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The acid–base chemistry of luteolin, a flavonoid with important pharmacological and dyeing properties, and of the related methyl ether derivatives have been investigated by DFT and MP2 methods, testing different computational setups. We calculate the p K a ’s of all the possible deprotonation sites, for which no experimental assignment could be achieved. The calculated p K a ’s deliver a different acidity order for the two most acidic deprotonation sites between luteolin and its methyl ether derivatives, due to intramolecular hydrogen bonding in luteolin. A lowest pKa of 6.19 is computed for luteolin, in good agreement with available experimental data.

We report a theoretical investigation of β-elimination reactions in systems activated by the pyridine ring. The investigated reaction, the acetohydroxamate-induced β-elimination in protonated N-[2-(2-pyridyl)ethyl]quinuclidinium, offers a unique opportunity to test computational methodologies since detailed kinetic experimental data are available. We calculated the pKas of the acetohydroxamic acid and the substrate and thoroughly characterized the reactive free-energy profile. The reaction proceeds via a stable carbanion intermediate. Except a discrepancy in the reproduction of the pKa of the acetohydroxamic acid, the calculated free-energy profile is in excellent agreement with the experiment, showing the general reliability of the present approach.

Density functional theory calculations have been performed on the main adsorption configurations of pentacene on the Si(100) surface and on the possible pathways for the following C-H bond cleavage. We considered possible candidates for all the orientations of pentacene experimentally observed with STM, i.e., on the top of silicon dimer rows, perpendicular to the dimer rows, diagonal to the dimer rows and between two adjacent dimer rows ("in between"). Our calculations indicate that the most stable adsorption configuration of pentacene on the Si(100) surface is the symmetric perpendicular structure with an adsorption energy of -128.3 kcal mol -1 , with the in between structure 10.5 kcal mol -1 and the symmetric parallel structure 13.0 kcal mol -1 higher in energy. Transition states for the dissociation of C-H and formation of Si-H bonds from the main adsorption configurations of pentacene have been characterized and the corresponding energy barriers estimated. We identified two kinds of adsorbed configurations of pentacene from which the breaking of two C-H bonds can be accessible: one on top of a silicon dimer row with one or both outer benzene rings di-σ- bonded through a [2 + 2] cycloaddition; one with one or more pentacene rings 1,4 di-σ-bonded across two dimer rows, such as the in between structure. The kinetically most favorable reactive channel is that from the in between configuration and involves the separate abstraction of two hydrogen atoms on the sp 3 carbon atoms by the two silicon atoms of the two dimers bearing an unpaired electron, with an energy barrier of 29-30 kcal mol -1 .

The objective of this study was to evaluate the use of micro-Raman spectroscopy as a non-invasive vibrational spectroscopic technique applied to the examination of wool samples, which may be applied to textile materials of cultural heritage interest. In this work, a selection of wool materials were primarily investigated in their unaged states through the utility of a natural wool reference together with selected samples dyed with different natural colorants, namely woad, weld and madder. The identification of the main modes of vibration of the wool fibre keratin was assessed in all the samples, which aided the determination of the changes within the protein structure, in particular, through the cysteine and peptide cross-linkages brought about by the addition of the dyes that can produce effects similar to degradation. The dye too was assessed importantly to enable its identification through its characteristic scattering or fluorescence emissions on a woollen matrix, as well as to ascertain whether a uniform covering across the surface of the wool was achieved or not. Regarding the artificial degradation of the samples it was possible to observe numerous modifications within the molecular structure of the wool, in particular, within the amide I, C-H bending, amide III and S-S stretchings along with the physical photo-yellowing of fibres given by the presence of lipids dispersed across the surface of the wool. The effects of ageing on the dyed samples were also investigated, indicating that many of the bands relative to the colorants were still present, yet so too were numerous vibrations from the wool that also indicated a certain level of stress and degradation to the underlying wool. Copyright (C) 2008 John Wiley & Sons, Ltd.

The in situ non invasive methods have experienced a significant development in the last decade because they meet specific needs of analytical chemistry in the field of cultural heritage where artworks are rarely moved from their locations, sampling is rarely permitted, and analytes are a wide range of inorganic, organic and organometallic substances in complex and precious matrices. MOLAB, a unique collection of integrated mobile instruments, has greatly contributed to demonstrate that it is now possible to obtain satisfactory results in the study of a variety of heritage objects without sampling or moving them to a laboratory. The current chapter describes an account of these results with particular attention to ancient, modern, and contemporary paintings. Several non-invasive methods by portable equipment, including XRF, mid- and near-FTIR, UV-Vis and Raman spectroscopy, as well as XRD, are discussed in detail along with their impact on our understanding of painting materials and execution techniques. Examples of successful applications are given, both for point analyses and hyperspectral imaging approaches. Lines for future perspectives are finally drawn.

We report time-dependent (TD) and coupled-perturbed (CP) DFT/HF investigations, on the linear and non-linear optical properties of M(II)-complexes of [5-[(4′-dimethylaminophenyl)-ethynyl]-15-[(4″-nitrophenyl)ethynyl]-10,20-diphenylporphyrin], with M = Zn, Cu, Ni. The TD-DFT absorption spectrum is in good agreement with the experimental one, allowing us to identify the transitions mainly responsible of the NLO response. CP-DFT/CP-HF calculations provide similar hyperpolarizability values for the three complexes, suggesting an irrelevant role of the metal center. A sharp hyperpolarizability increase is calculated at an incident laser wavelength of 1.064 μm compared to 1.907 μm, which seems to be responsible for the large differences between Zn, Cu and Ni complexes reported experimentally.

The energetics and reaction mechanism of prototypical organometallic reactions have been investigated by combining static and dynamic density functional calculations, based on the Car–Parrinello method. Such an approach allows us to dynamically sample the potential energy surface of the reactive system at finite temperature, providing useful insights into the reaction mechanism and evidencing the presence of reaction intermediates. Applications of this methodology are presented, ranging from the migratory insertions of carbon monoxide and alkyl-isocyanides into different metal–carbon bonds, to the SiH oxidative addition to Pt(PH 3 ) 2 and the acetylene to vinylidene isomerization in the coordination sphere of a transition metal center.

Nineteen samples of medieval transparent-glazed pottery and archaic majolica from Orvieto (central Italy) were studied. They were classified by archaeological criterion as follows: five transparent-glazed fragments with green and brown decorations (first half of the 13th century), eight green transparent-glazed fragments (13th century) and six tin-glazed fragments with green and brown decorations (second half of the 13th century). SEM–EDX, XRD (the Rietveld method) and XRF were used to characterize the chemical and mineralogical compositions both of the bodies and the coatings. In all of the samples, the paste is Ca-rich with CaO contents as high as 13–20 wt%. The mineralogical composition is compatible with a firing temperature of about 950°C, which is the typical temperature reached in a wood kiln. No difference was observed between the bodies of transparent- and tin-glazed pottery. In the case of transparent glazes, the burial conditions lead to heavy weathering of the samples. However, on the basis of the analyses carried out in non-weathered areas, the typical composition is PbO 55–65 wt%, SiO231–35 wt%. In tin glazes, the tin is scattered on the mass of the glaze as SnO2crystals with a concentration of 7–14 wt%. Concerning the decorations, it is established that the green colour is due to the presence of copper, while manganese is responsible for the brown colour. These pigments, which represent the typical colours of ‘archaic majolica’, are spread through the glaze homogeneously, apart from one case in which there is clear evidence of manganese oxide crystals.

The intramolecular coupling of the two iminoacyl units in the bis(η 2 -iminoacyl) complexes lcalix[4](OMe) 2 (O) 2 -Zr(η 2 -MeCNBU t ) 2 ]and [(2,6-Bu t 2 C 6 H 3 O)2-Zr(η 2 -MeCNPh) 2 ] to generate the corresponding enediamido species has been investigated by means of both static and dynamic density functional calculations. For both systems we have characterized the stationary points of the potential energy surfaces for the coupling reaction and evaluated the overall energy profile. Car-Parrinello molecular dynamics simulations have been performed to gain insight into the detailed mechanistic features of the iminoacyl coupling and surprisingly show that this reaction occurs through an asynchronous reaction mechanism in which a decoordinated iminoacyl attacks the residual coordinated iminoacyl C-N double bond. A transition state search, performed without any symmetry constraint, led to structures consistent with the proposed mechanism 23.8 and 21.2 kcal mol - 1 above the starting bis-(η 2 -iminoacyl) reagents, in good agreement with experimental activation enthalpies. On the basis of the proposed reaction mechanism we are also able to reproduce the activation energy of the coupling reaction with electron-withdrawing substituents on the iminoacyl moiety. Inspection of the electronic structure changes along the proposed reaction pathway suggests that the iminoacyl coupling process can be described as an intramolecular attack of the decoordinated iminoacyl carbon lone-pair at the coordinated iminoacyl π* orbital, thus reconciling the iminoacyl coupling reaction mechanism with the generally accepted pattern of acyl and iminoacyl reactivity.

Throughout the years, a large number of paintings by Perugino have been investigated using the in situ non-destructive x-ray fluorescence (XRF) technique. Three anomalous characteristics were frequently identified, concerning a brown earth pigment containing zinc, the presence of manganese in some red lakes and the association of the presence of copper and tin with grey-blue regions. In an effort to understand these anomalies better, five micro-samples, taken from selected easel paintings by Perugino at the Galleria Nazionale dell'Umbria and a fresco at the Monastero di Sant'Agnese in Perugia, were studied by micro-Raman spectroscopy and scanning electron microscopy (SEM). Micro-Raman spectroscopy was a useful tool to investigate the molecular nature of such uncommon pigments and SEM provided useful information on the stratigraphy of the paint layers. The brown earth pigments, used by the master in the last period of his production, were definitely confirmed to be characterized by zinc impurities. The manganese contained in red lakes was shown to be due to ground alkaline glass, with a small quantity of manganese and iron, probably added to the oil binder in an attempt to speed up drying. Finally, in the sampled paintings, the grey-blue colour characterized by copper and tin was not present. Copyright (C) 2004 John Wiley Sons, Ltd.

The reaction of acenaphthylene (ACN) with the Si(001) surface has been explored by means of density functional cluster model calculations. We have considered seven reasonable bonding configurations...

The potential energy surface of the reaction between ethylene molecules and N + ions is investigated by using the DFT hybrid functional B3LYP with the 6-31G* basis set. The addition channel leading to the intermediate C 2 NH 4 + is considered. We study eighteen structures of the triplet C 2 NH 4 + cations and the transition states for their isomerizations. Then, we consider the release of a H atom to form the doublet C 2 NH 3 + cations. To obtain more accurate values of reaction energetics and barrier heights, coupled cluster CCSD(T) calculations with the 6-311G** basis set are performed on the B3LYP/6-31G* optimized geometries. The addition of N + into C 2 H 4 is computed as a barrierless process leading to the triplet 1-aziridynil cation which, by ring opening, can easily evolve into the 2-azaallyl isomer. This species can then release a hydrogen atom to form the 2-azaallene cation, process that is computed to be the most likely channel.

The reaction of phenylium and d-phenylium ions with molecular deuterium has been investigated both experimentally and theoretically. Theoretical calculations have been carried out at the B3LYP/6-31G* level of theory. The key features of the potential energy surfaces and all the relevant thermochemical parameters have been calculated. These results are in good agreement with previous theoretical studies concerning the unimolecular dissociation of benzenium ions. Theoretical calculations provide a clear insight on the reaction mechanisms for the system under study. Experimental studies have been carried out by means of a guided beam tandem mass spectrometer. We have measured the reaction cross section for four different reaction channels, as a function of the collision energy, in the range from thermal energies up to about 1 eV. The bimolecular reactivity of C6H5+ is dominated by the substitution of one or two hydrogen atoms by deuterium, leading to the formation of C6H4D+ and C6H3D2+ products. The reaction...

The energetics and reaction mechanism of the migratory insertion of carbon monoxide and methyl isocyanide into the zirconium–carbon and titanium–carbon bonds in [calix[4](OMe)2(O)2–M–Me2], (M=Zr, Ti), have been investigated by combining static and dynamic density functional calculations. Two steps have been characterized: the coordination of the incoming nucleophilic moiety leading to relatively stable facial adducts; its subsequent insertion into the M–C bond, leading to η2-bound acyl or iminoacyl complexes, providing a rationale for the different behavior of CO and MeNC towards both insertion and deinsertion reactions. Our results indicate that the rate-determining step for the overall MeNC insertion into the M–C bond is its coordination to the electron-deficient metal center, with the titanium system featuring a higher energy barrier (12.7 versus 5.5 kcal mol−1). Ab initio molecular dynamics simulations have been performed on the Zr system by means of the Car–Parrinello method, to study the hitherto inaccessible mechanistic features of the insertion reactions.

In the last few years, astronomical spectra have revealed the presence of aromatic and polyaromatic molecules in extraterrestrial environments, near carbon stars, in molecular clouds and meteorites. Moreover, the recent observation of benzene in interstellar space has noticeably increased the interest in the entire class of molecules and in their chemical behavior. In this work, we have investigated the reaction between the benzene molecule and the atomic nitrogen cation and, in particular, the mechanisms by which the reactants are converted into cationic products containing at least one C–N bond, according to the general scheme C6H6+N+→HmCnN++CxHy. We have measured the energy dependence of the cross section in a guided ion beam tandem mass spectrometer. Relevant stationary points of the potential energy surface have been studied by using the density functional theory hybrid functional B3LYP with the 6-31G* basis set. Thermochemical calculations, and the comparison with experimental results, allow us to d...

Density functional calculations have been performed to investigate the functionalization of single-wall carbon nanotubes (SWNTs) with the Cr(CO)3 metal fragment, employing extended molecular models. A circumcoronene molecule (C54H18), made by the fusion of 19 hexagonal carbon rings, can be regarded as a fragment of a graphene sheet. To reproduce the curvature of the SWNT surface, suitable geometric constraints have been imposed on the C54H18 model, freezing the positions of the outer hydrogens along the directions of the nanotube C-C bonds. Geometry optimizations have then been performed under this constraint on the Cr(CO)3-C54H18 complexes, pointing out the most favourable coordination sites on the hexagonal rings of the carbon atom surface and the electronic properties of the resulting system. The effect of the curvature on the metal coordination to nanotubes has been analysed by investigating the interaction of the Cr(CO)3 metal complex with the C54H18 molecules, modelling (n, 0) nanotubes with differe...

The results from the first systematic analytical survey of three of Munch's paintings, Puberty, Anxiety and Vampire, dated to the 1890s, are reported. The study was carried out through the transnational access programme of MOLAB within the European Eu-ARTECH project (FP6), which offered access to a mobile analytical facility devoted to in-situ non-invasive investigations of art historical objects. The study aimed to provide a thorough examination of painting materials and of their present condition by a total non-invasive diagnostic approach. The acquired information constitutes the first basic step towards the definition of the most appropriate future conservation strategies targeted to the specific needs of these three paintings.

Computational schemes are presented with which to evaluate the electrostatic Coulomb energy in relativistic molecular electronic structure calculations using a basis of four-component Dirac spinor amplitudes. We demonstrate that algorithms may be constructed and implemented which differ only in minor details from those in common use in nonrelativistic quantum chemistry, and that the four-component formalism is neither as complicated nor as expensive as has been suggested recently in the literature. Spherically symmetrical atomic basis sets are presented which indicate that accurate representations of the Coulomb energy may be obtained using modest expansions of the electronic density in a scalar auxiliary basis set of spherical harmonic Gaussian-type functions.

Density functional calculations have been performed on the oxidative addition of a Pt(0) fragment, Pt(PH3)2, to one of the rim C−C bonds of semibuckminsterfullerene (C30H12), to give an η2-σ-bonded...

We have carried out a theoretical study of the migratory insertion step in the cationic Ni(II) [(dppp)Ni(CH3)(CO)]+ complex by means of both static and dynamic density functional methods to shed light on the mechanistic aspects of the migratory insertion and in particular on the role played by five-coordinate species. We find the addition-insertion pathway, taking place via a five-coordinate complex, to be thermodynamically and kinetically favored, with a highest energy barrier of 7.9 kcal mol-1, in agreement with the experimental data. Dynamics simulations have shown that the migratory insertion reaction takes place by a methyl attack on the resting carbonyl group.

Pyracylene, a polynuclear aromatic hydrocarbon which is made up of two benzene and two cyclopentadienyl rings, has been employed as a model to study the interaction of transition metal complexes with fullerenes. To reproduce adequately the geometric and electronic structure of fullerene with a pyracylene model, we had to impose suitable geometric constraints forcing the pyramidalisation angle on the two central carbon atoms to assume a value similar to that observed in C60. Density functional calculations were then performed on (PH3)2M(C14H8) (M = Ni, Pd, Pt) molecules. The results have been analysed in terms of the Chatt–Dewar–Duncanson model and show that the constrained pyracylene is a fairly good model to study the interaction of transition metals with fullerene: geometries are reproduced within 0.02 A and the bond dissociation energies are slightly underestimated by only 10–40 kJ mol−1.

In this work some Renaissance lustre decorated ceramics have been examined. Our attention was directed to lustre which is a thin decorative metallic film applied on the surfaces of previously glazed ancient pottery. Some 16th century lustre ceramics shards from Deruta, Umbria (Italy) have been analysed by small angle X-ray scattering (SAXS) in order to characterise the dimension of the metal nanocrystals forming the thin lustre layer. This technique appeared to be a powerful tool to characterise lustre films nanostructure and may be successfully used for this purpose together with transmission electron microscopy (TEM). Furthermore, SAXS measurements are extremely suitable for the determination of polydispersity and average interparticle distance. The lustre surfaces have been also analysed by scanning electron microscopy plus X-ray energy dispersive spectrometry (SEM–EDX) in order to identify the metals present (silver, copper or both of them) and to establish copper/silver ratios. From the comparison between SAXS results and compositional data, it was possible to conclude that copper particles are smaller than the silver ones. We have evidenced how the microtexture as well as the chemical composition of the lustre layers are responsible for the gold or red colour typical of the lustre films.

The lowest singlet 11A′ and 11A″ potential energy surfaces (PES) of the O(1D)+HBr system have been ab initio computed. The complete active space self-consistent field (CASSCF) method was used in most of the calculations, considering all the valence orbitals as active. The calculations were complemented with both analytical gradient calculations to characterize the stationary points and multireference configuration interaction (MRCI) calculations at selected nuclear geometries to improve the determination of the barrier heights and of the energetics. Electronic energy values for both PESs were then independently fitted by polynomial expansions in bond order coordinates. On the fitted surfaces quasi-classical trajectories were separately run. Single-surface calculations behave qualitatively different for the ground and the excited PES at low collision energies. A satisfactory agreement with existing experimental data was obtained by using the ground PES while calculations performed on the excited 11A″ PES worsened the agreement. However, when collision energy is increased, detailed experimental distributions are less well reproduced by calculations on the ground PES. This may imply the participation via nonadiabatic transitions of the 21A′ PES at higher energies while the adiabatic ground singlet PES well describes reactive scattering at low collision energy. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Density functional calculations have been performed on some calix[4]arenes complexes of early transition metals. Particular emphasis has been placed on the comparison of the main properties of these metal complexes with the analogous metal complexes based on four monodentate phenolate ligands to study the effect of the geometrical constraints imposed by the calixarenes framework on the electronic structure. The results show that the most stable geometry of titanium and molybdenum tetraphenolates is pseudotetrahedral (slightly flattened for molybdenum) and that the distortion to a square planar coordination requires, respectively, 52.0 and 21.5 kcal x mol(-1). However, a significant energy decrease is found when the four phenolate groups are bent in the same hemisphere, reproducing the calix[4]arene geometry. Such a coordination determines the energy decrease of the unoccupied metal d orbitals of sigma and pi symmetry, which leads to an increase of the electron-accepting properties of these metal fragments.

Density functional calculations have been carried out on a series of model hypothetical intermediates in the six-electron oxidation of porphyrinogen (5,10,15,20,22,24-hexahydroporphyrin) to porphyrin. Two possible reaction pathways have been investigated: the conventional one, supposed to be followed both in the chemical synthesis and the biosynthesis of porphyrins, and the unconventional one, which has been discovered on studying the oxidation of a stable form of porphyrinogen, namely meso-octaalkylporphyrinogen. The energetics of both pathways have fully been investigated for the free porphyrinogen. The conventional route is strongly preferred with respect to the unconventional one. The metal-assisted six-electron oxidation of porphyrinogen to porphyrin was also investigated by density functional calculations on several nickel and cobalt model complexes. The metal does not seem to be able to force the system to follow a different route; the conventional route is even more preferred with respect to the unconventional one.

Density functional calculations have been performed on (PH3)2M(η2-C60) (M = Ni, Pd, Pt) complexes. The optimized geometries have been found in good agreement with the X-ray experimental data. The electronic structure has been analyzed in terms of the Chatt−Dewar−Duncanson model, and the contribution from π back-donation was found to dominate over that from σ donation for all three complexes. Reliable values for the metal fullerene bond dissociation energies have been calculated and found higher than the corresponding metal ethylene complexes, but lower than metal tetrafluoro- and tetracyanoethylene complexes.

Density functional calculations have been carried out on the series of metallacumulene complexes [(CO)5Cr(C)nH2)] (n = 2−9) to study the electronic structure and the bonding of the CnH2 cumulene ca...

The electronic structure and the geometry of the trifluorotitanioacetamide, the trifluorotitanioacetylphosphine, the trifluorotitanioacetophenone and the trifluorotitaniomethylphenylsulphoxide have been investigated through ab initio calculations. The different coordination modes, η1–O, η3– and η1–C of the TiF3+ cation have been analysed. The η1–O coordination of the titanium towards the enolate anion is preferred, although in the acetamide enolate anion and the methylphenylsulphoxide enolate anion the η1–O and the η3 coordinations are almost isoenergetic. The η1–C coordination is destabilised in all systems. A comparison between TiF3+ and Li+ shows that TiF3+ is more oxophilic than Li+.

Density functional calculations have been performed for [M(PH3)2(C2X4)] complexes with M = Ni, Pd or Pt and X = H, F or CN to study the effect of electron-attracting substituents on the metal–olefin bonding. The optimised geometries have been found to be in good agreement with experimental crystal structure data. The electronic structure has been analysed in terms of the Chatt–Dewar–Duncanson model and the contribution from π back donation was found to dominate over that from σ donation for both ethylene and substituted ethylene complexes. Reliable values have been calculated for the metal–olefin bond dissociation energies and compared with the available experimental data.

Density functional calculations have been performed on molecular models of silica defects and their C 2 H 4 adducts. The results are consistent with a previous experimental infrared characterization that was interpreted in terms of C 2 H 4 addition to the SiO 2 skeleton at both the oxygen-bridge and silicon-link vacancy defects produced by argon bombardment. The geometries and thermodynamical stabilities of the proposed species and other possible adducts have been evaluated. The calculated C  C, C  O and C–H stretching frequencies are in good agreement with the experimental values and confirm the validity of the previous interpretation, helping to clarify some unclear details.

A class of (–LnM–Cm–)x hypothetical polymers, m = 2–4, conceptually derived from experimentally known analogous rigid-rod organometallic polymers and with different electron counts, obtained by varying the metal and the ligands in the MLn fragment, have been studied using extended-Huckel tight-binding calculations. The results suggest interesting conducting properties, depending on the electron count and the length of the bridging Cm chain.

This report concerns the formation and the main properties of Zr−C functionalities supported by the O4 matrix of either the monoalkylated (trianionic) or dialkylated (dianionic) forms of [p-But-calix[4]arene] (1). The synthesis of the starting materials [p-But-calix[4]-(OMe)2(O)2ZrCl2] (4) and [{μ-p-But-calix[4]-(OMe)(O)3}2 Zr2Cl2] (10) has been performed via the lithiation of the corresponding protic forms, [p-But-calix[4]-(OMe)2(OH)2] (2) and [p-But-calix[4]-(OMe)(OH)3] (8), followed by reaction with ZrCl4·(thf)2. Complex 4 undergoes a facile base-induced (base = Et3N, Py) demethylation, leading to the monomethoxy derivative [p-But-calix[4]-(OMe)(O)3ZrCl2]-[MeNEt3]+ (5) and ionization of the Zr−Cl bond to give [p-But-calix[4]-(OMe)2(O)2Zr(OTf)2] (6). The alkylation of 4 led to the corresponding dialkylaryl derivatives [p-But-calix[4]-(OMe)2(O)2ZrR2] (R = Me, 12; R = CH2Ph, 13; R = CH2SiMe3, 14; R = p-MeC6H4, 15]. They undergo a base-induced demethylation and dealkylation illustrated by the obtention of ...

The present report deals with the multistep migratory insertion of carbon monoxide and isocyanides into the metal−carbon bonds of the ZrR2 fragment anchored to a tetroxo matrix, defined by the dime...

Density-functional calculations have been carried out on a metathesis-like reaction between W2(OR)6 (R = alkyl) and alkynes to give tungsten alkylidyne complexes. Two possible pathways have been taken into consideration: (i) a parallel approach between the reactants to give 1,2-ditungstenacyclobutadiene; (ii) a perpendicular approach to yield a ditungstenatetrahedrane which then flattens giving a 1,3-ditungstenacyclobutadiene. The electronic structure of the compounds involved in the reaction, as well as several energy profiles corresponding to the formation and decomposition of these species, have been investigated in order to study the thermodynamics and kinetics of the metathesis-like reaction. The inclusion of relativistic effects is crucial in order to understand how the reaction proceeds.

Density functional calculations have been carried out on a trinuclear [{Fe(CO)2Cp}3(μ3-C3)]+ cation, and on related C3H3+ and C3(NH2)3+ molecules in order to study the electronic structure and the bonding of the C3+ unit to the metal fragments in this complex. An analysis of the MOs and of the Mulliken populations has been performed in order to understand the extent of the relative σ and π interactions between the C3+ and the Fe(CO)2Cp fragments. The results show that the iron−cyclopropenyl bond is mainly of σ character with a smaller, but important, π contribution. DFT calculations were also performed on the hypothetical mononuclear [Fe(CO)2Cp(C3H2)]+ complex to study the relative stabilities of the possible orientations of the Fe(CO)2Cp fragments with respect to the C3+ ring and to study its rotation about the Fe−C bond.

The first electronic structural study of the complete valence shell binding energy spectrum of molecular fluorine, encompassing both the outer and inner valence regions, is reported. These binding energy spectra as well as the individual orbital momentum profiles have been measured using an energy dispersive multichannel electron momentum spectrometer at a total energy of 1500 eV, with an energy resolution of 1.5 eV and a momentum resolution of 0.1 a.u. The measured binding energy spectra in the energy range of 14–60 eV are compared with the results of ADC(4) many-body Green's function and also direct-CI and MRSD-CI calculations. The experimental orbital electron momentum profiles are compared with SCF theoretical profiles calculated using the target Hartree-Fock approximation with a range of basis sets and with Density Functional Theory predictions in the target Kohn-Sham approximation with non-local potentials. The truncated (aug-cc-pv5z) Dunning basis sets were used for the Density Functional Theory calculations which also include some treatment of correlation via the exchange and correlation potentials. Comparisons are also made with the full ion-neutral overlap amplitude calculated with MRSD-CI wavefunctions. Large, saturated basis sets (199-GTO) were employed for both the high level SCF near Hartree-Fock limit and MRSD-CI calculations to investigate the effects of electron correlation and relaxation.

The controlled ionization of the linear [Cl–Ti–O–Ti–Cl] skeleton allowed the generation of the [Cl–Ti–O–Ti]+ dimer, which is nonsymmetrical as a consequence of extended Cl–Ti–O π interactions. The [TiO] unit thus formed is a building block for a variety of titanoxane structures. This chemistry has been investigated from a theoretical point of view by ab initio MO analysis of the [Cl–Ti–O–Ti–Cl] and [Cl–Ti–OTi]+ fragments. These calculations lead to the conclusion that single ionization generates the [TiO] unit, whereas double ionization does not affect the μ-oxo bonding mode in [Ti–O–Ti]2+ or [S–Ti–O–Ti–S]2+ (where S is a pure σ-donor ligand or solvent). This observation has been confirmed experimentally by ionizing the following model complexes: [(Cl)(acacen)-Ti–O–Ti(acacen)(Cl)] (3) (acacen = N,N'-ethylenebisacetylacetoneiminato dianion) and [(Cl)(salen)Ti–O–Ti(salen)-(Cl)] (4) (salen = N,N'-ethylenebissalicylideneiminato dianion), where the linear Cl–Ti–O–Ti–Cl unit is assured by the square-planar bonding mode of the tetradentate Schiff base ligand. The double ionization of 3 with AgNO3 gave the conventional μ-oxo derivative [(acacen)(η1-ONO2)Ti–O–Ti(acacen)(η1-ONO2)] (5). In contrast, the stepwise ionization of 3 and 4 with NaBPh4 in THF led to the nonsymmetrical [Cl–Ti–OTi]+ intermediates, which are the parent compounds for a variety of linear titanoxanes. The following species containing a TiO unit have been isolated from the NaBPh4-assisted ionization of 3: [(acacen)TiO–BPh3] (6) and [(L)(acacen)TiO–Ti(acacen)–O–(acacen)Ti–OTi(acacen)(L)]2+2 BPh-4 (L = THF, 7; L = none, 8). The same reaction carried out on 4 led to [(THF)-(salen)TiO – Ti (salen) – O – (salen)Ti-(THF)]2+2 BPh-4 (9) and [(L)(salen)-TiO–Ti(salen) – O – (salen)Ti–OTi-(salen)(L)]2+ 2BPh-4 (L = THF, 10; L = Py, 11; L = none, 12, polymeric form). A scheme is proposed to explain the formation of the species derived from the single ionization of 3 and 4, where the origin and the binding properties of the [TiO] unit play a major role.

A simple MO model allowing the prediction of the interaction mode of bridging “C2” units in dinuclear complexes has been developed. The three possible limiting structures, namely MC⋮ CM, MCCM, and M⋮CC⋮M, depend on the dn configuration and the oxidation state of the transition metal and upon the nature of its ancillary ligands. These conclusions have been drawn on the basis of density functional calculations carried out on the model complexes [{(H2O)n(OH)3-nM}2(μ-C2)] (M = Ti, V, Cr, Mn; n = 0, 1, 2) where the OH- ligand mimics an OR- ligand, a π-donor ligand which is widely used in organometallic chemistry. In addition, our calculations allowed the identification of two general classes of “C2” bridged dinuclear transition metal complexes on the basis of the metal's parameters and position in the periodic table.

The potential energy surface of the O(1D)+HCl reaction has been calculated at an ab initio level. The calculated values have been fitted using a bond‐order polynomial. On this potential energy surface quasiclassical trajectory calculations have been performed. These calculations reproduce most of the available experimental information better than the other existing potential energy surfaces.

Density functional calculations are carried out on the Cu5(C6H5)5, Ag4(C6H5)4 and Au5(C6H5)5 systems. Electronic structure and bonding aspects of the interaction between the Mn and (C6H5)n units are investigated. Calculations are performed on the corresponding naked clusters of four and five metal atoms in order to study the M-M bond and the stability trend as a function of cluster size. The following conclusions are reached: (i) M-M bonding is present in all the complexes (both naked and with phenyls) and (ii) the stability increases with cluster size, even if, for the complexes with phenyls, tetramers and pentamers show a comparable stability. Relativistic effects turn out to be essential for the description of gold systems but not remarkable for silver and copper clusters.

In recent years, in situ noninvasive spectroscopy has played an increasingly important role in art conservation. Spectroscopic methods can be used to gain a deep understanding of the material composition of art objects while fully respecting their integrity and value. Considerable improvements in detector technology, instrument–computer interfacing, focusing optics, and the performance of radiation sources have been made in the spectroscopic field and have led to the development and successful application of a series of noninvasive and portable analytical tools for point examination. In this context, current scientific interest is focused on the development of mapping/imaging multi-/hyperspectral methods, since area examination naturally meets the demands of a holistic art-historical approach by revealing not only the chemical composition of painting materials but also their semiquantitative spatial distribution with respect to what is visible to the naked eye. Recently, the possibility of mapping elemental distribution on paintings by means of a portable scanning macro X-ray fluorescence device was demonstrated to be useful for the investigation of the materials used by artists. The molecular identification and spatial distribution of a number of pigments can be inferred from reflection imaging in the visible (Vis: 400–750 nm) and near-infrared regions (NIR: 750–2500 nm) by combining information on electronic transitions in the visible range with overtone and combination vibrational bands in the near-infrared range which are associated with inorganic pigments containing hydroxy groups, such as lead white, azurite, and gypsum. The identification and mapping of organic compounds is a challenge for the noninvasive analysis of artworks. In comparison with inorganic pigments and fillers, there is a larger variety of organic compounds, and they are present in smaller amounts and more subject to chemical alteration. If both traditional and modern art are taken into consideration, just some of the organic compounds to be identified and localized may include: drying oils, proteins, acrylics, alkyds, polyvinyl acetates, natural and synthetic waxes, terpene resins, and natural and synthetic dyes. Recently, Ricciardi et al. demonstrated the potential of hyperspectral imaging in the NIR region (10000–4000 cm ) to discriminate between lipid and proteinaceous binders on illuminated manuscripts on the basis of the vibrational combination/overtone bands of methylene groups and amides. In contrast, the mid-infrared (MIR) range has not yet been exploited for the spatially resolved remote study of artworks, although the MIR range (4000–600 cm ) has proved to be very informative for the identification of artists materials by noninvasive point analysis 12] or microinvasively by cross-section imaging. Herein, we describe the potential of imaging MIR spectroscopy for painting analysis through the application of a novel hyperspectral imaging system (HI90, Bruker Optics). The system developed for the remote identification and mapping of hazardous compounds was adapted in this study for reflection measurements of paintings by the use of an external infrared radiation source. The subject of our study was a painting by Alberto Burri, Sestante 10 (1982), which is currently exhibited at the Ex-Seccatoi del Tabacco (Perugia, Italy). Three areas (ca. 9 9 cm) of the large painting (250 360 cm) were analyzed on site with the HI90 system. We also investigated several points within the same areas noninvasively with a portable FTIR spectrometer (Alpha-R, Bruker Optics) to validate the assignment made on the basis of the HI90 spectral data. In Figure 1a, the visible image of the investigated area I of Sestante 10 is shown. The resulting brightness temperature difference images in Figure 1b,c clearly highlight the use of a different binder for the orange sector to that used for the other sectors. More precisely, the image depicted in Figure 1b shows the false-color representation of the difference in the mean brightness temperature for a peak in the signature of the orange area (1154–1167 cm ) and the mean brightness temperature for a frequency range in which the reflectance is lower (1197–1209 cm ; see range (b) in Figure 1d). The area in the brightness temperature image in Figure 1b indicates the presence of an acrylic binder, as suggested by a comparison with the spectrum recorded with the HI90 instrument [*] Dr. F. Rosi, Dr. C. Miliani Istituto di Scienze e Tecnologie Molecolari CNR-ISTM, SMAArt Via Elce di sotto, 9 Perugia 06123 (Italy) E-mail: costanza.miliani@cnr.it

This paper highlights the efficacy of non-invasive portable spectroscopy for assessing the execution technique and constituent materials in one of the most important medieval manuscripts, the Book of Kells. An aimed campaign of in situ measurements by the MObile LABoratory (MOLAB) has analyzed its elemental composition and vibrational and electronic molecular properties. The ample analytical toolbox has afforded complementary diagnostic information of the pigment palette permitting the characterization of both inorganic and organic materials as pigments and dyes in the white, purple, blue, red, orange, green and black areas. in particular, the novel widespread use of calcinated gypsum (anhydrite) as both a white pigment and in correlation to the organic dyes in this manuscript has been noted. The non-invasive identification of the organic dye orchil is significant considering its rare non invasive detection in medieval manuscripts. Finally the occurrence of particular alterations of the organic black areas giving rise to calcium carboxylate and calcium oxalate has been specifically highlighted. importantly, this work elaborates complex aspects of the employed painting materials which have given rise to numerous significant points of interest for a more elaborate understanding of this irish treasure. © 2013 Elsevier B.V. All rights reserved.

A novel hyperspectral imaging system (HI90, Bruker Optics), working in the mid-infrared range and recently developed for the remote identification and mapping of hazardous compounds, has here been optimized for investigating painting surfaces. The painting Sestante 10 (1982) by Alberto Burri has been spectrally and spatially investigated with the HI90 system revealing the distribution of inorganic materials constituting the artworks. In order to validate the results obtainable by the imager for the pigment identification previous tests on laboratory models were performed. Yellow, white and blue pigments painted with different binders (namely egg, alkyd, acrylic and vinyl) were investigated by the HI90. Afterwards, the polychrome painting Sestante 10 was investigated focusing the attention on the inorganic material distribution revealing the presence of different extenders (kaolin, BaSO 4 , CaSO 4 ) mixed with the various silica-based pigments present in the painting. The brightness temperature spectra collected by HI90 have also been compared to single point reflection spectra acquired by a conventional portable FTIR spectrometer (Alpha-R by Bruker Optics) highlighting the good spectral quality of the imaging system. This comparison permitted also to evaluate the spectral response and the diagnostic strengths of the spectral range available by the HI90 imaging (1300-860 cm -1 ), validating the reliability of the obtained chemical images. This study clearly highlights the high potential of the new hyperspectral imaging system and opens up new perspectives in the current scientific interest devoted to the application of mapping and imaging methods for the study of painting surfaces.

The Musee Picasso in Antibes (France) houses a unique collection of 23 paintings and 44 works on paper by Pablo Picasso, completed during the fall of 1946 by the artist, working on the same premises occupied today by the Museum. Picasso painted with readily available materials including oleoresinous enamel paints, fibrocement, wood panels, paper sheets, and re-used canvases. In this paper the results of an extensive campaign of scientific analysis of 17 of these works with both non-invasive and micro-invasive techniques are described. The project elucidated the full palette of the paintings, dispelling myths about their execution solely with the renowned brand of enamel paint Ripolin. The effective combination of elemental and spectroscopic methods of analysis enabled fine discriminations among various types of white enamel paint used by Picasso in Antibes. Because the artist appeared to have used such paints in chronological sequence, the precise identification of the type of white paint present on each of the works allowed the assignment of revised dates to some of the undated paintings. Important new information on surface coatings of wax and modern polymeric varnishes, as well as the widespread presence of metal soaps including zinc oxalates, was also uncovered.

Ancient Mesoamerican codices represent the religious and historical legacy of the pre-Columbian people, they were produced to record the historical and religious matters. Codex Cospi, a divinatory book, is one of the fifteen extant pre-Hispanic Mesoamerican books which survived the destruction of the Spanish conquest. Thanks to the use of a set of portable non-invasive analytical techniques it was possible to study the Codex Cospi revealing valuable information on its constituting materials (dyes, pigments and substrates). The analytical results were compared with historical references contained in early colonial Mexican documents showing interesting parallels and providing hints for probable identification of colouring materials. (C)2011 Elsevier Ltd. All rights reserved.

The spectroscopic properties of indigo, one of the most important natural dyes present in nature, have been investigated by means of DFT and TD-DFT calculations and Raman and IR spectroscopies. The absorption spectra of this dye, in vacuo and in different solvents, have been computed. The formation of aggregates in solvent have been investigated by computing the electronic absorption spectra of the dimer and the trimer, thus evaluating the effects of the aggregation on the optical properties of indigo. The IR and Raman spectra have been measured and computed. The comparison between the experimental and theoretical spectra and the potential energy distribution (PED) of the computed normal modes have been used to perform the assignment of the experimental features in terms of functional group displacements. Finally, the effects of the intermolecular hydrogen bond present in the solid state have been evaluated by computing the vibrational spectra of the dimer. The intention of the present work is to give an insight into both the vibrational and optical properties of indigo as well as to evaluate DFT and TD-DFT potentialities in the study of organic dyes’ spectroscopic properties of interest in the cultural heritage field.