Formation of binary and ternary metal deposits on glass–ceramic carbon electrode surfaces: electron-probe X-ray microanalysis,total-reflection X-ray fluorescence analysis,X-ray photoelectron spectroscopy and scanning electron microscopy study

The features of the formation of binary and ternary alloys during the electrochemical deposition and co-deposition of copper, cadmium and lead from aqueous solutions on disc glass–ceramic carbon electrode surfaces were studied by electron-probe X-ray microanalysis, total-reflection X-ray fluorescence analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The macroscopic properties of electrodeposits such as morphology, lateral distribution of the elements along the disc electrode surface and depth distribution of the elements in the electrodeposit bulk were established. The mechanisms of metal nucleation and growth of thin films of electrodeposits were discussed.     

Study of ageing of ketone resins used as picture varnishes by FTIR spectroscopy,UV–Vis spectrophotometry,atomic force microscopy and scanning electron microscopy X-ray microanalysis

This paper presents a study of thin films of the commercial ketone resins Laropal K80, Keton N and MS2A, attempting to reproduce the pictorial layers and protective finishes commonly present in contemporary paintings. Chemical and morphological changes due to the degradation effect of environmental agents have been specially considered. For this purpose, three different accelerated ageing processes were applied to a series of specimens prepared from the studied commercial products: thermal, UV light and ageing in an SO(2)-polluted chamber. Spectroscopic techniques such as FTIR spectroscopy and UV-Vis spectrophotometry were applied in combination with microscopic examination techniques, namely, AFM and scanning electron microscopy energy dispersive X-ray microanalysis (SEM-EDX). Chemical changes due to UV light and thermal ageing are in good agreement with those previously reported in the literature. Bleaching exhibited by the three commercial products after exposure to a SO(2)-saturated atmosphere has been related to the diffusion of SO(2)-rich water vapour into the film. This effect was particularly strong in the MS2A resin due to the higher content of hydroxyl groups in this product.     

c(4 × 2) and related structural units on the SrTiO3(001) surface: scanning tunneling microscopy, density functional theory, and atomic structure

Density functional theory is used to simulate high-bias, constant-current scanning tunneling micrographs for direct comparison with experimental images. Coupled to previous spectroscopic data, these simulations are used to determine the atomic structure of Ti-rich nanostructures on strontium titanate (001) surfaces. These nanostructures have three consecutive TiO(x) surface layers and exploit the distinctive structural motif of the c(4 × 2) reconstruction as their main building block. A structural model of a characteristic triline defect is also proposed.     

The molecular conformation of butyl acrylate – A vibrational spectroscopy and computational study

Potential energy curves allow us to probe the flexibility of butyl acrylate molecule. We found two local minima belonging to C_s symmetry for s-cis and s-trans conformations. The optimized geometries at RHF and DFT using extended basis set are in good agreement with electron diffraction data of methyl acrylate, and the s-cis is the most stable form. Ab initio calculations of harmonic frequencies at the fully optimized geometries of the planar s-cis and s-trans conformers have been performed at the DFT//B3LYP/6-311+G** level of theory. Scaled harmonic frequencies and potential energy distribution are used for the assignment of the experimental IR and Raman bands. We noticed an acceptable qualitative agreement between the experimental and the computed spectra.     

How to obtain accurate results with molecular iodine and density functional theory?

Molecular iodine is found in many organic synthetic methodologies, both as reagent and as catalyst. Naturally, many groups have carried out computational studies involving this element. However, the choice of computational method proves to be more challenging than for other non-metals. We quantify herein the errors that some common theory levels can introduce in terms of both structural and energetic deviations. We also evaluate multiple post hoc corrections, namely, vibrational entropy, dispersion, and counter-poise corrections. Our results indicate the triple- $$ basis sets are essential to obtain quality results and that post hoc corrections are overall detrimental.     

Density functional theory (DFT) and ab initio investigations of the electronic and molecular structures of the monomer and the dimer of trimethylaluminium

The electronic and molecular structures of the monomer and dimer of trimethylalu-minium have been studied using density functional theory and ab initio MP2 method. The optimized geometry of the monomer Al(CH3)3 is of C3h symmetry, whereas that of the dimer [A1(CH3)3]2 contains a carbon-bridged four-membered ring structure with C2h symmetry. The hydrogen-bridged six-membered ring structure is found to be unstable. The calculated dimerization energy for the four-membered ring structure is 78 kJ/mol, in close proximity to the experimental value of 85.27 kJ/mol.     

Temperature dependent dielectric relaxation spectroscopy of amyl acetate-xylene solutions – An approach to molecular and co-operative dynamics

Dielectric relaxation parameters of AMA-Xylene solutions have been investigated thoroughly to discern the associativeness as well as heterogeneous behavior among the hetero molecules in the solutions such that dielectric constant (ε_o) and relaxation time (τ) of solutions has been determined. Complex permittivity spectra (CPS) for Amyl Acetate (AMA)-Xylene solutions were measured in 10 MHz–50 GHz frequency range using Time domain reflectometry (TDR) technique. It is exciting to explore the cooperative nature and association between AMA-Xylene. With co-operative domains (CDs), dynamics in AMA-AMA and AMA-Xylene molecules have been explicated while Kirkwood validates CDs with diverse exchanges through bonding. The experimental values of ε_o are compared with theoretical values obtained from the molecular parameters suggested by the Luzar. Thermodynamic parameters for AMA-Xylene show positive values of Enthalpy and Entropy for all concentrations, indicating that the system is endothermic and less ordered. Gibbs free energy decreases with increase in volume fraction of amyl acetate (V_AMA).     

The atomic structural dynamics of γ-Al2O3 supported Ir-Pt nanocluster catalysts prepared from a bimetallic molecular precursor: a study using aberration-corrected electron microscopy and X-ray absorption spectroscopy

This study describes a prototypical, bimetallic heterogeneous catalyst: compositionally well-defined Ir-Pt nanoclusters with sizes in the range of 1-2 nm supported on γ-Al(2)O(3). Deposition of the molecular bimetallic cluster [Ir(3)Pt(3)(μ-CO)(3)(CO)(3)(η-C(5)Me(5))(3)] on γ-Al(2)O(3), and its subsequent reduction with hydrogen, provides highly dispersed supported bimetallic Ir-Pt nanoparticles. Using spherical aberration-corrected scanning transmission electron microscopy (C(s)-STEM) and theoretical modeling of synchrotron-based X-ray absorption spectroscopy (XAS) measurements, our studies provide unambiguous structural assignments for this model catalytic system. The atomic resolution C(s)-STEM images reveal strong and specific lattice-directed strains in the clusters that follow local bonding configurations of the γ-Al(2)O(3) support. Combined nanobeam diffraction (NBD) and high-resolution transmission electron microscopy (HRTEM) data suggest the polycrystalline γ-Al(2)O(3) support material predominantly exposes (001) and (011) surface planes (ones commensurate with the zone axis orientations frequently exhibited by the bimetallic clusters). The data reveal that the supported bimetallic clusters exhibit complex patterns of structural dynamics, ones evidencing perturbations of an underlying oblate/hemispherical cuboctahedral cluster-core geometry with cores that are enriched in Ir (a result consistent with models based on surface energetics, which favor an ambient cluster termination by Pt) due to the dynamical responses of the M-M bonding to the specifics of the adsorbate and metal-support interactions. Taken together, the data demonstrate that strong temperature-dependent charge-transfer effects occur that are likely mediated variably by the cluster-support, cluster-adsorbate, and intermetallic bonding interactions.     

Molecular oxygen adsorption behaviors on the rutile TiO2(110)-1×1 surface: an in situ study with low-temperature scanning tunneling microscopy

A knowledge of adsorption behaviors of oxygen on the model system of the reduced rutile TiO(2)(110)-1×1 surface is of great importance for an atomistic understanding of many chemical processes. We present a scanning tunneling microcopy (STM) study on the adsorption of molecular oxygen either at the bridge-bonded oxygen vacancies (BBO(V)) or at the hydroxyls (OH) on the TiO(2)(110)-1×1 surface. Using an in situ O(2) dosing method, we are able to directly verify the exact adsorption sites and the dynamic behaviors of molecular O(2). Our experiments provide direct evidence that an O(2) molecule can intrinsically adsorb at both the BBO(V) and the OH sites. It has been identified that, at a low coverage of O(2), the singly adsorbed molecular O(2) at BBO(V) can be dissociated through an intermediate state as driven by the STM tip. However, singly adsorbed molecular O(2) at OH can survive from such a tip-induced effect, which implies that the singly adsorbed O(2) at OH is more stable than that at BBO(V). It is interesting to observe that when the BBO(V)s are fully filled with excess O(2) dosing, the adsorbed O(2) molecules at BBO(V) tend to be nondissociative even under a higher bias voltage of 2.2 V. Such a nondissociative behavior is most likely attributed to the presence of two or more O(2) molecules simultaneously adsorbed at a BBO(V) with a more stable configuration than singly adsorbed molecular O(2) at a BBO(V).     

Archaeological pottery from Nasca culture studied by Raman and Mössbauer spectroscopy combined with X-ray diffraction

In the present paper, we report on a study of archaeological fragments from Nasca ceramics using Raman and Mössbauer spectroscopy combined with X-ray diffraction (XRD). By combining results obtained by these methods it is possible to quantitatively determine the paints composition, temperature and environment during the firing. The samples were collected from the Ceremonial Centre of Cahuachi in Southern coast of Peru. Raman spectroscopy allows us to determine the composition of the different pigments used in the preparation of Nasca ceramic. The results show that the composition of the white pigments is formed by rutile and anatase while the black and red pigments are formed by amorphous carbon and hematite, respectively. The Mössbauer spectra were measured at room temperature (RT) and show the presence of components associated with Fe³⁺ indicating an oxidizing environment during the manufacturing process of the ceramic. The analysis is complemented by data obtained by X-ray diffraction suggesting firing temperatures around 950 °C, in agreement with Raman measurements.     

Binding structures of propylene glycol stereoisomers on the Si(001)-2×1 surface: a combined scanning tunneling microscopy and theoretical study

The binding configuration of propylene glycol stereoisomer molecules adsorbed on the Si(001)-2×1 surface was investigated using a combination of scanning tunneling microscopy (STM) and density functional theory calculations. Propylene glycol was found to adsorb dissociatively via two hydroxyl groups exclusively as a bridge between the ends of two adjacent dimers along the dimer row. The chirality was preserved during bonding to Si atoms and was identifiable with STM imaging. The large number of propylene glycol conformers in the gas phase was reduced to a single configuration adsorbed on the surface at low molecular coverage.     

Spin crossover of ferric complexes with catecholate derivatives. Single-crystal X-ray structure, magnetic and Mössbauer investigations

Complexes of general formula [(TPA)Fe(R-Cat)]X.nS were synthesised with different catecholate derivatives and anions (TPA = tris(2-pyridylmethyl)amine, R-Cat2- = 4,5-(NO2)2-Cat2- denoted DNC(2-); 3,4,5,6-Cl4-Cat2- denoted TCC2-; 3-OMe-Cat(2-); 4-Me-Cat(2-) and X = BPh4-; NO3-; PF6-; ClO4-; S = solvent molecule). Their magnetic behaviours in the solid state show a general feature along the series, viz., the occurrence of a thermally-induced spin crossover process. The transition curves are continuous with transition temperatures ranging from ca. 84 to 257 K. The crystal structures of [(TPA)Fe(DNC)]X (X = PF6-; BPh4-) and [(TPA)Fe(TCC)]X.nS (X = PF6-; NO3- and n= 1, S = H2O; ClO4- and n= 1, S = H2O; BPh4- and n= 1, S = C3H6O) were solved at 100 (or 123 K) and 293 K. For those two systems, the characteristics of the [FeN(4)O(2)] coordination core and those of the dioxolene ligands appear to be consistent with a prevailing Fe(III)-catecholate formulation. This feature is in contrast with the large quantum mixing between Fe(III)-catecholate and Fe(II)-semiquinonate forms recently observed with the more electron donating simple catecholate dianion. The thermal spin crossover process is accompanied by significant changes of the molecular structures as shown by the average variation of the metal-ligand bond distances which can be extrapolated for a complete spin conversion from ca. 0.123 to 0.156 A. The different space groups were retained in the low- and high-temperature phases.     

X-ray crystallographic studies and molecular calculations on 1∶1 inclusion complexes of cholic acid with acetophenone and its derivatives

Molecular calculations were applied to four channel-type inclusion complexes of cholic acid (CA) with acetophenone or its derivatives (3-, 4-fluoroacetophenone and 2-chloroacetophenone). According to the calculated results, both the total and van der Waals interaction energies between channel and included guests depend on the channel form determined by the guest species. Similarly, the channel form is responsible for the dipole moment of the channel. Further examination of the results suggests that dipole-dipole interaction does not play an important role in the determination of the guest orientation. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82193 (26 pages).     

Scanning tunneling microscopy/spectroscopy study of atomic and electronic structures of In2O on InAs and In0.53Ga0.47As(001)-(4×2) surfaces

Interfacial bonding geometry and electronic structures of In(2)O on InAs and In(0.53)Ga(0.47)As(001)-(4×2) have been investigated by scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS). STM images show that the In(2)O forms an ordered monolayer on both InAs and InGaAs surfaces. In(2)O deposition on the InAs(001)-(4×2) surface does not displace any surface atoms during both room temperature deposition and postdeposition annealing. Oxygen atoms from In(2)O molecules bond with trough In/Ga atoms on the surface to form a new layer of O-In/Ga bonds, which restore many of the strained trough In/Ga atoms into more bulklike tetrahedral sp(3) bonding environments. STS reveals that for both p-type and n-type clean In(0.53)Ga(0.47)As(001)-(4×2) surfaces, the Fermi level resides near the valence band maximum (VBM); however, after In(2)O deposition and postdeposition annealings, the Fermi level position is close to the VBM for p-type samples and close to the conduction band minimum for n-type samples. This result indicates that In(2)O bonding eliminates surface states within the bandgap and forms an unpinned interface when bonding with In(0.53)Ga(0.47)As/InP(001)-(4×2). Density function theory is used to confirm the experimental finding.     

Synthesis, spectroscopy and biological investigations of manganese(III) Schiff base complexes derived from heterocyclic β-diketone with various primary amine and 2,2'-bipyridyl

The mixed ligand mononuclear complex [Mn(bipy)(HPMFP)(OAc)]ClO(4) was synthesized by reaction of Mn(OAc)(3)·2H(2)O with HPMFP and 2,2'-bipyridyl. The corresponding Schiff base complexes were prepared by condensation of [Mn(bipy)(HPMFP)(OAc)]ClO(4) with ethylenediamine, ethanolamine and glycine (where HPMFP=1-phenyl-3methyl-4-formyl-2-pyrazolin-5one, bipy=2,2'-bipyridyl). All the compounds have been characterized by elemental analysis, magnetic susceptibility, conductometry measurements and (1)H and (13)C NMR, FT-IR, mass spectrometry. Electronic spectral and magnetic susceptibility measurements indicate square pyramidal geometry around manganese(III) ion. The thermal stabilities, activation energy E*, entropy change ΔS*, enthalpy change ΔH* and heat capacity of thermal degradation for these complexes were determined by TGA and DSC. The in vitro antibacterial and antifungal activity of four coordination compounds and ligand HPMFP were investigated. In vitro activates of Bacillus subtillis (MTCC-619), Staphylococcus aureus (MTCC-96), Escherichia coli (MTCC-722) and Klebsiella pneumonia (MTCC-109) bacteria and the fungus Candida albicans (ATCC-90028) were determined. All the compounds showed good antimicrobial activity. The antimicrobial activities increased as formation of Schiff base.     

Synthesis of copper(II) and zinc(II) complexes with chalcone–thiosemicarbazone hybrid ligands: X-ray crystallography,spectroscopy and yeast activity

Four chalcone–thiosemicarbazones (C-TSCs) of the type 2-((E)-3-(4-R-phenyl)-1-phenylallylidene)-N-phenylhydrazinecarbothioamide, where R?=?Cl (HL1), NO₂ (HL2), CH₃ (HL3) or CN (HL4), were prepared in good yields from the reaction of the respective chalcone with 4-phenyl-3-thiosemicarbazide and HCl in EtOH. Reaction of HL with CuCl₂·2H₂O or ZnCl₂ in the presence of Et₃N afforded the complexes [M(L)₂], M?=?Cu(II) or Zn(II). X-ray diffraction analysis revealed that the ligands coordinate in their deprotonated form, in a bidentate fashion through the iminic nitrogen and sulfur atoms. Yeast activities of the compounds were tested, where the ligand HL4 was the most damaging derivative, exhibiting cell viability at about 50%. On the other hand, lipid peroxidation assays revealed that the ligand HL1 was able to better induce membrane damage compared to the other compounds. It has been found that coordination with Cu(II) and Zn(II) did not increase the biological activities of the C-TSCs.     

Transition metal complexes with thiosemicarbazide-based ligand – Part LV: Synthesis and X-ray structural study of novel Ni(II) complexes with pyridoxal semicarbazone and pyridoxal thiosemicarbazone

Reaction of aqueous solutions of Ni(NO₃)₂ and pyridoxal semicarbazone (PLSC) in the presence of NaN₃ afforded two complexes, viz. green, paramagnetic binuclear octahedral [Ni₂(PLSC)₂(μ_1,1-N₃)₂(N₃)₂] · 2H₂O (1) and, as admixture, red, octahedral [Ni(PLSC–H)₂] · 2H₂O (2) complex. Under the same reaction conditions, pyridoxal thiosemicarbazone (PLTSC) gave only one diamagnetic square-planar, red complex [Ni(PLTSC–H)N₃] · H₂O (3). In the absence of NaN₃, the reaction of PLTSC and Ni(NO₃)₂ yielded brown paramagnetic octahedral complex [Ni(PLTSC)₂](NO₃)₂ · H₂O (4).     

Simultaneous optimization of Gaussian type function exponents for electron and positron with full-CI wavefunction – application to ground and excited states of positronic compounds with multi-component molecular orbital approach

In order to obtain the best wavefunction of positronic compound with molecular orbital (MO) treatment, the full-configuration interaction (full-CI) fully variational MO (FVMO) method is proposed for multi-component systems, in which all the variational parameters in electronic and positronic wavefunctions are optimized under the full-CI scheme. We have applied the full-CI multi-component FVMO method to the ground and positronic-excited states of [H⁻;e⁺] system. Our treatment gives good improvement in the basis functions for positronic compounds owing to the extension of flexibility in the variational space, though the convergence of electron–positron correlation term is slower than that of conventional electron correlation.