TiN Molecules Research Articles

Interplay between different metal–ligand binding modes in tin(II) complexes with pyridine

In this work, the π-complexation interaction between simple tin(II) molecules SnX2 (X = H, F, Cl, Br, I) and the π-cloud of pyridine (py) in a series of their model complexes SnX2·py was characterized using a variety of quantum chemical methods. Moreover, the coexistence of this interaction and the well-known σ-complexation interaction between the lone pair on the N atom of py and another SnX2 molecule was studied in the corresponding series of model complexes SnX2·py·SnX2. The interplay between the two metal–ligand binding modes was established in terms of structural changes, interaction energies, interaction energy components and topological electron density parameters. The interaction between SnX2 and py in their SnX2·py π-complexes is weak and its strength is further diminished by the σ-complexation of another SnX2 molecule, forming the SnX2·py·SnX2 complexes. The weakening is in fact mutual yet the strength of the σ-complexation interaction is reduced only marginally.

NMR Coupling Constants Based on the Bethe–Salpeter Equation in the GW Approximation

We present the first steps to extend the Green's function GW method and the Bethe-Salpeter equation (BSE) to molecular response properties such as nuclear magnetic resonance (NMR) indirect spin-spin coupling constants. We discuss both a nonrelativistic one-component and a quasi-relativistic two-component formalism. The latter describes scalar-relativistic and spin-orbit effects and allows us to study heavy-element systems with reasonable accuracy. Efficiency is maintained by the application of the resolution of the identity approximation throughout. The performance is demonstrated using conventional central processing units (CPUs) and modern graphics processing units (GPUs) for molecules involving several thousand basis functions. Our results show that a large amount of Hartree-Fock exchange is vital to provide a sufficient Kohn-Sham starting point to compute the GW quasi-particle energies. As the GW-BSE approach is generally less accurate for triplet excitations or related properties such as the Fermi-contact interaction, the admixture of the Kohn-Sham correlation kernel through the contracted BSE (cBSE) method improves the results for NMR coupling constants. This leads to remarkable results when combined with the eigenvalue-only self-consistent variant (evGW) and Becke's half and half functional (BH&HLYP) or the CAM-QTP family. The developed methodology is used to calculate the Karplus curve of tin molecules, illustrating its applicability to extended chemically relevant molecules. Here, the GW-cBSE method improves upon the chosen BH&HLYP Kohn-Sham starting points.

Inorganic "Conductive Glass" Approach to Rendering Mesoporous Metal-Organic Frameworks Electronically Conductive and Chemically Responsive.

A representative mesoporous metal-organic-framework (MOF) material, NU-1000, has been rendered electronically conductive via a robust inorganic approach that permits retention of MOF crystallinity and porosity. The approach is based on condensed-phase grafting of molecular tin species onto the MOF nodes via irreversible reaction with hydroxyl and aqua ligands presented at the node surface, a self-limiting process termed solvothermal installation (of metal ions) in MOFs (SIM, a solution-phase analog of atomic layer deposition in MOFs). Treatment of the modified MOF with aerated steam at 120 °C converts the grafted tin molecules to tetratin(IV)oxy clusters, with the clusters being sited between insulating pairs of zirconia-like nodes (the zirconium component being key to endowing the parent material with requisite chemical and thermal stability). By introducing new O-H presenting ligands on the modified-MOF node, the high-temperature steam step additionally serves to reset the material to reactive form, thus enabling a second self-limiting tin-grafting step to be run (and after further steam treatment, enabling a third). Difference-envelop-density (DED) analyses of synchrotron-derived X-ray scattering data, with and without installed tin species, show that the clusters formed after one cycle are spatially isolated, but that repetitive SIM cycling adds metal and oxygen ions in a way that enshrouds nodes, links clusters, and yields continuous one-dimensional strands of oxy-tin(IV), oriented exclusively along the c axis of the MOF. Two-probe conductivity measurements show that the parent MOF and the version containing isolated oxy-tin(IV) clusters are electrically insulating, but that the versions featuring continuous strands show an electrical conductivity of 1.8 × 10-7 S/cm after three Sn-SIM cycles. When combined with interdigitated microelectrodes, the solvent-free and conductive-glass-modified material (three Sn-SIM cycles) displays a substantial and persistent increase in electrical conductivity during exposure to 5% H2, indicating a role for dissociated H2 as an electronic dopant. The increase can be repetitively reversed by alternating H2 with air, illustrating the ability of the conductive MOF to function as a resistive sensor for H2 and suggesting further potential applications that may capitalize on the combination of high volumetric surface area, high mesoporosity, high chemical and thermal stability, and significant electrical conductivity.

Condensation Surface Temperature as a Means for Studying Film Formation Mechanisms

A rise in the condensation surface temperature during film growth is a result of energy dissipation on the condensation surface. An example of energy dissipation is the dissipation of chemical reaction heat, which releases during film deposition by reactive magnetron sputtering. The monitoring of the surface temperature during TiN film deposition by reactive (Ti–in–N2) and nonreactive (TiN–in–Ar or TiN–in–N2) sputtering methods has shown that this temperature is higher in the reactive case and decreases in the (TiN–in–Ar)–(TiN–in–N2) sequence of nonreactive sputtering modifications. It has been found that the composition and crystal structure of TiN films do not depend on the growth method and are identical to those of bulk titanium nitride. Based on these results, a formation mechanism of films obtained by the above methods has been suggested. In the case of reactive sputtering, the film was supposed to grow on the condensation surface through a reaction between titanium and nitrogen atoms. In the cases of nonreactive sputtering, the film forms from TiN molecules.

Preparation of Poly(lactic acid) Nanocomposite via Catalyst-Modified Montmorillonite

Biopolymer nanocomposite of polylactic acid was synthesized from lactic acid using tin ions exchanged Cloisite Ca++. The tin molecules between the Cloisite Ca++ layers catalyzed the lactic acid polymerization and also this clay played a role as a nanofiller. Presence of tin molecules increased the molecular weight of the polymer compared with the polymer that was synthesized with the presence of just Cloisite Ca++. Both exfoliated and intercalated nanocomposite structures were observed as the results of X-ray diffraction analysis and transmission electron microscopy images. Also, changes of polymer's thermal degradation and other thermal properties such as glass transition temperature, melting temperatures were investigated via thermogravimetric analysis and differential scanning calorimetry.

Application of a promiscuous Arthrobacter sp. from Antarctic in aerobic (R)-selective deracemization and anaerobic (S)-selective reduction

Inspired by enzyme-catalyzed reactions with microorganisms found in harsh marine environments, in which the amount of oxygen is restrict, we have shown that Arthrobacter sp. can perform different chemical transformations by switching from anaerobic to aerobic reaction conditions. Depending on the presence or absence of oxygen, either alcohol deracemization or ketone reduction with enantiocomplementary selectivities can be performed by the same microorganism. For example, reactions performed in the presence of oxygen favored the deracemization process, in which a racemic mixture of 1-(4-methylphenyl)ethanol was enriched to the (R)-alcohol in high conversion (94%) and high enantiomeric excess (94%). On the other hand, reaction in the absence of oxygen favored the reduction process, in which 4-methyl-acetophenone was converted to the (S)-alcohol in good conversion (58%) and excellent enantiomeric excess (>99%). These concepts were applied for both deracemization and enantioselective reduction of heteroatom-containing (silicon, phosphorus, tin and boron) molecules. Moreover, preparative scale reactions were also performed for both chemical processes.

Reaction of Hydrogen or Ammonia with Unsaturated Germanium or Tin Molecules under Ambient Conditions: Oxidative Addition versus Arene Elimination

The reactions of hydrogen or ammonia with germylenes and stannylenes were investigated experimentally and theoretically. Treatment of the germylene GeAr(#)(2) (Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2)) with H(2) or NH(3) afforded the tetravalent products Ar(#)(2)GeH(2) (1) or Ar(#)(2)Ge(H)NH(2) (2) in high yield. The reaction of the more crowded GeAr'(2) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)) with NH(3) also afforded a tetravalent amide Ar'(2)Ge(H)NH(2) (3), whereas with H(2) the tetravalent hydride Ar'GeH(3) (4) was obtained with Ar'H elimination. In contrast, the reactions with the divalent Sn(II) aryls did not lead to Sn(IV) products. Instead, arene eliminated Sn(II) species were obtained. SnAr(#)(2) reacted with NH(3) to give the Sn(II) amide {Ar(#)Sn(mu-NH(2))}(2) (5) and Ar(#)H elimination, whereas no reaction with H(2) could be observed up to 70 degrees C. The more crowded SnAr'(2) reacted readily with H(2), D(2), or NH(3) to give {Ar'Sn(mu-H)}(2) (6), {Ar'Sn(mu-D)}(2) (7), or {Ar'Sn(mu-NH(2))}(2) (8) all with arene elimination. The compounds were characterized by (1)H, (13)C, and (119)Sn NMR spectroscopy and by X-ray crystallography. DFT calculations revealed that the reactions of H(2) with EAr(2) (E = Ge or Sn; Ar = Ar(#) or Ar') initially proceed via interaction of the sigma orbital of H(2) with the 4p(Ge) or 5p(Sn) orbital, with back-donation from the Ge or Sn lone pair to the H(2) sigma* orbital. The subsequent reaction proceeds by either an oxidative addition or a concerted pathway. The experimental and computational results showed that bond strength differences between germanium and tin, as well as greater nonbonded electron pair stabilization for tin, are more important than steric factors in determining the product obtained. In the reactions of NH(3) with EAr(2) (E = Ge or Sn; Ar = Ar(#) or Ar'), the divalent ArENH(2) products were calculated to be the most stable for both Ge and Sn. However the tetravalent amido species Ar(2)Ge(H)NH(2) were obtained for kinetic reasons. The reactions with NH(3) proceed by a different pathway from the hydrogenation process and involve two ammonia molecules in which the lone pair of one NH(3) becomes associated with the empty 4p(Ge) or 5p(Sn) orbital while a second NH(3) solvates the complexed NH(3) via intermolecular N-H...N interactions.

Role of the composition and type of film-forming species in film structure formation

We present the results of an investigation into correlation between the type of film-forming species (FFS) (atoms and molecules) and the structure of the films deposited by reactive magnetron sputtering of W-30 at.%Ti alloy in an Ar–N2 working gas. Mass-spectrometric studies have revealed that the FFS flux contains both atomic (W, Ti, N) and molecular (WN, TiN) species and the flux composition depends on the nitrogen partial pressure in a working gas. At low nitrogen partial pressures (PN2<0.1 Pa) the FFS flux is mainly composed of W, Ti atoms and WN, TiN molecules and the film deposited from such flux is formed of biphase [W+(W,Ti)2 N] composite material with extremely small (approx. 10 nm) grain size. The films deposited from the flux containing mostly metal and nitrogen atoms (higher nitrogen partial pressures PN2>0.2 Pa) are formed from monophase (W,Ti)2 N material with 2–4 times larger crystallite size. The microhardness of the films deposited from the FFS flux containing mainly metal atoms and nitride molecules was noticeably higher than that of the films formed mostly from metal and nitrogen atoms.

Role of the composition and type of film-forming species in film structure formation

We present the results of an investigation into correlation between the type of film-forming species (FFS) (atoms and molecules) and the structure of the films deposited by reactive magnetron sputtering of W-30 at.%Ti alloy in an Ar–N 2 working gas. Mass-spectrometric studies have revealed that the FFS flux contains both atomic (W, Ti, N) and molecular (WN, TiN) species and the flux composition depends on the nitrogen partial pressure in a working gas. At low nitrogen partial pressures ( P N2<0.1 Pa) the FFS flux is mainly composed of W, Ti atoms and WN, TiN molecules and the film deposited from such flux is formed of biphase [W+(W,Ti) 2 N] composite material with extremely small (approx. 10 nm) grain size. The films deposited from the flux containing mostly metal and nitrogen atoms (higher nitrogen partial pressures P N2>0.2 Pa) are formed from monophase (W,Ti) 2 N material with 2–4 times larger crystallite size. The microhardness of the films deposited from the FFS flux containing mainly metal atoms and nitride molecules was noticeably higher than that of the films formed mostly from metal and nitrogen atoms.

Gas Phase Photoproduction of Diatomic Metal Nitrides During Metal Nitride Laser Chemical Vapor Deposition.

Photolysis of M(NEt2)4 in the gas phase produces diatomic MN molecules (M = Ti, Zr, Hf). TiN and ZrN molecules were identified in the gas phase under CVD conditions by emission spectroscopy and time-of-flight mass spectroscopy. Nanostructured deposits of TiN were formed on quartz substrates by irradiating Ti(NEt2)4 gas at 355 nm. These studies demonstrate the gas phase formation of diatomic molecules having the same stoichiometry as that of the desired solid-phase deposit.

Preparation of Ultrafine Monodispersed Indium−Tin Oxide Particles in AOT-Based Reverse Microemulsions as Nanoreactors

Monodispersed ultrafine indium−tin oxide (ITO) particles were prepared in AOT-based reverse microemulsions with indium nitrate and tin chloride dissolved in water droplets. The particle size distribution, calcination rate, chemical composition, and electrical resistivity of pellets manufactured with particles were measured and compared with analogous measurements of particles formed by bulk precipitation method. ITO particles formed in microemulsions showed a narrower size distribution, faster calcination rate, and lower electrical resistivity. It was also confirmed that tin molecules are doped into the indium oxide homogeneously rather than forming a discrete tin oxide domain in indium−tin oxide particles formed in microemulsions.

Shock tube study of the formation of TiN molecules and particles

The formation of both TiN molecules and particles in TiCl 4/NH 3/H 2 systems was studied behind reflected shock waves at temperatures between 1400 and 2500 K and pressures between land 2.3 bar by applying laser absorption spectroscopy. Only in a small temperature and concentration range, molecular absorption of TiN in the A 2 Π ← X 2 Σ system was observed. In most experiments, light extinction by TiN particles was found, showing an induction time that only depends on temperature and TiCl 4 concentration but not on NH 3, H 2 or on total pressure.

Mass and energy resolved detection of ions and neutral sputtered species incident at the substrate during reactive magnetron sputtering of Ti in mixed Ar+N2 mixtures

The fluxes of ions and neutral sputtered particles incident at the growth surface during the deposition of TiN by reactive magnetron sputtering from a Ti target in mixed Ar+N2 discharges were determined using a combination of in situ double-modulation mass spectrometry, Langmuir probe, discharge, deposition rate, and film composition measurements. The N2 fraction fN2 in the discharge was varied from 0 to 1 with the total pressure maintained at 3 mTorr (0.4 Pa). Target nitridation, observed directly through the detection of sputter-ejected TiN molecules, was found to occur over the narrow fN2 range between ≂0.035 and 0.06. With fN2&amp;lt;0.1, more than 94% of the ion flux incident at the substrate is Ar+ while for pure N2 discharges, N+2 accounts for more than 95% of the incident ions. Both the incident Ar+ and N+2 ion fluxes are highly monoenergetic with energies corresponding to eVs, where Vs is the applied negative substrate bias with respect to the plasma potential. However, the energy distributions of incident Ti+ and N+ ions are extended due to the high-energy tails in their sputter-ejection energy distributions. The primary sputter-ejected particles are Ti and N atoms. TiN, TiN+, and Ti+ do not contribute significantly to film growth kinetics.

Nitridation induced on metal surface by Ar +-ion impact under N 2 atmosphere

Nitridation of surfaces has been examined by bombarding transition metals with 0.3−8 keV Ar+-ions (4 μ A cm−2) under a nitrogen atmosphere (1 × 10−3 Pa) at room temperature. The surface N:Metal ratio determined by XPS increased with irradiation time at lower fluences and reached a plateau at higher fluences. Using reaction kinetics for the nitridation of a Ti target allows the rate of nitride formation, defined as the number of TiN molecules produced by one incident ion, to be determined. For this procedure it is estimated to be about 17. The saturation value of the N:Me ratio for various metal targets increased with decreasing Gibbs free energy for the thermochemical formation of a nitride. This suggests that the dominant mechanisms for ion-induced nitridation are the thermochemical processes which occur at the bombardment area of the target surface.

Mössbauer studies of FeSn molecules isolated in rare-gas solids and SCF–Xα–scattered-wave molecular-orbital analyses of Sn2and FeSn diatomic molecules

Iron–tin molecules were isolated in rare-gas solids and studied using both 57Fe and 119Sn Mössbauer isotopes. Experiments at very dilute concentrations were performed to detect FeSn diatomic molecules. Larger clusters were identified by concentration dependence studies and Monte Carlo calculations. The 57Fe and 119Sn isomer shifts (IS) for FeSn diatomic molecules suggest a covalent bonding between Fe and Sn atoms. Similar behaviour was observed for large iron–tin clusters (FexSny; x, y 3). SCF–Xα–SW calculations were performed for Sn2 and FeSn diatomic molecules. Sn2 shows a 3∑g ground state and gives a quadrupole splitting (QS) consistent with the experimentally measured value at an equilibrium distance of 2.75 Å. The most probable ground state for FeSn is a 7Δ{σ2(3dFe, 5sSn)σ1(3dFe)σ2(4sFe 5pSn)σ2(4pFe,5pSn)π2.75(3dFe)δ2.25(3dFe)π1(5pSn)} configuration which gives the QS values for iron and tin atoms in agreement with the experimentally measured values at an equilibrium distance of 2.5 Å.

Electronic Structure and Ground-State Properties of Titanium Mononitride

Electronic-band systems recently have been observed and attributed to the TiN and MoN molecules, but they have not been analyzed. This is the only available experimental evidence for the existence of nitride molecules of the transition elements, although oxide and halide molecules of these metals are well known and have been studied extensively. Approximate wavefunctions based on the matrix Hartree—Fock method of Roothaan have been calculated for TiN in this study to provide some information not otherwise available on the ground-state-term type and molecular properties of this molecule. It is found that TiN has a 2Σ+ ground state at re≃1.55 Å and a reasonable dissociation energy of about 5 eV. For thermodynamic reasons, however, gaseous TiN is unstable in equilibrium systems and absent in measurable concentrations.