Trinitromethyl-Substituted 1H-1,2,4-Triazole Bridging Nitropyrazole: A Strategy of Utterly Manipulable Nitration Achieving High-Energy Density Material.

Nitro groups have been demonstrated to play a decisive role in the development of the most powerful known energetic materials. Two trinitromethyl-substituted 1H-1,2,4-triazole bridging nitropyrazoles were first synthesized by straightforward routes and were characterized by chemical (MS, NMR, IR spectroscopy, and single-crystal X-ray diffraction) and experimental analysis (sensitivity toward friction, impact, and differential scanning calorimetry-thermogravimetric analysis test). Their detonation properties (detonation pressure, detonation velocity, etc.) were predicted by the EXPLO5 package based on the crystal density and calculated heat of formation with Gaussian 09. These new trinitromethyl triazoles were found to show suitable sensitivities, high density, and highly positive heat of formation. The combination of exceedingly high performances superior to those of HMX (1,3,5,7-tetranitrotetraazacyclooctane), and its straightforward preparation highlights compound 8 as a promising high-energy density material (HEDM). This work supports the effectivity of utterly manipulable nitration and provides a generalizable design synthesis strategy for developing new HEDMs.

Mononuclear indium(III) photosensitizers for photo-dehalogenation and olefin reduction.

Photoactive main-group complexes have been relatively underexplored in photocatalytic applications. Herein, we report a family of indium(III) complexes (In-1-In-4) containing pyridylpyrrolide ligands with different amounts of methyl groups, which all exhibit intense visible-light absorption as well as blue-green emission with nanosecond emission lifetimes and emission quantum yields of 6.7-12.5%. Electrochemical studies and quantum chemical calculations indicate that their (photo-)redox processes involve only ligand-centered events, which efficiently mediate photocatalytic dehalogenation and olefin reduction.

Synthesis and detonation characters of 3,4,5-1H-trinitropyrazole and its nitrogen-rich energetic salts.

The development of energetic materials is still facing challenges due to the inherent contradiction between energy and sensitivity. Two new nitrogen-rich energetic salts of 3,4,5-1H-trinitropyrazole (HTNP) were synthesized. They are fully characterized by X-ray diffraction, NMR, MS and IR spectroscopy. The DSC and BAM tests were carried out as well. These TNP salts show high thermostability and high positive heat of formation. Their detonation performances were calculated by the EXPLO5 program. Most noteworthy is that DATr salt exhibits superior sensitivity and detonation performance comparable to secondary explosive RDX, making it promising for use as a new-generation green energetic material.

N-Site Regulation of Pyridyltriazole in Cp*Ir(N̂N)(H2O) Complexes Achieving Catalytic FA Dehydrogenation.

A series of novel Cp*Ir complexes with nitrogen-rich N̂N bidentate ligands were developed for the catalytic dehydrogenation of formic acid in water under base-free conditions. These complexes were synthesized by using pyridyl 1,2,4-triazole, methylated species, or pyridyl 1,2,3-triazole as a N-site regulation ligand and were fully characterized. Complex 1-H2O bearing 1,2,4-triazole achieved a high turnover frequency of 14192 h-1 at 90 °C in 4 M FA aqueous solution. The terminal and bridged Ir-H intermediates of 1-H2O were successfully detected by 1H NMR and mass spectrometry measurements. Kinetic isotope effect experiments and density functional theory (DFT) calculations were performed; then a plausible mechanism was proposed involving the ß-hydride elimination and formation of H2. Water-assisted H2 release was proven to be the rate-determining step of the reaction. The distribution of Mulliken charges on N atoms of triazole ligand internally revealed that the ortho site N2 of 1-H2O with a higher electron density was conducive to efficient proton transfer. Additionally, the advantage of water-assisted short-range bridge of 1,2,4-triazole moieties led to a higher catalytic activity of 1-H2O. This study demonstrated the effectiveness of nitrogen-rich ligands on FA dehydrogenation and revealed a good strategy for N site regulation in the development of new homogeneous catalysts.

Precisely Controlling Ancillary Ligands to Improve Catalysis of Cp*Ir Complexes for CO2 Hydrogenation.

The regulation of ancillary ligands is critical to improve catalysis of Cp*Ir complexes for CO2 hydrogenation. Herein, a series of Cp*Ir complexes with N^N or N^O ancillary ligands were designed and synthesized. These N^N and N^O donors were derived from the pyridylpyrrole ligand. The solid-state structures of Cp*Ir complexes featured a pendant pyridyl group in 1-Cl and 1-SO4 and a pyridyloxy group in 2-Cl, 3-Cl, 2-SO4, and 3-SO4. These complexes were employed as catalysts for CO2 hydrogenation to formate in the presence of alkali under a pressure range of 0.1-8 MPa and temperature range of 25-120 °C. The catalytic activity of 2-SO4 with a pyridyloxy pendant group dramatically outperformed that of 1-SO4 and 3-SO4. The TOF of conversion of CO2 into formate reached 263 h-1 at 25 °C under a total pressure of 8 MPa (CO2/H2 = 1:1). The experiments and density functional theory calculations revealed that a pendant base in metal complexes plays a key role in the rate-determining heterolytic H2 splitting and enhancing the proton transfer by forming a hydrogen bonding bridge thereby improving the catalytic activity.

Three-Dimensional Metal-Organic Frameworks as Super Heat-Resistant Explosives: Potassium 4,4'-Oxybis[3,3'-(5-tetrazol)]furazan and Potassium (1,2,4-Triazol-3-yl)tetrazole.

Heat-resistant explosives play an irreplaceable role in specialized applications. Two energetic metal-organic frameworks (EMOFs), potassium 4,4'-oxybis[3,3'-(5-tetrazol)]furazan and potassium (1,2,4-triazol-3-yl)tetrazole, featuring a three-dimensional metal-organic framework structure, were first synthesized and characterized by chemical (1H NMR, 13C NMR, MS, IR spectroscopy, and single-crystal XRD) and physicochemical analyses (sensitivity toward friction, impact, electrostatic, and DSC-TGA test). The new 3D EMOFs were found to show high thermostability, highly positive heat of formation, and suitable sensitivities. The Hirshfeld surface was further analyzed in order to explore the effect on sensitivities. Their detonation properties (detonation velocity, detonation pressure, etc.) were calculated by the EXPLO5 program. K2NTT exhibits extremely high decomposition temperatures of up to 361 °C; meanwhile, its detonation performance is comparable to that of TATB and other energetic potassium salts, which makes it a promising heat-resistant explosive.

Homoleptic Al(III) Photosensitizers for Durable CO2 Photoreduction.

Exploiting noble-metal-free systems for high-performance photocatalytic CO2 reduction still presents a key challenge, partially due to the long-standing difficulties in developing potent and durable earth-abundant photosensitizers. Therefore, based on the very cheap aluminum metal, we have deployed a systematic series of homoleptic Al(III) photosensitizers featuring 2-pyridylpyrrolide ligands for CO2 photoreduction. The combined studies of steady-state and time-resolved spectroscopy as well as quantum chemical calculations demonstrate that in anerobic CH3CN solutions at room temperature, visible-light excitation of the Al(III) photosensitizers leads to an efficient population of singlet excited states with nanosecond-scale lifetimes and notable emission quantum yields (10-40%). The results of transient absorption spectroscopy further identified the presence of emissive singlet and unexpectedly nonemissive triplet excited states. More importantly, the introduction of methyl groups at the pyrrolide rings can greatly improve the visible-light absorption, reducing power, and durability of the Al(III) photosensitizers. With triethanolamine, BIH (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole), and an Fe(II)-quaterpyridine catalyst, the most methylated Al(III) photosensitizer achieves an apparent quantum efficiency of 2.8% at 450 nm for selective (>99%) CO2-to-CO conversion, which is nearly 28 times that of the unmethylated one (0.1%) under identical conditions. The optimal system realizes a maximum turnover number of 10250 and higher robustness than the systems with Ru(II) and Cu(I) benchmark photosensitizers. Quenching experiments using fluorescence spectroscopy elucidate that the photoinduced electron transfer in the Al(III)-sensitized system follows a reductive quenching pathway. The remarkable tunability and cost efficiency of these Al(III) photosensitizers should allow them as promising components in noble-metal-free systems for solar fuel conversion.

Quantitative and Qualitative Research on Management Strategies for Dyspnoea in Elderly Patients with Coronary Heart Disease Complicated with Chronic Heart Failure.

Objective: To investigate the most effective strategies for the management of dyspnoea in elderly patients with coronary atherosclerotic heart disease (CHD) complicated with chronic heart failure (CHF). Methods: The best management plans for dyspnoea were evaluated using quantitative and qualitative research techniques for a total of 120 senior patients with CHD complicated with CHF. A self-made questionnaire on dyspnoea management strategies served as the survey instrument for the cross-sectional quantitative investigation. A phenomenological approach served as the framework for the qualitative study, which involved semi-structured interviews with 12 elderly patients who had CHD complicated by CHF. Data were gathered through audio recordings, and the Colaizzi method was used to analyse the data. Results: A data analysis of the qualitative research results revealed the four strategies for dyspnoea management that were most effective: using drugs, inhaling oxygen, staying in a comfortable position and maintaining air circulation. These were consistent with the most effective strategies identified by the quantitative findings. There was no significant difference in the choice of dyspnoea management strategies for men and women (t = 0.968, P = 0.806); patients tended to use multiple integrated strategies to manage dyspnoea. Conclusion: Health care providers should consider employing individualised combinations of dyspnoea management strategies to assist elders with CHD complicated with CHF during acute exacerbations of dyspnoea.

Efficient Electrochemical Water Oxidation Mediated by Pyridylpyrrole-Carboxylate Ruthenium Complexes.

Spurred by the rapid growth of Ru-based complexes as molecular water oxidation catalysts (WOCs), we propose novel ruthenium(II) complexes bearing pyridylpyrrole-carboxylate (H2ppc) ligands as members of the WOC family. The structure of these complexes has 4-picoline (pic)/dimethyl sulfoxide (DMSO) in [Ru(ppc)(pic)2(dmso)] and pic/pic in [Ru(ppc)(pic)3] as axial ligands. Another ppc2- ligand and one pic ligand are located at the equatorial positions. [Ru(ppc)(pic)2(dmso)] behaves as a WOC as determined by electrochemical measurement and has an ultrahigh electrocatalytic current density of 8.17 mA cm-2 at 1.55 V (vs NHE) with a low onset potential of 0.352 V (vs NHE), a turnover number of 241, a turnover frequency of 203.39 s-1, and kcat of 16.34 s-1 under neutral conditions. The H2O/pic exchange of the complexes accompanied by oxidation of a ruthenium center is the initial step in the catalytic cycle. The cyclic voltametric measurements of [Ru(ppc)(pic)2(dmso)] at various scan rates, Pourbaix diagrams (plots of E vs pH), and kinetic studies suggested a water nucleophilic attack mechanism. HPO42- in a phosphate buffer solution is invoked in water oxidation as the proton acceptor.

Metal-Ligand Cooperation in Cp*Ir-Pyridylpyrrole Complexes: Rational Design and Catalytic Activity in Formic Acid Dehydrogenation and CO2 Hydrogenation under Ambient Conditions.

Interconversion between CO2 + H2 and FA/formate is the most promising strategy for the fixation of carbon dioxide and reversible hydrogen storage; however, FA dehydrogenation and CO2 hydrogenation are usually studied separately using different catalysts for each reaction. This report describes of the catalysis of [Cp*Ir(N∧N)(X)]n+ (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; X = Cl, n = 0; X = H2O, n = 1) bearing a proton-responsive N∧N pyridylpyrrole ligand for both reactions. Complex 2-H2O catalyzes FA dehydrogenation at 90 °C with a TOFmax of 45 900 h-1. Its catalysis is more active in aqueous solution than in neat solution under base-free conditions. These complexes also catalyze CO2 hydrogenation in the presence of base to formate under atmospheric pressure (CO2/H2 = 0.05 MPa/0.05 MPa) at 25 °C with a TOF value of 4.5 h-1 in aqueous solution and with a TOF value of 29 h-1 in a methanol/H2O mixture solvent. The possible mechanism is proposed by intermediate characterization and KIE experiments. The extraordinary activity of these complexes are mainly attributed to the metal-ligand cooperative effect of the the pyrrole group to accept a proton in the dehydrogenation of formic acid and assist cooperative heterolytic H-H bond cleavage in CO2 hydrogenation.

Synthesis and characterization of promising insensitive energetic salts based on 3-amino-5-hydrazinopyrazole.

The development of green energetic materials is based on environmental friendliness, safety and performance improvement. It is of great significance to design and synthesize new nitrogen rich salts for a new generation of green energetic materials. In the present work, a series of 3-amino-5-hydrazinopyrazole energetic salts comprising energetic anions were synthesized and were characterized using elemental analysis, IR spectroscopy and differential scanning calorimetry (DSC). Compounds 1-5 were further confirmed by single crystal X-ray diffraction and the sensitivities were measured by the standard BAM methods. Additionally, the structure-property relationship was elucidated from the experimental results and theoretical calculations. Energetic salts of 2 and 5 exhibited high heat of formation (5, 1160.06 kJ mol-1), high decomposition temperature (2, 172 °C; 5, 186 °C), excellent detonation performance (2, Dv, 9076 m s-1, P 34.1 GPa; 5, Dv, 8974 m s-1, P 31.9 GPa), moderate sensitivity towards outer stimuli and high nitrogen contents (2, 41.03%; 5, 63.84%). This work increases future prospects for the design of insensitive and novel high-energy green energetic material.

Neutral Cyclometalated Ir(III) Complexes with Pyridylpyrrole Ligand for Photocatalytic Hydrogen Generation from Water.

To explore structure-activity relationships with respect to light-harvesting behavior, a family of neutral iridium complexes [Ir(ppy)2(LR)] 1-4 (where ppy = 2-phenylpyridine, and N̂N = 2-(1H-pyrrol-2-yl)pyridine and its functionalized derivatives) were designed and synthesized. The structural modifications in metal complexes are accomplished through the attributions of electron-donating CH3 in 2, OCH3 in 3, and electron-withdrawing CF3 in 4. The structural analysis displays that the pyridylpyrrole acts as one-negative charged bidentated ligand to chelate the iridium center. The electrochemical and photophysical properties of these complexes were systematically studied. The neutral 1-4 as well as the ionic structurally analogous [Ir(ppy)2(bpy)](PF6) (5) were utilized as PSs in photocatalytic hydrogen generation from water with [Co(bpy)3](PF6)2 as catalyst and triethanolamine (TEOA) as electron sacrificial agent in the presence of salt LiCl. Complex 1 maintains activity for more than 144 h under irradiation, and the total turnover number is up to 1768. The electrochemical properties and the quenching reaction indicate the H2 generation by neutral complexes 1-4 is involved exclusively in the oxidative quenching process.

3D Uranyl Organic Frameworks Supported by Rigid Octadentate Carboxylate Ligand: Synthesis, Structure Diversity, and Luminescence Properties.

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH4 ][(UO2 )3 (HTTDS)(H2 O)] (1), [(UO2 )4 (HTTDS)2 ](HIM)6 (2, IM=imidazole), [(UO2 )4 (TTDS)(H2 O)2 (Phen)2 ] (3, Phen=1,10-phenanthroline), [Zn(H2 O)4 ]0.5 [(UO2 )3 (HTTDS)(H2 O)4 ] (4), and {(UO2 )2 [Zn(H2 O)3 ]2 (TTDS)} (5), {Zn(UO2 )2 (H2 O)(Dib)0.5 (HDib)(HTTDS)} (6, Dib=1,4-di(1H-imidazol-1-yl)benzene) and [Na]{(UO2 )4 [Cu3 (u3 -OH)(H2 O)7 ](TTDS)2 } (7) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5-dicarboxyphenyl)silicon(H8 TTDS). These UOFs have different 3D self-assembled structures as a function of co-ligands, structure-directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO7 pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N-donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO2 ]2+ units as co-ligands. The second metal centers were introduced in the syntheses of 4-7, and in all cases, they are part of the final structures, either as a counterion (4) or as a component of framework (5-7). Interesting, in 7, a rare polyoxometalate [Cu3 (µ3 -OH)O7 (O2 CR)4 ] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO2 )2 (O2 CR)4 ] unit. Those uranyl carboxylates were sufficiently determined by single crystal X-ray diffraction, and their topological structures and luminescence properties were analyzed in detail.

Design of functionalized bridged 1,2,4-triazole N-oxides as high energy density materials and their comprehensive correlations.

The demand for high energy density materials (HEDMs) remains a major challenge. Density functional theory (DFT) methods were employed to design a new family of bridged 1,2,4-triazole N-oxides by the manipulation of the linkage and oxygen-containing groups. The optimized geometry, electronic properties, energetic properties and sensitivities of new 40 molecules in this study were extensively evaluated. These designed compounds exhibit high densities (1.87-1.98 g cm-3), condensed-phase heat of formation values (457.31-986.40 kJ mol-1), impressive values for detonation velocity (9.28-9.49 km s-1) and detonation pressure (21.22-41.31 GPa). Their sensitivities (impact, electrostatic, and shock) were calculated and compared with 1,3,5-triamino-2,4,6-trinitrobenzene (TABT) and 4,6-dinitrobenzofuroxan (DNBF). Some new compounds 4,4'-trinitro-5,5'-bridged-bis-1,2,4-triazole-2,2'-diol (TN1-TN8) and 4,4'-dinitro-5,5'-ammonia-bis-1,2,4-triazole-2,2'-diol (DN3) were distinguished from this system, making them promising candidates for HEDMs. In addition, we found that the gas-relative parameters (detonation heat, oxygen balance, φ) were as important as the density, which were highly correlated to the detonation properties (P, D). Their comprehensive correlations should also be considered in the design of new energetic molecules.

Furan-containing double tetraoxa[7]helicene and its radical cation.

An unprecedented furan-based double oxa[7]helicene 1 was achieved, featuring a stable twisted conformation with π-overlap at both helical ends. The excellent conformational stability allowed for optical resolution of 1, which provided a pair of enantiomers exhibiting pronounced mirror-imaged circular dichroism and circularly polarized luminescence activity. The radical cation of 1 was obtained by chemical oxidation as evidenced by UV-Vis-NIR absorption, electron paramagnetic resonance spectroscopy and in situ spectroelectrochemistry. The present work is the starting point for the investigation of open-shell oxahelicenes.

Zinc complexes supported by pyridine-N-oxide ligands: synthesis, structures and catalytic Michael addition reactions.

New dipyridylpyrrole N-oxide ligands HL1 and HL2 are designed and synthesized via oxidation of 2-(5-(pyridin-2-yl)-1H-pyrrol-2-yl)pyridine (Hdpp) by using 3-chloroperbenzoic acid (m-CPBA) in CH2Cl2. The treatment of ZnEt2 with two equiv. of HL1 and HL2 affords [Zn(L1)2] and [Zn(L2)2] in medium yield, respectively. These ligands and zinc complexes are fully characterized by NMR, IR, UV-vis and ESI-MS spectroscopy and X-ray diffraction analysis. The structure of HL1 and HL2 shows a planar geometry. The intramolecular hydrogen-bond interactions between the imino hydrogen and N-oxide oxygen atom are observed. In [Zn(L1)2] and [Zn(L2)2], two ligands chelate to the zinc metal with a cross perpendicular geometry. The zinc complexes were employed as a highly efficient catalyst for the thiol-Michael addition of thiols to α,ß-unsaturated ketones in EtOH at room temperature. The loading of the catalyst is lowered to 0.01 mol%. The catalytic mechanism was proposed based on NMR and ESI-MS experiments.

Structural, spectroscopic and electronic properties of a family of face-shared bi-octahedral Ru25+/6+ complexes with a bridging 2,5-di(2-pyridyl)pyrrolide ligand.

A family of Ru2 dimers, [Ru2(µ-κ2N,N':κ2N',N''-dpp)2(µ-X)(X)2]q+ (X = Cl, Br, q = 0 and X = I, q = 1) is synthesized from a [Ru2(OAc)4Cl] paddlewheel starting material. The neutral products are mixed-valence Ru25+ dimers with a Ru-Ru bond order of 0.5, while the cationic iodide is a Ru26+ dimer with formal bond order of 1.0. The Ru-Ru distance is strikingly independent of the identity of the halide and the oxidation state of ruthenium, most likely a consequence of the small bridging nitrogen which constrains the geometry. The spectroscopic properties (EPR, UV/Vis) of the Br complex are consistent with a large σ-σ* splitting in [Ru2(µ-κ2N,N':κ2N',N''-dpp)2(µ-Br)(Br)2].

Formation of Iridium(III) Complexes via Selective Activation of the C-H and N-H Bonds of a Dipyridylpyrrole Ligand.

Treatment of [Ir(PPh3)3Cl] with 2-[5-(pyridin-2-yl)-1H-pyrrol-2-yl]pyridine (Hdpp) in refluxing toluene affords an unexpected pyrrole-metalated iridium(III) hydride complex, [Ir(K2C,N-dpp)(H)(Cl)(PPh3)2] (1), via Cpyrrole-H activation, while the presence of the base KOtBu as the deprotonation reagent produces a pyridine-metalated iridium(III) hydride complex, [Ir(K3C,N,N-dpp)(H)(PPh3)2] (2), via Cpyridine-H activation. Treatment of [Ir(PPh3)3Cl] prepared by a convenient method with Hdpp in the presence of KOtBu under the refluxing mixture solvent toluene/methanol (2:1, v/v) generates the N,N-chelating complex [Ir(K2N,N-dpp)(H)(Cl)(PPh3)2] (3) together with 1 and the N,N-chelating dihydride complex [Ir(K2N,N-dpp)(H)2(PPh3)2] (4). Complex 4 is also readily produced by the reaction of [Ir(PPh3)3Cl] and Hdpp in the presence of KOtBu under refluxing methanol or by the reaction of IrCl3 and PPh3 in refluxing 2-ethoxyethanol. Complexes 1-4 are fully characterized by NMR, IR, and UV-vis spectroscopy and X-ray diffraction analysis. The dpp-/dpp2- ligand shows rich coordination capability, of which pyridine- and pyrrole-cyclometalated coordination modes are first reported. The formation of structural isomers 1 and 3 involved the selective activation of the C-H and N-H bonds of Hdpp is rationalized by theoretical calculations.

A new oxygen-rich energetic salt dihydrazine tetranitroethide: a promising explosive alternative with high density and good performance.

A novel high-energy salt with good oxygen balance, dihydrazine tetranitroethide (5), has been synthesized and characterized by FT-IR spectroscopy, NMR spectroscopy, elemental analysis, and X-ray single crystal diffraction. Compound 5 exhibits high crystal density (1.81 g cm-3) and impressive detonation velocity (9508 m s-1) and detonation pressure (37.9 GPa), showing potential applications as a high performance explosive and a promising additive of propellants.

Reversible pyrrole-based proton storage/release in ruthenium(ii) complexes.

Newly designed ruthenium(ii) complexes are reported which contain a pyridylpyrrole ligand featuring fast-responsive and reversible proton storage/release on the pyrrole group. The protonated pyrrolium acts as an acidic initiator and is capable of triggering the polymerization of 2,2-dimethyloxirane.