DFT calculations, DRIFT spectroscopy and kinetic studies on the hydrolysis of isocyanic acid on the TiO2-anatase (1 0 1) surface

The co-adsorption of isocyanic acid (HNCO) and water (H₂O) and their reaction to ammonia and carbon dioxide on the anatase phase of TiO₂ were studied with ab initio density functional theory (DFT) calculations using a cluster model as well as with in situ DRIFTS investigations and kinetic experiments. We found that isocyanic acid can in principle adsorb both molecularly and dissociatively on the TiO₂(1 0 1) surface, but the moment at which water gets involved in the process, is vital for determining the further course of the surface reaction. In the absence of water, it was found that HNCO can adsorb in molecular form on the TiO₂ surface. Assuming this case to be the first step of the HNCO hydrolysis, the surface HNCO rearranges into an intermediate complex with a modified NCO skeleton. After decarboxylation water attacks the complex from the gas phase and ammonia is finally formed.

However, when water is present at the beginning of the hydrolysis reaction, it immediately attacks the NCO group present at the surface, yielding a carbamic acid complex, which is further transformed into a carbamate complex. After decarboxylation an NH₂ group remains at the surface. Finally, NH₃ is formed by hydrogen transfer from molecularly adsorbed water at a neighboring titanium center and the hydrolysis reaction is completed.

Since water is always present in diesel exhaust gas, only the second mechanism is relevant under practical conditions. Moreover, the calculated energy barrier is lower for the second mechanism compared to the first reaction pathway. The comparison between the sum of the theoretical vibrational spectra of the reaction intermediates with the in situ DRIFT spectra also strongly supports the accuracy of the second reaction pathway. The experimental investigation of the kinetics of the HNCO hydrolysis on TiO₂-anatase revealed a second order reaction—first order with respect to HNCO and first order with respect to water, which can only be reconciled with the second mechanism.     

Tunnelling under a conical intersection: application to the product vibrational state distributions in the UV photodissociation of phenols

When phenol is photoexcited to its S(1) (1(1)ππ?) state at wavelengths in the range 257.403 ≤ λ(phot) ≤ 275.133 nm the O-H bond dissociates to yield an H atom and a phenoxyl co-product, with the available energy shared between translation and well characterised product vibration. It is accepted that dissociation is enabled by transfer to an S(2) (1(1)πσ?) state, for which the potential energy surface (PES) is repulsive in the O-H stretch coordinate, R(O-H). This S(2) PES is cut by the S(1) PES near R(O-H) = 1.2 ? and by the S(0) ground state PES near R(O-H) = 2.1 ?, to give two conical intersections (CIs). These have each been invoked-both in theoretical studies and in the interpretation of experimental vibrational activity-but with considerable controversy. This paper revisits the dynamic mechanisms that underlie the photodissociation of phenol and substituted phenols in the light of symmetry restrictions arising from torsional tunnelling degeneracy, which has been neglected hitherto. This places tighter symmetry constraints on the dynamics around the two CIs. The non-rigid molecular symmetry group G(4) necessitates vibronic interactions by a(2) modes to enable coupling at the inner, higher energy (S(1)/S(2)) CI, or by b(1) modes at the outer, lower energy (S(2)/S(0)) CI. The experimental data following excitation through many vibronic levels of the S(1) state of phenol and substituted phenols demonstrate the effective role of the ν(16a) (a(2)) ring torsional mode in enabling O-H bond fission. This requires tunnelling under the S(1)/S(2) CI, with a hindering barrier of ～5000 cm(-1) and with the associated geometric phase effect. Quantum dynamic calculations using new ab initio PESs provide quantitative justification for this conclusion. The fates of other excited S(1) modes are also rationalised, revealing both spectator modes and intramolecular vibrational redistribution between modes. A common feature in many cases is the observation of an extended, odd-number only, progression in product mode ν(16a) (i.e., the parent mode which enables S(1)/S(2) tunnelling), which we explain as a Franck-Condon consequence of a major change in the active vibration frequency. These comprehensive results serve to confirm the hypothesis that O-H fission following excitation to the S(1) state involves tunnelling under the S(1)/S(2) CI-in accord with conclusions reached from a recent correlation of the excited state lifetimes of phenol (and many substituted phenols) with the corresponding vertical energy gaps between their S(1) and S(2) PESs.     

Addition of a thallium vertex to empty and centered nine-atom deltahedral zintl ions of germanium and tin

Nickel atoms were inserted into nine-atom deltahedral Zintl ions of E(9)(4-) (E = Ge, Sn) via reactions with Ni(cod)(2) (cod = cyclooctadiene), and [Ni@Sn(9)](3-) was structurally characterized. Both the empty and the Ni-centered clusters react with TlCp (Cp = cyclopentadienyl anion) and add a thallium vertex to form the deltahedral ten-atom closo-species [E(9)Tl](3-) and [Ni@E(9)Tl](3-), respectively. The structures of [Ge(9)Tl](3-) and [Ni@Sn(9)Tl](3-) showed that, as expected, the geometry of the ten-atom clusters is that of a bicapped square antiprism where the Tl-atom occupies one of the two capping vertices. This illustrates that centering a nine-atom cluster with a nickel atom does not change its reactivity toward TlCp. All compounds were characterized by electrospray mass spectrometry.     

Copolymers derived from rapeseed derivatives via ADMET and thiol-ene addition

Novel (co)polymers were synthesized from substances obtained from rapeseed via ADMET and thiol-ene additions. α,ω-Dienes derived from oleic and erucic acid were copolymerized with a ferulic acid derivative, a representative phenolic acid (p-hydroxycinnamic acid) present, for instance, in rapeseed cake. Copolymers with different ratios of these monomers were prepared via two different routes (ADMET and thiol-ene) and studied in detail. Both monomer and polymer synthesis were optimized in order to achieve high yielding synthetic procedures that meet the requirements of green chemistry. Some thermal properties of the resulting copolymer series were then studied and correlated to the co-monomer composition.     

Chemisorption of Exchange‐Coupled [Ni2L(dppba)]+ Complexes on Gold by Using Ambidentate 4‐(Diphenylphosphino)benzoate Co‐Ligands

A new strategy for the fixation of redox‐active dinickel(II) complexes with high‐spin ground states to gold surfaces was developed. The dinickel(II) complex [Ni₂L(Cl)]ClO₄ ( 1 ClO₄), in which L^2? represents a 24‐membered macrocyclic hexaaza‐dithiophenolate ligand, reacts with ambidentate 4‐(diphenylphosphino)benzoate (dppba) to form the carboxylato‐bridged complex [Ni₂L(dppba)]⁺, which can be isolated as an air‐stable perchlorate [Ni₂L(dppba)]ClO₄ ( 2 ClO₄) or tetraphenylborate [Ni₂L(dppba)]BPh₄ ( 2 BPh₄) salt. The auration of 2 ClO₄ was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated Ni^II₂Au^I complex [Ni^II₂L(dppba)Au^ICl]ClO₄ ( 3 ClO₄). Metathesis of 3 ClO₄ with NaBPh₄ produces [Ni^II₂L(dppba)Au^IPh]BPh₄ ( 4 BPh₄), in which the Cl^? is replaced by a Ph^? group. The complexes were fully characterized by ESI mass spectrometry, IR and UV/Vis spectroscopy, X‐ray crystallography ( 2 BPh₄ and 4 BPh₄), cyclic voltammetry, SQUID magnetometry and HF‐ESR spectroscopy. Temperature‐dependent magnetic susceptibility measurements reveal a ferromagnetic coupling J=+15.9 and +17.9 cm^?1 between the two Ni^II ions in 2 ClO₄ and 4 BPh₄ (H=?2 JS₁S₂). HF‐ESR measurements yield a negative axial magnetic anisotropy (D<0), which implies a bistable (easy axis) magnetic ground state. The binding of the [Ni₂L(dppba)]ClO₄ complex to gold was ascertained by four complementary surface analytical methods: contact angle measurements, atomic‐force microscopy, X‐ray photoelectron spectroscopy, and spectroscopic ellipsometry. The results indicate that the complexes are attached to the Au surface through coordinative Au? P bonds in a monolayer.     

Encapsulation of Metalloporphyrins in a Self‐Assembled Cubic M8L6 Cage: A New Molecular Flask for Cobalt–Porphyrin‐Catalysed Radical‐Type Reactions

The synthesis of a new, cubic M₈L₆ cage is described. This new assembly was characterised by using NMR spectroscopy, DOSY, TGA, MS, and molecular modelling techniques. Interestingly, the enlarged cavity size of this new supramolecular assembly allows the selective encapsulation of tetra(4‐pyridyl)metalloporphyrins (M^II(TPyP), M=Zn, Co). The obtained encapsulated cobalt–porphyrin embedded in the cubic zinc–porphyrin assembly is the first example of a catalytically active encapsulated transition‐metal complex in a cubic M₈L₆ cage. The substrate accessibility of this system was demonstrated through radical‐trapping experiments, and its catalytic activity was demonstrated in two different radical‐type transformations. The reactivity of the encapsulated Co^II(TPyP) complex is significantly increased compared to free Co^II(TPyP) and other cobalt–porphyrin complexes. The reactions catalysed by this system are the first examples of cobalt–porphyrin‐catalysed radical‐type transformations involving diazo compounds which occur inside a supramolecular cage.