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Two morphologically different porous gold layered on Cu-oxide-based electrochemical sensors were developed for the selective detection of dopamine in the presence of uric acid, ascorbic acid or dextrose. The nanoparticles were prepared by layering Au onto either a cubic or octahedron-shaped Cu-oxide crystal via a galvanic reaction. These were characterized with scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. The porous structure of the gold over layer was clearly visible on the scanning electron microscopy image while the macro morphology was maintained. X-ray photoelectron spectroscopy confirmed the presence of metallic gold while both CuI (CuO) and CuII (Cu2O) were present in the samples. These two Au/Cu-oxide nanocomposites were used to modify glassy carbon electrodes and were tested for their dopamine sensing ability. Differential pulse voltammetry was used to investigate the selectivity towards dopamine in the presence of different interfering molecules uric acid, ascorbic acid and dextrose). From the differential pulse voltammetry, the lowest limit of detection was found to be 1.1 μM, with a sensitivity of 3.4 μA mM−1 mm−2 in the linear range of 10–250 μM for the porous gold layered covering the octahedron Cu-oxide-modified glassy carbon electrode. [ABSTRACT FROM AUTHOR]

Tungsten carbide-based nano-catalysts (Ni-WC, Co-WC and NiCo-WC) and molybdenum carbide-based nano-catalysts (Ni-MoC, Co-MoC and NiCo-MoC) were synthesised using a carbothermal reduction method. X-ray diffraction, scanning electron microscopy coupled with electron dispersive spectroscopy, x-ray photoelectron spectroscopy and cyclic voltammetry were used to evaluate the prepared electrocatalysts. The cyclic voltammetry results showed that Ni-WC coated electrode displayed the best hydrogen evolution reaction catalytic activity with the lowest overpotential of 1.421 V at a current density of 10 mA cm−2, and a Tafel slope of 135 mV dec−1 which is marginally lower than the benchmark Pt/C coated electrodes. Ni-MoC and Co-MoC coated electrocatalysts also produced current more effectively with a change in potential as compared to the Pt/C coated electrode. The durability test showed Co-WC, NiCo-WC and Ni-MoC coated electrodes to have high stability within a wide range of current densities. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance measurements confirm that, as expected, the mer isomer of tris(β-diketonato) cobalt(III) complexes is more stable (mer isomers are more stable because they are less affected by steric hindrance and they have lower dipoles). An excess of the mer isomer or only the mer isomer is experimentally observed. The existence of both fac and mer isomers is predicted by density functional theory calculations. At room temperature, the nuclear magnetic resonance peaks of phenyl-containing mer complexes are broad due to the intermediate rotation of bulky phenyl groups resulting in only the average orientation of the non-equivalent protons in the mer complexes. However, upon heating to 55°C (thus speeding up the rotation) or cooling to −50°C (slowing down the rotation), this broad peak is resolved into three sets of carbon peaks appearing in the 13C NMR spectrum, as well as splitting of the ¹H NMR peaks for the non-equivalent protons in the mer isomer. In solid-state 13C NMR the aromatic rings do not rotate, resulting in the splitting of all the 13C NMR peaks. Two sets of well-defined peaks are observed for the fluorine-containing compound [Co(CF3COCHCOCPh)3] in both the 13C and 19F NMR spectra, indicating that both the fac and mer isomers are present with a ratio of fac:mer = 0.1:1. The X-ray photoelectron spectroscopy measured binding energy of the Co 2p3/2 photoelectron lines are influenced by the subtle electronic (electron-donating or electron-withdrawing) properties of the R groups on the β-diketonato ligands. Various relationships are established between the binding energy of Co 2p3/2 and several physical and density functional theory–calculated properties, confirming good electronic communication (the measurable electronic effect that a molecular fragment has on the physical properties of another molecular fragment in the molecule) of the substituent groups through the pseudo aromatic system of the β-diketonato backbones to the metal. [ABSTRACT FROM AUTHOR]

Several morphologically different Cu-oxide nanocrystals (cube, exposing only the (100) facets; elongated octahedron, exposing only the (111) facets; normal octahedron, exposing only the (111) facets; rounded octahedron, exposing only the (111) facets; truncated edge cube, exposing the (100), (110), and (111) facets) have been prepared. Mixed oxidation state facets were obtained, with the X-ray Photoelectron Spectroscopy revealing that both CuI and CuII are present in the samples. The % CuI and CuII vary for the different morphologies. Morphologies exposing the (111) facet showed the highest % CuI present, with the morphologies exposing the (100) facet showing the least amount of CuI. The glassy carbon electrode's surface was modified with these Cu-oxide nanocrystals and their sensing performance for glucose detection was investigated. The limits of detection (LOD) observed for all the Cu-oxide nanocrystal electrodes were < 2 µM. Electrodes modified with Cu-oxide nanocrystals exposing the (111) facets and having more CuI present in the sample resulted in better glucose detection limits. [ABSTRACT FROM AUTHOR]

Truncated cubic Cu-oxide nanocrystals with edge lengths of ca. 600 nm were prepared employing the low-cost copper (II) chloride as the precursor. XRD revealed that the truncated cubic Cu-oxide nanocrystals are present in both the CuI and Cu0 state. XPS characterisation gives insight into the amount of each state present in the as-prepared, oxidised, reduced and recovered catalyst species. The catalytic activity of the truncated cubic Cu-oxide nanocrystals was tested for the reduction of nitrophenols using NaBH4. After one catalytic cycle of the reduction of 4-nitrophenol, the activity almost halved. The SEM images revealed that the recovered catalyst showed some disfigurement of the structure, and XPS confirmed the reduction of the CuI to metallic Cu0. [ABSTRACT FROM AUTHOR]

A systematic analysis of the XPS Fe 2p 3/2 core-level photoelectron lines and their satellite structures gave insight into the electronic properties of a series of ferrocenyl-containing chalcones with the structure Fc CO CH CH C 6 H 4 R, where R is in the para -position on the phenyl ring and R OCH 3 ( 1 ), CH 3 ( 2 ), C 6 H 5 ( 3 ), t Bu ( 4 ), H ( 5 ), Br ( 6 ) and CF 3 ( 7 ). A V-shaped correlations obtained between the binding energy of the Fe 2p 3/2 photoelectron line and Hammett constants (σ R ) of the R-groups as well as the oxidation potential of the Fe II /Fe III couple, E pa , indicates that there are different modes of zwitterion formation, of electron-donating and electron-withdrawing R-substituents, after photoemission of an electron during the XPS measurements. The intensity of the satellite peak ( I ratio ) within the substructure of the photoelectron line is an indication of the amount of charge being transfer from the donor (ferrocenyl-fragment) to the acceptor fragments. The link between the Gordy group electronegativities, λ R , and I ratio show that more charge is being transfer from Fc in chalcone with more electron withdrawing R-groups. During electron transfer processes (like electrochemical oxidation or photoemission) the chalcone undergoes inner-sphere reorganisation to compensate for the positively charged species which is formed. The I ratio is also an indication of the degree of inner-sphere reorganisation, while the carbonyl stretching frequency ( v CO as measured by ATR FTIR) is a measure of the amount of energy of required for this inner-sphere reorganisation. The link between I ratio and v CO showed that as the degree of inner-sphere reorganisation increases, more energy is required for this inner-sphere reorganisation. [ABSTRACT FROM AUTHOR]

A series of ferrocenyl-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)3] with R = CF3, CH3, Ph (phenyl) and Fc (ferrocenyl) was subjected to a systematic XPS study of the Mn 2p3/2 and Fe 2p3/2 core-level photoelectron lines and their satellite structures. A charge-transfer process from the β-diketonato ligand to the Mn(III) metal center is responsible for the prominent shake-up satellite peaks of the Mn 2p photoelectron lines and the shake-down satellite peaks of the Fe 2p photoelectron lines. Multiplet splitting simulations of the photoelectron lines of the Mn(III) center of [Mn(FcCOCHCOR)3] resemble the calculated Mn 2p3/2 envelope of Mn3+ ions well, indicating the Mn(III) centers are in the high spin state. XPS spectra of complexes with unsymmetrical β-diketonato ligands (i.e., R not Fc) were described with two sets of multiplet splitting peaks representing fac and the more stable mer isomers respectively. Stronger electron-donating ligands stabilize fac more than mer isomers. The sum of group electronegativities, ΣχR, of the β-diketonato pendant side groups influences the binding energies of the multiplet splitting and charge transfer peaks in both Mn and Fe 2p3/2 photoelectron lines, the ratio of satellite to main peak intensities, and the degree of covalence of the Mn-O bond. [ABSTRACT FROM AUTHOR]

A rhodium(I) dicarbonyl on HY zeolite prepared from [Rh(CH 3 COCHCOCH 3 )(CO) 2 ] were charaterised by Attenuated Total Reflectance Fourier Transformed Infrared (ATR FTIR) and X-ray Photoelectron Spectroscopy (XPS). The ATR FTIR spectra of the anchored rhodium complex showed that [Rh(CH 3 COCHCOCH 3 )(CO) 2 ] reacted with the HY zeolite by loosing the [CH 3 COCHCOCH 3 ] − ligand to form Rh(CO) 2 /HY zeolite and [CH 3 COCHCOCH 3 ]/HY zeolite. The sharpness of the v (CO) bands measured by the ATR FTIR showed that the rhodium(I) dicarbonyl complex are distributed fairly uniform over the zeolite support. This heterogeneous catalyst was monitored for the oxidative addition of methyl iodide in the liquid phase, followed by reductive elimination of acetyl iodide upon treatment with CO gas. These reactions were monitored by following the carbonyl stretching frequencies from ATR FTIR measurements and the change in binding energy of the Rh 3d 5/2 photoelectron line as measured by XPS, observed rate constants determined were mutually consistent with each other. [ABSTRACT FROM AUTHOR]

Reaction of [Mn3(OAc)6O•3H2O]+ (1) with ferrocenyl β-diketones of the type FcCOCH2COR with R = CF3 (2a) and CH3 (2b), Ph = C6H5 (2c), and Fc = FeII(η5-C5H4)(η5-C5H5) (2d) yielded a series of ferrocene-functionalized β-diketonato manganese(III) complexes 3a-3d, respectively, of general formula [Mn(FcCOCHCOR)3]. The mixed-ligand β-diketonato complex [Mn(FcCOCHCOFc)2(FcCOCHCOCH3)] (4) was obtained by reacting mixtures of diketones 2b and 2d with 1. A single-crystal X-ray structure determination of 3b (Z = 2, triclinic, space group P1̅) highlighted a weak axial elongating Jahn-Teller effect and a high degree of bond conjugation. An X-ray photoelectron spectroscopic study, by virtue of linear relationships between group electronegativities of ligand R groups, χR, or ∑χR, and binding energies of both the Fe 2p3/2 and Mn 2p3/2 photoelectron lines, confirmed communication between molecular fragments of 2a-2d as well as 3a-3d. This unprecedented observation allows prediction of binding energies from known β-diketonato side group χR values. [ABSTRACT FROM AUTHOR]

The electrochemical analysis, theoretical examination, as well as the first X-ray photoelectron spectroscopic (XPS) study on molybdenum(0) Fischer carbene complexes are presented. The intramolecular communication between the carbene ligand, molybdenum metal centre, and the ancillary ligands is illustrated by linear relationships and trends obtained between experimentally measured redox and XPS binding energy values and theoretically calculated energies and charges. The ease of oxidation of the three series of Mo(0) Fischer carbene complexes presented, namely four pentacarbonyl Mo(0) Fischer carbene complexes of general formula [(CO) 5 MoC(OEt)(Ar)], with Ar = 2-thienyl ( 1 ), 2-furyl ( 2 ), 2-(N-methyl)pyrrolyl ( 3 ), 2,2'-bithienyl ( 4 ), four triphenylphosphine-substituted tetracarbonyl Mo(0) Fischer carbene complexes of general formula [(CO) 4 (PPh 3 )MoC(OEt)(Ar)], with Ar = 2-thienyl ( 5 ), 2-furyl ( 6 ), 2-(N-methyl)pyrrolyl ( 7 ), 2,2'-bithienyl ( 8 ), and four triphenylarsine-substituted tetracarbonyl Mo(0) Fischer carbene complexes of general formula [(CO) 4 (AsPh 3 )MoC(OEt)(Ar)], with Ar = 2-thienyl ( 9 ), 2-furyl ( 10 ), 2-(N-methyl)pyrrolyl ( 11 ), 2,2'-bithienyl ( 12 ), all showed the same trend, namely (most difficult to oxidize at a higher potential): 2-thienyl ≈ 2,2'-bithienyl > 2-furyl > 2-(N-methyl)pyrrolyl. The pentacarbonyl complexes [(CO) 5 MoC(OEt)(Ar)] have the highest oxidation potentials, followed by the oxidation potential of [(CO) 4 (PPh 3 )MoC(OEt)(Ar)], while [(CO) 4 (AsPh 3 )MoC(OEt)(Ar)] oxidized at a potential 0.12 − 0.15 V lower than the PPh 3 substituted complexes [(CO) 4 (PPh 3 )MoC(OEt)(Ar)]. Substitution of carbonyl ligand(s) in the pentacarbonyl complexes 1 – 4 , by one (complexes 5 – 12 ) or two ([(dppe)(CO) 3 MoC(OEt)(2-furyl)] complex ( 13 ), dppe = 1,2-bis(diphenylphosphino)ethane) weaker π-acceptor ligands (phosphines/arsines) in Fischer carbene complexes leads to a decrease in the binding energy of the Mo 3d 5/2 photoelectron lines of the X-ray photoelectron spectra of the Fischer carbene complexes and an increase in the binding energy of the carbene carbon C 1 s photoelectron lines. [ABSTRACT FROM AUTHOR]

In methanol solutions, [Rh(FcCOCHCOR)(CO)(PPh 3)] and [Rh(FcCOCHCOR)(CO) 2 ] complexes do not undergo substitution or oxidative addition by MeOH. In contrast, when the same compounds are spin-coated on (OH)-capped silicon wafers, XPS measurements showed that, in the solid state, both ligand substitution and oxidative addition by Si-OH functionalities occur. Rh XPS binding energies are linearly related to RhI oxidation potentials and group electronegativities of the R-groups (CF 3 , CH 3 , phenyl and ferrocenyl). [Display omitted] A series of rhodium β-diketonato complexes [Rh(FcCOCHCOR)(CO) 2 ] and [Rh(FcCOCHCOR)(CO)(PPh 3)] with R = CF 3 , CH 3 , Ph = C 6 H 5 and Fc (ferrocenyl = FeII(C 5 H 5)(C 5 H 4)) were spin-coated on two-dimensional silanol-functionalised silicon wafers. Chemical reactions were observed that do not occur in ethanol solutions. Si-OH fragments on the wafers substituted ligands and oxidatively added to the Rh(I) centres. A multitude of different surface species could be identified with X-ray photoelectron spectroscopy (XPS). These included the parent spin-coated rhodium(I) complexes and rhodium(I) species that resulted from β-diketonato displacement from parent rhodium complexes by surface silanol OH's to generate [wafer-(O) 2 -Rh-(CO) 2 ]⊝ and [wafer-(O) 2 -Rh-(CO)(PPh 3)]⊝ units. Several RhIII surface species that inter alia resulted from oxidative addition of surface Si-OH groups to surface-coordinated RhI core atoms were also identified. Efficacy of β-diketonato ligand substitution by the silanol surfaces is a kinetically driven process and can be related to the rate of solution-phase β-diketonato substitution by 1,10-phenanthroline from parent [Rh(FcCOCHCOR)(CO) 2 ] and [Rh(FcCOCHCOR)(CO)(PPh 3)] complexes. The binding energies of the RhI and RhIII 3 d 5/2 photoelectron lines were found to be functions of Gordy scale R-group electronegativities and they are also linearly related to electrochemically determined RhI oxidation potentials. [ABSTRACT FROM AUTHOR]

Graphical abstract The electrochemical behavior of the Fc/Fc+ of ferrocenyl-terpyridine coordination metal complexes is related to the charge transfer and binding energy of the Fe 2p photoelectron lines as measured by XPS, giving insight into the electronic properties of the complexes. Highlights • Preparation of coordinated ferrocenyl-terpyridine complexes. • Electrochemical study of the coordinated ferrocenyl-terpyridine complexes. • X-ray photoelectron spectroscopy of ferrocenyl-terpyridine coordination complexes. • The intensity of satellite structures in XPS indicated the amount of charge transferred. • Single crystal structure of [Rh(Fctpy) 2 ][PF 6 ] 3. Abstract A series of 4′-ferrocenyl-2,2′:6′,2′'-terpyridine coordination metal complexes, [M(Fctpy) 2 ][PF 6 ] x with M = Co (2), Fe (3), and Rh (4) and x = 2 (for 2 and 3) or 3 (for 4), was subjected to an electrochemical and X-ray photoelectron spectroscopic study. The formal reduction potential of the Fc/Fc+ couple of the ferrocenyl-moiety (FeII) is related to the Allred Rochow electronegativities of the different coordinated metals, as well as with binding energies of the Fe 2p 3/2 photoelectron lines (as measured by XPS). The binding energy position of the main Fe 2p 3/2 photoelectron line, spin–orbit splitting between the main and satellite structure (charge transfer band) of the Fe 2p 3/2 photoelectron line as well as the intensity ratio between the of the main and satellite structure of the Fe 2p 3/2 photoelectron line (I ratio , this gives the relative amount of charge being transferred) gave insight in the electronic structure of these ferrocenyl-terpyridine coordination metal complexes, 2 – 4. A single crystal X-ray structure determination of 4 highlighted the disorder of the PF 6 counter anions as well as double occupancy of the central metal atom of Rh (in 4) with Fe, the Fe:Rh ratio is 0.14:0.85. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of the first triphenylstibine-containing Fischer carbene complexes of Mo(0) with general formula [(SbPh 3 )(CO) 4 MoC(OEt)(Ar)] with Ar = 2-thienyl ( 1 ), 2-furyl ( 2 ), 2-(N-methyl)pyrrolyl ( 3 ), and 2,2′-bithienyl ( 4 ) are reported. The solid state crystal structures of these complexes show a syn conformation of the 2-thienyl and 2,2′-bithienyl groups relative to the ethoxy group, and an anti conformation of the 2-furyl group relative to the ethoxy group. Density functional theory calculations using natural bonding orbital (NBO) and quantum theory of atoms in molecules (QTAIM) calculations gave insight into the electronic structure and preferred conformations of these novel complexes. X-ray photoelectron spectroscopy measurements show that the binding energy of the Mo 3d 5/2 photoelectron line for the 2-(N-methyl)pyrrolyl-containing Fischer carbene complex, 3 , is the smallest; followed by 2 and then 1 . This implies that the Mo metal centre is more electron rich in 3 , relative to the 2-furyl or 2-thienyl containing Fischer carbene complexes, 2 and 1 , respectively. [ABSTRACT FROM AUTHOR]

The electrochemical behaviour of triphenylstibine-containing Fischer carbene complexes of Mo(0) of the type [(SbPh 3 )(CO) 4 MoC(OEt)(Ar)] with Ar = 2-thienyl ( 1 ), 2-furyl ( 2 ), 2-(N-methyl)pyrrolyl ( 3 ) or 2,2'-bithienyl ( 4 ) is reported. Results are compared to the related complexes [(L,L')(CO) 3 MoC(OEt)(Ar)] where L,L' = CO,CO; PPh 3 ,CO; AsPh 3 ,CO; or dppe (1,2-bis(diphenylphosphino)ethane). Linear trends and relationships obtained between HOMO/LUMO energies, oxidation/reduction potentials, ionization energies/electron affinities and X-ray photoelectron spectroscopic binding energies of the Mo 3d 5/2 photoelectron lines, show that the electronic influences of the heteroaryl carbene substituent and pnictogen ligands in Mo(0) Fischer ethoxycarbene complexes are transmitted well through the bonds to the Mo metal centre. [ABSTRACT FROM AUTHOR]

Ethoxy chromium (0) Fischer carbene pentacarbonyl complexes [(CO) 5 CrC(OEt)R]; R = 2-thienyl ( 1 ), 2-furyl ( 2 ) were covalently anchored onto aminopropyltrimethoxysilane-functionalized silicon-wafers to form Cr-grafted Si-wafers S1 and S2 that were characterized by X-ray photoelectron spectroscopy (XPS). X-ray photoelectron spectroscopy determined that binding energy of the Cr 2p 3/2 photoelectron line of the thienyl-containing complexes were smaller than that of the furyl-containing complexes. The binding energy of the Cr 2p 3/2 photoelectron line of the ethoxycarbene complexes was smaller than that of aminocarbenes. The binding energy of the Cr 2p 3/2 photoelectron line of the Cr-grafted Si-wafers were ca. 1 eV higher than that of the related aminocarbenes. A 25–33% anchoring of the Cr-complexes 1 and 2 on the aminopropyltrimethoxysilane-functionalized silicon-wafers was achieved. [ABSTRACT FROM AUTHOR]