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The oxidation and photo-oxidation of water on the rutile TiO 2 (110) surface is investigated using density functional theory (DFT) calculations. We investigate the relative stability of different surface terminations of TiO 2 interacting with H 2 O and analyze the overpotential needed for the electrolysis and photoelectrolysis of water. We found that the most difficult step in the splitting of water process is the reaction of a H 2 O molecule with a vacancy in the surface to form an adsorbed hydroxyl group (OH*). Comparison to experiment shows that the computed overpotential for O 2 evolution (0.78 V) is available under the experimental conditions required for both oxygen and hydrogen evolution.

The electronic structure and the stability of both neutral and singly charged (TiO2)n clusters with n = 1-9 have been investigated using the density functional B3LYP/LANL2DZ method. The lowest-lying singlet clusters tend to form some compact structures with one or two terminal Ti-O bonds, which are about 1.4-2.5 eV more stable than the corresponding triplet structures. For the lowest-lying structures, strong infrared absorption lines at 988-1020 cm(-1) due to terminal Ti-O bonds and below 930 cm(-1) due to Ti-O-Ti bridging bonds may be observed, with some characteristic lines at 530-760 cm(-1) due to 3-fold coordinated O-atoms that are comparable with the spectra of rutile and anatase bulk. The holes and excited electrons within triplet structures tend to be localized on the least coordinated O- and Ti-atoms, respectively, with some exceptions possibly due to the electron-hole interaction. The extra electrons within (TiO2)n- clusters and the holes within (TiO2)n+ clusters show a clearer preference of location on the least coordinated Ti- and O-atoms, respectively. For the lowest-lying (TiO2)n clusters, the cluster formation energy per TiO2 unit and the electron affinity tend to increase whereas the ionization potential tends to decrease with the cluster size n. On the other hand, the singlet-triplet and HOMO-LUMO gaps represent the lower and upper limits of the TiO2 bulk band gaps, respectively. The theoretical results agree well with the available experimental data and may be helpful for understanding the chemistry of small (TiO2)n clusters.

We review recent theoretical studies of the photodissociation of ozone in the wavelength region from 200 nm to 1100 nm comprising four major absorption bands: Hartley and Huggins (near ultraviolet), Chappuis (visible), and Wulf (near infrared). The quantum mechanical dynamics calculations use global potential energy surfaces obtained from new high-level electronic structure calculations. Altogether nine electronic states are taken into account in the theoretical descriptions: four 1A', two 1A'', one 3A' and two 3A'' states. Of particular interest is the analysis of diffuse vibrational structures, which are prominent in all absorption bands, and their dynamical origin and assignment. Another focus is the effect of non-adiabatic coupling on lifetimes in the excited states and on the population of the specific electronic product channels.

9-H-9-Borafluorene (H(8)C(12)BH; 5) can be generated in situ from 9-Br-9-borafluorene and Et(3)SiH in benzene or hexane. Monitoring of the reaction by NMR spectroscopy at rt in C(6)D(6) reveals that 5 forms C(1)-symmetric dimers (5)(2) under these conditions. DFT calculations on conceivable isomers of (5)(2) and a comparison of calculated and experimentally determined (1)H, (13)C, and (11)B NMR shift values lead to the conclusion that (5)(2) is not a classical dimer H(8)C(12)B(μ-H)(2)BC(12)H(8), but contains one B-H-B three-center, two-electron bond together with a boron-bridging phenyl ring. Addition of 1 equiv of pyridine to (5)(2) leads to the clean formation of the pyridine adduct H(8)C(12)BH(py) (5·py). Likewise, (5)(2) can be employed in hydroboration reactions, as evidenced by its transformation with 0.5 equiv of tert-butylacetylene, which gives the hydroboration products tBuC(H)(2)C(H)(BC(12)H(8))(2) (9) and tBuC(H)C(H)BC(12)H(8) in almost quantitative yield. (5)(2) is not long-term stable in benzene solution. Addition of pyridine to aged reaction mixtures allowed the isolation of the adduct (py)H(2)B-C(6)H(4)-C(6)H(4)-(py)BC(12)H(8) (10·py(2)) of a ring-opened dimer of 5. Storage of a hexane solution of 9-Br-9-borafluorene and Et(3)SiH for 1-2 weeks at rt leads to the formation of crystals of a ring-opened pentamer H[-(H)B-(C(6)H(4))(2)-](4)BC(12)H(8) (11) of 5 (preparative yields are obtained after 1-4 months). The polymer main chain of 11 is reinforced by four intrastrand B-H-B three-center, two-electron bonds. Apart from the main product 11, we have also isolated minor amounts of closely related oligomers carrying different chain ends, i.e., H(8)C(12)B-(C(6)H(4))(2)[-(H)B-(C(6)H(4))(2)-](2)BC(12)H(8) (12) and H[-(H)B-(C(6)H(4))(2)-](5)BH(2) (13). When the reaction between 9-Br-9-borafluorene and Et(3)SiH is carried out in refluxing toluene, the cyclic dimer [-(μ-H)B-(C(6)H(4))(2)-](2) (14) can be obtained in a crystalline yield of 25%. The compounds 9, 10·py(2), 11, 12, 13, and 14 have been structurally characterized by X-ray crystallography. The entire reaction pathway leading from 5 to 10, 11, 12, 13, and 14 has been thoroughly elucidated by DFT calculations and we propose a general mechanistic scenario applicable for ring-opening polymerization reactions of 9-borafluorenes.