Me3SiSiMe2(OnBu): a disilane reagent for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement

Herein, a readily available disilane Me₃SiSiMe₂(OⁿBu) has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement. This protocol enables the incorporation of a silylene into different starting materials, including acrylamides, alkene-tethered 2-(2-iodophenyl)-1H-indoles, and 2-iodobiaryls, via the cleavage of Si–Si, Si–C, and Si–O bonds, leading to the formation of spirobenzosiloles, fused benzosiloles, and π-conjugated dibenzosiloles in moderate to good yields. Preliminary mechanistic studies indicate that this transformation is realized by successive palladium-catalyzed bis-silylation and Brook- and retro-Brook-type rearrangement of silane-tethered silanols.

A readily available disilane Me₃SiSiMe₂(OⁿBu) as a silylene source has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement.     

Impact of anion polarizability on ion pairing in microhydrated salt clusters

Despite longstanding interest in the mechanism of salt dissolution in aqueous media, a molecular level understanding remains incomplete. Here, cryogenic ion trap vibrational action spectroscopy is combined with electronic structure calculations to track salt hydration in a gas phase model system one water molecule at a time. The infrared photodissociation spectra of microhydrated lithium dihalide anions [LiXX′(H₂O)_n]⁻ (XX′ = I₂, ClI and Cl₂; n = 1–3) in the OH stretching region (3800–2800 cm⁻¹) provide a detailed picture of how anion polarizability influences the competition among ion–ion, ion–water and water–water interactions. While exclusively contact ion pairs are observed for n = 1, the formation of solvent-shared ion pairs, identified by markedly red-shifted OH stretching bands (<3200 cm⁻¹), originating from the bridging water molecules, is favored already for n = 2. For n = 3, Li⁺ reaches its maximum coordination number of four only in [LiI₂(H₂O)₃]⁻, in accordance with the hard and soft Lewis acid and base principle. Water–water hydrogen bond formation leads to a different solvent-shared ion pair motif in [LiI₂(H₂O)₃]⁻ and network formation even restabilizes the contact ion pair motif in [LiCl₂(H₂O)₃]⁻. Structural assignments are exclusively possible after the consideration of anharmonic effects. Molecular dynamics simulations confirm that the significance of large amplitude motion (of the water molecules) increases with increasing anion polarizability and that needs to be considered already at cryogenic temperatures.

Infrared spectroscopy of microhydrated salt clusters provides a detailed picture of how anion polarizability influences the interactions between ions and water.     

Enthalpies of the formation and decomposition of hydrogen trioxide HOOOH in an aqueous solution

The enthalpies of the formation and decomposition of hydrogen trioxide are estimated from the heating curves of peroxide-radical condensates synthesized from gaseous O₂ + H₂ mixtures. Enthalpy of decomposition Н₂О₃(aq.) → Н₂О(liq.) + О₂(gas) is ?31.2 ± 1.5 kcal/mol, and enthalpy of formation Δ_fH(H₂O₃, aq.) =–37.5 ± 1.6 kcal/mol. Both values correspond to the temperature range of 240–265 K.     

Primärprodukte der Wasserphotolyse bei 1849 Å

Zusammenfassung Die Photolyse des Wassers bei 1849 Å wurde unter Verwendung von 0,01m-Formiat als Fänger für die H-Atome und OH-Radikale untersucht. Dabei diente 5m-Äthanol als Aktinometer mit einem korrigierten Wert für (H₂)=0,50. In diesem Fall wurde eine Quantenausbeute der Wasserphotolyse (H, OH)=0,36±0,01 bestimmt. Bezieht man die exper. Daten auf das N₂O-Aktinometer bei (–N₂O)=1,0, dann ist (H, OH)=0,29±0,01. In diesem Wert ist auch die Quantenausbeute der reaktionsfähigen angeregten Wassermoleküle, die mit Formiat reagieren, inbegriffen. Auf Grund von experimentellen Daten wurde ferner die Bildung von solvatisierten Elektronen (e ^–aq) vorgeschlagen. Durch Sättigung der Formiatlösung mit Kohlensäure, die sowohl vone ^–aq als auch von H₂O^* reduziert werden kann, wurde (e ^–aq, H₂O^*)>0,02<0,04 bestimmt.

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Liquid water photolysis at 1849 Å was investigated by using 0,01m-formate as scavenger for the H and OH radicals. 5M-ethyl alcohol serviced as actinometer with a corrected value of (H₂)=0,50. The quantum yield of water photolysis was determined in this case to be (H, OH)=0,36±0,01. When the experimental results are related to N₂O actinometer with (–N₂O)=1,0, a quantum yield of (H, OH)=0,29±0,01 is obtained. This value includes also the quantum yield of the excited water molecules which react with the formate. Based on experimental data the formation of solvated electrons (e ^–aq) is proposed. By saturation of the formate solution with carbon dioxide, which can be reduced bye ^–aq as well as by H₂O^*, (e ^–aq, H₂O^*>0,02<0,04 was determined.

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Mit 4 Abbildungen     

Modelling local structural and electronic consequences of proton and hydrogen-atom uptake in VO2 with polyoxovanadate clusters

We report the synthesis and characterisation of a series of siloxide-functionalised polyoxovanadate–alkoxide (POV–alkoxide) clusters, [V₆O₆(OSiMe₃)(OMe)₁₂]ⁿ (n = 1−, 2−), that serve as molecular models for proton and hydrogen-atom uptake in vanadium dioxide, respectively. Installation of a siloxide moiety on the surface of the Lindqvist core was accomplished via addition of trimethylsilyl trifluoromethylsulfonate to the fully-oxygenated cluster [V₆O₇(OMe)₁₂]²⁻. Characterisation of [V₆O₆(OSiMe₃)(OMe)₁₂]¹⁻ by X-ray photoelectron spectroscopy reveals that the incorporation of the siloxide group does not result in charge separation within the hexavanadate assembly, an observation that contrasts directly with the behavior of clusters bearing substitutional dopants. The reduced assembly, [V₆O₆(OSiMe₃)(OMe)₁₂]²⁻, provides an isoelectronic model for H-doped VO₂, with a vanadium(iii) ion embedded within the cluster core. Notably, structural analysis of [V₆O₆(OSiMe₃)(OMe)₁₂]²⁻ reveals bond perturbations at the siloxide-functionalised vanadium centre that resemble those invoked upon H-atom uptake in VO₂ through ab initio calculations. Our results offer atomically precise insight into the local structural and electronic consequences of the installation of hydrogen-atom-like dopants in VO₂, and challenge current perspectives of the operative mechanism of electron–proton co-doping in these materials.

We report the synthesis and characterisation of a series of siloxide-functionalised polyoxovanadate–alkoxide clusters, [V₆O₆(OSiMe₃)(OMe)₁₂]ⁿ (n = 1⁻, 2⁻), that serve as molecular models for proton and hydrogen-atom uptake in vanadium dioxide.     

Synthesis and hydrogenation of polycyclic aromatic hydrocarbon-substituted diborenes via uncatalysed hydrogenative B–C bond cleavage

The classical route to the PMe₃-stabilised polycyclic aromatic hydrocarbon (PAH)-substituted diborenes B₂Ar₂(PMe₃)₂ (Ar = 9-phenanthryl 7-Phen; Ar = 1-pyrenyl 7-Pyr) via the corresponding 1,2-diaryl-1,2-dimethoxydiborane(4) precursors, B₂Ar₂(OMe)₂, is marred by the systematic decomposition of the latter to BAr(OMe)₂ during reaction workup. Calculations suggest this results from the absence of a second ortho-substituent on the boron-bound aryl rings, which enables their free rotation and exposes the B–B bond to nucleophilic attack. 7-Phen and 7-Pyr are obtained by the reduction of the corresponding 1,2-diaryl-1,2-dichlorodiborane precursors, B₂Ar₂Cl₂(PMe₃)₂, obtained from the SMe₂ adducts, which are synthesised by direct NMe₂–Cl exchange at B₂Ar₂(NMe₂)₂ with (Me₂S)BCl₃. The low-lying π* molecular orbitals (MOs) located on the PAH substituents of 7-Phen and 7-Pyr intercalate between the B–B-based π and π* MOs, leading to a relatively small HOMO–LUMO gap of 3.20 and 2.72 eV, respectively. Under vacuum or at high temperature 7-Phen and 7-Pyr undergo intramolecular hydroarylation of the B B bond to yield 1,2-dihydronaphtho[1,8-cd][1,2]diborole derivatives. Hydrogenation of 7-Phen, 7-Pyr and their 9-anthryl and mesityl analogues III and II, respectively, results in all cases in splitting of the B–B bond and isolation of the monoboranes (Me₃P)BArH₂. NMR-spectroscopic monitoring of the reactions, solid-state structures of isolated reaction intermediates and computational mechanistic analyses show that the hydrogenation of the three PAH-substituted diborenes proceeds via a different pathway to that of the dimesityldiborene. Rather than occurring exclusively at the B–B bond, hydrogenation of 7-Ar and III proceeds via a hydroarylated intermediate, which undergoes one B–B bond-centered H₂ addition, followed by hydrogenation of the endocyclic B–C bond resulting from hydroarylation, making the latter effectively reversible.

In contrast to classical B–B bond-centred diborene hydrogenation, polycyclic aromatic hydrocarbon-substituted diborenes first undergo thermal intramolecular hydroarylation, followed by hydrogenation of the remaining B–B and endocyclic B–C bonds.     

Synthesis and thermochemistry of SrB2O4·4H2O and SrB2O4

Two pure strontium borates SrB₂O₄·4H₂O and SrB₂O₄ have been synthesized and characterized by means of chemical analysis and XRD, FT-IR, DTA-TG techniques. The molar enthalpies of solution of SrB₂O₄·4H₂O and SrB₂O₄ in 1 mol dm⁻³ HCl(aq) were measured to be −(9.92 ± 0.20) kJ mol⁻¹ and −(81.27 ± 0.30) kJ mol⁻¹, respectively. The molar enthalpy of solution of Sr(OH)₂·8H₂O in (HCl + H₃BO₃)(aq) were determined to be −(51.69 ± 0.15) kJ mol⁻¹. With the use of the enthalpy of solution of H₃BO₃ in 1 mol dm⁻³ HCl(aq), and the standard molar enthalpies of formation for Sr(OH)₂·8H₂O(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(3253.1 ± 1.7) kJ mol⁻¹ for SrB₂O₄·4H₂O, and of −(2038.4 ± 1.7) kJ mol⁻¹ for SrB₂O₄ were obtained.     

The thermodynamic characteristics of hydrogen peroxide in H2SO4-H2O solutions

The paper presents experimental data and an analysis of literature data on hydrogen peroxide forms in concentrated solutions of sulfuric acid, H₂O₂(aq), H₃O ₂ ⁺ (aq), and HSO ₅ ^? (aq). The thermodynamic constants of the parallel equilibria $\begin{array}{*{20}c} {H_2 O_2 (aq) + H_3 O^ + (aq) \Leftrightarrow H_3 O_2^ + (aq) + H_2 O (K_1 (298) = 8 \times 10^{ - 4} ),} \\ {H_2 O_2 (aq) + HSO_4^ - (aq) \Leftrightarrow HSO_5^ - (aq) + H_2 O (K_2 (298) = 1.2 \times 10^{ - 2} )} \\ \end{array} $ were determined. The activity coefficients of H₂O₂ and Henry constants for solutions of H₂O₂ in sulfuric acid were calculated.     

Spatial reorganization of analytes in charged aqueous microdroplets

Imprinted charged aqueous droplets of micrometer dimensions containing spherical gold and silver nanoparticles, gold nanorods, proteins and simple molecules were visualized using dark-field and transmission electron microscopies. With such studies, we hoped to understand the unusual chemistry exhibited by microdroplets. These droplets with sizes in the range of 1–100 μm were formed using a home-built electrospray source with nitrogen as the nebulization gas. Several remarkable features such as mass/size-selective segregation and spatial localization of solutes in nanometer-thin regions of microdroplets were visualized, along with the formation of micro–nano vacuoles. Electrospray parameters such as distance between the spray tip and surface, voltage and nebulization gas pressure influenced particle distribution within the droplets. We relate these features to unusual phenomena such as the enhancement of rates of chemical reactions in microdroplets.

Microscopic visualization of charged aqueous microdroplets reveals mass/size-selective segregation and spatial localization of solutes in the nanometer-thin air–water interface, along with the formation of micro–nano vacuoles at the droplet interior.     

Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

Dilute aqueous phosphoric acid solutions have been studied by Raman spectroscopy at room temperature and over a broad temperature range from 5 to 301?°C. R-normalized spectra (Bose?CEinstein correction) have been constructed and used for quantitative analysis. The vibrational modes of H₃PO₄(aq) (pseudo C_3v symmetry) have been assigned. The band with the highest intensity, the symmetric stretch ?? _s{P(OH)₃}(?? ₁(a ₁)) is strongly polarized while ?? ₄(e), the antisymmetric stretch ?? _asP(OH)₃) is depolarized. The stretching mode of the phosphoryl group (?CP=O), ?? ₂(a₁) occurs at 1178?cm^?1 and is polarized. In the range between 300 and 600?cm^?1, the deformation modes are observed. The deformation mode, ??{PO?CH}, involving the O?CH group has been detected at 1250?cm^?1 as a very weak and broad mode. In addition to the modes of phosphoric acid, modes of the dissociation product $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -}(\mathrm{aq})$ have been observed. The mode at 1077?cm^?1 has been assigned to ?? _s{PO₂}, and the mode at 877?cm^?1 to ?? _s{P(OH)₂} which is overlapped by ?? _s{P(OH)₃} of H₃PO₄(aq). The modes of $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -} \mathrm{(aq)}$ have been measured in dilute solution and were assigned and presented as well. H₃PO₄ is hydrated in aqueous solution, which can be verified with Raman spectroscopy by following the modes ?? ₂(a₁) and ?? ₁(a₁) as a function of temperature. These modes show a strong temperature dependency. The mode ?? ₁(a₁) broadens and shifts to lower wavenumbers. The mode ?? ₂(a₁) on the other hand, shifts to higher wavenumbers and broadens considerably with increases in temperature. At 301?°C the phosphoric acid is almost molecular in nature. In very dilute H₃PO₄ solutions at room temperature, however, the dissociation product, $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -} \mathrm{(aq)}$ is the dominant species. In these dilute H₃PO₄(aq) solutions no spectroscopic features could be detected for a hydrogen bonded dimeric species of the formula $\mathrm{H}_{5}\mathrm{P}_{2}\mathrm{O}_{8}^{ -}$ (or the neutral dimeric acid H₆P₂O₈). Pyrophosphate formation, although favored at high temperatures, could not be detected in dilute solution even at 301?°C due to the high water activity. In highly concentrated solutions, however, pyrophosphate formation is observable and in hydrate melts the formation of pyrophosphate is already noticeable at room temperature. Quantitative Raman measurements have been carried out to follow the dissociation of H₃PO₄(aq) over a very broad temperature range. In the temperature interval from 5.0 to 301.0?°C the pK ₁ values for H₃PO₄(aq) have been determined and thermodynamic data have been derived.     

Osmium(ii) tethered half-sandwich complexes: pH-dependent aqueous speciation and transfer hydrogenation in cells

Aquation is often acknowledged as a necessary step for metallodrug activity inside the cell. Hemilabile ligands can be used for reversible metallodrug activation. We report a new family of osmium(ii) arene complexes of formula [Os(η⁶-C₆H₅(CH₂)₃OH)(XY)Cl]^+/0 (1–13) bearing the hemilabile η⁶-bound arene 3-phenylpropanol, where XY is a neutral N,N or an anionic N,O⁻ bidentate chelating ligand. Os–Cl bond cleavage in water leads to the formation of the hydroxido/aqua adduct, Os–OH(H). In spite of being considered inert, the hydroxido adduct unexpectedly triggers rapid tether ring formation by attachment of the pendant alcohol–oxygen to the osmium centre, resulting in the alkoxy tethered complex [Os(η⁶-arene-O-κ¹)(XY)]ⁿ⁺. Complexes 1C–13C of formula [Os(η⁶:κ¹-C₆H₅(CH₂)₃OH/O)(XY)]⁺ are fully characterised, including the X-ray structure of cation 3C. Tether-ring formation is reversible and pH dependent. Osmium complexes bearing picolinate N,O-chelates (9–12) catalyse the hydrogenation of pyruvate to lactate. Intracellular lactate production upon co-incubation of complex 11 (XY = 4-Me-picolinate) with formate has been quantified inside MDA-MB-231 and MCF7 breast cancer cells. The tether Os–arene complexes presented here can be exploited for the intracellular conversion of metabolites that are essential in the intricate metabolism of the cancer cell.

New Os(ii) half-sandwich complexes bearing a pendant alcohol prompt reversible tether-ring formation upon aquation, protecting Os against deactivation. Excitingly, these complexes mediate hydrogenation of pyruvate to lactate inside cancer cells.     

The Solubility of Sodium Sulfate and the Reduction of Aqueous Sulfate by Magnetite under Near-Critical Conditions

The solubility of Na₂SO₄ (s) (thenardite) and the interactions between magnetiteand aqueous Na₂SO₄ near the critical point of water have been determined in azirconium-alloy flow reactor at temperatures 350°C t 375°C and isobaricpressures 190 p 305 bar. The experimental solubility data are describedwell as a function of temperature and solvent density ₁ byln x(Na₂SO₄, aq.) = –10.47 – 27550/T +(4805/T) ln ₁.The interaction between magnetite and Na₂SO₄ (aq.) was examined from 250 to370°C at molalities near the saturation composition of Na₂SO₄ (s). While no solidreaction products were observed, HS^– (aq.) was observed to form above 350°Cby sulfate reduction, as a product of the reaction8 Fe₃O₄(s) + Na₂SO₄ (aq.) + H₂O(l)= 12 Fe₂O₃ (s) + NaHS (aq.) + NaOH (aq.).The reduction reaction appears to be controlled by surface reaction kinetics, ata level well below the equilibrium molality of HS^– (aq.). Metallic iron reactedwith Na₂SO₄ (aq.) in a similar fashion at temperatures above 350°C, to yieldhigher molalities of HS^– (aq.).     

Etude Experimentale et Modelisation des Equilibres Solide—Liquide du Systeme Binaire H2O—UO2(NO3)2

The binary system H₂O—UO₂(NO₃)₂ was studied by solubility measurements and constant heat flow thermal analysis. Temperature and composition of the eutectic transformation between ice and uranyl nitrate hexahydrate were accurately defined. A new hydrate with 24 molecules of water decomposes at –21°C according to the peritectoid reaction<UO₂(NO₃)₂·24H₂O> <UO₂(NO₃)₂·6H₂O> + 18<H₂O>The quasi-ideal model was applied to the solid—liquid equilibria, using the following reaction hypothesis:((UO ₂ ²⁺ )) + 2((NO ₃ ^– ))+ h((H₂O)) ((UO₂OH⁺aq)) + ((H₃O⁺aq + 2((NO ₃ ^– aq))A complete calculation of the binary system was carried out with a global ionic hydration number h equal to 9 in the aqueous solutions. It allowed to the melting enthalpies of uranyl nitrate hydrates.

This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermodynamics of the hydrolysis reactions of adenosine 3′,5′-(cyclic)phosphate(aq) and phosphoenolpyruvate(aq); the standard molar formation properties of 3′,5′-(cyclic)phosphate(aq) and phosphoenolpyruvate(aq)

Molar calorimetric enthalpy changes Δ_rH_m(cal) have been measured for the biochemical reactions {cAMP(aq) + H₂O(l)=AMP(aq)} and {PEP(aq) + H₂O(l)=pyruvate(aq) + phosphate(aq)}. The reactions were catalyzed, respectively, by phosphodiesterase 3^′,5^′-cyclic nucleotide and by alkaline phosphatase. The results were analyzed by using a chemical equilibrium model to obtain values of standard molar enthalpies of reaction Δ_rH_m^∘ for the respective reference reactions {cAMP⁻(aq) + H₂O(l)=HAMP⁻(aq)} and {PEP³⁻(aq) + H₂O(l)=pyruvate⁻(aq) + HPO²⁻₄(aq)}. Literature values of the apparent equilibrium constants K^′ for the reactions {ATP(aq)=cAMP(aq) + pyrophosphate(aq)}, {ATP(aq) + pyruvate(aq)=ADP(aq) + PEP(aq)}, and {ATP(aq) + pyruvate(aq) + phosphate(aq)=AMP(aq) + PEP(aq) + pyrophosphate(aq)} were also analyzed by using the chemical equilibrium model. These calculations yielded values of the equilibrium constants K and standard molar Gibbs free energy changes Δ_rG_m^∘ for ionic reference reactions that correspond to the overall biochemical reactions. Combination of the standard molar reaction property values (K, Δ_rH_m^∘, and Δ_rG_m^∘) with the standard molar formation properties of the AMP, ADP, ATP, pyrophosphate, and pyruvate species led to values of the standard molar enthalpy Δ_fH_m^∘ and Gibbs free energy of formation Δ_fG_m^∘ and the standard partial molar entropy S_m^∘ of the cAMP and PEP species. The thermochemical network appears to be reasonably well reinforced and thus lends some confidence to the accuracy of the calculated property values of the variety of species involved in the several reactions considered herein.     

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate species H₃PO ₄ ⁰ (aq),H₂PO ₄ ^? (aq),HPO ₄ ^2? (aq) or PO ₄ ^3? (aq). Many divalent, trivalent and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation require comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier, with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ?mol^?1 per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq) ions at 298.15 K and p?° =1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S _m ^o (H₂PO ₄ ^? , aq, 298.15 K) = (90.6±1.5) J?K^?1?mol^?1 was obtained.     

Thermodynamics of Aqueous Diethylenetriaminepentaacetic Acid (DTPA) Systems: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous H2DTPA3−, DTPA5−, CuDTPA3−, and Cu2DTPA− from 10 to 55°C

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na₅DTPA + NaOH, Na₃CuDTPA + NaOH, and NaCu₂DTPA + NaOH, and the single electrolyte Na₃H₂DTPA (DTPA=diethylenetriaminepentaacetic acid) at temperatures from 10 to 55°C. The experimental results have been analyzed in terms of Young's rule with the Guggenheim form of the extended Debye–Hückel equation and the Pitzer ion-interaction model. These calculations led to standard partial molar heat capacities and volumes for the species H₂DTPA^3–(aq), DTPA^5–(aq), CuDTPA^3–(aq), and Cu₂DTPA^–(aq) at each temperature. The partial molar properties at 0.1 m ionic strength were also calculated. The standard partial molar properties were extrapolated to elevated temperatures with the revised Helgeson–Kirkham–Flowers (HKF) model. Values for the partial molar heat capacities from the HKF model have been combined with the literature data to estimate the ionization constants of H₂DTPA^3–(aq) and the formation constant of the CuDTPA^3–(aq) copper complex at temperatures up to 300°C.     

Site-selective amination and/or nitrilation via metal-free C(sp2)–C(sp3) cleavage of benzylic and allylic alcohols

Benzylic/allylic alcohols are converted via site-selective C(sp²)–C(sp³) cleavage to value-added nitrogenous motifs, viz., anilines and/or nitriles as well as N-heterocycles, utilizing commercial hydroxylamine-O-sulfonic acid (HOSA) and Et₃N in an operationally simple, one-pot process. Notably, cyclic benzylic/allylic alcohols undergo bis-functionalization with attendant increases in architectural complexity and step-economy.

Benzylic/allylic alcohols are converted via site-selective C(sp²)–C(sp³) cleavage to value-added nitrogenous motifs, viz., anilines and/or nitriles as well as N-heterocycles, utilizing commercial hydroxylamine-O-sulfonic acid (HOSA) and Et₃N in an operationally simple, one-pot process.     

Second-sphere effects on H2O2 activation by non-heme FeII complexes: role of a phenol group in the [H2O2]-dependent accumulation of FeIVO vs. FeIIIOOH

Redox metalloenzymes achieve very selective oxidation reactions under mild conditions using O₂ or H₂O₂ as oxidants and release harmless side-products like water. Their oxidation selectivity is intrinsically linked to the control of the oxidizing species generated during the catalytic cycle. To do so, a second coordination sphere is used in order to create a pull effect during the activation of O₂ or H₂O₂, thus ensuring a heterolytic O–O bond cleavage. Herein, we report the synthesis and study of a new non-heme Fe^II complex bearing a pentaazadentate first coordination sphere and a pendant phenol group. Its reaction with H₂O₂ generates the classical Fe^IIIOOH species at high H₂O₂ loading. But at low H₂O₂ concentrations, an Fe^IVO species is generated instead. The formation of the latter is directly related to the presence of the 2nd sphere phenol group. Kinetic, variable temperature and labelling studies support the involvement of the attached phenol as a second coordination sphere moiety (weak acid) during H₂O₂ activation. Our results suggest a direct Fe^II → Fe^IVO conversion directed by the 2nd sphere phenol via the protonation of the distal O atom of the Fe^II/H₂O₂ adduct leading to a heterolytic O–O bond cleavage.

A new Fe^II complex with a phenol group attached as a second coordination sphere moiety activates H₂O₂ to yield Fe^IVO following a mechanism reminiscent of peroxidase enzymes.     

M-Carboxylic Acid Induced Formation of New Coordination Polymers for Efficient Photocatalytic Degradation of Ciprofloxacin

Four new 2–3D materials were designed and synthesized by hydrothermal methods, namely, {[(L1·Cu·2H₂O) (4,4-bipy)_0.5] (β-Mo₈O₂₆)_0.5·H₂O} (1), {[(L1·Cu)₂·(4,4-bipy)] (Mo₅O₁₆)} (2), {Co(L1)₂}_n (3), and {[(L1)₂][β-Mo₈O₂₆]_0.5·5H₂O} (4). [L1=5-(4-aminopyridine) isophthalic acid]. The degradation of ciprofloxacin (CIP) in water by compounds 1–4 was studied under visible light. The experimental results show that compounds 1–4 have obvious photocatalytic degradation effect on CIP. In addition, for compound 1, the effects of temperature, pH, and adsorbent dosage on photocatalytic performance were also investigated. The stability of compound 1 was observed by a cycle experiment, indicating that there was no significant change after three cycles of CIP degradation.     

Thermochemistry of NaRb[B4O5(OH)4]·4H2O

The enthalpies of solution of NaRb[B₄O₅(OH)₄]·4H₂O in approximately 1 mol dm⁻³ aqueous hydrochloric acid and of RbCl in aqueous (hydrochloric acid + boric acid + sodium chloride) were determined. From these results and the enthalpy of solution of H₃BO₃ in approximately 1 mol dm⁻³ HCl(aq) and of sodium chloride in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(5128.02 ± 1.94) kJ mol⁻¹ for NaRb[B₄O₅(OH)₄]·4H₂O was obtained from the standard molar enthalpies of formation of NaCl(s), RbCl(s), H₃BO₃(s) and H₂O(l). The standard molar entropy of formation of NaRb[B₄O₅(OH)₄]·4H₂O was calculated from the Gibbs free energy of formation of NaRb[B₄O₅(OH)₄]·4H₂O computed from a group contribution method.