Asma Marzouk

Covalent Grafting of Organic–Inorganic Polyoxometalates Hybrids onto Mesoporous SBA-15: A Key Step for New Anchored Homogeneous Catalysts

Covalent grafting of heteropolyanions hybrids B,α-[As(III)W9O33{P(O)(CH2CH2CO2H)}2](5-) on 3-aminopropyl functionalized SBA-15 has been achieved through the formation of peptide bonds. The covalent link has been confirmed by using IR and (13)C CP MAS NMR spectroscopies. Electrostatic interactions between carboxylate and protonated amines have been discarded on the basis of the retention of POMs after repeated washings of the resulting material by ionic liquid (bmimCl). This is the first example of anchored monovacant polyoxometalates (POM) in which nucleophilic oxygen atoms are still available after incorporation into mesoporous supports. Further characterization of the textural properties of grafted materials has shown that they still retain an important mesoporosity, which is compatible with their potential use in heterogeneous catalysis. Such systems are thus interesting candidates for the preparation of anchored homogeneous catalysts in which the POMs would play the role of polydentate inorganic ligands for the active centers.

Hydrogen Bonding and Stability of Hybrid Organic-Inorganic Perovskites.

In the past few years, the efficiency of solar cells based on hybrid organic-inorganic perovskites has exceeded the level needed for commercialization. However, existing perovskites solar cells (PSCs) suffer from several intrinsic instabilities, which prevent them from reaching industrial maturity, and stabilizing PSCs has become a critically important problem. Here we propose to stabilize PSCs chemically by strengthening the interactions between the organic cation and inorganic anion of the perovskite framework. In particular, we show that replacing the methylammonium cation with alternative protonated cations allows an increase in the stability of the perovskite by forming strong hydrogen bonds with the halide anions. This interaction also provides opportunities for tuning the electronic states near the bandgap. These mechanisms should have a universal character in different hybrid organic-inorganic framework materials that are widely used.

Electronic structure and chemical bonding in the OTi-N2 complexes: a systematic ab initio and DFT study.

Two OTi-N2 complexes, experimentally observed in the TiO + N2 reaction, have been theoretically studied using several density functionals as well as ab initio approaches and various basis sets. The benchmark results calculated with coupled-cluster singles, doubles, and perturbative triples CCSD(T) and sufficiently large correlation-consistent basis set were used to assess the performance of other theoretical models, especially four density functional families, pure functional, hybrid, double-hybrid, and long-range corrected ones. It has been shown that, out of twenty-three density functionals used in this work, only three functionals, namely TPSS0, LC-TPSS, and B2PLYP, are able to reproduce the CC-reference data quantitatively. Particularly, the B2PLYP double-hybrid (with or without addition of empirical dispersion) is the most promising functional, providing the closest results to the reference ones. The nature of bonding within products has been investigated using two topological techniques and a localized orbital approach.

Solar Cell Materials by Design: Hybrid Pyroxene Corner-Sharing VO4 Tetrahedral Chains

Hybrid organic-inorganic frameworks provide numerous combinations of materials with a wide range of structural and electronic properties, which enable their use in various applications. In recent years, some of these hybrid materials-especially lead-based halide perovskites-have been successfully used for the development of highly efficient solar cells. The large variety of possible hybrid materials has inspired the search for other organic-inorganic frameworks that may exhibit enhanced performance over conventional lead halide perovskites. In this study, a new class of low-dimensional hybrid oxides for photovoltaic applications was developed by using electronic structure calculations in combination with analysis from existing materials databases, with a focus on vanadium oxide pyroxenes (tetrahedron-based frameworks), mainly due to their high stability and nontoxicity. Pyroxenes were screened with different cations [A] and detailed computational studies of their structural, electronic, optical and transport properties were performed. Low-dimensional hybrid vanadate pyroxenes [A]VO3 (with molecular cations [A] and corner-sharing VO4 tetrahedral chains) were found to satisfy all physical requirements needed to develop an efficient solar cell (a band gap of 1.0-1.7 eV, strong light absorption and good electron-transport properties).

A combined experimental and theoretical study of the Ti2 + N2O reaction.

The reactivity of diatomic titanium with nitrous oxide has been studied in solid neon. Two molecules with the same Ti2-N2O stoichiometry are identified from concentration, temperature, and irradiation effects. The more stable one is characterized by five fundamental vibrational transitions located below 1000 cm(-1), the high frequency one at 946 cm(-1) corresponding to a pure TiO stretching mode. Its structure, a rhombus OTiNTiN with the extra O atom fixed on one Ti, is confirmed by quantum chemical calculations, at the CCSD(T) level, which predict a Cs structure in the singlet state with a Ti-O bond length close to 1.66 Å, two nonequivalent Ti-N distances close to 1.94 and 1.75 Å, and a OTiTi angle of 119.2°. The second Ti2-N2O molecule, only observed after annealing, is easily converted into the first one upon irradiation above 12 000 cm(-1) and its kinetics of photoconversion allows vibrational transitions to be identified. The strongest one located at 2123.4 cm(-1) characterizes an N-N stretching mode. Corresponding ab initio calculations complete this picture with details on the electronic structure and allow us to identify a most adequate density functional to describe the spectroscopic properties of the studied species in a simpler broken-symmetry open-shell DFT context. The theoretical results predict the existence of a metastable product OTi2N2 and correctly account for the observed spectra of the various isotopic varieties.

Vibrational Spectra and Structures of Ti–N2O and OTi–N2: A Combined IR Matrix Isolation and Theoretical Study

The reaction of atomic titanium with nitrous oxide has been reinvestigated using matrix isolation in solid neon coupled to infrared spectroscopy and by quantum chemical methods. Our technique of sublimation of Ti atoms from a filament heated at about 1500 °C allowed the formation of three species: one Ti-N(2)O pair of van der Waals (vdW) type characterized by small red shift with respect to N(2)O monomer, and two isomers of OTi-N(2) pair where N(2) is in interaction with the OTi moiety either with end-on or side-on structure. Interconversion between these structures has been performed with several wavelengths. In the visible and near-ultraviolet the conversion vdW → OTi-N(2) (end-on) is observed with characteristic times strongly varying according to the wavelength. In the near-infrared the conversion OTi-N(2) (end-on) → OTi-N(2) (side-on) occurs, the vdW species remaining unchanged. These selectivities allow 8, 6, and 4 vibrational transitions to be assigned for vdW, (3)[OTi(η(1)-NN)] (end-on), and (1)[OTi(η(2)-NN)] (side-on), respectively. Electronic and geometrical structures are also investigated with double-hybrid functionals. It has been shown that the side-on geometry corresponds to the ground state of (1)[OTi(η(2)-NN)] in the singlet electronic state. The theoretical vibrational analysis supports well the experimental attributions.