The bottom-up formation of MgxOy(OH)z nanoparticles leading to Mg(OH)2 nanoparticles was modeled in two steps by using an evolutionary global optimization approach: (1) the formation of small MgnOm+nH2m clusters via the hydrolysis of (MgO)n and (2) the formation of multilayered (Mg(OH)2)n clusters via monolayer stacking. The sheet-like (Mg(OH)2)n structures were predicted as the energetically favorable reaction products for the (MgO)n + nH2O reaction, whereas more compact structures were found to dominate for the products of (MgO)n + mH2O, m < n. The stepwise hydrolysis reactions most likely follow the compact reaction path until the crossover point is reached. Multistep structural rearrangements are required for the conversion between the compact products and the sheet-like products even after the crossover point. The protective shell formed by the hydroxyl groups may inhibit the further hydrolysis reaction of the compact products, even though the hydrolysis reactions are both exothermic and exergonic; such an effect is less significant in the smaller structures. The hydrolysis of (MgO)n is not suitable for the preparation of the large sized (Mg(OH)2)n nanoparticles but may be used to synthesize the ultrasmall (Mg(OH)2)n nanoparticles. A fragment-based model was used to determine the structure-energy relationship for the monolayered (sheet-like) and multilayered (Mg(OH)2)n nanoparticles. The normalized clustering energy as a function of the size n was obtained for the raw particles and for the particles including solvent effects. The thermodynamically favored (Mg(OH)2)n nanoparticle types are (1) rhombic monolayers for n < 40, (2) hexagonal monolayers for 40 < n < 53, (3) rhombic multilayers for 53 < n < 78, and (4) hexagonal multilayers for n > 78 in vacuum at 0 K. In the presence of solvent, the critical sizes for the transition of the dominating particle shapes are shifted, and the growth rates in each dimension also change. This work provides a basis for controlling nanoparticle morphologies in the selective bottom-up synthesis of brucite-like (Mg(OH)2)n-related nanoparticles.

Adsorption of CO2 to uranium oxide, (UO3)n, clusters was modeled using density functional theory (DFT) and coupled cluster theory (CCSD(T)). Geometries and reaction energies were predicted for carbonate formation (chemisorption) and Lewis acid–base addition of CO2 (physisorption) to these (UO3)n clusters. Chemisorption of multiple CO2 moieties was also modeled for dimer and trimer clusters. Physisorption and chemisorption were both predicted to be thermodynamically allowed for (UO3)n clusters, with chemisorption being more thermodynamically favorable than physisorption. The most energetically favored (UO3)3(CO2)m clusters contain tridentate carbonates, which is consistent with solid-state and solution structures for uranyl carbonates. The calculations show that CO2 exposure is likely to convert (UO3)n to uranyl carbonates.

Density functional theory (DFT) and coupled cluster theory (CCSD(T)) were used to study the addition of CO2 to group 4 (MO2)n and group 6 (MO3)n (n = 1, 2, 3) nanoclusters. The structures and energetics arising from Lewis acid–base addition (physisorption) and formation of CO32– (chemisorption) of CO2 to these clusters were predicted. Physisorption and chemisorption of CO2 are predicted to be thermodynamically allowed for group 4 (MO2)n clusters, with chemisorption being more favored energetically. Correlations of the ligand binding energies (LBEs) for the group 4 clusters are made with the fluoride affinities and M–O and M═O bond strengths of the clusters. The LBEs for chemisorption on the Zr and Ti clusters are consistent with published experimental and computational studies of bulk solids. Physisorption LBEs for the Ti and Zr clusters are more exothermic than the bulk values, as the cluster models allow for better relaxation at the metal sites. Chemisorption is not predicted to occur with group 6 (MO3)n clusters, as the larger chemisorbed structures were all found to be metastable. CO2 is predicted to weakly physisorb to (WO3)n with physisorption correlating with the Lewis acidity of the metal site.

Homoleptic thorium isocyanide complexes have been prepared via the reactions of laser-ablated thorium atoms and (CN)2 in a cryogenic matrix, and the structures of the products were characterized by infrared spectroscopy and theoretical calculations. Thorium atoms reacted with (CN)2 under UV irradiation to form the oxidative addition product Th(NC)2, which was calculated to have closed-shell singlet ground state with a bent geometry. Further reaction of Th(NC)2 and (CN)2 resulted in the formation of Th(NC)4, a molecule with a tetrahedral geometry. Minor products such as ThNC and Th(NC)3 were produced upon association reactions of CN with Th and Th(NC)2. Homoleptic thorium cyanide isomers Th(CN)x (x = 1–4) are predicted to be less stable than the corresponding isocyanides. The C–N stretches of thorium cyanides were calculated to be between 2170 and 2230 cm–1 at the B3LYP level, more than 120 cm–1 higher than the N–C stretches of isocyanides and with much weaker intensities. No experimental absorptions appeared where Th(CN)x should be observed.

Correlated molecular orbital theory at the coupled cluster CCSD(T) level with augmented correlation consistent basis sets including F12 explicit correlation has been used to predict the structure and energetic properties of the isomers of [C,N,O,P] and [C,N,S,P]. The predicted ground states are the species derived from a trivalent P with a P═O or P═S bond and a cyano group bonded to the P. The other low energy isomers are the isonitriles and they are 1.4 kcal/mol and 6.6 less stable than the ground state for P═O and P═S, respectively. An analysis of the bond energies is provided and the values are compared to the corresponding [N,N,C,O] isomers. Data are provided for searching for these species in interstellar regions.

The low-energy isomers of Irx(CO)y(NHC)z (x = 1, 2, 4) are investigated with density functional theory (DFT) and correlated molecular orbital theory at the coupled cluster CCSD(T) level. The structures, relative energies, ligand dissociation energies, and natural charges are calculated. The energies of tetrairidium cluster are predicted at the CAM-B3LYP level that best fit the CCSD(T) results compared with the other four functionals in the benchmark calculations. The NHC’s behave as stronger σ donors compared with CO’s and have higher ligand dissociation energies (LDEs). For smaller isomers, the increase in the LDEs of the CO’s and the decrease in the LDEs of the NHC’s as more NHC’s are substituted for CO’s are due to π-back-bonding and electron repulsion, whereas the trend of how the LDEs change for larger isomers is not obvious. We demonstrate a μ3-CO resulting from the high electron density of the metal centers in these complexes, as the bridging CO’s and the μ3-CO’s can carry more negative charge and stabilize the isomers. Comparison of calculations for a mixed tetrairidum cluster consisting of two calixarene-phosphine ligands and a single calixarene-NHC ligand in the basal plane demonstrated good agreement in terms of both the ligand substitution symmetry (C3v derived), as well as the infrared spectra. Similar comparisons were also performed between calculations and experiment for novel monosubstituted calixarene-NHC tetrairidium clusters.

AbstractMgO-supported osmium dioxo species, described as Os(=O)2{−Osupport}1 or 2 (the brackets denote O atoms of the MgO surface), formed from Os3(CO)12 via supported Os(CO)2, and characterized by spectroscopy, microscopy, and theory, react with ethylene at 298 K to form osmium glycol species or with CO to give osmium mono- and di-carbonyls. Os(=O)2{−Osupport}1 or 2 is the precursor of a CO oxidation catalyst characterized by a turnover frequency of 4.0×10−3 (molecules of CO)/(Os atom×s) at 473 K; the active species are inferred to be osmium monocarbonyls. The structures and frequencies calculated at the level of density functional theory with the B3LYP functional bolster the experimental results and facilitate structural assignments. The lowest-energy structures have various osmium oxidation and spin states. The results demonstrate not only new chemistry of the supported single-site catalysts but also their complexity and the value of complementary techniques used in concert to unravel the chemistry.

The total atomization energies for BeH and BeH2 have been calculated using the Feller–Peterson–Dixon approach to better than ±1 kcal/mol. The calculations are based on CCSD(T) all-electron calculations extrapolated to the complete limit, and CCSDT and CCSDTQ corrections are included. A scalar relativistic correction and a diagonal Born–Oppenheimer correction are included. Accurate zero-point energies are used. The total atomization energies at 0 K are 47.7 kcal/mol for BeH and 140.0 kcal/mol for BeH2 with error of at most ±0.3 kcal/mol.

Thorium atoms from laser ablation react with phosphine during condensation in excess argon to produce two new infrared absorptions at 1467.2 and 1436.6 cm–1 near weak bands for ThH and ThH2, which increase on annealing to 25 and 30 K, indicating spontaneous reactions. Analogous experiments with uranium produced two similar bands at 1473.4 and 1456.7 cm–1 above UH at 1423.8 cm–1 and another absorption at 1388.2 cm–1. Electronic structure calculations at the coupled cluster CCSD(T) for Th and density functional theory calculations for U as well as their proximity to other actinide hydride absorptions support assignments of these bands to the simplest molecules HP═ThH2, HP═UH2, and PH2–UH. Arsine gave the analogous products HAs═ThH2, HAs═UH2, and AsH2–UH. The HE═AnH2 molecules (E = P, As; An = Th, U) have strong agostic An–H(E) interactions with H–E–An angles in the range of 60–64°. The calculated agostic bond distances are 9% to 12% longer than terminal single An–H bonds, which suggests that these strong agostic bonds can be considered as bridge bonds since similar relationships are found for the dibridged M2H6 molecules (M = Al, Ga, In). The NBO analysis and the molecular orbitals show the presence of a σ and a π bond for HE═AnH2 molecules that are heavily polarized with most of the density on the P or As.

The reactions of laser-ablated lanthanide metal atoms with hydrogen peroxide or hydrogen plus oxygen mixtures have been studied experimentally in a solid argon matrix and theoretically with the ab initio MP2 and CCSD(T) methods. The Ln(OH)3 and Ln(OH)2 molecules and Ln(OH)2+ cations are the major products, and the reactions to form those hydroxides are predicted to be highly exothermic at the CCSD(T) level. Vibronic interactions are hypothesized to contribute to the abnormalities in deuterium shifts for Ln–OH(D) stretching modes for several hydroxides, consistent with CASSCF calculations. Additional new absorptions were assigned as HLnO or LnOH and OLnOH molecules. The tetrahydroxides of Ce, Pr, and Tb have also been observed. These reactive intermediates were identified from their matrix infrared spectra by using D2O2, HD, D2, 16,18O2, and 18O2 isotopic substitution, by matching observed frequencies with values calculated by electronic structure methods, and by following the trends observed in frequencies going through different lanthanide metal hydroxide series across the periodic table. The lanthanides are in the +II oxidation state for Ln(OH)2 and are in the +III oxidation state for Ln(OH)3 and Ln(OH)2+.

•Addition of SO2 to the Group IV (MO2)n and VI (MO3)n (n = 1, 2, 3) nanoclusters.•Lewis acid-base addition (physisorption) or SO32−/SO42− formation (chemisorption)•Mo and W clusters dominated by physisorption and Cr by SO42− chemisorption.•Group IV clusters have both physisorption and chemisorption by SO32− formation.•Energies calculated at the CCSD(T) using large basis sets.The addition of SO2 to the Group IV (MO2)n and VI (MO3)n (n = 1, 2, 3) nanoclusters was studied using density functional theory (DFT) and coupled cluster theory (CCSD(T)). Structures and ligand binding energies were predicted for the Lewis acid-base addition (physisorption), or SO32− or SO42− formation (chemisorption) of SO2 to these clusters. Physisorption is predicted to be thermodynamically allowed for the Mo and W clusters at 298K, and for Cr only at lower temperatures. Chemisorption by SO42− formation is thermodynamically allowed only for Cr clusters due to the higher reducibility of the metal center. Correlations were made between the ligand binding energies (LBEs) of the (MO3)nSO2 clusters and the chemical properties of the parent (MO3)n clusters (Lewis acidity, reducibility, and MO and MO bond strengths). Physisorption and chemisorption by SO32− formation is predicted to be thermodynamically possible for Group IV clusters, and SO4−2 formation is predicted not to occur, suggesting that sulfate formation does not proceed by the direct reaction of a pure metal oxide surface and SO2.Download high-res image (74KB)Download full-size image

The structures of TiO2 ultra-small nanoparticles (USNPs) at the atomistic level have been predicted because of their potential importance in catalytic, environmental, biological and energy applications. Low energy (TiO2)n clusters and USNPs (n up to 80 at the B3LYP/DZVP2 level, and up to 384 at the PM6 level) were found using a novel bottom-up global optimization approach that is based on all-atom real-space calculations. These structures include USNPs that belong to 1-D, 2-D and 3-D USNP series where all the members share the same fragment types and local translational symmetries. Most of the metastable 2-D and 3-D USNPs contain tubular building blocks similar to the 1-D USNPs. The 3-D USNPs that resemble the bulk anatase are predicted to be energetically favorable structures for 64 ≤ n ≤ 384. A fragment-based model was developed to relate the energy with geometry for the 1-D, 2-D and 3-D USNPs. Surface energy densities were predicted for surface fragments at the different positions of the USNPs using this new model. Based on the predicted surface energy densities and the partial density of states, the most catalytically active sites for the anatase-like 3-D USNPs were predicted to be the kink sites on Face-x surfaces consisting of an octahedral-Ti, the step (edge) sites between the Face-x and Face-y surfaces consisting of a square pyramidal-Ti (on Face-x), and the step sites consisting of a trigonal bipyramidal Ti on the Face-y surfaces.

Reactions of laser ablated cerium atoms with hydrogen peroxide or hydrogen and oxygen mixtures diluted in argon and condensed at 4 K produced the Ce(OH)3 and Ce(OH)2 molecules and Ce(OH)2+ cation as major products. Additional minor products were identified as the Ce(OH)4, HCeO, and OCeOH molecules. These new species were identified from their matrix infrared spectra with D2O2, D2, and 18O2 isotopic substitution and correlating observed frequencies with values calculated by density functional theory. We find that the amounts of Ce(OH)3 and of the Ce(OH)2+ cation increase on UV (λ > 220 nm) photolysis, while Ce(OH)2, Ce(OH)4, and HCeO are photosensitive. The observed major species for Ce are in the +III or +II oxidation state, and the minor product, Ce(OH)4, is in the +IV oxidation state. The calculations for the vibrational frequencies with the B3LYP functional agree well with the experiment. The NBO analysis shows significant backbonding to the metal 4f and 5d orbitals for the closed shell species. Most open shell species have the excess spin in the 4f with paired spin in the 5d due to backbonding. The heats of formation of the observed species were derived from the available data from experiment and the calculated reaction energies. The major products in this study are different from similar reactions for Th where the tetrahydroxide was the major species.

The heats of formation and the normalized clustering energies (NCEs) for the group 4 and group 6 transition metal oxide (TMO) trimers and tetramers have been calculated by the Feller–Peterson–Dixon (FPD) method. The heats of formation predicted by the FPD method do not differ much from those previously derived from the NCEs at the CCSD(T)/aT level except for the CrO3 nanoclusters. New and improved heats of formation for Cr3O9 and Cr4O12 were obtained using PW91 orbitals instead of Hartree-Fock (HF) orbitals. Diffuse functions are necessary to predict accurate heats of formation. The fluoride affinities (FAs) are calculated with the CCSD(T) method. The relative energies (REs) of different isomers, NCEs, electron affinities (EAs), and FAs of (MO2)n (M = Ti, Zr, Hf, n = 1–4) and (MO3)n (M = Cr, Mo, W, n = 1–3) clusters have been benchmarked with 55 exchange-correlation density functional theory (DFT) functionals including both pure and hybrid types. The absolute errors of the DFT results are mostly less than ±10 kcal/mol for the NCEs and the EAs and less than ±15 kcal/mol for the FAs. Hybrid functionals usually perform better than the pure functionals for the REs and NCEs. The performance of the two types of functionals in predicting EAs and FAs is comparable. The B1B95 and PBE1PBE functionals provide reliable energetic properties for most isomers. Long range corrected pure functionals usually give poor FAs. The standard deviation of the absolute error is always close to the mean errors, and the probability distributions of the DFT errors are often not Gaussian (normal). The breadth of the distribution of errors and the maximum probability are dependent on the energy property and the isomer.

The prediction of the heats of formation of group IV and group VI metal oxide monomers and dimers with the coupled cluster CCSD(T) method has been improved by using Kohn–Sham density functional theory (DFT) and Brueckner orbitals for the initial wave function. The valence and core–valence contributions to the total atomization energies for the CrO3 monomer and dimer are predicted to be significantly larger than when using the Hartree–Fock (HF) orbitals. The predicted heat of formation of CrO3 with CCSD(T)/PW91 is consistent with previous calculations including high-order corrections beyond CCSD(T) and agrees well with the experiment. The improved heats of formation with the DFT and Brueckner orbitals are due to these orbitals being closer to the actual orbitals. Pure DFT functionals perform slightly better than the hybrid B3LYP functional due to the presence of exact exchange in the hybrid functional. Comparable heats of formation for TiO2 and the second- and the third-row group IV and group VI metal oxides are predicted well using either the DFT PW91 orbitals, Brueckner orbitals, or HF orbitals. The normalized clustering energies for the dimers are consistent with our previous work except for a larger value predicted for Cr2O6. The prediction of the reaction energy for UF6 + 3Cl2 → UCl6 + 3F2 was significantly improved with the use of DFT or Brueckner orbitals as compared to HF orbitals.

A series of substituted 9-borafluorenes were studied both experimentally and computationally in order to assess substituent effects on the optical and electronic properties and the stability of 9-borafluorenes. The previously unknown 9-substituted-9-borafluorenes MesFBF (MesF = 2,4,6-tris(trifluoromethyl)phenyl), TipBF(OMe)2 (Tip = 2,4,6-tris(triisopropyl)phenyl, (OMe)2= methoxy at the borafluorene 3 and 6 positions), and iPr2NBF (iPr2N = diisopropylamino) were synthesized and structurally characterized. The previously reported TipBF, ClBF (9-chloro-9-borafluorene) and tBuOBF (9-(tert-butoxy)-9-borafluorene) were also included in this study. All of the aryl borafluorenes (TipBF, TipBF(OMe)2, MesFBF), and tBuOBF are moderately air-stable. Both iPr2NBF and ClBF degrade rapidly in air. Cyclic voltammogram measurements and density functional theory (DFT) calculations reveal that (a) borafluorenes have higher electron affinities relative to comparable boranes and (b) substituents have a strong influence on the lowest unoccupied molecular orbital (LUMO) levels of borafluorenes but less influence over the highest occupied molecular orbital (HOMO) levels. The DFT calculations show that, in general, borafluorenes exhibit low electron reorganization energies, a predictor of good electron mobility. However, the MesF group, which is finding popularity as a stabilizing group in borane chemistry, significantly increases the electron reorganization energy of MesFBF compared to the other borafluorenes. The Lewis acidities of the borafluorenes were probed using Et3P═O as a Lewis base (the Gutmann–Beckett method) and found to be dictated primarily by steric considerations. Calculated fluoride affinities (Lewis acidities) correlate with the LUMO energies of the borafluorenes. UV–visible and fluorescence spectroscopic measurements showed that compared to the Tip substituent, the MesF, Cl, and methoxy groups only cause subtle changes to the optical properties of the borafluorenes. The absorption spectra of both iPr2NBF and tBuOBF are blue-shifted due to substituent π-backbonding with the p-orbital on boron. The results of this study provide insights into substituent effects on conjugated boron systems and will help in the design of future boron containing materials.

Correlated molecular orbital theory at the coupled cluster CCSD(T) level with augmented correlation consistent basis sets has been used to predict the structure and energetic properties of the isomers of [Si,N,S] and [Si,P,S]. The predicted ground states are linear 2SNSi and cyclic 2SPSi. The other two isomers are predicted to be ∼20 to 50 kcal/mol less stable than the ground state. The excess spin is mainly on S for 2SNSi and on P for 2SPSi. The calculated total atomization energies with the CBS limits derived from different methods differ by ∼2 kcal/mol. The results provide the best available heats of formation for these species. The bond dissociation energies (BDEs) in 2SNSi are comparable to those in the corresponding diatomic molecules. For cyclic 2SPSi, the formation of 4P + 2SSi requires less energy than the other bond dissociation processes. The BDEs in the higher energy isomers are substantially smaller than the corresponding diatomic species.

Reactions of laser–ablated U atoms with (CN)2 produce UNC, U(NC)2, and U(NC)4 as the major products, identified from their Ar matrix infrared spectra and precursors partially and fully substituted with 13C and 15N. Mixed isotopic multiplets substantiate product stoichiometries. Band positions and quantum chemical calculations verify the isocyanide bonding.

•Predicted ligand binding energies for zeolite supported single site metal catalysts.•Small Al(OH)4M model and a large M-Zeo(48-T) give similar results for energies.•Calculated vibrational frequencies are in agreement with experiment.•Carbene and carbyne isomeric (to ethylene) ligands exist as stable intermediates.•PES for ethylene hydrogenation depends on the ligands and the metal.The chemistry of zeolite-supported site-isolated cobalt, rhodium, and iridium complexes that are essentially molecular was investigated with density functional theory (DFT) and the results compared with experimentally determined spectra characterizing rhodium and iridium species formed by the reactions of Rh(C2H4)2(acac) and Ir(C2H4)2(acac) (acac = acetylacetonate) with acidic zeolites such as dealuminated HY zeolite. The experimental results characterize ligand exchange reactions and catalytic reactions of adsorbed ligands, including olefin hydrogenation and dimerization. Two molecular models were used to characterize various binding sites of the metal complexes in the zeolites, and the agreement between experimental and calculated infrared frequencies and metal–ligand distances determined by extended X-ray absorption fine structure spectroscopy was generally very good. The calculated structures and energies indicate a metal–support-oxygen (M(I)O) coordination number of two for most of the supported complexes and a value of three when the ligands include the radicals C2H5 or H. The results characterizing various isomers of the supported metal complexes incorporating hydrocarbon ligands indicate that some carbene and carbyne ligands could form. Ligand bond dissociation energies (LDEs) are reported to explain the observed reactivity trends. The experimental observations of a stronger MCO bond than M(C2H4) bond for both Ir and Rh match the calculated LDEs, which show that the single-ligand LDEs of the mono and dual-ligand complexes for CO are ∼12 and ∼15 kcal/mol higher in energy (when the metal is Rh) and ∼17 and ∼20 kcal/mol higher (when the metal is Ir) than the single-ligand LDEs of the mono and dual ligand complexes for C2H4, respectively. The results provide a foundation for the prediction of the catalytic properties of numerous supported metal complexes, as summarized in detail here.Potential energy surface (PES) for the hydrogenation reaction of C2H4 on a model of a single site Ir catalyst embedded in a zeolite with and without a CO ligand present in kcal/mol. The predicted results for the PES, ligand bond dissociation energies, and vibrational frequencies are in good agreement with the experimental observations.

•The structures and energetics of isomers of Irx(PH3)y(CO)z (x = 1, 2, 4) are investigated using DFT and CCSD(T) theory.•The relative energies of different isomers are calculated for the first time.•CO and PH3 ligand dissociation energies are calculated for the first time.•The best functional is ωB97X-D and it was used for calculations of iridium tetramers.•A novel process occurs on dissociation of a bridging ligand leading to a hydrogen atom transfer.There is significant interest in the catalytic properties of substituted iridium carbonyl clusters but little thermodynamic information available characterizing them. The low-energy isomers of Irx(PH3)y(CO)z (x = 1, 2, 4) were investigated with density functional theory and correlated molecular orbital theory at the coupled cluster CCSD(T) level. The relative energies and ligand dissociation energies were calculated. Differences in relative energies are consequences of both electronic and steric effects of the phosphines and carbonyls. The calculations predict three fundamental structural types for Ir2(PH3)y(CO)z: C2v, C2, and D3d. Ten exchange–correlation functionals were used for the ligand dissociation energy calculations in addition to CCSD(T) for the smaller clusters. The ωB97X-D functional gave the most consistent ligand dissociation energies as compared with the CCSD(T) benchmark calculations, and, so it was used to predict the dissociation energies for larger clusters when CCSD(T) calculations were infeasible. The dissociation energies characteristic of Ir4(PH3)y(CO)z were in the range of ∼30 to ∼60 kcal/mol. Dissociation of a bridging ligand often involved a hydrogen atom transfer from a phosphine to a coordinatively unsaturated iridium atom and a phosphine converting from a bridging site to an equatorial site. The products of such reactions are predicted to have lower relative energies than other isomers. Phosphines act as σ-electron donors, and there is a trend of an increase in carbonyl ligand dissociation energies as more phosphines are substituted in the small clusters.The calculated ligand dissociation energies of Irx(PH3)y(CO)z (x = 1, 2, 4) provide insights into the bonding and structures of these complexes relevant to single site catalysis.

The potential energy surfaces for the reactions of H2O with ThO2, PaO2+, UO22+, and UO2+ have been calculated at the coupled cluster CCSD(T) level extrapolated to the complete basis set limit with additional corrections including scalar relativistic and spin–orbit. The reactions proceed by the formation of an initial Lewis acid–base adduct (H2O)AnO20/+/2+ followed by a proton transfer to generate the dihydroxide AnO(OH)20/+/2+. The results are in excellent agreement with mass spectrometry experiments and prior calculations of hydrolysis reactions of the group 4 transition metal dioxides MO2. The differences in the energies of the stationary points on the potential energy surface are explained in terms of the charges on the system and the populations on the metal center. The use of an improved starting point for the coupled cluster CCSD(T) calculations based on density functional theory with the PW91 exchange–correlation functional or Brueckner orbitals is described. The importance of including second-order spin–orbit corrections for closed-shell molecules is also described. These improvements in the calculations are correlated with the 5f populations on the actinide.

The low energy structures of the (TiO2)n(H2O)m (n ≤ 4, m ≤ 2n) and (TiO2)8(H2O)m (m = 3, 7, 8) clusters were predicted using a global geometry optimization approach, with a number of new lowest energy isomers being found. Water can molecularly or dissociatively adsorb on pure and hydrated TiO2 clusters. Dissociative adsorption is the dominant reaction for the first two H2O adsorption reactions for n = 1, 2, and 4, for the first three H2O adsorption reactions for n = 3, and for the first four H2O adsorption reactions for n = 8. As more H2O’s are added to the hydrated (TiO2)n cluster, dissociative adsorption becomes less exothermic as all the Ti centers become 4-coordinate. Two types of bonds can be formed between the molecularly adsorbed water and TiO2 clusters: a Lewis acid–base Ti–O(H2) bond or an O···H hydrogen bond. The coupled cluster CCSD(T) results show that at 0 K the H2O adsorption energy at a 4-coordinate Ti center is ∼15 kcal/mol for the Lewis acid–base molecular adsorption and ∼7 kcal/mol for the H-bond molecular adsorption, in comparison to that of 8–10 kcal/mol for the dissociative adsorption. The cluster size and geometry independent dehydration reaction energy, ED, for the general reaction 2(−TiOH) → −TiOTi– + H2O at 4-coordinate Ti centers was estimated from the aggregation reaction of nTi(OH)4 to form the monocyclic ring cluster (TiO3H2)n + nH2O. ED is estimated to be −8 kcal/mol, showing that intramolecular and intermolecular dehydration reactions are intrinsically thermodynamically allowed for the hydrated (TiO2)n clusters with all of the Ti centers 4-coordinate, which can be hindered by cluster geometry changes caused by such processes. Bending force constants for the TiOTi and OTiO bonds are determined to be 7.4 and 56.0 kcal/(mol·rad2). Infrared vibrational spectra were calculated using density functional theory, and the new bands appearing upon water adsorption were assigned.

Correlated molecular orbital theory at the coupled cluster CCSD(T) level with density functional theory geometries is used to study ethanol dehydration, dehydrogenation, and condensation reactions on an the Al8O12 cluster which is a model for γ-Al2O3. The Al in the active site on the cluster is a strong Lewis acid. The reactions begin with formation of a very stable Lewis acid–base ethanol–cluster adduct. Dehydration proceeds by β-H transfer to a bicoordinate oxygen leading to the direct formation of ethylene and two OH groups following an E2 mechanism. Dehydrogenation proceeds directly by α-H transfer to the active metal center and a proton transfer to a bicoordinate bridge O to form acetaldehyde plus a metal hydride and a hydroxyl, again an E2 mechanism. After addition of a second ethanol, diethyl ether is generated by an α-C transfer from the first to the second ethanol, an acid-driven SN2 mechanism. Condensation and dehydration with two alcohols have comparable energy barriers. The addition of a second ethanol or a water molecule raises the energy barriers. Condensation and dehydration are predicted to be more likely than dehydrogenation. The computational results for the mechanism and the energetics agree well with the available experimental data.

Reactions of laser–ablated U atoms with (CN)2 produce UNC, U(NC)2, and U(NC)4 as the major products, identified from their Ar matrix infrared spectra and precursors partially and fully substituted with 13C and 15N. Mixed isotopic multiplets substantiate product stoichiometries. Band positions and quantum chemical calculations verify the isocyanide bonding.