Modulation of [CuOH/O]+ Properties in [2,2'-Bipyridine]2 Homoleptic Complexes through Substitution at the 6,6' Position by Methyl Groups

In this paper, data from a DFT-based computational study on the reactivity of [Cu(2,2'-S-bpy)2]+PF6- (S indicating substitution by methyl groups at the 6 and/or 6' position and ranging from 0 to 100% through 50%) homoleptic complexes based toward tButOOH were presented. Computational results, supported by cyclic voltammetry analysis, prove the feasibility of finely tuning the chemical properties of the complexes and their reactivity by means of insertion of methyl moieties in selected positions within the bipyridine scaffold.

Breaking with trends in forensic dating: A likelihood ratio-based comparison approach

Further steps toward understanding the time-related information contained within bloodstains found at the crime scene are rightly considered a top priority in forensic science. Contrary to widely held assumptions, the reason for the delayed exploitation of bloodstains dating methods in practice is not the lack of suitable analytical techniques for monitoring degradation processes. The problem lies in the variability of the environmental and circumstantial conditions, playing a vital role in the degradation kinetics of blood deposits. The present article demonstrates the possibility of breaking with current approaches based on absolute age estimations to finally answer time-centered questions in real forensic scenarios. The proposed novel framework for situating forensic traces in time is based on the likelihood ratio assessment of the (dis)similarity between the evidence decomposition and sets of reference materials obtained through supervised aging. In such a strategy, every dating procedure is constructed on a case-by-case basis to fit examined blood traces, thereby limiting the adverse influence of external factors on the validity of age estimations and providing a way for future crime scene implementation.

CeO2 Frustrated Lewis Pairs Improving CO2 and CH3OH Conversion to Monomethylcarbonate

Frustrated Lewis pairs (FLPs), discovered in the last few decades for homogeneous catalysts and in the last few years also for heterogeneous catalysts, are stimulating the scientific community's interest for their potential in small-molecule activation. Nevertheless, how an FLP activates stable molecules such as CO₂ is still undefined. Through a careful spectroscopic study, we here report the formation of FLPs over a highly defective CeO₂ sample prepared by microwave-assisted synthesis. Carbon dioxide activation over FLP is shown to occur through a bidentate carbonate bridging the FLP and implying a Ce³⁺-to-CO₂ charge transfer, thus enhancing its activation. Carbon dioxide reaction with methanol to form monomethylcarbonate is here employed to demonstrate active roles of FLP and, eventually, to propose a reaction mechanism clarifying the role of Ce³⁺ and oxygen vacancies.

Quinoid-Thiophene-Based Covalent Organic Polymers for High Iodine Uptake: When Rational Chemical Design Counterbalances the Low Surface Area and Pore Volume

A novel 2D covalent organic polymer (COP), based on conjugated quinoid-oligothiophene (QOT) and tris(aminophenyl) benzene (TAPB) moieties, is designed and synthesized (TAPB-QOT COP). Some DFT calculations are made to clarify the equilibrium between different QOT isomers and how they could affect the COP formation. Once synthetized, the polymer has been thoroughly characterized by spectroscopic (i.e., Raman, UV-vis), SSNMR and surface (e.g., SEM, BET) techniques, showing a modest surface area (113 m² g^-1) and micropore volume (0.014 cm³ g^-1 with an averaged pore size of 5.6-8 Å). Notwithstanding this, TAPB-QOT COP shows a remarkably high iodine (I₂) uptake capacity (464 %wt) comparable to or even higher than state-of-the-art porous organic polymers (POPs). These auspicious values are due to the thoughtful design of the polymer with embedded sulfur sites and a conjugated scaffold with the ability to counterbalance the relatively low pore volumes. Indeed, both morphological and Raman data, supported by computational analyses, prove the very high affinity between the S atom in our COP and the I₂. As a result, TAPB-QOT COP shows the highest volumetric I₂ uptake (i.e., the amount of I₂ uptaken per volume unit) up to 331 g cm^-3 coupled with a remarkably high reversibility (>80% after five cycles).

Functional Piezoresistive Polymer Composites Based on CO2 Laser-Irradiated Graphene Oxide-Loaded Polyurethane: Morphology, Structure, Electrical and Piezoresistive Properties

Nanocomposite materials have recently attracted great attention for their wide range of applications, such as in smart materials, flexible electronics, and deformation sensing applications. Such materials make it possible to combine a polymer with functional fillers. In this study, flexible artificial leathers, exhibiting insulating properties and containing 1.5 or 2wt.% of graphene oxide (GO) in the polyurethane (PU) layer, were electrically activated via CO₂ laser irradiation to obtain conductive paths at the surface exposed to the laser beam. As the material retained its insulating properties out of the irradiation areas, the laser scribing method allowed, at least in principle, a printed circuit to be easily and quickly fabricated. Combining a variety of investigation methods, including scanning electron microscopy (SEM), optical profilometry, IR and Raman spectroscopies, and direct current (DC) and alternate current (AC) electrical measurements, the effects of the laser irradiation were investigated, and the so-obtained electrical properties of laser-activated GO/PU regions were elucidated to unveil their potential use in both static and dynamic mechanical conditions. In more detail, it was shown that under appropriate CO₂ laser irradiation, GO sheets into the GO/PU layer were locally photoreduced to form reduced-GO (RGO) sheets. It was verified that the RGO sheets were entangled, forming an accumulation path on the surface directly exposed to the laser beam. As the laser process was performed along regular paths, these RGO sheets formed electrically conductive wires, which exhibited piezoresistive properties when exposed to mechanical deformations. It was also verified that such piezoresistive paths showed good reproducibility when subjected to small flexural stresses during cyclic testing conditions. In brief, laser-activated GO/PU artificial leathers may represent a new generation of metal-free materials for electrical transport applications of low-current signals and embedded deformation sensors.

A multi-technique approach to unveil the redox behaviour and potentiality of homoleptic CuI complexes based on substituted bipyridine ligands in oxygenation reactions

The effect of differently substituted 2,2'-bipyridine ligands (i.e. 6,6'-dimethyl-2,2'-bipyridine, 5,5'-dimethyl-2,2'-bipyridine, 6,6'-dimethoxy-2,2'-bipyridine and 2,2'-bipyridine) on the reversible oxidation of the resulting Cu^I homoleptic complexes is investigated by means of a multi-technique approach (electronic and vibrational spectroscopies, DFT, electrochemistry). Among the four tested complexes, [Cu^I(6,6'-dimethyl-2,2'-bipyridine)₂] (PF₆) shows a peculiar behavior when oxidized with an organic peroxide (i.e. tert-butyl hydroperoxide, tBuOOH). The simultaneous use of UV-Vis-NIR and Raman spectroscopy methods and cyclovoltammetry, supported by DFT based calculations, allowed identifying (i) the change in the oxidation state of the copper ion and (ii) some peculiar modification in the local structure of the metal leading to the formation of a [Cu^IIOH]⁺ species. The latter, being able to oxidize a model molecule (i.e. cyclohexene) and showing the restoration of the original Cu^I complex and the formation of cyclohexanone, confirms the potential of these simple homoleptic Cu^I complexes as model catalysts for partial oxygenation reactions.

Catalyst sites and active species in the early stages of MTO conversion over cobalt AlPO-18 followed by IR spectroscopy

Reaction-time resolved IR spectroscopy highlights the role of CO and surface –OCH3 in the MTO conversion catalysed by CoAPO-18 with maximised concentration of acidic sites.

Ullmann homocoupling of arenediazonium salts in a deep eutectic solvent. Synthetic and mechanistic aspects

DES is exploited as a solvent media in Ullmann homocoupling of arenediazonium salts. Computational study supported by Raman spectroscopy is presented, aiming to elucidate the reaction mechanism.

Multifunctional Conductive Paths Obtained by Laser Processing of Non-Conductive Carbon Nanotube/Polypropylene Composites

Functional materials are promising candidates for application in structural health monitoring/self-healing composites, wearable systems (smart textiles), robotics, and next-generation electronics. Any improvement in these topics would be of great relevance to industry, environment, and global needs for energy sustainability. Taking into consideration all these aspects, low-cost fabrication of electrical functionalities on the outer surface of carbon-nanotube/polypropylene composites is presented in this paper. Electrical-responsive regions and conductive tracks, made of an accumulation layer of carbon nanotubes without the use of metals, have been obtained by the laser irradiation process, leading to confined polymer melting/vaporization with consequent local increase of the nanotube concentration over the electrical percolation threshold. Interestingly, by combining different investigation methods, including thermogravimetric analyses (TGA), X-ray diffraction (XRD) measurements, scanning electron and atomic force microscopies (SEM, AFM), and Raman spectroscopy, the electrical properties of multi-walled carbon nanotube/polypropylene (MWCNT/PP) composites have been elucidated to unfold their potentials under static and dynamic conditions. More interestingly, prototypes made of simple components and electronic circuits (resistor, touch-sensitive devices), where conventional components have been substituted by the carbon nanotube networks, are shown. The results contribute to enabling the direct integration of carbon conductive paths in conventional electronics and next-generation platforms for low-power electronics, sensors, and devices.

Nanostructured liquid crystalline particles as delivery vectors for isofuranodiene: Characterization and in-vitro anticancer activity

Isofuranodiene is an oxygenated sesquiterpene containing a furan ring isolated from the essential oil of Smyrnium olusatrum L. (Apiaceae) owning notable anticancer activity. Despite its biological potential, the high lipophilicity along with a relatively low stability due to Cope rearrangement giving rise to a less active compound, make the perspective of its therapeutical use unlikely. On this basis, in the present work we evaluated bulk and dispersed non lamellar liquid crystalline phases as effective delivery vectors for isofuranodiene, and capable of preserving its structure and enhancing the biological activity. Small-angle X-ray scattering, dynamic light scattering, and UV resonance Raman spectroscopy were used to characterize the nanosystems in an integrated experimental approach. Encapsulation of isofuranodiene in the lipid matrix resulted in a transition from a cubic Im3m to a reversed hexagonal phase because of the highly lipophilic character of the drug, as obtained in SAXS measurements, and in significant shifts in the components of the Raman spectrum of isofuranodiene. The anticancer activity of isofuranodiene-loaded lipidic nanoparticles was assessed on MDA-MB 231 cell line by MTT assay and was found to be higher than that of pristine isofuranodiene.

Bimetallic hexanuclear clusters in Ce/Zr-UiO-66 MOFs: in situ FTIR spectroscopy and modelling insights

In situ FTIR and DFT modelling were used to study the stoichiometry of the hexanuclear clusters in Ce/Zr-UiO-66 compounds.

A spectroscopic and computational study of a tough MOF with a fragile linker: Ce-UiO-66-ADC

A spectroscopic and computational insight in the defective nature of the acetylene dicarboxylic acid based Ce-MOF, having UiO-66 topology and denoted as Ce-UiO-66-ADC MOF.

Partial and Complete Substitution of the 1,4-Benzenedicarboxylate Linker in UiO-66 with 1,4-Naphthalenedicarboxylate: Synthesis, Characterization, and H2-Adsorption Properties

We describe the synthesis and corresponding full characterization of the set of UiO-66 metal-organic frameworks (MOFs) with 1,4-benzenedicarboxylate (C₆H₄(COOH)₂, hereafter H₂BDC) and 1,4-naphthalenedicarboxylate (C₁₀H₆(COOH)₂, hereafter H₂NDC) mixed linkers with NDC contents of 0, 25, 50, and 100%. Their structural (powder X-ray diffraction, PXRD), adsorptive (N₂, H₂, and CO₂), vibrational (IR/Raman), and thermal stability (thermogravimetric analysis, TGA) properties quantitatively correlate with the NDC content in the material. The UiO-66 phase topology is conserved at all relative fractions of BDC/NDC. The comparison between the synchrotron radiation PXRD and 77 K N₂-adsorption isotherms obtained on the 50:50 BDC/NDC sample and on a mechanical mixture of the pure BDC and NDC samples univocally proves that in the mixed linkers of the MOFs the BDC and NDC linkers are shared in each MOF crystal, discarding the hypothesis of two independent phases, where each crystal contains only BDC or NDC linkers. The careful tuning of the NDC content opens a way for controlled alteration of the sorption properties of the resulting material as testified by the H₂-adsorption experiments, showing that the relative ranking of the materials in H₂ adsorption is different in different equilibrium-pressure ranges: at low pressures, 100NDC is the most efficient sample, while with increasing pressure, its relative performance progressively declines; at high pressures, the ranking follows the BDC content, reflecting the larger internal pore volume available in the MOFs with a higher fraction of smaller linkers. The H₂-adsorption isotherms normalized by the sample Brunauer-Emmett-Teller specific surface area show, in the whole pressure range, that the surface-area-specific H₂-adsorption capabilities in UiO-66 MOFs increase progressively with increasing NDC content. Density functional theory calculations, using the hybrid B3LYP exchange correlation functional and quadruple-ζ with four polarization functions (QZ4P) basis set, show that the interaction of H₂ with the H₂NDC linker results in an adsorption energy larger by about 15% with respect to that calculated for adsorption on the H₂BDC linker.

MoS2 Nanoparticles Decorating Titanate-Nanotube Surfaces: Combined Microscopy, Spectroscopy, and Catalytic Studies

MoS2/TNTs composites have been obtained by impregnation of titanate nanotubes (TNTs) with a centrifuged solution of nanosized MoS2 particles in isopropyl alcohol (IPA). The characterization has been performed by combining UV-vis-NIR, Raman, AFM, and HRTEM analyses, before and after impregnation. HRTEM images show that the contact between single-layer MoS2 nanoparticles and the support is efficient, so justifying the decoration concept. The volatility of IPA solvent allows the preparation of composites at low temperature and free of carbonaceous impurities. MoS2 nanoparticles have strong excitonic transitions, which are only slightly shifted with respect to the bulk because of quantum size effects. Concentrations of MoS2, less than 0.1 wt %, are enough to induce strong absorption in the visible. Photodegradation of methylene blue (MB) has been performed on TNTs and MoS2/TNTs to verify the effect of the presence of MoS2. The first layer of adsorbed MB is consumed first, followed by clustered MB in the second and more external layers. The presence of low concentrated MoS2 nanoparticles does not substantially alter the photocatalytic properties of TNTs. This result is due to poor overlapping between the high frequency of MoS2 C, D excitonic transitions and the TNTs band gap transition.

Development of a multifunctional TiO2/MWCNT hybrid composite grafted on a stainless steel grating

A multifunctional TiO₂/MWCNT hybrid material grafted on durable and thermally inert stainless-steel grating is proposed, thus combining photodegradation with magnetic properties, which makes the recovery of a solution from a photocatalyst easier.

Spectroscopic investigation of the encapsulation and the reactivity towards NO of a Co(II)-porphyrin inside a cross-linked polymeric matrix

A highly dispersed cobalt(II) porphyrin (PhCo(II)) encapsulated inside a highly cross-linked poly(4-ethylstyrene-co-divinylbenzene) matrix (St-DVB) is investigated by means of FTIR, Raman, UV-Vis and EPR spectroscopies. The adoption of the highly porous St-DVB support is the key factor in reaching an optimum porphyrin dispersion in undiluted conditions ( approximately 10 wt% of porphyrin). It is demonstrated that the encapsulated PhCo(II) are characterized by the absence of any axial interactions involving the polymeric matrix, that can be considered a "non-coordinating" solvent. Finally, the permanent porosity of the encapsulating matrix allows gaseous molecules to reach the Co(II) cations also in the absence of swellable solvents. In particular, the reactivity of the isolated Co(II) porphyrin species towards nitric oxide (NO) is investigated, with possible implications in the understanding of the crucial role played by NO in biological systems.

Photo-degradation of yperite over V, Fe and Mn-doped titania-silica photocatalysts

The photocatalytic decomposition of yperite (bis(2-chloroethyl)sulfide), a chemical warfare agent, was achieved by using titania-silica catalysts doped with several transition metal ions. The preparation of these catalysts was achieved by impregnation of a titania-silica mixed oxide previously synthesized using a sol-gel route with salts of the doping elements (vanadium, iron, manganese). The above catalysts were characterized using several spectroscopic techniques: FTIR, Raman, DR-UV-Vis, and XPS. The band gap energy was measured for each photocatalytic system. The reaction was carried out in two different types of reactors, i.e. naturally aerated and a closed quartz tube aerated under a constant flow, and using two types of irradiation, UV-Vis and Vis. The investigated systems proved to be extremely active, leading to an almost complete degradation of yperite in 2 h of irradiation. An excellent correlation between the photocatalytic performances and the band gap has been found. Based on the characterization data and on the temporal evolution of the reaction products, a reaction mechanism has been suggested. This mechanism considers two distinct pathways for the decomposition of yperite, namely the C-S bond cleavage and the S oxidation.

Furfuryl alcohol polymerization in H-Y confined spaces: reaction mechanism and structure of carbocationic intermediates

The acid-catalyzed polymerization and resinification, in the 300-673 K interval, of furfuryl alcohol adsorbed in the framework of a protonic Y zeolite is studied by means of FTIR, Raman, and UV-vis spectroscopies. The idea is that restricted spaces can impose a constraint to the growth of the oligomeric chains, therefore moderating the formation of conjugated sequences responsible for the color of the products and allowing their observation by means of spectroscopic techniques. The detailed study of the evolution of UV-vis, FTIR, and Raman spectra upon dosed amount, contact time, and temperature has allowed the spectroscopic features of some of the single species, either neutral and positively charged (carbocationic intermediates), to be singled out and assigned to understand the mechanism of initiation. The vibrational assignments have been confirmed by computer simulations on model compounds and compared with the results of the mechanistic description of the reaction mechanism made in the past (Choura, et al. Macromolecules 1996, 29, 3839-3850). The spectroscopic methods have been applied in a large temperature range in order to follow also the formation of more complex products into the pores, associated with longer conjugated sequences, gradually filling the open spaces of the zeolite. For samples contacted with furfuryl alcohol at 673 K, this methodology gives information also on the incipient carbonization process, leading to the formation of a carbonaceous replica phase inside the internal porosity of the zeolite.

Maya blue: a computational and spectroscopic study

Maya Blue pigment, used in pre-Colombian America by the ancient Mayas, is a complex between the clay palygorskite and the indigo dye. The pigment can be manufactured by mixing palygorskite and indigo and heating to T > 120 degrees C. The most quoted hypothesis states that the dye molecules enter the microchannels which permeate the clay structure, thus creating a stable complex. Maya Blue shows a remarkable chemical stability, presumably caused by interactions formed between indigo and clay surfaces. This work aims at studying the nature of these interactions by means of computational and spectroscopic techniques. The encapsulation of indigo inside the clay framework was tested by means of molecular modeling techniques. The calculation of the reaction energies confirmed that the formation of the clay-organic complex can occur only if palygorskite is heated at temperatures well above the water desorption step, when the release of water is entropically favored. H-bonds between the clay framework and the indigo were detected by means of spectroscopic methods. FTIR spectroscopy on outgassed palygorskite and freshly synthesized Maya Blue samples showed that the presence of indigo modifies the spectroscopic features of both structural and zeolitic water, although no clear bands of the dye groups could be observed, presumably due to its very low concentration. The positions and intensities of delta(H2O) and nu(H2O) modes showed that part of the structural water molecules interact via a hydrogen bond with the C=O or N-H groups of indigo. Micro-Raman spectra clearly evidenced the presence of indigo both in original and in freshly synthesized Maya Blue. The nu(C=O) symmetric mode of Maya Blue red-shifts with respect to pure indigo, as the result of the formation of H-bonds with the nearest clay structural water. Ab initio quantum methods were applied on the indigo molecule, both isolated and linked through H-bonds with water, to calculate the magnitude of the expected vibrational shifts. Calculated and experimental vibrational shifts appeared to be in good agreement. The presence of a peak at 17.8 ppm and the shift of the N-H signal in the 1H MAS NMR spectrum of Maya Blue provide evidence of hydrogen bond interactions between indigo and palygorskite in agreement with IR and ab initio methods.

(I2)n Encapsulation inside TiO2: A Way To Tune Photoactivity in the Visible Region

We report on the synthesis of nanovoid-structured TiO(2) material via a sol-gel route using titanium isopropoxide as precursor. The nanovoids are formed during the thermal treatment in air at 773 K. The surfaces of internal cavities are populated by the partial oxidation products of the organic part of the Ti precursor (CO(2), hydrogen carbonates, and residual isopropoxide groups). The thermal treatment in air at 773 K allows the maintainence, in the internal voids, of the encapsulated species. Addition of iodine in the synthesis procedure results in a new nanovoid-structured titanium oxide able to absorb light in the whole visible part of the electromagnetic spectrum. The origin of this absorption is attributed to the presence of (I(2))(n) adducts encapsulated in the nanocavities. These species coexist with partial combustion products of isopropoxide groups. Due to the protection of the TiO(2) walls, the (I(2))(n) adducts are not destroyed by thermal treatments in air. We have investigated whether the electron promoted in the excited state of the dye molecule (upon absorption of visible light from the (I(2))(n) adducts) can be injected into either the TiO(2) conduction band or some titanium-localized acceptor, followed by migration of the injected electron to the surface where it reduces adsorbed organic molecules. Preliminarily experiments conducted with sunlight show that the surface-specific efficiency of this process, tested by following the degradation of methylene blue, is about 10 times higher than that of the P25 commercial TiO(2) photocatalyst.

Reactivity of Ti(iv) species hosted in TS-1 towards H2O2–H2O solutions investigated by ab initio cluster and periodic approaches combined with experimental XANES and EXAFS data: a review and new highlights

This work is intended to underline how the most-advanced experimental and theoretical physical chemistry tools must be used synergistically to understand the reactivity of Ti-silicalite-1 (TS-1) in an important number of low-temperature oxidation reactions with aqueous H(2)O(2) as the oxidant. Literature results are carefully reviewed and accompanied with new, unpublished highlights of both experimental and computational origin. The first part of this work is devoted to a discussion of the defective nature of the material and to the synergic role played by Si vacancies and Ti insertion in the framework. A summary of the experimental Ti-K-edge EXAFS and XANES literature concerning the activated material in vacuo conditions is then presented and compared to the corresponding Ti geometries obtained by ab initio calculations. From such a comparison, the excellent agreement between experiment and theory is evident. A very good agreement is also obtained for the interaction with water and ammonia. For both H(2)O and NH(3), the agreement is due to the possibility to perform experiments in which the probe molecule is dosed from the gas phase, thus allowing to reach the 1 : 1 (or 1 : 2) ratio between the adsorbing Ti sites and the adsorbed molecule. Then, interaction with hydrogen peroxide is discussed, underlining the problems faced in reaching a common view between experimental and theoretical results, owing to the difficulties both in performing experiments where anhydrous H(2)O(2) is dosed on TS-1, and in taking into account the role played by the aqueous medium in the reactivity of Ti(iv) centres toward H(2)O(2) using ab initio calculations. Only once such difficulties have been overcome, by increasing the complexities of both experiments and ab initio models, is a joint-view finally obtained. Where needed, comparison with other experimental results (X-ray and neutron diffraction, NMR, IR, Raman, UV-vis and resonant Raman) is made.

FTIR spectroscopy and thermodynamics of hydrogen adsorbed in a cross-linked polymer

The adsorption of H(2) in a cross-linked poly(styrene-co-divinylbenzene) (St-DVB) microporous polymer (BET surface area 920 m(2) g(-1)) is studied by volumetric and gravimetric methods, FTIR spectroscopy at variable temperature (300-14 K) and ab initio calculations. At 77 K the polymer reversibly stores up to 1.3 mass% H(2) at a pressure of 1 bar and 1.8 mass% at 10 bar. The adsorption process involves the specific interaction of H(2) with the structural phenyl rings through weak dispersive forces. The interacting molecules become IR active and give rise to vibrational and rotational-vibrational manifestations which are affected by the temperature, the contact time and the H(2) equilibrium pressure. The spectra of the H(2)/St-DVB system reported here represent the first IR evidence of the adsorption of hydrogen on unsaturated molecules. The adsorption enthalpy is evaluated by the VTIR (variable temperature IR spectroscopy) method (C. Otero Areán et al., Phys. Chem. Chem. Phys., 2007, DOI: 10.1039/b615535a) and compared with the results of ab initio calculations for the H(2)/benzene interaction and with literature data.

Theoretical characterization of dihydrogen adducts with halide anions

The interaction between a hydrogen molecule and the halide anions F(-), Cl(-), Br(-), and I(-) has been studied at different levels of theory and with different basis sets. The most stable configurations of the complexes have a linear geometry, while the t-shaped complexes are saddle points on the potential energy surface, opposite to what is observed for alkali cations. An electrostatic analysis conducted on the resulting adducts has highlighted the predominance of the electrostatic term in the complexation energy and, in particular, of the quadrupole- and dipole-polarizability dependent contributions. Another striking difference with respect to the positive ions, is the fact that although the binding energies have similar values (ranging between 25 and 3 kJ /mol for F(-) and I(-), respectively), the vibrational shift of the nu(H-H) and in general the perturbation of the hydrogen molecule in complexes are much greater in the complexes with anions (Delta nu(H-H) ranges between -720 and -65 cm(-1)). Another difference with respect to the interaction with cations is a larger charge transfer from the anion to the hydrogen molecule. The Delta nu is the result of the cooperative role of the electrostatics and of the charge transfer in the interaction. The correlation between binding energies and vibrational shift is far from linear, contrary to what is observed for cation complexes, in accordance with the higher polarizability and dynamic polarizability of the molecule along the molecular axis. The observed correlation may be valuable in the interpretation of spectra and thermodynamic properties of adsorbed H(2) in storage materials.

Vibration Frequencies of Ca3Fe2Si3O12 Andradite: An ab Initio Study with the CRYSTAL Code

The vibrational spectrum of Ca3Fe2Si3O12 andradite is calculated at the Gamma point by using the periodic ab initio CRYSTAL program that adopts an all-electron Gaussian-type basis set and the B3LYP Hamiltonian. The full set of frequencies (17 IR active, 25 Raman active, and 55 inactive modes) is calculated. The effect of the basis set on the calculated frequencies is discussed. The modes are characterized by direct inspection of the eigenvectors and isotopic substitution. The present calculations permit us to clarify some of the assignment problems raised by experiments. The mean absolute differences of the various modes with respect to the available experimental IR and Raman data are as small as 9 and 5 cm(-1), respectively.

Surface Modifications of Bioglass Immersed in TRIS-Buffered Solution. A Multitechnical Spectroscopic Study

Bioglass 45S5 is used in the medical field as a bone regenerative material. In fact, when immersed in body fluid, a layer of hydroxy carbonate apatite (HCA), an analogue to the mineral phase that bones are made of, is deposited on its surface. A mechanism that would explain this process has been hypothesized and includes cation leaching from the glass to the solution and formation of both a silica-rich layer and a Ca/P-rich surface layer, prior to the actual crystallization of HCA. The present paper analyzes the dissolution of 2-mum-size particles of Bioglass in TRIS-buffered solution, focusing on the modifications occurring at the surface of the particles. Results from Transmission FT-IR, Raman, and X-ray Photoelectron Spectroscopy were compared in order to obtain this information. In all cases, precise spectral band assignments were obtained by comparing Bioglass spectra, before and after reaction, with the spectra registered on some selected reference samples. The results confirm the hypothesized mechanism of Bioglass reactivity and yield new insights on the surface modifications of the samples. In particular, the following is shown: the strength of the surface H-bonding system and of water coordination decreases during the reaction; surface carbonates, initially mainly bound to Na, are substituted by an increasing amount of Ca-bound carbonates; and the final calcium phosphate layer obtained is very similar, but not identical, to carbonated hydroxyapatite.

FTIR Investigation of the H2, N2, and C2H4 Molecular Complexes Formed on the Cr(II) Sites in the Phillips Catalyst: a Preliminary Step in the understanding of a Complex System

This work reports the first complete FTIR characterization of H2, N2 and C2H4 molecular complexes formed on the Cr(II) sites in the Phillips catalyst. The use of a silica aerogel as support for Cr(II) sites, substituting the conventional aerosil material, allowed us to obtain a remarkable increase in the signal-to-noise ratio of the IR spectra of adsorbed species. The improvement is directly related to an increase of the surface area of the support (approximately 700 m2 g(-1)) and to an almost complete absence of scattering [Groppo et al., Chem. Mater. 2005, 17, 2019-2027]. The use of this support and the adoption of suitable experimental conditions results, for the first time, in the clear observation of H2 and N2 adducts formed on two different types of Cr(II) sites, thus yielding important information on the coordinative state of the Cr(II) ions, which well agrees with the evidences provided in the past by other probe molecules. Furthermore, we report the first complete characterization of the C2H4 pi-complexes formed on Cr(II) sites. These results are particularly important in the view of the understanding of the polymerization mechanism, since the C2H4 coordination and the formation of pi-bonded complexes are the first steps of the reaction.

Theoretical characterization of dihydrogen adducts with alkaline cations

As part of an extended fundamental study on the interaction of molecular hydrogen with the surfaces of potential storage materials, this work describes the interaction of dihydrogen with bare alkaline cations (Li(+),Na(+),K(+),Rb(+)) by means of ab initio and density functional calculations. The effects of method and basis set are evaluated, and an estimate of the electrostatic contributions to the binding energy is evaluated. All methods predict a t-shaped coordination geometry, in accord with the quadrupolar nature of the molecule. The binding energies at the MP2/aug-cc-pVQZ (MP2-Møller-Plesset method truncated at second order) level ranges between 24 kJ/mol for Li(+) and 5 kJ/mol for Rb(+). Basis set size has minor effect on the binding energy of the complexes, although the poorer sets have severe limitations in the description of the electrostatics of the isolated molecule. The electrostatic contribution to the binding energy calculated from the electrostatic properties of the isolated molecule are in fact strongly basis set dependent. Their careful analysis shows that the predominant terms of the interaction are those due to the quadrupole and dipole-polarizability terms. The vibrational spectra of the adducts are evaluated and compared with a large set of experimental and theoretical results from the literature. This review highlights a linear correlation between the frequency shift and the binding energy, which is valuable in the understanding of adsorption phenomena by means of spectroscopic methods.

Electronic and vibrational properties of a MOF-5 metal–organic framework: ZnO quantum dot behaviour

UV-Vis DRS and photoluminescence (PL) spectroscopy, combined with excitation selective Raman spectroscopy, allow us to understand the main optical and vibrational properties of a metal-organic MOF-5 framework. A O(2-)Zn(2+)[rightward arrow] O(-)Zn(+) ligand to metal charge transfer transition (LMCT) at 350 nm, testifies that the Zn(4)O(13) cluster behaves as a ZnO quantum dot (QD). The organic part acts as a photon antenna able to efficiently transfer the energy to the inorganic ZnO-like QD part, where an intense emission at 525 nm occurs.