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Solid-state light-emitting diodes (LEDs) are driving the lighting industry towards efficient and environmentally friendly lighting and displays. Current challenges encompass efficient and low-cost down-shifting phosphors with tuned emission colors. Green light lies on the low-loss optical transmission window in plastic optical fibers and plays a special role in the regulation of the human and plant circadian rhythms. Moreover, green-emitting phosphors may suppress the “green gap” found in semiconductor-based LEDs. In this work, a UV-photostable green-emitting complex, Tb(NaI)3(H2O)2, with NaI = nalidixic acid (1-ethyl-1,4-dihydro-7-methyl-4-oxo-1,8-naftiridine-3-carboxylic acid), was incorporated into tripodal organic-inorganic hybrid materials. The hybrid hosts boost the absolute emission quantum yield from ≈ 0.11 (isolated complex) to ≈ 0.82 (doped hybrid), which is the largest value reported for Tb3+-based hybrid phosphors. A green-emitting LED was fabricated by coating a near-UV LED (365 nm) with a Tb3+-activated organic-inorganic hybrid having pure-green-colored light with Commission International de l'Eclairage color coordinates and an efficacy value of (0.33, 0.59) and 1.3 lm W–1, respectively. published

The biobased polyester poly(ethylene 2,4-furanoate) (2,4-PEF) is a potentially interesting yet insufficiently studied polymer whose resistance to crystallization fundamentally stems from the asymmetric nature of the 2,4-furandicarboxylic acid monomer. A combination of vibrational spectroscopy (infrared, Raman and inelastic neutron scattering) and ab initio calculations has been used to assess the conformational and regiochemistry preferences of 2,4-PEF. The latter polymerizes following a random distribution of monomer orientation, thereby rendering the formation of periodic interchain C-H···O contacts wholly unfeasible and ultimately favoring the formation of randomly coiled chains based on gauche-ethylene glycol segments. In the absence of C-H···O stabilization, the ordered crystalline arrangement is disfavored and polymer chains - adopting several quasi iso-energetic structures - prefer to solidify into an amorphous mess.

Montelukast (MLK), an oral antiasthmatic drug with growing use, requires special care in formulation and storage to avoid its degradation by action of light and water. This work investigates the increase in the stability of montelukast as the effect of molecular encapsulation with gamma-cyclodextrin (γ-CD) by means of a solvent-free method, cogrinding. As a first step, a 1:1 preferred stoichiometry is established for this hostguest system using a combination of molecular modeling and the continuous variation method. The solid 1:1 inclusion compound, γ-CD·MLK, is obtained by 2 comilling procedures. For comparison purposes, γ-CD·MLK is also prepared by a classical codissolution procedure and isolated by freeze-drying. Products were characterized by powder X-ray diffraction, 13C{1H} CP-MAS NMR, scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry, which confirm inclusion, demonstrate the formation of amorphous products by comilling, and highlight the importance of the amorphous nature of the starting materials for the stability of the comilled final product. The dissolution profile of montelukast when released from the comilled products shows equivalent concentrations to those obtained with the same mass of the pure drug, with the extra advantage of keeping the solution stability (unaltered concentration) for longer periods.

This work presents a comprehensive spectroscopic analysis of crystalline isoniazid, one of the main drugs in tuberculosis chemotherapy, using a blend of spectroscopic and computational methods. Mid- and far-infrared, Raman, and inelastic neutron scattering spectroscopies, with contribution of isotopic substitution are combined with discrete and periodic DFT quantum chemical calculations. This combined approach successfully reproduces the whole spectral range, allowing a sound assignment of all the vibrational bands. Previous misassignments have been corrected and several spectral features of isoniazid crystal are reported for the first time. Virtues and limitations of the computational approach (periodic and discrete) are also discussed in light of the present state-of-the-art in the field.

The dynamics of 2-methoxybenzaldehyde, 4-methoxybenzaldehyde, and 4-ethoxybenzaldehyde in the solid state are assessed through INS spectroscopy combined with periodic DFT calculations. In the absence of experimental data for 4-ethoxybenzaldehyde, a tentative crystal structure, based on its similarity with 4-methoxybenzaldehyde, is considered and evaluated. The excellent agreement between calculated and experimental spectra allows a confident assignment of the vibrational modes. Several spectral features in the INS spectra are unambiguously assigned and torsional potential barriers for the methyl groups are derived from experimental frequencies. The intramolecular nature of the potential energy barrier for methyl rotation about O– CH3 bonds compares with the one reported for torsion about saturated C–CH3 bonds. On the other hand, the intermolecular contribution to the potential energy barrier may represent 1/3 of the barrier height in these systems. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

A thorough vibrational spectroscopy and molecular modeling study on poly(ethylene 2,5-furandicarboxylate) (PEF) explores its conformational preferences, in the amorphous and crystalline regions, while clarifying structure–property correlations. Despite the increasing relevance of PEF as a sustainable polymer, some of its unique characteristics are not yet fully understood and benefit from a deeper comprehension of its microstructure and intermolecular bonding. Results show that in the amorphous domains, where intermolecular interactions are weak, PEF chains favor a helical conformation. Prior to crystallization, polymeric chains undergo internal rotations extending their shape in a zigzag pattern—an energetically unfavorable geometry which is stabilized by C–H···O bonds among adjacent chain segments. The zigzag conformation is the crystalline motif present in the α and β PEF polymorphs. The energy difference among the amorphous and crystalline chains of PEF is higher than in PET poly(ethylene terephthalat...

Photoluminescent isotypical phosphonate-based metal–organic frameworks, [Ln(H5btp)]·2H2O [where Ln3+ = Tb3+ (1) or Gd3+ (2) and H8btp = [1,1′-biphenyl]-3,3′,5,5′-tetrayltetrakis(phosphonic acid)] prepared under solvo(hydro)thermal conditions exhibit a three-dimensional supramolecular structure built up from phosphonate linkers bridging Ln3+ ions. Single-crystal X-ray diffraction of 1 revealed hydrogen bonds along the a-axis between the crystallization water molecules and the phosphonate groups. The network features lozenge-shaped tubular channels with intermolecular interactions between adjacent organic ligand molecules. Crystal packing forces bring together two ligand biphenyl groups in a parallel arrangement, forming an excimer. A ratiometric luminescent thermometer operative close to room temperature was built based on the excimer and the 5D4 → 7F5 Tb3+ emissions, exhibiting a maximum relative thermal sensitivity of 1.26%·K–1 and a minimum temperature uncertainty of 0.75 K at 319 K. This performance is...

A thorough vibrational portrait of 4-fluorobenzaldehyde is presented, covering Infrared (Mid- and Far-), Raman and Inelastic Neutron Scattering (INS) spectra. Periodic DFT calculations (CASTEP) of a model 4FB crystal proved useful for vibrational assignment, yielding estimates of experimental spectra with near one-to-one correspondence – including the correct estimation of overtone and combination modes. A striking similarity among the Far-IR spectrum of liquid 4FB and that estimated based on a periodic structure indicates that the solid-liquid transition induces soft structural changes which leave most vibrational modes unaffected – except for those directly involved in Csingle bondH…O bonding, where crystal field splitting is observed. published

Bacterial nanocellulose (BC)-based composites containing poly(2-hydroxyethyl methacrylate) (PHEMA), poly(methacroylcholine chloride) (PMACC) or poly(methacroylcholine hydroxide) (PMACH) were characterized by inelastic neutron scattering (INS) spectroscopy, combined with DFT (density functional theory) calculations of model systems. A reasonable match between calculated and experimental spectral lines and their intensities was used to support the vibrational assignment of the observed bands and to validate the possible structures. The differences between the spectra of the nanocomposites and the pure precursors indicate that interactions between the components are stronger for the ionic poly(methacrylate) derivatives than for the neutral counterpart. Displaced anions interact differently with cellulose chains, due to the different ability to compete with the O&ndash, H&middot, &middot, O hydrogen bonds in cellulose. Hence, the INS is an adequate technique to delve deeper into the structure and dynamics of nanocellulose-based composites, confirming that they are true nanocomposite materials instead of simple mixtures of totally independent domains.

The present work emphasizes the value of periodic density functional theory (DFT) calculations in the assessment of the vibrational spectra of molecular crystals. Periodic calculations provide a nearly one-to-one match between the calculated and observed bands in the inelastic neutron scattering (INS) spectrum of crystalline 4-phenylbenzaldehyde, thus validating their assignment and correcting previous reports based on single molecule calculations. The calculations allow the unambiguous assignment of the phenyl torsional mode at ca. 118&ndash, 128 cm&minus, 1, from which a phenyl torsional barrier of ca. 4000 cm&minus, 1 is derived, and the identification of the collective mode involving the antitranslational motion of CH&middot, &middot, O bonded pairs, a hallmark vibrational mode of systems where C-H&middot, O contacts are an important feature.

The present work aims at exploiting a polyelectrolyte nanocomposite based on poly(4-styrene sulfonic acid) (PSSA) and bacterial cellulose (BC) as an eco-friendly proton-exchange membrane (PEM) for application in microbial fuel cells (MFCs). The PSSA/BC-based PEM was confirmed as a true nanocomposite by inelastic neutron scattering (INS) vibrational spectroscopy. Moreover, this PEM exhibited thermal stability up to 155 °C, Young's modulus of 11.7 ± 0.9 GPa, ion exchange capacity of 1.85 mmol g−1, and maximum protonic conductivity of 1.73 S m−1. The application of the PSSA/BC nanocomposite membrane in a single-chamber lab-scale MFC with a pure culture of Shewanella frigidimarina yielded a maximum power density of 2.42 mW m−2, open circuit voltage of 0.436 V, and internal resistance of 15.1 kΩ. These results are superior to those obtained with a commercial Nafion® membrane and, thus, confirm the potential of this bio-based PSSA/BC nanocomposite as a PEM for MFCs.

This work explores the dynamics of hydrogen bond networks in cellulose through inelastic neutron scattering (INS) and periodic CASTEP calculations. Estimated spectra were based on the crystal structure of cellulose Iα and Iβ and replicate the INS spectrum of cellulose samples with remarkable similarity, allowing a reliable assignment of INS bands to vibrational modes of cellulose. Comparison of cellulose samples from varied sources, from bacterial to kraft pulp, allows the identification of characteristic INS bands, arising from C2-OH torsional motions, which easily identify which allomorph-Iα or Iβ-is prevalent. A high crystallinity index is revealed by the presence of well-defined INS bands associated with highly cooperative CH bending modes along the chain. Hydrating kraft cellulose samples clearly affects those INS bands related with the hydroxymethyl group, identified as the preferred binding site for water molecules. At high humidity content level, a significant proportion of the water molecules is aggregated in clusters within the amorphous cellulose domains. The formation of ice microcrystals leads to a partial disruption of the hydrogen-bond network, as can be concluded from the observed red-shift of the torsional OH vibrational modes. The full assignment and interpretation of cellulose's INS spectra herein provided is a sound basis for future use of INS spectroscopy in the characterization of functionalized cellulose fibers and composite materials.

Widespread microplastic pollution is raising growing concerns as to its detrimental effects upon living organisms. A realistic risk assessment must stand on representative data on the abundance, size distribution and chemical composition of microplastics. Raman microscopy is an indispensable tool for the analysis of very small microplastics (

There is a lack of fundamental knowledge on deep eutectic solvents, even for the most extensively studied mixtures, such as the mixture of cholinium chloride and urea, which prevents a judicious choice of components to prepare new solvents. The objective of this work is to study and understand the fundamental interactions between cholinium chloride and urea that lead to the experimentally observed melting temperature depression. To do so, the structure of urea was strategically and progressively modified, in order to block certain interaction centres, and the solid–liquid equilibrium data of each new binary system was experimentally measured. Using this approach, it was concluded that the most important interaction between cholinium chloride and urea occurs through hydrogen bonding between the chloride anion and the amine groups. Any blockage of these groups severely hampers the melting point depression effect. Raman spectroscopy and DFT calculations were utilized to study in more detail this hydrogen bonding and its nuances. This work was developed in the scope of the project CICECO – Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (Ref. FCT UID/CTM/50011/2019) and Associate Laboratory LSRELCM, POCI-01-0145-FEDER-006984 (Ref. FCT UID/EQU/50020/2019), and project MultiBiorefinery (POCI-01-0145-FEDER-016403), all financed by national funds through the FCT/ MCTES (PIDDAC) and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. M. A. R. M. acknowledges financial support from NORTE-01-0145-FEDER-000006 – funded by NORTE2020 through PT2020 and ERDF. L. P. S. acknowledges FCT for her PhD grant (SFRH/BD/135976/2018). C. F. A. acknowledges FCT for her PhD grant (SFRH/BD/129040/2017). M. M. N. and M. M. F. acknowledge FCT for their researcher contracts (IF/01468/2015 and IF/00894/2015 respectively) under the program IF 2015. info:eu-repo/semantics/publishedVersion

The photophysical properties of a new alternating copolymer containing fluorene, terpyridine, and complexed sites with trivalent europium (Eu(3+)) ions (LaPPS66Eu) were investigated, using the non-complexed backbone (LaPPS66) and a low molecular weight compound of similar chemical structure of the ligand/Eu(3+) site (LaPPS66M) as a model compound. The analogous gadolinium complex (LaPPS66Gd) was also synthesized to determine the triplet state of the complex. (1)H and (13)C nuclear magnetic resonance (NMR) analysis, Fourier transform infrared (FT-IR) spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), elemental analyses, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) characterized the chemical structure and thermal properties of the synthesized materials. A level of Eu(3+) insertion of 37% (molar basis) in the polymer backbone was achieved. The photoluminescence studies were performed in the solid state showing the occurrence of polymer-to-Eu(3+) energy transfer brought about by the spectral overlap between the absorption spectra of the Eu(3+) complex and the emission of the polymer backbone. A detailed theoretical photoluminescence study performed using time-dependent DFT (TD-DFT) calculations and the recently developed LUMPAC luminescence package is also presented. The high accuracy of the theoretical calculations was achieved on comparison with the experimental values. Aiming at a deeper level of understanding of the photoluminescence process, the ligand-to-Eu(3+) intramolecular energy transfer and back-transfer rates were predicted. The complexed materials showed a dominant pathway involving the energy transfer between the triplet of the dbm (dibenzoylmethane) ligand and the (5)D1 and (5)D0 Eu(3+) levels.

The solids choline chloride and urea, mixed in a 1 : 2 molar proportion, form the iconic deep eutectic solvent “Reline”. A combination of computational and vibrational spectroscopy tools, including inelastic neutron scattering (INS), have been used to probe intermolecular interactions in the eutectic mixture. Reline's experimental spectra were estimated using discrete and periodic ab initio calculations of a molecular aggregate with two choline chloride and four urea units. This is the minimum size required to achieve satisfactory agreement with experiment, as smaller clusters cannot represent all of reline's significant intermolecular interactions. The INS spectrum of reline, compared with that of pure choline chloride, reveals a displacement of chloride anions away from their preferred positions on top of choline's methyl groups, whose torsional movement becomes less hindered in the mixture. Urea, which adopts a planar (sp2) shape in the crystal, becomes non-planar (sp3) in reline, a feature herein discussed for the first time. In reline, urea molecules form a wide range of hydrogen bonds, from soft contacts to stronger associations, the latter being responsible for the deviation from ideality. The chloride's interactions with choline are largely conserved at the hydroxyl end while becoming weaker at the cationic headgroup. The interplay of soft and strong interactions confers flexibility to the newly formed hydrogen-bond network and allows the ensemble to remain liquid at room temperature.

The inelastic neutron scattering (INS) spectra of cyclopentanone were obtained for pure and 50% CCl4 solution forms. Spectra are compared with infrared and Raman data, and with DFT calculated eigenvectors. This exercise aims to find spectroscopic evidence in the neutron spectra for the presence of C–H⋯O hydrogen bonds. These are weak interactions with an energy of ca. −6 kJ mol−1 as predicted by DFT. The neutron spectra show narrow and sharp bands which allows for an assignment of the vibrational modes. The simulated neutron spectrum of C–H⋯O bonded cyclopentanone dimers matches the experimental spectrum of the pure compound, whereas the monomer simulation monomer matches the experimental spectrum of the diluted solution, meaning that such interaction can be probed by INS. Assignment of the 95 cm−1 band to the νH⋯O anti-translational mode, being supported by DFT results and in agreement with previous literature data, is considered and discussed.

Luminol, one of the most popular electrochemiluminescence systems used in forensic chemistry, proved to be a suitable system to study the importance of cooperativity in hydrogen-bond chains. The computational pairwise approach PiMM was applied to the system and a thorough band assignment was accomplished. Hydrogen-bond and hydrogen-bond cooperativity effects were assessed through a confrontation of energy, geometry and wavenumber changes from monomer and dimer on one hand and dimer and \"full-cluster\" trimer on the other. For the first time the PiMM method was also used to successfully predict changes in band relative intensities. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

The complete vibrational spectra assignment of dihydrocoumarin is performed through a combined vibrational spectroscopy and DFT calculations approach. To provide effective information, vibrational analysis was also performed for α-pyrone and coumarin related systems. The presence of extra components in the νC O band profile can only be understood by both Fermi resonance and monomer/dimer equilibrium phenomena, the latter established by C–H···O hydrogen bond with Δ H ° value of −8.4 ± 0.9 kJ mol −1 . The analysis of the ν C–H region indicates that both the methylene and aromatic C–H groups have a significant contribution to the formation of C–H···O bonded dimers in liquid dihydrocoumarin.

The dioxomolybdenum(VI) complexes [MoO2Cl2(PzPy)] (1) and [MoO2(OSiPh3)2(PzPy)] (5) (PzPy = 2-[3(5)-pyrazolyl]pyridine) were synthesized and characterized by vibrational spectroscopy, with assignments being supported by DFT calculations. Complex 5 was additionally characterized by single crystal X-ray diffraction. Recrystallization of 1 under different conditions originated crystal structures containing either the mononuclear [MoO2Cl2(PzPy)] complex co-crystallized with 2-[3(5)-pyrazolyl]pyridinium chloride, binuclear [Mo2O4(μ2-O)Cl2(PzPy)2] complexes, or the oxodiperoxomolybdenum(VI) complex [MoO(O2)2Cl(PzPyH)], in which a 2-[3(5)-pyrazolyl]pyridinium cation weakly interacts with the Mo(VI) center via a pyrazolyl N-atom. The crystal packing in the different structures is mediated by a variety of supramolecular interactions: hydrogen bonding involving the pyridinium and/or pyrazolyl N-H groups, weak CH · · · O and CH · · · π contacts, and strong π-π stacking. Complexes 1 and 5 are moderately active catalysts for the epoxidation of cis-cyclooctene at 55 °C using tert-butylhydroperoxide as oxidant, giving 1,2-epoxycyclooctane as the only reaction product. Insoluble materials were recovered at the end of the first catalytic runs and characterized by IR spectroscopy, elemental analysis, scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS), and powder X-ray diffraction. For complex 5 the loss of the triphenylsiloxy ligands during the catalytic run resulted in the formation of a tetranuclear complex, [Mo4O8(μ2-O)4(PzPy)4]. The recovered solids could be used as efficient heterogeneous catalysts for the epoxidation of cyclooctene, showing no loss of catalytic performance between successive catalytic runs.

In this work, the usefulness of the Pairs in Molecular Materials (PiMM) approach to elucidate unknown structures of molecular crystals is assessed. This methodology aims to assist the prediction of probable crystal structures from the vibrational spectra, through the identification of the most relevant motifs in the potential energy landscape of the crystal. The method is successfully applied to the elucidation of 4-(dimethylamino)benzaldehyde crystal structure, considered to be “unknown” to illustrate the applicability of the PiMM approach. The proposed crystal structure, based on weak CH⋯O hydrogen bonding and π-stacking interactions, is in full agreement with the recently reported crystal structure.

The inclusion compounds of α-, β- and γ-cyclodextrins (α-CD, β-CD and γ-CD) with trans-cinnamic acid (t-CIA), 3-hydroxy-trans-cinnamic acid (t-3OHCIA), 4-hydroxy-trans-cinnamic acid (t-4OHCIA) and 3,4-dihydroxy-trans-cinnamic acid (t-3,4OHCIA) were prepared and characterized, in the solid state, by means of thermogravimetry and Raman spectroscopy. The effects of the inclusion process on the guest molecules and on the hydrogen bond interactions of the guest were studied by monitoring sensitive vibrational modes, such as CO, CC and ring CH stretching modes. By combining Raman and TG data with ab initio calculations and information from CSD database on similar compounds, inclusion geometries for the different compounds are proposed. The size of the host cavity and the maximization of host/guest hydrogen-bonding contacts appear to be the main factors determining the inclusion geometries. Copyright © 2009 John Wiley & Sons, Ltd.

A computationally-assisted methodology to assign the vibrational spectra of molecular materials (PiMM) has been successfully applied to the Raman and infrared (IR) spectra of trans-cinnamic acid (t-CIA) in the solid state. The effects of molecular association through OH···O hydrogen-bonding in both the wavenumber and the intensity of the bands are accurately described by a single dimer structure. This supports the discrimination between the possible conformers in the solid, the complete evaluation of hydrogen-bonding effects, and the full assignment of the vibrational spectra of t-CIA. Copyright © 2008 John Wiley & Sons, Ltd.

Organic-inorganic mesoporous materials of the MCM-41 type are important materials that can be prepared by either post-synthesis or one-pot synthesis procedures. A complete control of the characteristics at a local level is of the utmost importance in view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared samples by post-synthesis derivatization of materials from Si-based MCM-41, with bidentate nitrogen ligands bearing one or two silylated arms, and by one-pot synthesis of organic-inorganic hybrid materials. The bulk properties of the two kinds of materials were comparable. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and Raman spectroscopy were used to investigate the local environment, namely, the number of OH groups and distribution of SiO 4 units (large and small ring units). Hydrophilicity correlates with both the type of organic moiety used (mono- or disily-lated), as well as with the synthetic procedure. The same vibrational studies showed how the structure in the channels changes as a function of pressure, reflecting the low mechanical stability of the mesoporous materials.

Inclusion complexes comprising niobocene dichloride, Cp2NbCl2, and either native β-cyclodextrin (β-CD) or permethylated β-CD (TRIMEB) were prepared with a host:guest molar ratio of 1:1. The adducts were characterized in the solid state by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), 13C{1H} CP/MAS NMR, FTIR, and FT Raman spectroscopies. Ab initio calculations were performed in order to elucidate the possible inclusion geometries and calculate vibrational frequencies for Cp2NbCl2 in the region 100−1800 cm-1. The vibrational spectra indicated that neither the hosts nor the guest were chemically modified upon inclusion complexation. Small wavenumber shifts in C−H, C−C, and metal−ligand vibrational modes were attributed to the effect of the host−guest interaction. Powder XRD showed that the β-CD adduct was of low crystallinity, while the TRIMEB adduct was quite crystalline. The powder XRD pattern of the TRIMEB adduct could be satisfactorily indexed in the monoclinic system with the space ...

A series of europium Eu- and La-doped complexes with two different crystal structures, namely, EuxLa1-x(phen)(2)(NO3)(3) [phen = 1,10-phenanthroline, x = 1.0 (1), 0.88 (2), 0.73 (3), and 0.52 (4)] and {[EuxLa1-x(phen)(2)(H2O)(2)(NO3)(2)](NO3)2(phen)(H2O)} [x = 0.28 (5) and 0.0 (6)], were synthesized in aqueous solution by using different Eu/La ratios.The complexes were characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetry, and scanning electron microscopy. Compounds 1-4 and 5, 6 were obtained for Eu/La molar ratios higher than 5:5 and smaller than 3:7, respectively. The photoluminescence properties of these compounds depend on the crystal structure, which is determined by the Eu/La reactant ratio. Complexes 1-4 exhibit a quantum efficiency ( = 55%) and quantum yield (q = 31%) higher than 5 ( = 23% and q = 6%). The photophysical properties assessed by using the LUMPAC software are in good accord with the experimental values, particularly, the calculated (26%) and measured emission quantum yields (31%; excitation at the ligands at 255 nm).

The suitability of the computer package LUMPAC to calculate the photoluminescence properties of metal-organic frameworks was assessed by considering three systems based on the ditopic 1,4-phenylenebis(methylene)diphosphonic acid (H(4)pmd) ligand and Ln(3+) ions, namely, [Eu(Hpmd)(H2O)] (1), [La-2(H(2)pmd)(pmd)(H2O)(2)] (2) and [La-2(H(2)pmd)(3)(H2O)(12)] (3, previously reported) and their isotypical materials doped with Eu3+ cations, [(La0.95Eu0.05)(2)(H(2)pmd)(pmd)(H2O)(2)] (4) and [(La0.95Eu0.05)(2)(H(2)pmd)(3)(H2O)(12)] (5). These materials were prepared, and their structures and luminescence properties were characterized. A straightforward approximation based on the simple crystallographic structural subunits of these materials was used and resulted in an excellent agreement between the calculated and experimental properties. The intramolecular energy transfer and back-transfer rates were predicted, and the (T1D1)-D-5 channel was shown to be the dominant pathway (9.03x10(4) s(-1) for 1, 1.06x10(4) s(-1) for 4 and 2.18x10(5) s(-1) for 5).

The reaction of [MoO2Cl2(pzpy)] (1) (pzpy = 2-[3(5)-pyrazolyl]pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 degrees C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 degrees C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo3O9(pzpy)](n) (2) as a microcrystalline powder in yields of 72-79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO3, pzpy, and H2O at 160 degrees C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)(2)(MoCl4) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl42- anion, and the tetranuclear compound [Mo4O12(pzpy)(4)] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O-2)(2)(pzpy)(4)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, a hybrid organic inorganic one-dimensional (1D) polymer, (1)(infinity)[Mo3O9(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO3 and 1D chains of corner-sharing distorted {MoO4N2} octahedra. Compound 2 exhibits moderate activity and high selectivity when used as a (pre)catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction.

The combination of the glycine-derivative supramolecular salt 4,6-bis(carboxymethylamino)-2-oxo-2,3-dihydro-1,3,5-triazin-1-ium chloride (H(2)bodt center dot HCl) and lanthanide(III) chloride hydrates under hydrothermal conditions (120 degrees C, 48 h) led to the formation of a family of isotypical materials formulated as [Ln(bodt)(Hbodt)] [where Ln(3+) = La3+ (1), (La0.95Eu0.05)(3+) (2) and (La0.95Tb0.05)(3+) (3)]. The synthesis of the novel precursor H(2)bodt center dot HCl is detailed. The structures of H(2)bodt center dot HCl and its intermediate compound were unveiled by single-crystal X-ray diffraction and characterized by standard liquid-state techniques. The crystallographic details of compound 1 were unveiled in the monoclinic P2/c space group by using single-crystal X-ray diffraction, with the crystal structure of 1 comprising a one-dimensional (1)(infinity)[La(bodt)(Hbodt)] coordination polymer. All polymeric materials were fully characterized by FT-IR, electron microscopy (SEM and EDS), powder X-ray diffraction, and elemental and thermogravimetric analyses. The photoluminescent properties of 1 and of the mixed-lanthanide materials 2 and 3 were investigated at ambient and low temperatures. An excited-state intermolecular proton transfer (ESPT) process, induced by intermolecular hydrogen-bonding interactions, is proposed to account for the observed anomalous emission and excitation spectra of 1. Aiming at providing an in-depth understanding of the emission (fluorescence and phosphorescence) properties of the ligand, time-dependent density functional theory (TD-DFT) calculations were also performed.

A regular MCM-41 type mesostructured silica was used as a support for the incorporation of the highly luminescent tris(beta-diketonate) complex Eu(tta)(3)ephen yielding the hybrid MCM-Eu material. Suitable characterization by powder X-ray diffraction (XRD), thermogravimetric analyses (TGA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), C-13 and Si-21 solid state NMR spectroscopy and photoluminescence was accomplished. The combination of ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence techniques shows that the complex incorporation seems to modify essentially the second Eu3+ coordination shell. For a material that has a simply impregnated lanthanide complex, the herein reported maximum D-5(0) quantum yield value of 0.31 is a significantly high value, being almost in the same scale of the values obtained for the materials with covalently bonded complexes. A detailed theoretical photoluminescence study of the MCM-Eu with the recently developed Luminescence Package - LUMPAC is presented. The high accuracy of the theoretical calculations is achieved through the comparison with the experimental values. Aiming at a deeper understanding of the photoluminescence process, the ligand-to-Eu3+ intramolecular energy transfer and back-transfer rates were also predicted. The dominant pathway involves the energy transfer between the lowest energy ligand triplet and the D-5(0) level (9.70 x 10(7) s(-1)).

The -substituted -diketonate [Ln(3Cl-acac)(3)(H2O)(2)] [Ln=Tb, Gd] complexes (with 3Cl-acac(-) being 3-chloro-2,4-pentanedionate) were characterized by elemental analysis, infrared, ultraviolet (UV)-visible and photoluminescence spectroscopies. For comparison purposes regarding photoluminescence, the well-known [Tb(acac)(3)(H2O)(2)] complex was also synthesized. By considering the phosphorescence spectra of [Gd(3Cl-acac)(3)(H2O)(2)], the effect of chloride replacement of hydrogen on the triplet state energy of the 3Cl-acac ligand was revealed. To support the interpretation and rationalization of the experimental results, Time-dependent DFT calculations were performed on Tb(3Cl-acac)(3)(H2O)(2). Additionally, the possibility of Tb(3Cl-acac)(3)(H2O)(2) to be used as potential green-emitting phosphor material for solid-sate light emitting diodes was evaluated. A prototype was successfully fabricated coating a near-UV LED (370nm) with the Tb(3Cl-acac)(3)(H2O)(2) complex.

Europium (t-Eu) and gadolinium (t-Gd) beta-diketonate complexes with photoactive t-bpete ligand, [Ln-(btfa)(3)(t-bpete)(MeOH)] (Ln = Eu, Gd), where btfa(-) and t-bpete are 4,4,4-trifluoro-1-phenyl-1,3-butanedionate and trans-1,2bis(4-pyridyl)ethylene, respectively, were synthesized, characterized by vibrational, absorption (reflectance) and photoluminescence spectroscopies and their crystal structure was determined using single-crystal X-ray diffraction. B3LYP calculations were performed to support the interpretation and rationalization of the experimental results. The complexes, under UV irradiation, do not display the typical photodegradation of the beta-diketonate ligands exhibiting, in turn, an unprecedented photostability during, at least, 10 h. During UV-A exposure (>330 nm), the emission intensities of both complexes increase drastically (similar to 20 times), whereas for t-Eu the emission quantum yield is enhanced at least 30 fold A mechanism based on a photoclick trans-to-cis isomerization of both t- and c-bpete moieties was proposed to explain the abnormal photostability of these compounds, either in solid state or in solution. The experimental and computational results are consistent with a photostationary state involving the trans-to-cis isomerization of the bpete ligand under continuous UV -A exposure, which thus diverts the incident radiation from other deleterious photochemical or photophysical processes that cause the typical photobleaching behavior of chelate lanthanide complexes. This shielding mechanism could be extended to other ligands permitting the design of new lanthanide-based photostable systems under UV exposure for applications in lighting, sensing, and displays.

In many Eu(III)-based materials, the presence of an intermediate energy level, such as ligand-to-metal charge transfer (LMCT) states or defects, that mediates the energy transfer mechanisms can strongly affect the lifetime of the (5)D(0) state, mainly at near-resonance (large transfer rates). We present results for the dependence of the (5)D(0) lifetime on the excitation wavelength for a wide class of Eu(III)-based compounds: ionic salts, polyoxometalates (POMs), core/shell inorganic nanoparticles (NPs) and nanotubes, coordination polymers, β-diketonate complexes, organic-inorganic hybrids, macro-mesocellular foams, functionalized mesoporous silica, and layered double hydroxides (LDHs). This yet unexplained behavior is successfully modelled by a coupled set of rate equations with seven states, in which the wavelength dependence is simulated by varying the intramolecular energy transfer rates. In addition, the simulations of the rate equations for four- and three-level systems show a strong dependence of the emission lifetime upon the excitation wavelength if near-resonant non-radiative energy transfer processes are present, indicating that the proposed scheme can be generalized to other trivalent lanthanide ions, as observed for Tb(III)/Ce(III). Finally, the proper use of lifetime definition in the presence of energy transfer is emphasized.

Spectroscopic evidence for C-H...O hydrogen bonding in chloroform...acetone [Cl(3)CH...O=C(CH(3))(2)] mixtures was obtained from vibrational inelastic neutron scattering (INS) spectra. Comparison between the INS spectra of pure samples and their binary mixtures reveals the presence of new bands at about 82, 130 and 170 cm(-1). Assignment of the 82 cm(-1) band to the nuO...H anti-translational mode is considered and discussed. In addition, the betaC-H mode of CHCl(3) at 1242 cm(-1) is split in the spectra of the mixtures, and the high-wavenumber component is assigned to the hydrogen-bonded complex. The plot of the integrated intensity of this component shows a maximum for x=0.5, in agreement with the 1:1 stoichiometry of the chloroformacetone complex, with a calculated complexation constant of 0.15 dm(3) mol(-1). Results also show that the complex behaves as an independent entity, that is, despite being weak, such interactions play a key role in supramolecular chemistry.

FT-Raman spectroscopy turns out to be a powerful technique to evaluate the amount of polymorphic and pseudopolymorphic forms in crystalline samples – which is particularly relevant in pharmaceutical sciences. This paper presents a methodology that allows successful quantitative evaluation of the solid-state hydration and dehydration processes, using FT-Raman spectroscopy. All the steps required for a reliable evaluation of the hydration/dehydration process are illustrated for the caffeine system, a particularly challenging system presenting limited spectral differences between the pseudopolymorphs. The hydration process of caffeine was found to occur in a single-step process with a half-life time of ca 13 h, while the dehydration occurs through a two-step mechanism. The critical relative humidity was found to be atca 81 and 42% for anhydrous and hydrate caffeine forms, respectively. Copyright c � 2009 John Wiley & Sons, Ltd.

Theophylline is known to undergo vapor phase induced hydrate-anhydrate pseudopolymorphic transformations, which can affect its bioavailability. In this work, the kinetics of the pseudopolymorphic transitions of theophylline crystals in different storage conditions is studied using a vibrational spectroscopic technique. While the hydration is a single-step process with a half-life time of ca. 5 h, the dehydration occurs through a two-step mechanism. In addition, the phase stability of hydrate-anhydrate systems in different relative humidity (RH) conditions was probed. The critical RH for anhydrous teophylline was found to be at ca. 79%, while the critical RH for dehydration is ca. 30%. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1366-1379, 2007

Dioxomolybdenum(VI) complexes of general formula [MoO2X2L2] (X = Cl, OSiPh3; L2 = 2-(1-butyl-3-pyrazolyl)pyridine, ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate) were prepared and characterised by 1H NMR, IR and Raman spectroscopy. The assignment of the vibrational spectra was supported by ab initio calculations. A single crystal X-ray diffraction study of the complex [MoO2Cl2{ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate}] showed that the compound is monomeric and crystallises in the tetragonal system with space group P41. The four complexes are active and selective catalysts for the liquid-phase epoxidation of olefins by tert-butylhydroperoxide. Selectivities to the corresponding epoxides were mostly 100% (for conversions of at least 34%) for the substrates cyclooctene, cyclododecene, 1-octene, trans-2-octene and (R)-(+)-limonene. For styrene epoxidation, the corresponding diol was also formed in significant quantities. The turnover frequencies for cyclooctene epoxidation at 55 °C were around 340 mol molMo−1 h−1 for the chloro complexes and 160 mol molMo−1 h−1 for the triphenylsiloxy complexes. The addition of co-solvents (1,2-dichloroethane or n-hexane) had a detrimental effect on catalytic activities. Kinetic studies for the two complexes bearing the ligand ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate revealed an apparent first order dependence of the initial rate of cyclooctene conversion with respect to cyclooctene or oxidant concentration.

A new computationally-assisted methodology (PiMM), which accounts for the effects of intermolecular interactions in the crystal, is applied to the complete assignment of the Raman and infrared vibrational spectra of room temperature forms of crystalline caffeine, theobromine, and theophylline. The vibrational shifts due to crystal packing interactions are evaluated from ab initio calculations for a set of suitable molecular pairs, using the B3LYP/6-31G* approach. The proposed methodology provides an answer to the current demand for a reliable assignment of the vibrational spectra of these methyl-xanthines, and clarifies several misleading assignments. The most relevant intermolecular interactions in each system and their effect on the vibrational spectra are considered and discussed. Based on these results, significant insights are obtained for the structure of caffeine in the anhydrous form (stable at room temperature), for which no X-ray structure has been reported. A possible structure based on C((8))--H...N((9)) and C((1,3))--H...O intermolecular interactions is suggested.