Helena I. S. Nogueira

Studies on polyoxo and polyperoxo-metalates part 5: Peroxide-catalysed oxidations with heteropolyperoxo-tungstates and -molybdates

Abstract The new complexes [(LO 4 ){MO(O 2 ) 2 } 2 {MO(O 2 ) 2 (H 2 O)}] 3− (L = P, As; M = W, Mo) are reported and their use as catalysts in the presence of hydrogen peroxide for epoxidation of alkenes and oxidations of alcohols, tertiary amines and sulfides discussed. Similar oxidations are reported for salts of [(LO 3 (OH)){MO(O 2 ) 2 } 2 ] 2− (L = P, As; M = W, Mo), [(PhPO 3 ){MO(O 2 ) 2 } 2 {MO(O 2 ) 2 (H 2 O)}] 3− (M = W, Mo) and [(R 2 LO 2 ){MO(O 2 ) 2 } 2 ] − (R = Ph, Me; L = P, As; M = W, Mo). Alkene epoxidations and alcohol oxidations are also reported for [PW 11 O 39 ] 7− , [Ln III {PW 11 O 39 } 2 ] 11− (Ln = Y, La, Ce, Pr, Sm, Tb, Yb) and [M IV {PW 11 O 39 } 2 ] 10− (M = Ce, Th).

FT-IR, FT-Raman, SERS and computational study of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole.

FT-IR, FT-Raman and surface-enhanced Raman scattering spectra of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian09 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution calculations. The presence of CH(2), SO(2) and CH(3) modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface which affects the orientation and metal molecule interaction. The synthesis, NMR spectra and antibacterial properties are reported. The title compound shows more inhibitory effect against Pseudomonas aeruginosa than ampicillin and found to be more potent against Klebsiella pneumoniae and drug-resistant Bacillus subtilis than the other microorganisms. A computation of the first hyperpolarizability indicates that the compound may be a good candidate as a NLO material. The RMS errors of the observed Raman and IR bands are found to be 30.93, 29.77 for HF and 9.57, 6.75 for DFT methods, respectively.

Coordination modes of 3-hydroxypicolinic acid: synthesis and crystal structures of palladium(II), platinum(II) and rhenium(V) complexes

The new palladium and platinum complexes with 3-hydroxypicolinic acid (HpicOH) [M(PPh3)2Cl(picOH)]·CHCl3, [M(bipy)(picOH)]Cl [M=Pd(II) or Pt(II)], K[PdCl(picOH)2] and [Pt(picOH)2] and the new rhenium complexes [ReOI2(PPh3)(picOH)] and [ReO(PPh3)(picOH)2]I have been prepared. The crystal structures of [M(PPh3)2Cl(picOH)]·CHCl3 [M=Pd(II) 1 or Pt(II) 2] and [ReOI2(PPh3)(picOH)] 3 were determined by X-ray diffraction. Complex 3 exhibits a distorted octahedral geometry with the picOH− ligand showing N,O-chelation with a small bite angle O–Re–N of 74.8(3)°. In complexes 1 and 2 the metal centre is surrounded by a NP2Cl donor set in a distorted square planar arrangement. Therefore, the picOH− ligand is bound through the nitrogen atom, but the distances found between the metal and the carboxylate oxygen [Pd···O(71) 2.773(5) A or Pt···O(71) 2.734(4) A] suggest a [4+1] coordination consistent with N,O-chelation for palladium and platinum centres. Infrared, Raman, 1H and 13C-{1H} NMR spectroscopic data for the complexes are consistent with the crystallographic results. In the solid state the complex units of 1 and 3 are aggregated in centrosymmetric dimers based on C–H···Cl or C–H···O hydrogen bonding interactions between the chlorine of the Pd–Cl bond (in 1) or the phenolic oxygen of the picOH− anion (in 3) and a hydrogen atom of a phenyl group of a PPh3 ligand.

Studies on polyoxo and polyperoxo-metalates ☆: Part 7. Lanthano- and thoriopolyoxotungstates as catalytic oxidants with H2O2 and the X-ray crystal structure of Na8[ThW10O36]·28H2O

Abstract The effectiveness of salts of [Ln III W 10 O 36 ] 9− (Ln=Y, La, Ce, Pr, Sm, Eu, Gd, Dy, Er, Lu) and [M IV W 10 O 36 ] 8− (M=Ce, Th) as catalysts with H 2 O 2 for alcohol oxidations and alkene epoxidations has been studied. It appears that catalysis arises from the polyperoxotungstates formed from H 2 O 2 . The X-ray crystal structure of the title complex shows that in the [ThW 10 O 36 ] 8− anion the thorium has square antiprismatic geometry in which eight oxygen atoms from two W 5 O 18 moieties form vertex-sharing bonds; Raman data suggest that the structure of the anion is retained in aqueous solution. New 31 P[ 1 H]-NMR data for [Ln III {PW 11 O 39 } 2 ] 11− (Ln=Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Yb, Lu) and [Ce IV {PW 11 O 39 } 2 ] 10− in the solid state, in water and in H 2 O 2 solution are presented; these species have also been used for oxidation catalysis.

Surface-enhanced Raman scattering (SERS) of 3-aminosalicylic and 2-mercaptonicotinic acids in silver colloids

Abstract The surface-enhanced Raman (SER) spectra of 3-aminosalicylic acid and 2-mercaptonicotinic acid on silver colloids were obtained. Comparison of the SER spectra with the spectra in solution, those of the solids and in one case of a silver complex are made. 3-Aminosalicylic acid (an O,N donor ligand) is thought to adsorb parallel to the silver surface while 2-mercaptonicotinic acid (an O,S donor ligand) lies perpendicular to the surface.

Lanthanide complexes as oxidation catalysts for alcohols and alkenes

Abstract Studies on the use of lanthanide species and lanthanopolyoxotungstates [LnW 10 O 36 ] 9- and [Ln{PW 11 O 39 } 2 ] 11- as catalysts for the oxidation of alcohols and the expoxidation of alkenes are reported. In a number of such oxidations reported in the literature it appears that the lanthanide centre plays little or no catalytic role. The effectiveness of the cerium (IV)-bromate catalytic system for the oxidation of alcohols is, however confirmed and its use extended.

Lanthanopolyoxotungstates in silica nanoparticles: multi-wavelength photoluminescent core/shell materials

Photoluminescent lanthanopolyoxotungstate core/shell nanoparticles are prepared by the encapsulation of lanthanide-containing polyoxometalates (POMs) with amorphous silica shells. The preparation of morphological well-defined core/shell nanoparticles is achieved by the hydrolysis of tetraethoxysilane in the presence of POMs using a reverse microemulsion method. The POMs used are decatungstolanthanoates of [Ln(W5O18)2]9− type (Ln(III) = Eu, Gd and Tb). Photoluminescence studies show that there is efficient emission from the POM located inside the SiO2 shells, through excitation paths that involve O → Eu/Tb and O → W ligand-to-metal charge transfer. It is also shown that the excitation of the POM containing europium(III) may be tuned towards longer wavelengths via an antenna effect, by coordination of an organic ligand such as 3-hydroxypicolinate. The POM/SiO2 nanoparticles form stable suspensions in aqueous solution having the advantage of POM stabilization inside the core and the possibility of further surface grafting of chemical moieties via well known derivatization procedures for silica surfaces. These features together with the possibility of tuning the excitation wavelength by modifying the coordination sphere in the lanthanopolyoxometalate, make this strategy promising to develop a new class of optical bio-tags composed of silica nanobeads with multi-wavelength photoluminescent lanthanopolyoxometalate cores.

One-dimensional silver(I) chain of lacunary α-Keggin anions

A novel chain-like silver polyoxotungstophosphate is formed when AgI metal centres, exhibiting an unusual eight-coordination fashion, bridge a monolacunary [PW11O39]7− anion to four bridging μ2-oxygen atoms of a neighbouring lacunary α-Keggin anion.

IR, Raman and SERS Spectra of 2-(Methoxycarbonylmethylsulfanyl)-3,5-dinitrobenzene Carboxylic Acid

O acido carboxilico 2-(metoxicarbonilmetilsulfanil)-3,5-dinitrobenzeno foi preparado por substituicao nucleofilica. Seus espectros de infravermelho e Raman com transformada de Fourier foram obtidos e analisados. O espalhamento Raman intensificado pela superficie (SERS) foi obtido sobre prata coloidal. Os numeros de onda vibracionais foram computados pela teoria do funcional de densidade (DFT) com a base hibrida B3LYP/6-31G* e foram comparados com valores experimentais com boa concordância. Interacoes metal-molecula significativas foram substanciadas por um sinal Ag-O intenso nos espectros SERS, indicando a proximidade dos grupos nitro e carbonila a superficie de prata. Estudos SERS sugerem uma orientacao inclinada da molecula sobre a superficie metalica. 2-(Methoxycarbonylmethylsulfanyl)-3,5-dinitrobenzenecarboxylic acid was prepared by nucleophilic substitution. FT-IR and FT-Raman spectra of 2-(methoxycarbonylmethylsulfanyl)-3,5dinitrobenzenecarboxylic acid were recorded and analyzed. Surface enhanced Raman scattering (SERS) spectrum was recorded on a silver colloid. The vibrational wavenumbers were computed by density functional theoretical (DFT) computations at the B3LYP/6-31G* level and they were found to be in good agreement with the experimental values. Significant metal-molecule interaction has been substantiated by the appearance of intense Ag-O mode in the SERS spectrum and this is indicative of the nearness of nitro and carbonyl group to the silver surface. SERS studies suggest a tilted orientation of the molecule at the metal surface.

Coordination modes of 2-hydroxynicotinic acid in second- and third-row transition metal complexes

Abstract The new Pd(II), Pt(II), Re(V), Mo(VI) and W(VI) complexes of 2-hydroxynicotinic acid (H2nicO), trans-[PdCl(HnicO)(PPh3)2]·0.75CH3CN (1), K[PdCl(HnicO)2]·H2O (2), [Pd(HnicO)2(bipy)] (3), cis-[PtCl(HnicO)(PPh3)2]·0.75CH3OH·0.5H2O (4), [PtCl(HnicO)(bipy)] (5), cis-[ReOI2(HnicO)(PPh3)] (6), Na2[Mo2O6(HnicO)2]·5H2O (7), Na2[Mo4O12(HnicO)2]·2H2O (8) and Na2[W2O6(HnicO)2]·5H2O (9) have been prepared. The crystal structures of 1 and 4, were determined by X-ray diffraction and show the HnicO− ligand coordinated to palladium or platinum through the nitrogen atom only. Infrared, Raman, 1H and 13C{1H} NMR spectroscopic data for the complexes are presented and are in agreement with the crystallographic results.