Kristallstruktur des Zinkamids Zn[N(SiMe3)2]2

Crystal Structure of the Zinc Amide Zn[N(SiMe₃)₂]₂ X‐ray quality crystals of Zn[N(SiMe₃)₂]₂ (monoclinic, P2₁/c) are obtained by sublimation of the zinc amide Zn[N(SiMe₃)₂]₂ at —30 °C in vacuo (300 torr). According to the result of the X‐ray structural analysis, Zn[N(SiMe₃)₂]₂ contains an almost linear N‐Zn‐N unit with two short N‐Zn bonds.     

Proton shuttle efficiency of bicarbonate: A theoretical study on tautomerization and CO2 hydration

The efficiency of bicarbonate molecule (HCO₃⁻) as a proton shuttle in the tautomerization and (non)enzymatic CO₂ hydration reactions has been investigated with the aid of computational chemistry methods (DFT and ab initio). The results revealed that bicarbonate can decrease the barrier height of tautomerization (keto-enol, azo-hydrazo and imine-amine) more than 70%. This value is around 45% for water molecules. Also, HCO₃⁻ can catalyze the CO₂ hydration both inside (enzymatic) and outside (nonenzymatic) the active site of human carbonic anhydrases II (HCA II). In the absence of enzyme, bicarbonate molecule can lower the CO₂ hydration from ∼50 kcal mol⁻¹ in the gas phase to ∼14 kcal mol⁻¹ in the aqueous media. This reaction maintains its barrier (∼15 kcal mol⁻¹) for bicarbonate-Zn complex in the active site of enzyme; it has been observed that amino acid residues, mainly Thr199 and Glu106, are actively involved in the proton transfer network and facilitate CO₂ hydration ability of bicarbonate.     

Enhanced Electrocatalytic Activity of a Zinc Porphyrin for CO2 Reduction: Cooperative Effects of Triazole Units in the Second Coordination Sphere

The control of the second coordination sphere in a coordination complex plays an important role in improving catalytic efficiency. Herein, we report a zinc porphyrin complex ZnPor8T with multiple flexible triazole units comprising the second coordination sphere, as an electrocatalyst for the highly selective electrochemical reduction of carbon dioxide (CO₂) to carbon monoxide (CO). This electrocatalyst converted CO₂ to CO with a Faradaic efficiency of 99 % and a current density of −6.2 mA cm⁻² at −2.4 V vs. Fc/Fc⁺ in N,N-dimethylformamide using water as the proton source. Structure-function relationship studies were carried out on ZnPor8T analogs containing different numbers of triazole units and distinct triazole geometries; these unveiled that the triazole units function cooperatively to stabilize the CO₂-catalyst adduct in order to facilitate intramolecular proton transfer. Our findings demonstrate that incorporating triazole units that function in a cooperative manner is a versatile strategy to enhance the activity of electrocatalytic CO₂ conversion.     

Carboxysome-Inspired Electrocatalysis using Enzymes for the Reduction of CO2 at Low Concentrations**

The electrolysis of dilute CO₂ streams suffers from low concentrations of dissolved substrate and its rapid depletion at the electrolyte-electrocatalyst interface. These limitations require first energy-intensive CO₂ capture and concentration, before electrolyzers can achieve acceptable performances. For direct electrocatalytic CO₂ reduction from low-concentration sources, we introduce a strategy that mimics the carboxysome in cyanobacteria by utilizing microcompartments with nanoconfined enzymes in a porous electrode. A carbonic anhydrase accelerates CO₂ hydration kinetics and minimizes substrate depletion by making all dissolved carbon available for utilization, while a highly efficient formate dehydrogenase reduces CO₂ cleanly to formate; down to even atmospheric concentrations of CO₂. This bio-inspired concept demonstrates that the carboxysome provides a viable blueprint for the reduction of low-concentration CO₂ streams to chemicals by using all forms of dissolved carbon.     

CO2‐Speicherung. Chancen und Risiken

Anthropogenic emissions of carbon dioxide (CO₂) into the atmosphere have had a significant impact on the Earth's carbon cycle. As part of the global effort to reduce climate change, the geological storage of CO₂ has been accepted as a method that may provide up to 25 % of the total reduction of emissions, although this figure is still subject to change. In Germany and worldwide, geological storage capacities are expected to be sufficient for several decades. Carbon dioxide can be captured from sources such as large‐scale industrial (energy, steel, cement or chemical) facilities and transported to long‐term storage sites in deep saltwater‐bearing aquifers. Above the porous sandstone reservoirs in which the CO₂ is to be stored, an impermeable cap rock is required to provide a barrier for the upward‐migrating gas. In time, a significant quantity of the CO₂ can be retained within the reservoir pore space by capillary forces, dissolved in water to form carbonic acid, or deposited as carbonate minerals. The storage site must be free of potential leakage pathways. To this end, extensive monitoring programs need to be carried out. The Ketzin pilot site, an example of such a program, has shown CO₂ storage on a research scale to be safe and reliable.     

Basische Carbonate des Dysprosiums: Dy2O2(CO3) und Dy(OH)(CO3)

Basic Carbonates of Dysprosium: Dy₂O₂(CO₃) and Dy(OH)(CO₃) Single crystals of the basic carbonates Dy₂O₂(CO₃) and Dy(OH)(CO₃) are obtained via hydrothermal synthesis from a mixture of DyCl₃ · 6 H₂O and K₂CO₃ and Cs₂CO₃, respectively, as well as CO₂ and H₂O in a steel autoclave at 480 and 400 °C, respectively. The crystal structures are isotypic with those of II‐Nd₂O₂(CO₃) and B–Nd(OH)(CO₃), respectively; Dy₂O₂(CO₃): hexagonal, P6₃/mmc, Z = 2; a = 386.9(2), c = 1516.3(3) pm; Dy(OH) · (CO₃): hexagonal, P‐6, Z = 18; a = 1201.0(1), c = 971.8(9) pm.     

Fluorinated surfactants in supercritical CO2

Liquid or supercritical carbon dioxide has important environmental and economic advantages over petrochemical solvents currently used for industrial processes. However, low solubility in CO₂, particularly of polar compounds, is a hurdle to its implementation as an acceptable alternative. These solubility problems have been overcome by employing specialised fluorinated surfactants to stabilise water nano-droplets as water-in-supercritical/liquid CO₂ microemulsions. Such novel microemulsions can now facilitate innovative ‘green-and-clean’ applications of carbon dioxide technology.     

Theoretical study of carbonic anhydrase-catalyzed hydration of co2: A brief review

Quantum mechanical calculations have been used to study the reaction mechanism of human carbonic anhydrase-catalyzed hydration of CO₂. This reaction is responsible for fast metabolism of CO₂ in the human body. For each of the reaction steps, possible catalytic effects of active site residues are examined. The pertinent results are as follows. (1) For CO₂ binding, the experimentally observed 2.5 cm^?1 frequency shift of the asymmetic stretching frequency between measurements taken in the aqueous solution and in the enzyme is reproduced in our theoretical calculations. Our results suggest that CO₂ binds to the zinc ion within the hydrophobic pocket. (2) No energy barrier is found for the nucleophilic attack from Zn²⁺?bound OH^? to C of CO₂ to form Zn²⁺?bound HCO₃^?. (3) For the internal proton transfer within zinc-bound HCO₃^?, the barrier of 35.6 kcal/mol for the direct internal proton transfer is reduced to 3.5 and 1.4 kcal/mol, respectively, when one or two water molecules are included for proton relay. (4) Displacement of Zn²⁺?bound HCO₃^? by H₂O is facilitated by the presence of the negatively charged Glu 106-Thr 199 chain and by the association and the subsequent ionization of a fifth water ligand. (5) For the intramolecular proton transfer between Zn²⁺-bound H₂O and His 64, the Zn²⁺ ion lowers the pK_a of Zn²⁺?bound water and repels the proton. His 64, or a similar proton receptor with a larger proton affinity than H₂O, functions as proton receiver; and the active site water molecules visualized by x-ray crystallography are important for the proton relay function. In summary, it is demonstrated that in order to achieve effective catalysis, a sequence of precisely coordinated catalytic events among all participating catalytic elements in the enzyme's active site is essential.     

Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2

The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO₂ revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO₂ co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion.     

A vibrational-spectroscopic study of the species present in the CO2−H2O system

Raman and infrared spectra have been recorded of water and heavy-water solutions of carbon dioxide, potassium bicarbonate, and potassium carbonate. The structures of the carbonate and bicarbonate ions and CO₂ (aqueous solution) have been determined from a consideration of Raman and infrared data. The results reveal the presence of solvent effects in the carbonate and CO₂ water solutions. No bands characteristic of H₂CO₃ were observed in the Raman spectrum of aqueous solutions of CO₂.     

Kinetic studies of methanol synthesis from CO_2+H_2 over copper based catalysts

The catalytic activity for the synthesis of methanol from carbon dioxide and hydrogen wasmeasured on various binary and ternary catalysts containing copper oxide under a pressure of 10 atm.Among these samples the catalysts, CuO/ZnO/γ-Al_2O_3, demonstrated the highest activity andselectivity to methanol; MnO, as third component, had no promotional effect on the activity of meth-anol formation. Based on a simple power rate law the apparent activation energy estimation and par-tial pressure dependence measurement were accomplished over eight catalysts. The activation energiesvaried from 40 to 120 kJ / mol depending on the composition of catalysts. The rates of methanol for-mation to be 0.3 -- 0.9 order in H_2 and about 0.1 -- 0.2 order in CO_2 were reported.     

Bioinspired Design of a Giant [Mn86] Nanocage-Based Metal-Organic Framework with Specific CO2 Binding Pockets for Highly Selective CO2 Separation

Adsorption-based removal of carbon dioxide (CO₂) from gas mixtures has demonstrated great potential for solving energy security and environmental sustainability challenges. However, due to similar physicochemical properties between CO₂ and other gases as well as the co-adsorption behavior, the selectivity of CO₂ is severely limited in currently reported CO₂-selective sorbents. To address the challenge, we create a bioinspired design strategy and report a robust, microporous metal–organic framework (MOF) with unprecedented [Mn₈₆] nanocages. Attributed to the existence of unique enzyme-like confined pockets, strong coordination interactions and dipole-dipole interactions are generated for CO₂ molecules, resulting in only CO₂ molecules fitting in the pocket while other gas molecules are prohibited. Thus, this MOF can selectively remove CO₂ from various gas mixtures and show record-high selectivities of CO₂/CH₄ and CO₂/N₂ mixtures. Highly efficient CO₂/C₂H₂, CO₂/CH₄, and CO₂/N₂ separations are achieved, as verified by experimental breakthrough tests. This work paves a new avenue for the fabrication of adsorbents with high CO₂ selectivity and provides important guidance for designing highly effective adsorbents for gas separation.     

Toward efficient catalysts for electrochemical CO2 conversion to C2 products

With impressive progress in carbon capture and renewable energy, carbon dioxide (CO₂) conversion into useful chemicals has become a potential tool against climate change. Electrochemical CO₂ conversion into C₂ products (ethylene and ethanol) is an especially economically promising approach and an active research area. Nonetheless, catalyst layer design for CO₂ conversion is challenging because of the complex CO₂-to-C₂ reaction pathways. In this review, we highlight key ideas in catalyst layer design for CO₂ conversion to C₂ in the past few years. We identify three fundamental principles to control catalyst selectivity—local CO₂ and CO concentration, local pH, and intermediate–catalyst interaction. To achieve these goals, we introduce design strategies for both catalytic materials and overall catalyst layer morphology.     

Infrared and mass spectral studies of proton irradiated H2O + CO2 ice: Evidence for carbonic acid

The effects of proton irradiation on mixed H₂O + CO₂ (1:1) ices at 20 K were investigated by infrared and mass spectroscopy. Infrared bands due to several radical (HCO, CO₃) and molecular (CO) product species were identified. In addition, several new broad and complex i.r. features were observed. On slow warming, the broad features evolved into a 215–250 K residual film whose absorptions have been tentatively assigned to carbonic acid. This identification agrees with the spectral data for irradiated H₂O + ¹³CO₂ ice and the results of an approximate normal coordinate analysis.     

CO2 sequestration by high initial strength Portland cement pastes

During the formation of pastes, mortar and concretes have been used to capture CO₂. This work presents a methodology to estimate the carbon dioxide (CO₂) sequestered by high strength and sulfate-resistant Portland cement pastes during their early stages of hydration, by Thermogravimetry and Derivative Thermogravimetry. Water to cement ratio equal to 0.50 and 0.70 were evaluated and the captured CO₂ amount was determined through TG/DTG curve data on initial cement mass basis, obtained during accelerated carbonation from the fluid state and accelerated carbonation after a first hydration process. The experiments were performed in a controlled chamber, maintaining the CO₂ content at 20 vol % and the temperature at 25 °C, at different relative humidity (RH) (60 and 80 %) ambient. The procedure allows one to estimate the amount of CO₂ sequestered by the initial cement mass of a given volume of paste, as well as to evaluate the RH and W/C ratio influence on the amount of hydrated formed products, mainly on the Ca(OH)₂, important for CO₂ fixation.     

A Luminescent Zinc(II) Coordination Polymer for Selective Detection of Fe3+ and Cr2O72− in Water and Catalytic CO2 Fixation

Fluorescence-based detection technique using coordination polymer has been considered an attractive alternative over conventional approaches. Herein, a new luminescent zinc(II) coordination polymer, [Zn(4-ABPT)(NIPA)(H₂O)], SSICG-5 , is synthesized by using a Lewis acidic Zn(II) ion, aromatic nitro group containing ligand 5-nitroisophthalic acid (H₂NIPA), and basic −NH₂ rich ligand 3,5-di(pyridine-4-yl)-4H-1,2,4-triazol-4-amine (4-ABPT). SSICG-5 can detect Fe³⁺ and Cr₂O₇²⁻ selectively with a LOD of 0.16 μM and 1.94 μM, respectively. Additionally, carbon dioxide (CO₂) fixation via one-pot CO₂ cycloaddition reaction has significant importance for reduced waste formation, minimizing reaction time and lowering chemical usage. Zn metal centre of SSICG-5 possesses a replaceable coordinated water molecule. The active metal sites combined with the Lewis acidic and basic sites of the ligands make SSICG-5 an ideal bifunctional heterogeneous catalyst for efficient CO₂ cycloaddition reaction under room temperature (RT), solvent-free conditions. Notably, SSICG-5 exhibits near quantitative conversion (turnover number (TON) of 198) of propylene oxide to its carbonate compound under mild reaction conditions.     

The Effect of the Modification of Carbon Spheres with ZnCl2 on the Adsorption Properties towards CO2

Zinc chloride and potassium oxalate are often applied as activating agents for carbon materials. In this work, we present the preparation of ZnO/carbon spheres composites using resorcinol-formaldehyde resin as a carbon source in a solvothermal reactor heated with microwaves. Zinc chloride as a zinc oxide source and potassium oxalate as an activating agent were applied. The effect of their addition and preparation conditions on the adsorption properties towards carbon dioxide at 0 °C and 25 °C were investigated. Additionally, for all tested sorbents, the CO₂ sorption tests at 40 °C, carried out utilizing a thermobalance, confirmed the trend of sorption capacity measured at 0 and 25 °C. Furthermore, the sample activated using potassium oxalate and modified using zinc chloride (a carbon-to-zinc ratio equal to 10:1) displayed not only a high CO₂ adsorption capacity (2.69 mmol CO₂/g at 40 °C) but also exhibited a stable performance during the consecutive multicycle adsorption–desorption process.     

Rate Determination of the CO2* Chemiluminescence Reaction CO + O + M CO2* + M

Electronically excited carbon dioxide (CO₂*) is known for its broadband emission, and its detection can lead to valuable information; however, owing to its broadband characteristics, CO₂* is difficult to isolate experimentally, and its chemical kinetics are not well known. Although numerous works have monitored CO₂* chemiluminescence, a full kinetic scheme for the excited species has yet to be developed. To this end, a series of shock‐tube experiments was performed in H₂‐N₂O‐CO mixtures highly diluted in argon at conditions where emission from CO₂* could be isolated and monitored. These results were used to evaluate the kinetics of CO₂*, in particular the main CO₂* formation reaction CO + O + M CO₂* + M (R1). Based on collision theory, the quenching chemistry of CO₂* was estimated for 11 collision partners. The final mechanism developed for CO₂* consists of 14 reactions and 13 species. The rate for (R1) was determined to within about ±60% using low‐pressure experiments performed in five different (H₂‐)N₂O‐CO‐Ar mixtures, as follows: where R is the universal gas constant in cal/mol‐K and T is the temperature in K. Final mechanism predictions were compared with experiments at low and high pressures, with good agreement at both conditions for the temperature dependence of the peak CO₂* and the CO₂* species time histories. Comparisons were also made with previous experiments in methane–oxygen mixtures, where there was slight overprediction of CO₂* experimental trends, but with the results otherwise showing a dramatic improvement over an earlier mechanism. Experimental results and model predictions were also compared with past literature rates for CO₂*, with good agreement for peak CO₂* trends and slight discrepancies in CO₂* species time histories. Overall, the ability of the CO₂* mechanism developed in this work to reproduce a range of experimental trends represents an important improvement over the existing knowledge base on chemiluminescence chemistry.     

Polysulfonylamine. CLIV [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 7 [2] Ein dreidimensionales Koordinationspolymer aus Schichten und Pfeilern: Kristallstruktur von Ba[(CH3SO2)2N]2·2H2O

Polysulfonylamines. CLIV. Crystal Structures of Metal Di(methanesulfonyl)amides. 7. A Three‐Dimensional Coordination Polymer Built up from Layers and Pillars: Crystal Structure of Ba[(CH₃SO₂)₂N]₂·2H₂O The barium compound BaA₂·2H₂O, derived from HA = di(methanesulfonyl)amine, has been characterized by single crystal X‐ray diffraction at —95 °C (monoclinic, space group P2₁/n, Z = 4). Despite numerous metal‐ligand bonds, the independent anions A^— and A′^— retain the pseudo‐C₂ symmetric conformation that commonly occurs in organic onium salts BH⁺A^—. The large cation attains ninefold coordination via interactions with one (O, N)‐chelating A^—, three κ¹O‐bonding A^—, two κ¹O‐bonding A′^— and two monodentate water molecules; if a distinctly longer barium‐water distance is included, the coordination number may alternatively be viewed as 9 + 1 and one water molecule regarded as an asymmetrically μ₂‐bridging ligand. In contrast to the previously reported layer structures of SrA₂ and PbA₂, the present crystal displays a three‐dimensional coordination assembly consisting of layers formed by the cations, the water molecules and the pentadentate A^— ligands, and of interlayer pillars provided by the bidentate A′^— ligands; however, the Ba²⁺/A^— substructure turns out to be topologically and crystallographically congruent with the corresponding M²⁺/A^— substructures in SrA₂ and PbA₂. The crystal cohesion of the barium complex is reinforced by four O(W)—H···O=S hydrogen bonds and several non‐classical C—H···O=S hydrogen bonds.     

Eine alternative Synthese des Oligoalumosiloxans [Ph2SiO]8[Al(O)OH]4 und seiner Alkohol‐Addukte

The oligoalumosiloxanes {[Ph₂SiO]₈[Al(O)OH]₄·2,5Et₂O·HOtBu} ( 6 ) and {[Ph₂SiO]₈[Al(O)OH]₄·2Et₂O·2HOiPr} ( 7 ) have been obtained from the reaction of diphenylsilanediol with aluminium‐tri‐tert‐butoxide and aluminium‐tri‐iso‐propoxide in ethyl ether with reasonable yields. In a 1:1 molar mixture of toluene and the respective alcohol (iso‐propanol or tert‐butanol), the ethyl ether molecules in {[Ph₂SiO]₈[Al(O)OH]₄·4Et₂O}, in 6 or 7 can be completely displaced forming the compounds [Ph₂SiO]₈[Al(O)OH]₄·4HOiPr ( 8 ) and [Ph₂SiO]₈[Al(O)OH]₄·nHOtBu ( 9 ). Whereas 6 , 7 and 8 are crystalline, 9 is obtained as a viscous liquid. An X‐ray structure determination on {[Ph₂SiO]₈[Al(O)OH]₄·3Et₂O·HOtBu} reveals different bonding modes of the diethyl ether molecules to the oligoalumosiloxane compared to the tert‐butanol, which forms two hydrogen bonds (one to the OH‐group of the inner Al₄(OH)₄ cycle and one through the alcohol OH‐group to a Si–O–Al moiety. The alcohol adducts have been characterized in solution through ¹H‐, ¹³C‐ and ²⁹Si‐NMR and show dynamic equilibria between the oligoalumosiloxane [Ph₂SiO]₈[Al(O)OH]₄ and the alcohol molecules.