New Nuclear‐Spin‐Induced Cotton–Mouton Effect in Fluids at High DC Magnetic Field

Based on Buckingham and Pople’s theory of magnetic double refraction, a theoretical expression is derived for a new Cotton–Mouton effect ${\phi _{{\rm{C}} - {\rm{M}}}^{(IB)} }$ in liquid induced by the crossed effect between the high dc magnetic field B₀ and the nuclear magnetic moment ${m_z^{(I)} }$ . It contains temperature‐independent and ‐dependent parts. The latter is proportional to the product between anisotropy of polarizability and the nuclear magnetic shielding tensor. For this new effect ${\phi _{{\rm{C}} - {\rm{M}}}^{(IB)} }$ , its order in magnitude for a molecule with large polarizability anisotropy is estimated to be comparable to the nuclear‐spin‐induced optical Faraday rotation (NSOFR). In the multipass approach, ${\phi _{{\rm{C}} - {\rm{M}}}^{(IB)} }$ can be eliminated by time‐reversal symmetry arguments, but NSOFR is enhanced.     

Water Oxidation Catalysis by Synthetic Manganese Oxides with Different Structural Motifs: A Comparative Study

Manganese oxides are considered to be very promising materials for water oxidation catalysis (WOC), but the structural parameters influencing their catalytic activity have so far not been clearly identified. For this study, a dozen manganese oxides (MnO_x) with various solid‐state structures were synthesised and carefully characterised by various physical and chemical methods. WOC by the different MnO_x was then investigated with Ce⁴⁺ as chemical oxidant. Oxides with layered structures (birnessites) and those containing large tunnels (todorokites) clearly gave the best results with reaction rates exceeding 1250 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h^?1 or about 50 μmol_O2 m^?2 h^?1. In comparison, catalytic rates per mole of Mn of oxides characterised by well‐defined 3D networks were rather low (e.g., ca. 90 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h^?1 for bixbyite, Mn₂O₃), but impressive if normalised per unit surface area (>100 ${{\rm{{\rm \mu} mol}}_{{\rm{O}}_{\rm{2}} } }$ m^?2 h^?1 for marokite, CaMn₂O₄). Thus, two groups of MnO_x emerge from this screening as hot candidates for manganese‐based WOC materials: 1) amorphous oxides with tunnelled structures and the well‐established layered oxides; 2) crystalline Mn^III oxides. However, synthetic methods to increase surface areas must be developed for the latter to obtain good catalysis rates per mole of Mn or per unit catalyst mass.     

Tautomerism and Atropisomerism in Free‐Base (meso)‐Strapped Porphyrins: Static and Dynamic Aspects

We report herein some outstanding examples of atropisomerism and tautomerism in five (meso‐)strapped porphyrins. Porphyrins S0 – S4 have been synthesised, characterised and studied in detail by spectroscopic and spectrometric techniques, and their isomeric purity verified by HPLC analysis. In particular, they exhibit perfectly well‐defined NMR spectra that display distinct patterns depending on their average symmetry at room temperature: C_2v, D_2d, C_2h, C_2v, and D_2h for S0 – S4 , respectively. NH tautomerism was evidenced by variable‐low‐temperature ¹H NMR experiments in [D₂]dichloromethane performed on S0 (Δ${G{{{\ne}\hfill \atop {\rm 298K}\hfill}}}$ =48±1 kJ mol^?1) and S1 (Δ${G{{{\ne}\hfill \atop {\rm 298K}\hfill}}}$ =55±3 kJ mol^?1), which has led to an understanding of the average spectra observed for the five porphyrins at room temperature. On the other hand, S2 and S3 are stable atropisomers at room temperature, easily separated and characterised, as a result of restricted rotation of their strapped bridges due to their high rotational barrier energies. Upon heating to 82 °C, they slowly equilibrate to a thermodynamic ratio of 64:36 in favour of the more stable S2 isomer. This atropisomerisation process was evidenced by ¹H NMR spectroscopy and monitored by HPLC, from which high rotational energy barriers of 115.2 (Δ${G{{{\ne}\hfill \atop {\rm S2}\rightarrow {\rm S3}\hfill}}}$ ) and 116.9 kJ mol^?1 (Δ${G{{{\ne}\hfill \atop {\rm S2}\rightarrow {\rm S3}\hfill}}}$ ) were deduced.     

Experimental and Theoretical Study of the Broadening and Shifting of N2H+ Rotational Lines by Helium

Pressure broadening and pressure shift of N₂H⁺ rotational lines perturbed by collisions with He are studied for the first time using experiment and theory. Results are reported from measurements at 88 K for the rotational transitions ${j = 3 \leftarrow 2}$ , ${4 \leftarrow 3}$ , ${5 \leftarrow 4}$ and ${6 \leftarrow 5}$ with frequencies ranging from 0.28 to 0.56 THz. The agreement between experiment and theoretical data derived from close coupling calculations confirms the reliability of a theoretical framework used for state‐to‐state transition rates of interest in the interpretation of spectroscopic data from interstellar molecular clouds. The influence of hyperfine effects on shifts and widths of the rotational lines is discussed in detail. Although in principle possible, experiment and theoretical considerations lead to the conclusion that hyperfine effects only play a minor role.     

On the 4JHH long‐range coupling in 2‐bromocyclohexanone: conformational insights

2‐Bromocyclohexanone is a model compound in which a ⁴J_{H2, H6} coupling constant is observed, whereas the corresponding ⁴J_{H2, H4} is absent. The observed long‐range coupling is not only a result of the known W‐type coupling, in the axial conformation, but also because of the less usual diaxial spin–spin coupling in the equatorial conformer. The carbonyl group plays a determining role in describing the coupling pathway, as concluded by natural bond orbital (NBO) analysis; although the and interactions in the axial conformer contribute for transmitting the spin information associated with the W‐type coupling, the strong and hyperconjugations in the equatorial conformer define an enhanced coupling pathway for ⁴J_{H2, H6}, despite the inhibition of this coupling because of interaction and the large carbonyl angle. These findings provide the experimental evidence that orbital interactions contribute for the conformational isomerism of 2‐bromocyclohexanone. Copyright © 2008 John Wiley & Sons, Ltd.     

Calixarene‐Based Surfactants: Conformational‐Dependent Solvation Shells for the Alkyl Chains

Thermodynamic parameters obtained from studying the micellization of amphiphilic p‐sulfonatocalix[n]arenes were correlated with the alkyl chain length and with the number of monomeric units (n) in the calix[n]arene structure. The micellization Gibbs free energy (Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) becomes more negative upon increasing the alkyl chain length of the p‐sulfonatocalix[4]arene. This is in agreement with the trend generally observed for other surfactants. However, the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ value for transferring one CH₂ group from the bulk aqueous medium to the micelle [Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH₂)] is lower than the value generally observed for single‐chain surfactants, suggesting the existence of intramolecular interactions between the alkyl chains of the free unimers. On the other hand, the critical micelle concentration (cmc; per alkyl chain unit) increased with the increasing number of monomeric units. These results are explained on the basis of the conformation adopted by the calixarene in the bulk solution. The calix[4]arene derivatives are preorganized into the cone conformation, which is favorable for the formation of globular aggregates. The calix[6]arene and calix[8]arene derivatives do not adopt cone conformations. Changing these conformations to the more favorable cone conformer in the aggregates implies an energetic cost that contributes to making Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ less efficient. In the case of the calix[6]arene derivative this energetic cost is enthalpic, whereas in the case of the octamer it is both enthalpic and entropic. Both the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH₂) value and the change in heat capacity (ΔC${{\rm p}{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) seem to indicate that for the cone calix[4]arene derivatives all alkyl chains are solvated by the same hydration shell, whereas in the case of the highly flexible calix[8]arene derivative each alkyl chain is individually hydrated.     

Crystal Structures and Emitting Properties of Trifluoromethylaminoquinoline Derivatives: Thermal Single‐Crystal‐to‐Single‐Crystal Transformation of Polymorphic Crystals That Emit Different Colors

2,4‐Trifluoromethylquinoline (TFMAQ) derivatives that have amine ( 1 ), methylamine ( 2 ), phenylamine ( 3 ), and dimethylamine ( 4 ) substituents at the 7‐position of the quinoline ring were prepared and crystallized. Six crystals including the crystal polymorphs of 2 (crystal GB and YG) and 3 (crystal B and G) were obtained and characterized by X‐ray crystallography. In solution, TFMAQ derivatives emitted relatively strong fluorescence (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =418–469 nm and Φ_f(s)=0.23–0.60) depending on the solvent polarity. From Lippert–Mataga plots, Δμ values in the range of 7.8–14 D were obtained. In the crystalline state, TFMAQ derivatives emitted at longer wavelengths (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464–530 nm) with lower intensity (Φ_f(c)=0.01–0.28) than those in n‐hexane solution. The polymorphous crystals of 2 and 3 emitted different colors: 2 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =470 and 530 nm with Φ_f(c)=0.04 and approximately 0.01 for crystal GB and YG, respectively; and 3 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464 and 506 nm with Φ_f(c)=0.28 and approximately 0.28 for crystal B and G, respectively. In both crystal polymorphs of 2 and 3 , crystals GB and G showed emission color changes by heating/melting/cooling cycles that were representative. By following the color changes in heating at the temperature below the melting point with X‐ray diffraction measurements and X‐ray crystallography, the single‐crystal‐to‐single‐crystal transformations from crystal GB to YG for 2 and from crystal B to G for 3 were revealed.     

Density functional study of electronic,bonding, and vibrational properties of Ca (NH2BH3)2

We present structural, electronic, bonding and vibrational properties of new type hydrogen storage material calcium amidoborane ${\rm Ca}({\rm NH}_{2}{\rm BH}_{3})_{2}$ by first principles density functional theory using plane wave pseudopotential method. The calculated ground state properties are in good agreement with experiments. The computed Bulk modulus of ${\rm Ca}({\rm NH}_{2}{\rm BH}_{3})_{2}$ is found to be 28.7 GPa which is slightly higher than that of ${\rm NH}_{3}{\rm BH}_{3}$ indicating that the material is hard over ${\rm NH}_{3}{\rm BH}_{3}$ . From the band structure calculations, the compound is found to be a direct band gap insulator with a band gap of 3.27 eV at the Γ point. The calculated bandstructure shows that the top of the valance band is from the p states of N and the bottom of the conduction band is from d states of Ca. The Mulliken bond populations, Born effective charges and charge density distributions are used to analyze the bonding nature of the compound. It is found that the N‐H and B‐H bonds are covalent in nature. Further we also compared the phonon density of states and vibrational frequencies of ${\rm Ca}({\rm NH}_{2}{\rm BH}_{3})_{2}$ with ${\rm NH}_{3}{\rm BH}_{3}$ . The study reveals that in both the cases the heavier mass atoms Ca, N, B are involved in the low frequency vibrations whereas the higher frequency vibrations are from H atoms. It is also observed that the vibrational frequencies of B‐H bonds are soft in ${\rm Ca}({\rm NH}_{2}{\rm BH}_{3})_{2}$ when compared to ${\rm NH}_{3}{\rm BH}_{3}$ and thereby concluded that ${\rm Ca}({\rm NH}_{2}{\rm BH}_{3})_{2}$ is a potential hydrogen storage material for fuel cell applications when compared to ${\rm NH}_{3}{\rm BH}_{3}$ . © 2012 Wiley Periodicals, Inc.     

Guanidinium Alkynesulfonates with Single‐Layer Stacking Motif: Interlayer Hydrogen Bonding Between Sulfonate Anions Changes the Orientation of the Organosulfonate R Group from “Alternate Side” to “Same Side”

Hydrolyses of HC?CSO₃SiMe₃ ( 1 ) and CH₃C?CSO₃SiMe₃ ( 2 ) lead to the formation of acetylenic sulfonic acids HC?CSO₃H?2.33 H₂O ( 3 ) and CH₃C?CSO₃H?1.88 H₂O ( 4 ). These acids were reacted with guanidinium carbonate to yield [⁺C(NH₂)₃][HC?CSO₃^?] ( 5 ) and [⁺C(NH₂)₃][CH₃C?CSO₃^?] ( 6 ). Compounds 1 – 6 were characterized by spectroscopic methods, and the X‐ray crystal structures of the guanidinium salts were determined. The X‐ray results of 5 show that the guanidinium cations and organosulfonate anions associate into 1D ribbons through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions, whereas association of these ions in 6 is achieved through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) and ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) interactions. The ribbons in 5 associate into 2D sheets through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{3\hfill \atop 6\hfill}}}$ (12) rings, whereas those in 6 are connected through ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) and ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{4\hfill \atop 6\hfill}}}$ (14) rings. Compound 6 exhibits a single‐layer stacking motif similar to that found in guanidinium alkane‐ and arenesulfonates, that is, the alkynyl groups alternate orientation from one ribbon to the next. The stacking motif in 5 is also single‐layer, but due to interlayer hydrogen bonding between sulfonate anions, the alkynyl groups of each sheet all point to the same side of the sheet.     

Polysulfide Chemistry in Sodium–Sulfur Batteries and Related Systems— A Computational Study by G3X(MP2) and PCM Calculations

The sodium–sulfur (NAS) battery is a candidate for energy storage and load leveling in power systems, by using the reversible reduction of elemental sulfur by sodium metal to give a liquid mixture of polysulfides (Na₂S_n) at approximately 320 °C. We investigated a large number of reactions possibly occurring in such sodium polysulfide melts by using density functional calculations at the G3X(MP2)/B3LYP/6‐31+G(2df,p) level of theory including polarizable continuum model (PCM) corrections for two polarizable phases, to obtain geometric and, for the first time, thermodynamic data for the liquid sodium–sulfur system. Novel reaction sequences for the electrochemical reduction of elemental sulfur are proposed on the basis of their Gibbs reaction energies. We suggest that the primary reduction product of S₈ is the radical anion ${{\rm S}{{{{\bullet}}- \hfill \atop 8\hfill}}}$ , which decomposes at the operating temperature of NAS batteries exergonically to the radicals ${{\rm S}{{{{\bullet}}- \hfill \atop 2\hfill}}}$ and ${{\rm S}{{{{\bullet}}- \hfill \atop 3\hfill}}}$ together with the neutral species S₆ and S₅, respectively. In addition, ${{\rm S}{{{{\bullet}}- \hfill \atop 8\hfill}}}$ is predicted to disproportionate exergonically to S₈ and ${{\rm S}{{2- \hfill \atop 8\hfill}}}$ followed by the dissociation of the latter into two ${{\rm S}{{{{\bullet}}- \hfill \atop 4\hfill}}}$ radical ions. By recombination reactions of these radicals various polysulfide dianions can in principle be formed. However, polysulfide dianions larger than ${{\rm S}{{2- \hfill \atop 4\hfill}}}$ are thermally unstable at 320 °C and smaller dianions as well as radical monoanions dominate in Na₂S_n (n=2–5) melts instead. The reverse reactions are predicted to take place when the NAS battery is charged. We show that ion pairs of the types ${{\rm NaS}{{{{\bullet}}\hfill \atop 2\hfill}}}$ , ${{\rm NaS}{{- \hfill \atop n\hfill}}}$ , and Na₂S_n can be expected at least for n=2 and 3 in NAS batteries, but are unlikely in aqueous sodium polysulfide except at high concentrations. The structures of such radicals and anions with up to nine sulfur atoms are reported, because they are predicted to play a key role in the electrochemical reduction process. A large number of isomerization, disproportionation, and sulfurization reactions of polysulfide mono‐ and dianions have been investigated in the gas phase and in a polarizable continuum, and numerous reaction enthalpies as well as Gibbs energies are reported.     

Synthesis and Characterization of Stereo Multiblock Poly(lactic acid)s with Different Block Lengths by Melt Polycondensation of Poly(L‐lactic acid)/Poly(D‐lactic acid) Blends

Stereo multiblock PLAs with different block lengths are synthesized by melt polycondensation of low‐molecular‐weight poly(L ‐lactic acid)/poly(D ‐lactic acid) blends with a wide variety of $\overline {M} _{{\rm w}} $ in the range of 1.1–5.2 × 10³ g · mol^–1. The average block length (ν_av) of the stereo multiblock PLAs increases with increasing $\overline {M} _{{\rm w}} $ of the blend and with the reaction temperature, whereas $\overline {M} _{{\rm w}} $ and PDI of the stereo multiblock PLAs increases with increasing $\overline {M} _{{\rm w}} $ of the blend, the reaction time, and the temperature. Stereo multiblock PLAs with ν_av > 7 are crystallizable to form stereocomplex crystallites, and the crystallinity and melting temperature of the stereo multiblock PLAs increases with increasing ν_av and $\overline {M} _{{\rm w}} $ of the stereo multiblock PLAs.

     

Hydrogen isotope effects on covalent and noncovalent interactions: The case of protonated rare gas clusters

We investigate hydrogen isotope and nuclear quantum effects on geometries and binding energies of small protonated rare gas clusters (Rg $_n$ X $^ +$ , Rg = He,Ne,Ar, X = H,D,T, and $n$ = 1–3) with the any particle molecular orbital (APMO) MP2 level of theory (APMO/MP2). To gain insight on the impact of nuclear quantum effects on the different interactions present in the Rg $_n$ X $^ +$ systems, we propose an APMO/MP2 energy decomposition analysis scheme. For RgH $^ +$ ions, isotopic substitution leads to an increase in the stability of the complex, because polarization and charge transfer contributions increase with the mass of the hydrogen. In the case of Rg $_2$ H $^ +$ complexes, isotopic substitution results in a shortening and weakening of the rare gas‐hydrogen ion bond. For Rg $_3$ X $^ +$ complexes, the isotope effects on the rare gas binding energy are almost negligible. Nevertheless, our results reveal that subtle changes in the charge distribution of the Rg $_2$ X $^ +$ core induced by an isotopic substitution have an impact on the geometry of the Rg $_3$ X $^ +$ complex. © 2012 Wiley Periodicals, Inc.     

Photochemistry of RuII 4,4′‐Bi‐1,2,3‐triazolyl (btz) Complexes: Crystallographic Characterization of the Photoreactive Ligand‐Loss Intermediate trans‐[Ru(bpy)(κ2‐btz)(κ1‐btz)(NCMe)]2+

We report the unprecedented observation and unequivocal crystallographic characterization of the meta‐stable ligand loss intermediate solvento complex trans‐[Ru(bpy)(κ²‐btz)(κ¹‐btz)(NCMe)]²⁺ ( 1 a ) that contains a monodentate chelate ligand. This and analogous complexes can be observed during the photolysis reactions of a family of complexes of the form [Ru($\widehat{NN}$ )(btz)₂]²⁺ ( 1 a – d : btz=1,1′‐dibenzyl‐4,4′‐bi‐1,2,3‐triazolyl; $\widehat{NN}$ =a) 2,2′‐bipyridyl (bpy), b) 4,4′‐dimethyl‐2,2′‐bipyridyl (dmbpy), c) 4,4′‐dimethoxy‐2,2′‐bipyridyl (dmeobpy), d) 1,10‐phenanthroline (phen)). In acetonitrile solutions, 1 a – d eventually convert to the bis‐solvento complexes trans‐[Ru($\widehat{NN}$ )(btz)(NCMe)₂]²⁺ ( 3 a – d ) along with one equivalent of free btz, in a process in which the remaining coordinated bidentate ligands undergo a new rearrangement such that they become coplanar. X‐ray crystal structure of 3 a and 3 d confirmed the co‐planar arrangement of the $\widehat{NN}$ and btz ligands and the trans coordination of two solvent molecules. These conversions proceed via the observed intermediate complexes 2 a – d , which are formed quantitatively from 1 a – d in a matter of minutes and to which they slowly revert back on being left to stand in the dark over several days. The remarkably long lifetime of the intermediate complexes (>12 h at 40 °C) allowed the isolation of 2 a in the solid state, and the complex to be crystallographically characterized. Similarly to the structures adopted by complexes 3 a and d , the bpy and κ²‐btz ligands in 2 a coordinate in a square‐planar fashion with the second monodentate btz ligand coordinated trans to an acetonitrile ligand.     

Peculiar kinetics of the complex formation in the iron(III)–sulfate system

The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+$ step and k₂ = 1.1 × 10³ M^?1 s^?1 for the ${\rm FeSO}_4^+ + {\rm SO}_4^{2-} \stackrel{k_2}{\rightleftharpoons}\, {\rm Fe}({\rm SO}_4)_2^-$ step. The mono‐sulfate complex is also formed in the ${\rm Fe}({\rm OH})^{2+} + {\rm SO}_4^{2-} \stackrel{k_{1b}}{\longrightarrow} {\rm FeSO}_4^+$ reaction with the k_1b = 2.7 × 10⁵ M^?1 s^?1 rate constant. The most surprising result is, however, that the 2 FeSO? Fe³⁺ + Fe(SO₄) equilibrium is established well before the system as a whole reaches its equilibrium state, and the main path of the formation of Fe(SO₄) is the above fast (on the stopped flow scale) equilibrium process. The use and advantages of our recently elaborated programs for the evaluation of equilibrium and kinetic experiments are briefly outlined. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 114–124, 2008     

Two‐Dimensional Infrared Correlation Spectroscopy and Principal Component Analysis on the Carbonation of Sterically Hindered Alkanolamines

Despite the academic and industrial importance of the chemical reaction between carbon dioxide (CO₂) and alkanolamine, the delicate and precise monitoring of the reaction dynamics by conventional one‐dimensional (1D) spectroscopy is still challenging, due to the overlapped bands and the restricted static information. Herein, we report two‐dimensional infrared correlation spectroscopy (2D IR COS) and principal component analysis (PCA) on the reaction dynamics of a sterically hindered amine, 2‐[(1,1‐dimethylethyl)amino]ethanol (TBAE) and CO₂. The formation of carbonate rather than carbamate species, which contribute to the unusual high working capacity of ～1 mole CO₂ per mole of TBAE at 40 °C, occurs through deprotonation of the hydroxyl group, protonation on the nitrogen atom of the amino group, and formation of a carbonate species due to the steric hindrance of the tert‐butyl group. In particular, PCA captures the chemical transition into a carbonate species and the main contributions of ${\nu _{{\rm{CO}}_2 } }$ , ${\nu _{{\rm{OH}}} }$ , ${\nu _{{\rm{C - N}}} }$ , and ${\nu _{{\rm{C}} = {\rm{O}}} }$ bands to the carbonation, while 2D IR COS verifies the interrelation of four bands and their changes. Therefore, these results provide a powerful analytic method to understand the complex and abnormal reaction dynamics as well as the rational design strategy for the CO₂ absorbents.     

Unprecedented Electron‐Poor Octahedral Ta6 Clusters in a Solid‐State Compound: Synthesis,Characterisations and Theoretical Investigations of Cs2BaTa6Br15O3

The crystal structure of Cs₂BaTa₆Br₁₅O₃ has been elucidated by using synchrotron X‐ray powder diffraction and absorption experiments. It is built from edge‐bridged octahedral [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^4? cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta₆ clusters is similar to that of Cs₂LaTa₆Br₁₅O₃ exhibiting 14‐MEs per [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^5? motif. The poorer electron‐count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge‐bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13‐ and 14‐ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid‐state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron‐poor Ta₆ cluster in the solid state.     

Steric and Chain Length Effects in the (${\sqrt {(3)} }$×${\sqrt {(3)} }$)R30° Structures of Alkanethiol Self‐Assembled Monolayers on Au(111)

The translational and orientational potential energy surfaces (PESs) of n‐alkanethiols with up to four carbon atoms are studied for (${\sqrt {(3)} }$ ×${\sqrt {(3)} }$ )R30° self‐assembled monolayers (SAMs). The PESs indicate that methanethiol may form SAM structures that are not accessible for long‐chain thiols. The tilt of the thiol molecules is determined by a compromise between the preferred binding geometry at the sulfur atom and the steric requirements of the alkane chains. The Au? S bond lengths, offset from the bridge position (brg), and the Au? S? C bond angles result in tilt angles of the S? C bond in the range of 55–60°. As DFT/generalized gradient approximation systematically underestimates chain–chain interactions, the binding energies are corrected by comparison to MP2 interaction energies of alkane dimers in SAM‐like configurations. The resulting thiol binding energies increase by approximately 1 kcal mol^?1 per CH₂ group, which results in a substantial stabilization of long‐chain SAMs due to chain–chain interactions. Furthermore, as the chain length increases, the accessible range of backbone tilt angles is constrained due to steric effects. The combination of these two effects may explain why SAM structures with long‐chain thiols exhibit higher order in experiments. For each thiol two favorable SAM structures are found with the sulfur head group at the fcc‐brg and hcp‐brg positions, respectively. These domains may coexist in thermal equilibrium. In combination with the symmetry of the gold (111) surface, this raises the possibility of up to six different domains on single‐crystal terraces. Reconstructions by an adatom or vacancy of ethanethiol SAMs with (${\sqrt {(3)} }$ ×${\sqrt {(3)} }$ )R30° lattice are also studied using PES scans. The results indicate that adsorption of thiols next to a vacancy is favorable and may lead to point defects inside SAMs.     

Electron Transfer Processes at Aryl‐Modified Glassy Carbon Electrode

The effect of a layer of electrochemically grafted 4‐diazo‐N,N‐diethylaniline (DEA) groups on the electron transfer kinetics of redox systems, displaying fast and slow heterogeneous electron transfer rate constants at edge and basal planes of carbon, was investigated. The properties of the modified electrode were characterized by cyclic voltammetry using four different inorganic redox systems (Fe(CN) , Co(phen) , Ru(NH₃) , and IrCl in acidic, neutral, and basic media. Two distinct blocking behaviors and electrostatic effects were observed. More precisely, a strong blocking effect of the grafted layer on Fe(CN) and Co(phen) was found, whereas Ru(NH₃) and IrCl showed to be rather unaffected by the presence of the DEA grafted layer.     

Stepwise Strategy to Cyclometallated PtII Complexes with N‐Heterocyclic Carbene Ligands: A Luminescence Study on New β‐Diketonate Complexes

The imidazolium salt 3‐methyl‐1‐(naphthalen‐2‐yl)‐1H‐imidazolium iodide ( 2 ) has been treated with silver(I) oxide and [{Pt(μ‐Cl)(η³‐2‐Me‐C₃H₄)}₂] (η³‐2‐Me‐C₃H₄=η³‐2‐methylallyl) to give the intermediate N‐heterocyclic carbene complex [PtCl(η³‐2‐Me‐C₃H₄)(H$\widehat{CC}$ *‐κC*)] ( 3 ) (H$\widehat{CC}$ *‐κC*=3‐methyl‐1‐(naphthalen‐2‐yl)‐1H‐imidazol‐2‐ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five‐membered platinacycle compound [{Pt(μ‐Cl)($\widehat{CC}$ *)}₂] ( 4 ). Chlorine abstraction from 4 with β‐diketonate Tl derivatives rendered the corresponding neutral compounds [Pt($\widehat{CC}$ *)(L‐O,O′)] {L=acac (HL=acetylacetone) 5 , phacac (HL=1,3‐diphenyl‐1,3‐propanedione) 6 , hfacac (HL=hexafluoroacetylacetone) 7 }. All of the compounds ( 3 – 7 ) were fully characterized by standard spectroscopic and analytical methods. X‐ray diffraction studies were performed on 5 – 7 , revealing short Pt?Pt and π–π interactions in the solid‐state structure. The influence of the R‐substituents of the β‐diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5 , as phosphor converter has also been studied.