Density functional theory and coupled cluster theory are used to study the hydrolysis reactions of (TiO2) n (n = 1–4) nanoclusters to provide insight into H2O activation on TiO2. The singlet–triplet energy gaps of (TiO2) n are predicted to lie between 30 and 65 kcal/mol, depending on the cluster size and structure, consistent with our previous studies. The excitation energies for the various hydroxides, Ti n O2n–m (OH)2m (n = 1–4, 1 ≤ m ≤ n) are predicted to be, in general, higher than those for (TiO2) n . The partial charge on Ti increases as the Ti O bonds are replaced with the Ti–OH bonds. The TiO and Ti–O frequencies in the triplet state of (TiO2) n and Ti n O2n–m (OH)2m are, in general, lower than those in the singlet state. The first H2O adsorption (physisorption) energies for these TiO2 nanoclusters are predicted to be −10 to −35 kcal/mol for the singlet states and −10 to −50 kcal/mol for the triplet states. These physisorption energies depend on the cluster size and the site of adsorption, consistent with existing experimental studies. In general, H2O prefers to physisorb on the Ti site with one TiO bond and two Ti–O bonds and at the Ti site with no TiO bond and three Ti–O bonds. The first hydrolysis (dissociative chemisorption) reaction energies of the TiO2 nanoclusters are predicted to be −20 to −70 kcal/mol for the singlet states and −15 to −80 kcal/mol for the triplet states. Both singlet and triplet potential energy surfaces for the hydrolysis are calculated. Our calculations show that H2O readily reacts with both the singlet and the triplet states of the TiO2 nanoclusters to form the hydroxides with reaction barriers of 5–16 kcal/mol for the singlet states and 5–26 kcal/mol for the triplet states for the first hydrolysis steps, which are, in general, less than the H2O complexation energies. Because H2O splitting to form H2 and O2 is a strongly endothermic process by ∼116 kcal/mol, photocatalytic processes are necessary only in the subsequent steps.

The hydrolysis of titanium tetrachloride (TiCl(4)) to produce titanium dioxide (TiO(2)) nanoparticles has been studied to provide insight into the mechanism for forming these nanoparticles. We provide calculations of the potential energy surfaces, the thermochemistry of the intermediates, and the reaction paths for the initial steps in the hydrolysis of TiCl(4). We assess the role of the titanium oxychlorides (Ti(x)O(y)Cl(z); x = 2-4, y = 1, 3-6, and z = 2, 4, 6) and their viable reaction paths. Using transition-state theory and RRKM theory, we predicted rate constants including the effect of tunneling. Heats of formation at 0 and 298 K are predicted for TiCl(4), TiCl(3)OH, TiOCl(2), TiOClOH, TiCl(2)(OH)(2), TiCl(OH)(3), Ti(OH)(4), and TiO(2) using the CCSD(T) method with correlation consistent basis sets extrapolated to the complete basis set limit and compared with the available experimental data. Clustering energies and heats of formation are calculated for neutral clusters. The calculated heats of formation were used to study condensation reactions that eliminate HCl or H(2)O. The reaction energy is substantially endothermic if more than two HCl molecules are eliminated. The results show that the mechanisms leading to formation of TiO(2) nanoparticles and larger ones are complicated and will have a strong dependence on the experimental conditions.

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for KrF+, KrF-, KrF2, KrF3+, KrF4, KrF5+, and KrF6 from coupled-cluster theory (CCSD(T)) calculations with effective core potential correlation-consistent basis sets for krypton. To achieve near chemical accuracy (+/-1 kcal/mol), three corrections were added to the complete basis set binding energies based on frozen core coupled-cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, and a correction for first-order atomic spin-orbit effects. Vibrational zero point energies were computed at the coupled-cluster level of theory. The calculated value for the heat of formation of KrF2 is in excellent agreement with the experimental value. Contrary to the analogous xenon fluorides, KrF2, KrF4, and KrF6 are predicted to be thermodynamically unstable with respect to loss of F2. An analysis of the energetics of KrF4 and KrF6 with respect to fluorine atom loss together with calculations of the transition states for the intramolecular loss of F2 show that fluorine atom loss is the limiting factor determining the kinetic stabilities of these molecules. Whereas KrF4 possesses a marginal energy barrier of 10 kcal/mol toward fluorine atom loss and might be stable at moderately low temperatures, the corresponding barrier in KrF6 is only 0.9 kcal/mol, suggesting that it could exist only at very low temperatures. Although the simultaneous reactions of either two or four fluorine atoms with KrF2 to give KrF4 or KrF6, respectively, are exothermic, they do not represent feasible synthetic approaches because the attack of the fluorine ligands of KrF2 by the fluorine atoms, resulting in F2 abstraction, is thermodynamically favored over oxidative fluorination of the krypton central atom. Therefore, KrF6 could exist only at very low temperatures, and even the preparation of KrF4 will be extremely difficult.

N(2)F(+) salts are important precursors in the synthesis of N(5)(+) compounds, and better methods are reported for their larger scale production. A new, marginally stable N(2)F(+) salt, N(2)F(+)Sn(2)F(9)(-), was prepared and characterized. An ordered crystal structure was obtained for N(2)F(+)Sb(2)F(11)(-), resulting in the first observation of individual N[triple bond]N and N-F bond distances for N(2)F(+) in the solid phase. The observed N[triple bond]N and N-F bond distances of 1.089(9) and 1.257(8) A, respectively, are among the shortest experimentally observed N-N and N-F bonds. High-level electronic structure calculations at the CCSD(T) level with correlation-consistent basis sets extrapolated to the complete basis limit show that cis-N(2)F(2) is more stable than trans-N(2)F(2) by 1.4 kcal/mol at 298 K. The calculations also demonstrate that the lowest uncatalyzed pathway for the trans-cis isomerization of N(2)F(2) has a barrier of 60 kcal/mol and involves rotation about the N=N double bond. This barrier is substantially higher than the energy required for the dissociation of N(2)F(2) to N(2) and 2 F. Therefore, some of the N(2)F(2) dissociates before undergoing an uncatalyzed isomerization, with some of the dissociation products probably catalyzing the isomerization. Furthermore, it is shown that the trans-cis isomerization of N(2)F(2) is catalyzed by strong Lewis acids, involves a planar transition state of symmetry C(s), and yields a 9:1 equilibrium mixture of cis-N(2)F(2) and trans-N(2)F(2). Explanations are given for the increased reactivity of cis-N(2)F(2) with Lewis acids and the exclusive formation of cis-N(2)F(2) in the reaction of N(2)F(+) with F(-). The geometry and vibrational frequencies of the F(2)N=N isomer have also been calculated and imply strong contributions from ionic N(2)F(+) F(-) resonance structures, similar to those in F(3)NO and FNO.