Ignazio L. Fragalà

Synthesis and second-order nonlinear optical properties of bis(salicylaldiminato)M(II) metalloorganic materials

Abstract A new synthetic strategy to second-order nonlinear optical (NLO) metalloorganic chromophores has been developed. These materials exhibit a sizable nonlinearity, an excellent thermal stability, and can be easily incorporated in thermally stable main-chain polymers for poled polymer NLO applications. In addition, substituted donor–acceptor derivatives exhibit two-dimensional NLO characteristics. The effect of the metal center in such complexes is manifold; it templates the formation of acentric molecular structures, imparts high thermal stability to the chelate ring, and both ‘switches on’ and enhance NLO response. This paper briefly reviews recent research developed in our laboratory on this new class of NLO materials.

Energetics and mechanism of organolanthanide-mediated phosphinoalkene hydrophosphination/cyclization. A density functional theory analysis

This contribution focuses on organolanthanide-mediated hydroamination processes and analyzes the hydroamination/cyclization of a prototypical aminoalkene, NH2(CH2)3CHCH2, catalyzed by Cp2LaCH(TMS)2, using density functional theory. The reaction is found to occur in two steps, namely, cyclization to form La−C and C−N bonds, and subsequent La−C protonolysis. Calculations have been carried out for (i) insertion of the olefinic moiety into the La−N bond via a four-center transition state and (ii) protonolysis by a second substrate molecule. The cyclized amine then dissociates, thus restoring the active catalyst. DFT energy profiles have been determined for the turnover-limiting insertion of the 1-amidopent-4-ene CC double bond into the La−NH− bond. DFT calculations of geometries and the stabilities of reactants, intermediates, and products have been analyzed. The picture that emerges involves concerted, rate-limiting, slightly endothermic insertion of the alkene fragment into the La−N(amido) bond via a highly...

Deposition of thin films of cobalt oxides by MOCVD

The Co(hfa)2·2H2O (hfa = CF3C(O)CHC(O)CF3) precursor was used in MOCVD experiments to deposit cobalt oxides, on optically transparent SiO2 substrates. CoO and Co3O4 films have been obtained depending on the adopted deposition conditions. XRD measurements provided evidence that CoO consists of cubic, (100) oriented crystals, whilst Co3O4 films are only partially oriented along the (311) direction. Mean crystallite sizes were evaluated from the XRD line broadening and the band-gap for Co3O4 was determined from the optically induced transitions. Both optical spectra and resistivity measurements of Co3O4 thin films showed that they are semi-conducting. The surface structure of the films was investigated by XPS.

Fundamental and Technological Aspects of Organo-f-Element Chemistry

Organolanthanoides: Review and New Developments.- 4f-Elements in Organic Synthesis.- [8] Annulene Derivatives of Actinides and Lanthanides.- Actinide Hydrocarbyl and Hydride Chemistry.- Organoactinide Complexes Containing Classical Ligands.- Frontier Elements: Connections with f-Elements.- Electronic Structure and Optical Spectroscopy of fn Ions and Compounds.- NMR-Spectroscopy of Organo-f-Element and Pre-Lanthanoid Complexes: Some Current Trends.- Photoelectron Spectroscopy of f-Element Organometallic Complexes.- f-Element Photochemistry.- New Perspectives of Lanthanides in Catalysis.

Dipolar donor-acceptor-substituted schiff base complexes with large off-diagonal second-order nonlinear optical tensor components.

The synthesis, characterization, and two-dimensional second-order nonlinear optical (NLO) response of a dipolar NiII donor- acceptor Schiff base complex and the related ligand are reported. Electric-field-induced second-harmonic generation and harmonic light (hyper-Rayleigh) scattering techniques, in combination with INDO/SCI-SOS theoretical calculations, were used to investigate the vector part of the hyperpolarizability tensor and the two-dimensional character of the molecular nonlinearity, respectively. Off-diagonal hyperpolarizability tensors can be related to charge-transfer transitions that are polarized perpendicular to the molecular dipolar axis, while parallel transitions account for the diagonal hyperpolarizability tensor. The role of the metal center in enhancing the two-dimensional NLO response of such molecules is twofold since it acts both as the donor and the bridging moiety of the planar donor-(pi-conjugate-bridge)-acceptor system. These dipolar two-dimensional molecules are interesting candidates from the perspective of polarization-independent NLO materials.

A novel route to the second-generation alkaline-earth metal precursors for metal-organic chemical vapour deposition: one-step synthesis of M(hfa)2·tetraglyme (M=Ba, Sr, Ca and Hhfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedione)

A one-pot reaction for the synthesis of better performing alkaline-earth precursors for metal-organic chemical vapour deposition (MOCVD) applications, is reported. The reaction of metal hydroxides (Ba(OH)2·8H20, Sr(OH)2·8H2O) or oxide (CaO) with Hhfa and tetraglyme in air yields quantitatively monomeric, water-free, highly stable and volatile M(hfa)2-tetraglyme adducts. All the adducts have been characterized by TGA and DSC. MOCVD capabilities have been tested through depositions of metal fluoride for buffer layer applications and of BaCaCu matrices for HTc TIBaCaCu superconductor thin films.

Two-dimensional characteristics of the second-order nonlinear optical response in dipolar donor–acceptor coordination complexes

The two-dimensional (2D) nonlinear optical (NLO) response of a series of dipolar donor–acceptor bis(salicylaldiminato)Ni(II) Schiff base planar coordination complexes was investigated using the INDO/SCI-SOS formalism. The in-plane 2D NLO character of this class of materials can be related to various low-energy charge-transfer (CT) states and is achieved by an accurate design of substitution pattern of the unsubstituted bis(salicylaldiminato) framework. While z-polarised electronic transitions, parallel with respect the molecular dipolar (z) axis, contribute to the diagonal hyperpolarisability tensor component, perpendicularx-polarised transitions contribute to off-diagonal hyperpolarisability tensors. Unlike non-dipolar multidimensional NLO structures, whose nonlinearity within the framework of the sum-over-states formalism is necessarily due only to three-level terms, in this case the 2D nonlinearity is generally dominated by two-level terms. It necessarily requires the existence of a strong, lowest energy, perpendicular CT transition in order to provide a substantial two-level contribution to off-diagonal tensors.

Selective monitoring of parts per million levels of CO by covalently immobilized metal complexes on glass

Optical detection of parts-per-million (ppm) levels of CO by a structurally well-defined monolayer consisting of bimetallic rhodium complexes on glass substrates has been demonstrated.

Dielectric properties of Pr2O3 high-k films grown by metalorganic chemical vapor deposition on silicon

Praseodymium oxide (Pr2O3) thin films have been deposited on Si(100) substrates by metalorganic chemical vapor deposition using praseodymium tris-2,2,6,6-tetramethyl-3,5-heptandionate as source material. Film structural, morphological, and compositional characterizations have been carried out. Dielectric properties have been studied as well by capacitance–voltage and current–voltage measurements on metal-oxide-semiconductor capacitors of several areas. The Pr2O3 films have shown a dielectric constant e=23–25 and a leakage current density of 8.8×10−8 A/cm2 at +1 V.

Stepwise Assembly of Coordination-Based Metal−Organic Networks

Metal-organic networks (MONs) were created by a stepwise solution deposition approach from vinylpyridine-based building blocks and PdCl(2). The combined experimental and computational study demonstrates the formation of saturated, structurally organized systems on solid supports. The rigid nature and geometry of the components are well-suited to form honeycomb and parallelogram structures, as predicted by a computational study. Detailed structural information of the new MONs was obtained by optical (UV/vis) spectroscopy, ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and synchrotron X-ray reflectivity (XRR). Notably, the XPS elemental composition indicates the formation of a palladium coordination-based network.