L3)(2)](n) ()3 were synthesized using three novel pyridine and pyrazole supported 1,2,3-triazoles, 1-(4-picolyl)-4-butyl-1H-1,2,3-triazole (L1), 1-(4-picolyl)-4-pentyl-1H-1,2,3-triazole (L2) and 1-(4-picolyl)-4-(3,5-dimethylpyrazolylmethyl)-1H-1,2,3-triazole (L3). In both complexes 1 and 2, there co-exist a 1-D Cu(I) oligomer and Cu(4) tetrahedron cluster in the 3-D polymeric structures. Complex 3 shows a 2-D (4, 4) net with the stair-step Cu(4)I(4) as node and L3 as a building block. All three complexes exhibit photoluminescence.

Orthogonal array design for the optimization of closed-vessel microwave digestion parameters for the determination of trace metals in sediments

Abstract Orthogonal array design was applied to the optimization of the closed-vessel microwave digestion of sediment samples. Five variables related to the digestion efficiency were studied: the addition of HF in digestion acid, the ratio between HCl and HNO 3 , the maximum pressure setting, the output power and the digestion time. In the experimental assignment, the digestion time at two levels and other variables at four levels were tested using an OA 16 (4 4 × 2 3 ) matrix. The interactions between the parameters were neglected. From the results, the optimum conditions for the closed vessel microwave digestion for sediment samples were established.

Metal−Organic Frameworks Containing a Tetrapyridylcyclobutane Ligand Derived from Isomerization Reaction

The rctt isomer of tetrapyridylcyclobutane prepared from the solid-state [2 + 2] cycloaddition reaction of [bpeH(2)] x 2 CF(3)CO(2) [bpe = 1,2-bis(4-pyridyl)ethene] undergoes isomerization reaction to the rtct isomer in 100% yield, and this tetrahedral tetrapyridyl ligand forms two metal-organic frameworks having ptt and pts topology.

Oligo- and Polymeric Pd II and Pt II Using Pyridyl Carboxylate Spacers for Topology Control

An array of Pd(II) and Pt(II) supramolecular assemblies have been constructed using pyridyl carboxylates as spacers and phosphines [(C5H4PPh2)2Fe (dppf) and PPh3)] as supporting ligands. Different molecular topologies such as squares, triangles, rectangles, and polymers can be controlled by the spatial and directional character of the spacer. A change of the denticity of the phosphine does not affect the topological outcome. Significant differences, however, are observed for the congeneric analogues, with Pd(II) showing a more pronounced tendency toward coordination polymer formation and its attached carboxyl a higher affinity toward Ag(+). The ability of these assemblies to capture cations, such as Na(+) in [Pt3Na(3-NC5H4CO2)3(OTf)3(PPh3)6](+) through hydrogen bonding or Ag(+) in [PdAg(2-NC5H4CO2)(OTf)2(dppf)] through dative bonding, is described and compared. All of the complexes are structurally characterized by single-crystal X-ray crystallography.

Molecular adducts of diorganotin dichloride with N-(2-oxidoarylideneaminoacidato) diorganotin(IV) complexes. Crystal structure of [Ph2Sn(2-OC10H6CH-NCH2COO)]SnPh2Cl2

Abstract Three new dinuclear tin complexes, [Me2Sn(2-OC6H4CH-NCH[Pri]COO)]SnMe2Cl2 (1), [Me2Sn(2-OC10H6CH-NCH2COO)SnMe2Cl2 (2) and [Ph2Sn(2-OC10H6CH-NCH2COO)]SnPh2Cl2 (3), were prepared and characterized by spectroscopic studies and elemental analyses as a 1 : 1 adduct between diorganotin dichloride (acceptor) and bicycloazastannoxide (donor). A full X-ray crystal structure analysis was performed on 3 and the results confirmed that the donor and the acceptor moieties of 3 are bonded with an Sn-O bond distance of 2.307A˚.

Microwave digestion of biological samples with tetramethylammonium hydroxide and ethylenediaminetetraacetic acid for element determination

A microwave-digestion system with a closed PTFE vessel was used to improve the leaching of inorganic constituents from biological samples with tetramethylammonium hydroxide (TMAH) and ethylenediaminetetraacetic acid (EDTA). The effects of microwave parameter settings and the quantities of TMAH and EDTA used on leaching efficiency were evaluated. This new digestion method has been applied to the standard reference materials NIST SRM 1577 B Bovine Liver 1515 Apple Leaves and NIES CRM No. 1 Pepperbush, No. 3 Chorella, No. 6 Mussel and No. 7 Tea Leaves. The major and minor elements in the digests were analyzed by flame atomic absorption spectrometry or graphite furnace atomic absorption spectrometry. Good agreement of the analytical results with the certified values was obtained.