Hydration of Alumina Cluster Anions in the Gas Phase

Surface Energy and Work Function Control of AlOx/Al Surfaces by Fluorinated Benzylphosphonic Acids

The performance of organic electronic devices can be significantly improved by modifying metal electrodes with organic monolayers, which alter the physical and chemical nature of the interface between conductor and semiconductor. In this paper we examine a series of 12 phosphonic acid compounds deposited on the native oxide layer of aluminum (AlOx/Al), an electrode material with widespread applications in organic electronics. This series includes dodecylphosphonic acid as a reference and 11 benzylphosphonic acids, seven of which are fluorinated, including five newly synthesized derivatives. The monolayers are experimentally characterized by contact angle goniometry and by X-ray photoemission spectroscopy (XPS), and work function data obtained by low-intensity XPS are correlated with molecular dipoles obtained from DFT calculations. We find that monolayers are formed with molecular areas ranging from 17.7 to 42.9 Å(2)/molecule, and, by the choice of appropriate terminal groups, the surface energy can be tuned from 23.5 mJ/m(2) to 70.5 mJ/m(2). Depending on the number and position of fluorine substituents on the aromatic rings, a variation in the work function of AlOx/Al substrates over a range of 0.91 eV is achieved, and a renormalization procedure based on molecular density yields a surprising agreement of work function changes with interface dipoles as expected from Helmholtz' equation. The ability to adjust energetics and adhesion at organic semiconductor/AlOx interfaces has immediate applications in devices such as OLEDs, OTFTs, organic solar cells, and printed organic circuits.

Structural and electronic properties of an [(Al2O3)4](+) cluster

Density functional theory (DFT) has been applied to investigate the structural and electronic properties of an [(Al2O3)4](+) cluster. Since there is no structural data available from experiment, the geometry of the cluster was obtained based on a model which produced the best agreement with vibrational IR-MPD data. A range of different exchange-correlation functionals were tested, and it was concluded that the best spectral agreement was produced using the CAM-B3LYP and B3LYP functionals, respectively. To further characterize the properties of the cluster, natural bond order analysis was performed, and it was concluded that an appropriate description for the system is [Al8O12](+). The frontier orbitals and spin densities of both cation and neutral systems were considered, and it was concluded that the unrestricted singlet and triplet spin densities of the neutral [Al8O12] system were nearly degenerate, representing a di-radical, with the triplet state being lower in energy.

Study of cluster anions generated by laser ablation of titanium oxides: a high resolution approach based on Fourier transform ion cyclotron resonance mass spectrometry

Laser ablation of titanium oxides at 355 nm and ion-molecule reactions between [(TiO(2))(x)](-•) cluster anions and H(2)O or O(2) were investigated by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) with an external ion source. The detected anions correspond to [(TiO(2))(x)(H(2)O)(y)OH](-) and [(TiO(2))(x)(H(2)O)(y)O(2)](-•) oxy-hydroxide species with x=1 to 25 and y=1, 2, or 3 and were formed by a two step process: (1) laser ablation, which leads to the formation of [(TiO(2))(x)](-•) cluster anions as was previously reported, and (2) ion-molecule reactions during ion storage. Reactions of some [(TiO(2))(x)](-•) cluster anions with water and dioxygen conducted in the FTICR cell confirm this assessment. Tandem mass spectrometry experiments were also performed in sustained off-resonance irradiation collision-induced dissociation (SORI-CID) mode. Three fragmentation pathways were observed: (1) elimination of water molecules, (2) O(2) loss for radical anions, and (3) fission of the cluster. Density functional theory (DFT) calculations were performed to explain the experimental data.

Laser ablation mass spectrometry of inorganic transition metal compounds. Additional knowledge for the understanding of ion formation

Laser ablation of transition-metal oxides have been investigated to better understand the formation processes of inorganic cluster ions. The study of binary oxide mixtures and the relative distribution of the ions produced suggest three salient mechanisms that occur after laser/matter interaction, that function to produce the observed ensemble of ionic species. Molecular recombination reactions, unimolecular dissociation processes, emission of small neutrals, including molecular oxygen from transition-metal oxide samples, or from species expelled in gas phase appear to be a significant mechanism, especially under high laser irradiance conditions. These processes are used to propose a set of pathways to rationalize the envelope of ionic clusters formed under photon bombardment.

Sequential addition of H2O, CH3OH, and NH3 to Al3O3−: A theoretical study

Photoelectron spectra of two species, Al3O3(H2O)2- and Al3O3(CH3OH)2-, that are produced by the addition of two water or methanol molecules to Al3O3- are interpreted with density-functional geometry optimizations and electron propagator calculations of vertical electron detachment energies. In both cases, there is only one isomer that is responsible for the observed spectral features. A high barrier to the addition of a second molecule may impede the formation of Al3O3N2H6- clusters in an analogous experiment with NH3.

Identification of hydrolysis products of AlCl3·6H2O in the presence of sulfate by electrospray ionizationtime-of-flight mass spectrometry and computational methods

ElectroSpray Ionization-Mass Spectrometry (ESI-MS) and computational methods (DFT, MP2, and COSMO) were used to investigate the hydrolysis products of aluminium chloride as a function of sulfate concentration at pH 3.7. With the aid of computational chemistry, structural information was deduced from the chemical compositions observed with ESI-MS. Many novel types of hydrolysis products were noted, revealing that our present understanding of aluminium speciation is too simple. The role of counterions was found to be critical: the speciation of aluminium changed markedly as a function of sulfate concentration. Ab initio calculations were used to reveal the energetically most favoured structures of aluminium sulfate anions and cations selected from the ESI-MS results. Several interesting observations were made. Most importantly, the bonding behaviour of the sulfate group changed as the number of aqua ligands increased. The accompanying structural rearrangement of the clusters revealed the highly active role of sulfate as a ligand. The gas phase calculations were expanded to the aquatic environment using a conductor-like screening model. As expected, the bonding behaviour of the sulfate group in the minimum energy structures was distinctly different in the aquatic environment compared to the gas phase. Together, these methods open a new window for research in the solution chemistry of aluminium species.

Addition of NH3 to Al3O3−

Recent computational studies on the addition of ammonia (NH3) to the Al3O3- cluster anion [A. Guevara-Garcia, A. Martinez, and J. V. Ortiz, J. Chem. Phys. 122, 214309 (2005)] have motivated experimental and additional computational studies, reported here. Al3O3- is observed to react with a single NH3 molecule to form the Al3O3NH3- ion in mass spectrometric studies. This is in contrast to similarly performed studies with water, in which the Al3O5H4- product was highly favored. However, the anion PE spectrum of the ammoniated species is very similar to that of Al3O4H2-. The adiabatic electron affinity of Al3O3NH3 is determined to be 2.35(5) eV. Based on comparison between the spectra and calculated electron affinities, it appears that NH3 adds dissociatively to Al3O3-, suggesting that the time for the Al3O3-NH3 complex to either overcome or tunnel through the barrier to proton transfer (which is higher for NH3 than for water) is short relative to the time for collisional cooling in the experiment.

Al–H bond formation in hydrated aluminum oxide cluster anions

Quantum chemical calculations have been performed to investigate the interaction of a water molecule with gas phase aluminum oxide cluster anions. While oxygen-rich clusters (AlxOy-,x<y) (including Al2O3- which resembles the stoichiometry of bulk alumina) form hydroxides as the end product, many aluminum-rich clusters (AlxOy-,x>y) generate metal hydrides. These hydride species are, in many cases, 30-35 kcal/mol more stable than their hydroxide counterparts. Our observations on such competing reaction pathways may be useful to understand the catalytic role of alumina nanoparticles in many chemical reactions.

The 3D quadrupole ion trap mass spectrometer as a complete chemical laboratory for fundamental gas-phase studies of metal mediated chemistry

Electrospray ionization provides a "treasure trove" of metal containing ions whose fundamental reactivity can be studied via collision induced dissociation and ion-molecule reactions using the multistage mass spectrometry capabilities of the quadrupole ion trap mass spectrometer. Examples of metal mediated chemistry relevant to catalysis, C-C bond coupling, bioinorganic and supramolecular chemistry are highlighted.

Addition of water to Al5O4− determined by anion photoelectron spectroscopy and quantum chemical calculations

The anion photoelectron spectra of Al5O4- and Al5O5H2- are presented and interpreted within the context of quantum chemical calculations on these species. Experimentally, the electron affinities of these two molecules are determined to be 3.50(5) eV and 3.10(10) eV for the bare and hydrated cluster, respectively. The spectra show at least three electronic transitions crowded into a 1 eV energy window. Calculations on Al5O4- predict a highly symmetric near-planar structure with a singlet ground state. The neutral structure calculated to be most structurally similar to the ground state structure of the anion is predicted to lie 0.15 eV above the ground state structure of the neutral. The lowest energy neutral isomer does not have significant Franck-Condon overlap with the ground state of the anion. Dissociative addition of water to Al5O4- is energetically favored over physisorption. The ground state structure for the Al5O4- +H(2)O product forms when water adds to the central Al atom in Al5O4- with -H migration to one of the neighboring O atoms. Again, the ground state structures for the anion and neutral are very different, and the PE spectrum represents transitions to a higher-lying neutral structure from the ground state anion structure.

Improved Heteroatom Nucleophilic Addition to Electron-Poor Alkenes Promoted by CeCl3·7H2O/NaI System Supported on Alumina in Solvent-Free Conditions

Conjugate addition of heteroatom nucleophiles to carbon-carbon double bonds conjugated with a strong electron-withdrawing group is one of the most important new bond-forming strategies in synthetic organic chemistry. Among the methods for these Michael additions, Lewis acids have shown the best promoter activity, and in particular, the use of reagents impregnated over inorganic supports is rapidly increased. With the increase of environmental consciousness in chemical research, the solvent-free Michael addition has attracted our attention. In continuation of our ongoing program to develop synthetic protocols utilizing cerium trichloride, we report an extension of the CeCl(3).7H(2)O/NaI combination supported under solvent-free conditions to promote heteroatom Michael addition. Using neutral alumina (Al(2)O(3)) as solid support permits us to circumvent some of the problems associated with the procedure where the inorganic support is silica gel. The CeCl(3).7H(2)O/NaI/Al(2)O(3) system works well for hetero-Michael additions utilizing weakly nucleophiles such as imidazoles and carbamates, and also the reaction proceeds with good yields in the case of Michael acceptors different from alpha,beta-unsaturated carbonyl compounds. An important synthetic application of this our methodology is the intramolecular aza-Michael reaction in producing 4-piperidinone derivatives, which are of interest as synthetic intermediates toward important classes of heterocycles.