Coordination-Induced N−H Bond Splitting of Ammonia and Primary Amine of CuI−MOFs

We report a porous three-dimensional anionic tetrazolium based Cu^I−MOF 1 , which is capable of cleaving the N−H bond of ammonia and primary amine, as well as the O−H bond of H₂O along with spontaneous H₂ evolution. In the gas-solid phase reaction of 1 with ammonia and water vapor, Cu^I−MOF 1 was gradually oxidized to NH₂−Cu^II−MOF and OH−Cu^II−MOF, through single-crystal-to-single-crystal (SCSC) structural transformations, which was confirmed by XPS, PXRD and X-ray single-crystal diffraction. Density functional theory (DFT) demonstrated that Cu^I−MOF could lower N−H bond dissociation free energy of ammonia through coordination-induced bond weakening and promote H₂ evolution by the reduction potential of 1 . To our knowledge, this is the first example of MOFs that activate ammonia and amine in gas-solid manner.     

Post-Synthetic Modification of Zr-based Metal-Organic Frameworks with Imidazole: Variable Optical Behavior and Sensing

UiO-66-NH₂-IM, a fluorescent metal-organic framework (MOF), was synthesized by post-synthetic modification of UiO-66-NH₂ with 2-imidazole carboxaldehyde via a Schiff base reaction. It was examined using various characterization techniques (PXRD, FTIR, NMR, SEM, TGA, UV-Vis DRS, and photoluminescence spectroscopy). The emissive feature of UiO-66-NH₂-IM was utilized to detect volatile organic compounds (VOCs), metal ions, and anions, such as acetone, Fe³⁺, and carbonate (CO₃²⁻). Acetone turns off the high luminescence of UiO-66-NH₂-IM in DMSO, with the limit of detection (LOD) being 3.6 ppm. Similarly, Fe³⁺ in an aqueous medium is detected at LOD=0.67 μM (0.04 ppm) via quenching. On the contrary, CO₃²⁻ in an aqueous medium significantly enhances the luminescence of UiO-66-NH₂-IM, which is detected with extremely high sensitivity (LOD=1.16 μM, i. e., 0.07 ppm). Large Stern-Volmer constant, K_sv, and low LOD values indicate excellent sensitivity of the post-synthetic MOF. Experimental data supported by density functional theory (DFT) calculations discern photo-induced electron transfer (PET), resonance energy transfer (RET), inner filter effect (IFE), or proton abstraction as putative sensing mechanisms. NMR and computational studies propose a proton abstraction mechanism for luminescence enhancement with CO₃²⁻. Moreover, the optical behavior of the post-synthetic material toward analytes is recyclable.     

Rational Synthesis,Structures and Properties of the Ionic Liquid Binary Iodine-Bromine Octahalide Series [InBr8−n]2− (n=0, 2, 3, 4)

A series of octanuclear iodine-bromine interhalides [I_nBr_8−n]²⁻ (n=0, 2, 3, 4) were prepared systematically in two steps. Firstly, addition of a dihalogen (Br₂ or IBr) to the triaminocyclopropenium bromide salt [C₃(NEt₂)₃]Br forms the corresponding trihalide salt with Br₃⁻ or IBr₂⁻ anions, respectively. Secondly, addition to Br₃⁻ of half an equivalent of Br₂ gives the octabromine polyhalide [Br₈]²⁻, whereas addition to IBr₂⁻ of half an equivalent of Br₂, IBr or I₂ gives the corresponding interhalides: [I₂Br₆]²⁻, [I₃Br₅]²⁻, and [I₄Br₄]²⁻, respectively. The four octahalides were characterized by X-ray crystallography, computational studies, Raman and Far-IR spectroscopies, as well as by TGA and melting point. All of the salts were found to be ionic liquids.     

Synthesis and physical studies on a new anion exchange material: Zirconium (IV) ethylenediamine and its application to the separation of MoO42− from other anionic species

Zirconium (IV) ethylenediamine has been prepared by interaction of aqueous solutions of zirconium oxychloride and ehtylenediamine at pH 4.4 and 9.6. Its anion exchange capacity, chemical and thermal stabilities, pH titration curve and chemical composition were studied. Infrared spectra using the KBr disc method, TGA and DTA were recorded. A tentative formula was proposed showing zirconium (IV) oxide : ethylenediamine in the ratio 3:1, [ZrO(OH)⁺²]₃ [NH₂ (CH₂) ₂NH₂]. 3 H₂O. Distribution coefficient (Kd) values of a number of anionic species were determined in distilled water, and various concentrations of ammonium nitrate solution. On the basis of the difference in Kd values, the separations such as Cl⁻ - MoO₄²⁻, Br - MoO₄²⁻, I⁻ - MoO₄²⁻, SO₄²⁻ - MoO₄²⁻ and C₂O₄²⁻ - MoO₄²⁻ have been achieved successfully on its column.     

The rate constants of the elementary reactions of NH3 with O and OH

Two sets of discordant rate constants reported recently for the high-temperature reactions of NH₃ with O and OH were examined by comparing the calculated concentration profiles of NH₃ and OH with experiments by the shock tube technique forNH₃-N₂O-Ar mixtures. The rate constants were confirmed tobe: k₄ = 3.1 × 10¹²exp(−25.5 kJ/RT) cm³ mol⁻¹ s⁻¹ for NH₃ + O → NH₂ + OH and k₅ = 3.2×10¹² exp(−8.4 kJ/RT) for NH₃ + OH → NH₂ + H₂O.     

Density Functional Theory Guided Investigation of Ligand-Induced Neptunyl-Neptunyl Interactions

Actinyl-actinyl interactions are particularly prevalent for the pentavalent neptunyl cation (Np(V)O₂)⁺ where these interactions appear either as a T - or D -shape (diamond-shape). T -shaped interactions have been previously identified in high concentration Np(V) solutions containing simple anions (NO₃⁻, ClO₄⁻, Cl⁻) whereas D -shaped have only been isolated in the solid-state in the presence of carboxylate ligands. In this study, Density Functional Theory (DFT) calculations were paired with Raman spectroscopy to evaluate the formation of D -shaped interactions in the presence of aliphatic (R=H (formate), CH₃ (acetate), CH₂CH₃ (propionate)) and aromatic (R=C₆H₅ (benzoate), C₆H₄OH (4-hydroxybenzoate), C₅H₄N (isonicotinate)) carboxylate ligands. DFT studies indicate that the ΔG to form hydrated T - and D -shaped forms are not spontaneous but become so with the addition of the carboxylate ligands. Raman spectra of the Np(V) carboxylate solutions contained vibrational modes associated with the D -shaped interactions, but spectral changes observed over time indicate a dynamic system. Crystallization experiments from the Np(V) carboxylate systems confirmed the presence of D- shaped dimers for the aromatic carboxylates, suggesting that the choice of the anion in solution favors actinyl-actinyl interactions even at low concentrations (≤20 mM) of Np(V).     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Vibrational spectra of Te(OH)6.2NH4H2AsO4 and Te(OH)6.2(NH4)2HAsO4

IR and Raman spectra of Te(OH)₆.2NH₄H₂AsO₄.(NH₄)₂HAsO₄ (compound I) and Te(OH)₆.2(NH₄)₂HAsO₄ (compound II) are recorded and analysed. The symmetry of different groups and the vibrational interaction between them are discussed. The observed spectra suggest the existence of HAsO²⁻₄ in II and coexistence of HAsO²⁻₄ and H₂AsO⁻₄ in I. The ammonium ion is found to execute hindered rotation in the lattice in both the compounds.     

Computational Analysis of Mesomerism in para-Substituted mer-NCN Pincer Platinum(II) Complexes,Including its Relationships with Hammett σp Substituent Parameters

Density Functional Theory studies of square-planar Pt^II pincer structures, (4-Z-NCN)PtCl ([4-Z-NCN]⁻=[4-Z-2,6-(Me₂NCH₂)₂C₆H₂-N,C,N]⁻, Z=H, NO₂, CF₃, CO₂H, CHO, Cl, Br, I, F, SMe, SiMe₃, tBu, OH, NH₂, NMe₂), enable characterisation of mesomerism for the pincer-Pt interaction. Relationships between Hammett σ_p substituent parameters of Z and DFT data obtained from NBO6 and AOMix computation are used to probe the interaction of the 5d_yz orbital of platinum with π-orbitals of the arene ring. Analogous computation for 2,6-(Me₂CH₂)₂C₆H₃Z (Z=H, CF₃, CHO, Cl, Br, I, F, SMe, SiMe₃, tBu, OH, NH₂) and (4-H-NCN)PtZ allows an estimation of the relative substituent effects of “(CH₂NMe₂)₂PtZ” on π-delocalisation in the pincer system.     

High-Quality Thin Films of UiO-66-NH2 by Coordination Modulated Layer-by-Layer Liquid Phase Epitaxy

We report the fabrication of macroscopically and microscopically homogeneous, crack-free metal-organic framework (MOF) UiO-66-NH₂ (UiO: Universitetet i Oslo; [Zr₆O₄(OH)₄(bdc-NH₂)₆]; bdc-NH₂²⁻: 2-amino-1,4-benzene dicarboxylate) thin films on silicon oxide surfaces. A DMF-free, low-temperature coordination modulated (CM), layer-by-layer liquid phase epitaxy (LPE) using the controlled secondary building block approach (CSA). Efficient substrate activation was determined as a key factor to obtain dense and smooth coatings by comparing UiO-66-NH₂ thin films grown on ozone and piranha acid-activated substrates. Films of 2.60 μm thickness with a minimal surface roughness of 2 nm and a high sorption capacity of 3.53 mmol g⁻¹ MeOH (at 25 °C) were typically obtained in an 80-cycle experiment at mild conditions (70 °C, ambient pressure).     

In Silico Partial N2 to NH3 Conversion with a Light Atom Molecule

N₂ can be stepwise converted in silico into one molecule NH₃ and a secondary amide with a bond activator molecule consisting only of light main group elements. The proposed N₂-activating pincer-related compound carries a silyl ion (Si⁽⁺⁾) center as well as three Lewis acidic (−BF₂) and three Lewis basic (−PMe₂) sites, providing an efficient binding pocket for gaseous N₂ within the framework of intramolecular frustrated Lewis pairs (FLP). In addition, it exhibits supportive secondary P−B and F⋅⋅⋅B contacts, which stabilize the structure. In the PSi⁽⁺⁾−N−N−BP environment the N≡N triple bond is extended from 1.09 Å to remarkable 1.43 Å, resembling a N−N single bond. The strongly activated N−N-fragment is prone to subsequent hydride addition and protonation steps, resulting in the energy efficient transfer of two hydrogen equivalents. The next hydride added causes the release of one molecule NH₃, but leaves the ligand system as poisoned R₃Si⁽⁺⁾−NH₂−PMe₂ or R₃Si⁽⁺⁾−NH₃ dead-end states behind. The study indicates that approximately tetrahedral constrained SiBP₂-pockets are capable to activate N₂, whereas the acid-rich SiB₃- and SiB₂P-pocktes, as well as the base-rich SiP₃-pockets fail, hinting towards the high relevance of the acid-base proportion and relative orientation. The electronic structure of the N₂-activated state is compared to the corresponding state of a recently published peri-substituted bond activator molecule featuring a PSi⁽⁺⁾−N−N−Si⁽⁺⁾P site (S. Mebs, J. Beckmann, Physical Chemistry Chemical Physics 2022 , 24, 20953–20967).     

Iodine Clathrated: A Solid-State Analogue of the Iodine–Starch Complex

Co-crystallizing iodine with a simple dicationic salt (1,8-diammoniumoctane chloride) results in the clathration of the iodine (I₂) molecules inside trigonal and hexagonal helical channels of the crystal lattice with 72 wt % overall I₂ loading. The I₂ inside the bigger trigonal channel forms a I−I⋅⋅⋅I−I⋅⋅⋅I−I halogen-bonded infinite helical chain, while the I₂ in the smaller hexagonal channel is disordered. In both channels the I₂ interaction with the channel wall happens through I−I⋅⋅⋅Cl⁻ halogen bonds. The helical channels in the crystal lattice are constructed via the strong charge-assisted H₂N⁺H⋅⋅⋅Cl⁻ hydrogen bonds between the dications and the chloride anions. The structure shows a marked similarity with the well-known starch–I₂ system, and thus may provide insight for the yet unresolved structure of the I₂ in the helical starch channel.     

Lead-free Perovskite Materials (NH4)3Sb2IxBr9−x

A family of perovskite light absorbers (NH₄)₃Sb₂I_xBr_9−x (0≤x≤9) was prepared. These materials show good solubility in ethanol, a low-cost, hypotoxic, and environmentally friendly solvent. The light absorption of (NH₄)₃Sb₂I_xBr_9−x films can be tuned by adjusting I and Br content. The absorption onset for (NH₄)₃Sb₂I_xBr_9−x films changes from 558 nm to 453 nm as x changes from 9 to 0. (NH₄)₃Sb₂I₉ single crystals were prepared, exhibiting a hole mobility of 4.8 cm² V⁻¹ s⁻¹ and an electron mobility of 12.3 cm² V⁻¹ s⁻¹. (NH₄)₃Sb₂I₉ solar cells gave an open-circuit voltage of 1.03 V and a power conversion efficiency of 0.51 %.     

A detailed chemical kinetic model for high temperature ethanol oxidation

A detailed chemical kinetic model for ethanol oxidation has been developed and validated against a variety of experimental data sets. Laminar flame speed data (obtained from a constant volume bomb and counterflow twin‐flame), ignition delay data behind a reflected shock wave, and ethanol oxidation product profiles from a jet‐stirred and turbulent flow reactor were used in this computational study. Good agreement was found in modeling of the data sets obtained from the five different experimental systems. The computational results show that high temperature ethanol oxidation exhibits strong sensitivity to the fall‐off kinetics of ethanol decomposition, branching ratio selection for C₂H₅OH + OH ↔ Products, and reactions involving the hydroperoxyl (HO₂) radical. The multichanneled ethanol decomposition process is analyzed by RRKM/Master Equation theory, and the results are compared with those obtained from earlier studies. The ten‐parameter Troe form is used to define the C₂H₅OH(+M) ↔ CH₃ + CH₂OH(+M) rate expression as k^∞ = 5.94E23 T^−1.68 exp(−45880 K/T) (s⁻¹) k^o = 2.88E85 T^−18.9 exp(−55317 K/T) (cm³/mol/sec) F_cent = 0.5 exp(−T/200 K) + 0.5 exp(−T/890 K) + exp(−4600 K/T) and the C₂H₅OH(+M) ↔ C₂H₄ + H₂O(+M) rate expression as k^∞ = 2.79E13 T^0.09 exp(−33284 K/T) (s⁻¹) k^o = 2.57E83 T^−18.85 exp(−43509 K/T) (cm³/mol/sec) F _cent = 0.3 exp(−T/350 K) + 0.7 exp(−T/800 K) + exp(−3800 K/T) with an applied energy transfer per collision value of <ΔE_down> = 500 cm⁻¹. An empirical branching ratio estimation procedure is presented which determines the temperature dependent branching ratios of the three distinct sites of hydrogen abstraction from ethanol. The calculated branching ratios for C₂H₅OH + OH, C₂H₅OH + O, C₂H₅OH + H, and C₂H₅OH + CH₃ are compared to experimental data. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 183–220, 1999     

Analysis of torsional spectra of molecules with two internal C3ν, rotors—XXVI. A far infrared study of 1,1-dimethylhydrazine

The infrared spectra of 1,1-dimethylhydrazine, (CH₃)₂NNH₂, and two isotopomers, (CD₃)₂NNH₂ and (CH₃)₂NND₂, have been recorded in the region between 600 and 100 cm⁻¹. Very rich and complex spectra were obtained and analysis of the data has been carried out. The interpretation of the spectra arising from the two methyl torsional modes of the −d₀ compound was carried out using a semi-rigid model, and the resulting potential function obtained is V₃₀ = 1685 ± 12 cm⁻¹ (4.82 ± 0.04 kcal mol⁻¹); V₀₃ = 1827 ± 16 cm⁻¹ (5.22 ± 0.05 kcal mol⁻¹); V₆₀ = −92±5cm⁻¹ (−0.26 ± 0.02 kcal mol⁻¹); V₀₆ = −41 ± 6cm⁻¹ (−0.12 ± 0.02 kcal mol⁻¹) and V^′₃₃ = −51 ± 5 cm⁻¹ (−0.15 ± 0.01 kcal mol⁻¹). Ab initio gradient calculations were carried out employing the 3–21G and 6–31G* basis sets, as well as the 6–31G* basis set with electron correlation at the MP2 level. The structural parameters, conformational stability, and three-fold barriers to internal rotation have been determined and the gauche conformer is calculated to be more stable than the trans form by 783 cm⁻¹ (2.24 kcal mol⁻¹) with the MP2/6–31G* basis set. These calculations were also used to re-evaluate the previously reported assignment of the fundamental modes, and to obtain a potential function for the asymmetric torsion. All of these results are discussed and compared with corresponding quantities for some similar compounds.     

New Palladium – ZrO2 Nano-Architectures from Thermal Transformation of UiO-66-NH2 for Carbonylative Suzuki and Hydrogenation Reactions

The new nanocomposites, Pd/C/ZrO₂, PdO/ZrO_2, and Pd/PdO/ZrO₂, were prepared by thermal conversion of Pd@UiO-66-Zr−NH₂ (MOF) in nitrogen or air atmosphere. The presence of Pd nanoparticles, uniformly distributed on the ZrO₂ or C/ZrO₂ matrix, was evidenced by transmission electron microscopy, scanning electron microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS) methods. All pyrolysed composites retained the shape of the MOF template. They catalyze carbonylative Suzuki coupling under 1 atm CO with an efficiency significantly higher than the original Pd@UiO-66-Zr−NH₂. The most active PdO/ZrO₂ composite, formed benzophenone with TOF up to 1600 h⁻¹, while by using Pd@UiO-66-Zr−NH₂, much lower TOF values, 51–95 h⁻¹, were achieved. After the reaction, PdO/ZrO₂ was recovered with the same composition and catalytic activity. Very good results were also obtained in the transfer hydrogenation of benzophenones to alcohols with Pd/C/ZrO₂ and PdO/ZrO₂ catalysts under microwave irradiation.     

Effect of inorganic anions on the titanium dioxide-based photocatalytic oxidation of aqueous ammonia and nitrite

In this study, we investigated the effects of four inorganic anions (Cl⁻, SO₄²⁻, H₂PO₄⁻/HPO₄²⁻, and HCO₃⁻/CO₃²⁻) on titanium dioxide (TiO₂)-based photocatalytic oxidation of aqueous ammonia (NH₄⁺/NH₃) at pH ∼ 9 and ∼10 and nitrite (NO₂⁻) over the pH range of 4–11. The initial rates of NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation are dependent on both the pH and the anion species. Our results indicate that, except for CO₃²⁻, which decreased the homogeneous oxidation rate of NH₄⁺/NH₃ by UV-illuminated hydrogen peroxide, OH scavenging by anions and/or direct oxidation of NH₄⁺/NH₃ and NO₂⁻ by anion radicals did not affect rates of TiO₂ photocatalytic oxidation. While HPO₄²⁻ enhanced NH₄⁺/NH₃ photocatalytic oxidation at pH ∼ 9 and ∼10, H₂PO₄⁻/HPO₄²⁻ inhibited NO₂⁻ oxidation at low to neutral pH values. The presence of Cl⁻, SO₄²⁻, and HCO₃⁻ had no effect on NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation at pH ∼ 9 and ∼10, whereas CO₃²⁻ slowed NH₄⁺/NH₃ but not NO₂⁻ photocatalytic oxidation at pH ∼ 11. Photocatalytic oxidation of NH₄⁺/NH₃ to NO₂⁻ is the rate-limiting step in the complete oxidation of NH₄⁺/NH₃ to NO₃⁻ in the presence of common wastewater anions. Therefore, in photocatalytic oxidation treatment, we should choose conditions such as alkaline pH that will maximize the NH₄⁺/NH₃ oxidation rate.     

Cu-Doped MoSi2N4 Monolayer as a Potential NH3 Sensor

Cu doped MoSi₂N₄ monolayer (Cu-MoSi₂N₄) was firstly proposed to analyze adsorption performances of common gas molecules including O₂, N₂, CO, NO, NO₂, CO₂, SO₂, H₂O, NH₃ and CH₄ via density functional theory (DFT) combining with non-equilibrium Green's function (NEGF). The electronic transport calculations indicate that Cu-MoSi₂N₄ monolayer has high sensitivity for CO, NO, NO₂ and NH₃ molecules. However, only NH₃ molecule adsorbs on the Cu-MoSi₂N₄ monolayer with moderate strength (−0.55 eV) and desorbs at room temperature (2.36×10⁻³ s). Thus, Cu-MoSi₂N₄ monolayer is demonstrated as a potential NH₃ sensor.     

Halogen bonding between substituted chlorobenzene and trimethylamine: Decisive role of σ–hole and C?Cl bond breaking energy

Theoretical studies have been carried out on the halogen bonding interaction between para substituted chlorobenzene (Y C₆H₄Cl, Y = H, NH₂, CH₃, F, CN, NO₂) and N(CH₃)₃ using ab initio MP2/aug‐cc‐pVDZ and DFT based wB97XD/6‐311++G(d,p) methods. The positive electrostatic potential (V_S,max) on the Cl atom and the heterolytic bond breaking enthalpy of the C Cl bond have been calculated and their role on halogen bonding is discussed. The heterolytic bond breaking enthalpy of the C Cl bond is proposed as a measure of the strength of the σ‐hole on Cl atom. The binding strength of the complexes ranging between −6.13 kJ mol⁻¹ and −9.29 kJ mol⁻¹ are linearly related to the V_S,max of the Cl atom and the bond breaking enthalpy of the C Cl bond. In addition, energy decomposition analysis was performed on the halogen bonded complexes via symmetry adapted perturbation theory (SAPT) to predict the dominant energy component and the nature of the N···Cl interaction.     

Incarceration of Iodine in a Pyrene-Based Metal–Organic Framework

A pyrene-based metal-organic framework (MOF) SION-8 captured iodine (I₂) vapor with a capacity of 460 and 250 mg g⁻¹_MOF at room temperature and 75 °C, respectively. Single-crystal X-ray diffraction analysis and van-der-Waals-corrected density functional theory calculations confirmed the presence of I₂ molecules within the pores of SION-8 and their interaction with the pyrene-based ligands. The I₂–pyrene interactions in the I₂-loaded SION-8 led to a 10⁴-fold increase of its electrical conductivity compared to the bare SION-8 . Upon adsorption, ≥95 % of I₂ molecules were incarcerated and could not be washed out, signifying the potential of SION-8 towards the permanent capture of radioactive I₂ at room temperature.