NH3 Complexes Research Articles

Unconventional Radical and Radical-Hole Site-Based Interactions in Halogen-Bearing Dimers and Trimers: A Comparative Study.

Radical (R•) and R•-hole site-based interactions are comparatively studied, for the first time, using ab initio methods. In this regard, R•-bearing molecules •XO3 (where X = Cl, Br, and I) were subjected to direct interaction with NH3 within dimeric and trimeric forms in the form of NH3···•XO3/•XO3···NH3 and NH3···•XO3···NH3 complexes, respectively. As confirmed by electrostatic potential analysis, the studied R•-bearing molecules •XO3 had the outstanding potentiality to interact as Lewis acid centers via two positive sites dubbed as R• and R•-hole sites. Such an observation proposed the potentiality of the considered •XO3 molecules to engage in unconventional R• and well-established R•-hole site-based interactions with Lewis bases. This was confirmed by negative interaction (E int) energies, ranging from -4.93 to -19.89 kcal/mol, with higher favorability for R• site-based interactions over the R•-hole site-based ones. MP2 energetic features furnished higher preferability for the R• site-based interactions than the R•-hole site-based ones in the case of chlorine- and bromine-bearing complexes, and the reverse was true for the iodine-bearing complexes. Moreover, elevated E int values were recorded for the NH3···•XO3···NH3 trimers over the NH3···•XO3 and •XO3···NH3 dimers, outlining the higher preference of the •XO3 molecules to engage in R• and R•-hole site-based interactions in the trimeric form over the dimeric one. These results might be considered a requisite linchpin for numerous forthcoming supramolecular chemistry and crystal engineering studies.

Synthesis and Reactivity of Fe(II) Complexes Containing Cis Ammonia Ligands.

The development of earth-abundant transition-metal complexes for electrocatalytic ammonia oxidation is needed to facilitate a renewable energy economy. Important to this goal is a fundamental understanding of how ammonia binds to complexes as a function of ligand geometry and electronic effects. We report the synthesis and characterization of a series of Fe(II)-NH3 complexes supported by tetradentate, facially binding ligands with a combination of pyridine and N-heterocyclic carbene donors. Electronic modification of the supporting ligand led to significant shifts in the FeIII/II potential and variations in NH bond acidities. Finally, investigations of ammonia oxidation by cyclic voltammetry, controlled potential bulk electrolysis, and through addition of stoichiometric organic radicals, TEMPO and tBu3ArO• are reported. No catalytic oxidation of NH3 to N2 was observed, and 15N2 was detected only in reactions with tBu3ArO•.

σ-Hole, lone-pair-hole, and π-hole site-based interactions in aerogen-comprising complexes: a comparative study.

Herein, the potential of ZO3 and ZF2 aerogen-comprising molecules (where Z = Ar, Kr, and Xe) to engage in σ-, lp-, and π-hole site-based interactions was comparatively studied using various ab initio computations. For the first time, a premier in-depth elucidation of the external electric field (EEF) influence on the strength of the σ-, lp-, and π-hole site-based interactions within the ZO3/ZF2⋯NH3 and ⋯NCH complexes was addressed using oriented EEF with disparate magnitude. Upon the energetic features, σ-hole site-based interactions were noticed with the most prominent preferability in comparison to lp- and π-hole analogs. This finding was ensured by the negative interaction energy values of -11.65, -3.50, and -2.74 kcal mol-1 in the case of σ-, lp-, and π-hole site-based interactions within the XeO3⋯ and XeF2⋯NH3 complexes, respectively. Detailedly, the strength of the σ- and lp-hole site-based interactions directly correlated with the atomic size of the aerogen atoms and the magnitude of the positively oriented EEF. Unexpectedly, an irregular correlation was noticed for the interaction energies of the π-hole site-based interactions with the size of the π-hole. Interestingly, the π-hole site-based interactions within Kr-comprising complexes exhibited higher negative interaction energies than the Ar- and Xe-comprising counterparts. Notwithstanding, a direct proportion between the interaction energies of the π-hole site-based interactions and π-hole size was obtained by employing EEF along the positive orientation with high strength. The present outcomes would be a fundamental basis for forthcoming progress in studying the σ-, lp-, and π-hole site-based interactions within aerogen-comprising complexes and their pertinent applications in materials science and crystal engineering.

Highly Selective Ammonia Oxidation on BiVO4 Photoanodes Co‐catalyzed by Trace Amounts of Copper Ions

AbstractHigh‐efficient photoelectrocatalytic direct ammonia oxidation reaction (AOR) conducted on semiconductor photoanodes remains a substantial challenge. Herein, we develop a strategy of simply introducing ppm levels of Cu ions (0.5–10 mg/L) into NH3 solutions to significantly improve the AOR photocurrent of bare BiVO4 photoanodes from 3.4 to 6.3 mA cm−2 at 1.23 VRHE, being close to the theoretical maximum photocurrent of BiVO4 (7.5 mA cm−2). The surface charge‐separation efficiency has reached 90 % under a low bias of 0.8 VRHE. This AOR exhibits a high Faradaic efficiency (FE) of 93.8 % with the water oxidation reaction (WOR) being greatly suppressed. N2 is the main AOR product with FEs of 71.1 % in aqueous solutions and FEs of 100 % in non‐aqueous solutions. Through mechanistic studies, we find that the formation of Cu−NH3 complexes possesses preferential adsorption on BiVO4 surfaces and efficiently competes with WOR. Meanwhile, the cooperation of BiVO4 surface effect and Cu‐induced coordination effect activates N−H bonds and accelerates the first rate‐limiting proton‐coupled electron transfer for AOR. This simple strategy is further extended to other photoanodes and electrocatalysts.

New insights into the activation mechanism of ammonium ions on the malachite sulfidization flotation

Ammonium sulfate [(NH4)2SO4] is an effective activator of malachite sulfidization flotation. In this work, we explored the effects of ammonium ion (NH4+) and copper ion (Cu2+) on malachite sulfidization flotation and investigated the underlying mechanism. Flotation experiments demonstrated that NH4+ can not only eliminate the negative effects of Cu2+, but also work together with Cu2+ to further promote malachite sulfidization flotation in a certain concentration range. Zeta potential, SEM-EDS, and X-ray photoelectron spectroscopy analysis results indicated that the single Cu2+ weakened the oxidation of S (II) species on the malachite surface and reduced the formation of sulfides. In the presence of NH4+, Cu2+ did not inhibit the formation of sulfides on malachite surface but worked with NH4+ to promote it. Aqueous speciation calculation and adsorption test revealed that NH4+ and Cu2+ interacted to form Cu (II)–NH3 complexes, which reacts with S (II) species to form a copper sulfide substance that is more easily adsorbed on the malachite surface than the copper sulfide colloid formed by the reaction between Cu2+ and S (II) species. This leads to the improvement of surface sulfidization.

Enhanced recovery of high purity Cu powder from reclaimed copper smelting fly ash by NH3·H2O–NH4Cl slurry electrolysis system

Reclaimed copper smelting fly ash (RCA) is a residue produced during the smelting process of waste miscellaneous copper, containing heavy metals such as Cu, Zn, and Cd. In this study, a slurry electrolysis system was used to recover Cu from RCA. The results showed that the recovery efficiency, current efficiency, and purity of Cu on cathode were 97.11 %, 91.22 %, and 98.47 %, respectively, when the concentration of NH3·H2O was 2 mol/L, the concentration of NH4Cl was 1 mol/L, the concentration of CuSO4·5H2O was 20 g/L, the solid-liquid ratio was 50 g/L, the electric current density was 30 mA/cm2 and the reaction time was 2 h. The content of Zn in the RCA decreased from 144.54 mg/g to 23.7 mg/g and Cd from 0.72 mg/g to 0.005 mg/g after slurry electrolysis, and other heavy metals in the RCA also decreased. The potential difference that occurs between the two poles under the NH3·H2O slurry electrolysis system promotes the leaching of Cu from the RCA, while the leached Cu2+ combines with NH4+ to form the Cu–NH3 complex (Cu(NH3)42+, Cu(NH3)2+), thus increasing the current efficiency and promoting the cathodic copper deposition. The high-purity Cu obtained at the cathode belongs to the face-centered cubic structure (111), (200) and (220) of the Cu crystalline surface. This study provides a new method for the resourceful recovery of copper from RCA.

Sigma-Hole and Lone-Pair-Hole Site-Based Interactions of Seesaw Tetravalent Chalcogen-Bearing Molecules with Lewis Bases.

For the first time, sigma (σ)- and lone-pair (lp)-hole site-based interactions of SF4 and SeF4 molecules in seesaw geometry with NH3 and FH Lewis bases were herein comparatively investigated. The obtained findings from the electrostatic potential analysis outlined the emergence of sundry holes on the molecular entity of the SF4 and SeF4 molecules, dubbed the σ- and lp-holes. The energetic viewpoint announced splendid negative binding energy values for σ-hole site-based interactions succeeded by lp-hole analogues, which were found to be -9.21 and -0.50 kcal/mol, respectively, for SeF4···NH3 complex as a case study. Conspicuously, a proper concurrence between the strength of chalcogen σ-hole site-based interactions and the chalcogen's atomic size was obtained, whereas a reverse pattern was proclaimed for the lp-hole counterparts. Further, a higher preference for the YF4···NH3 complexes with elevated negative binding energy was promulgated over the YF4···FH ones, indicating the eminent role of Lewis basicity. The indications of the quantum theory of atoms in molecules generally asserted the closed-shell nature of all the considered interactions. The observation of symmetry-adapted perturbation theory revealed the substantial contributing role of the electrostatic forces beyond the occurrence of σ-hole site-based interactions. In comparison, the dispersion forces were specified to govern the lp-hole counterparts. Such emerging findings would be a gate for the fruitful forthcoming applications of chalcogen bonding interactions in crystal engineering and biological systems.

Isotope effects on the stability of the hydrogen-bonded C2H2 NCH, H2O XH3 (X = N, P, As) and F2CH2 NH3 complexes

A computational study of three sets of binary hydrogen-bonded complexes was undertaken at the M062x/6–311++G(2d,2p) level of theory to investigate the relative stabilities of mono-deuterated isotopomers of these complexes. This work allows for a comparison of the relative magnitudes of hydrogen and deuterium bonds at low temperatures in (i) the linear and T-shaped optimized structures of C2H2 NCH, (ii) in the H2O XH3 (X = N, P, As) series, where the strength of red-shifted hydrogen bonding is systematically varied via the XH3 basicity and (iii) in the blue-shifted H-bonded F2CH2 NH3 interaction. The deuterium-bonded isotopomers predominate and this energetic preference is rationalized by reference to a simple theoretical model.

Intermolecular Covalent Interactions: Nature and Directionality.

Quantum chemical methods were employed to analyze the nature and the origin of the directionality of pnictogen (PnB), chalcogen (ChB), and halogen bonds (XB) in archetypal Fm Z⋅⋅⋅F- complexes (Z=Pn, Ch, X), using relativistic density functional theory (DFT) at ZORA-M06/QZ4P. Quantitative Kohn-Sham MO and energy decomposition analyses (EDA) show that all these intermolecular interactions have in common that covalence, that is, HOMO-LUMO interactions, provide a crucial contribution to the bond energy, besides electrostatic attraction. Strikingly, all these bonds are directional (i.e., F-Z⋅⋅⋅F- is approximately linear) despite, and not because of, the electrostatic interactions which, in fact, favor bending. This constitutes a breakdown of the σ-hole model. It was shown how the σ-hole model fails by neglecting both, the essential physics behind the electrostatic interaction and that behind the directionality of electron-rich intermolecular interactions. Our findings are general and extend to the neutral, weaker ClI⋅⋅⋅NH3 , HClTe⋅⋅⋅NH3 , and H2 ClSb⋅⋅⋅NH3 complexes.

Gold(III) derivatives as the noncovalent interaction donors: theoretical study of the π-hole regium bonds.

Except for the well-known σ-hole regium bonds formed by metal nanoparticles and M(I) (M = Cu, Ag, and Au) derivatives, the existence of π-hole regions located above and below the Au atom in gold(III) derivatives suggests that gold(III) also functions as an efficient electrophilic site. In this study, a comprehensive analysis was conducted on the electrophilicity of trichloro-(p-toluonitrilo-N)-gold(III) derivatives AuL3(NCC6H4X) (L = Cl, Br, CN; X = NH2, CH3, CF3, NC, and CN) and the nature of π-hole regium bonds in the AuL3(NCC6H4X)⋯LB (LB = NH3, N(NH3)3, CH2O, C2H2, C2H4, C6H6) and (AuCl3(NCC6H4Y))n (Y = Cl, CN, NC, NO2; n = 2, 3)) complexes. The characteristics of the π-hole regium bonds were studied with respect to the influence of ligands and substituents, the strength of intermolecular interactions between Au(III) derivatives and Lewis bases, and those in the polymers. In the case of the AuL3(NCC6H4X)⋯NH3 complexes, the strength of the regium bonds increases gradually in the order of L = Cl < Br < CN and X = NH2 < CH3 < CF3 ≈ NC < CN. The ligands (L) attached to the Au atom exert a significant effect on the strength of the π-hole regium bonds in comparison to the substituents (X) on the benzene ring. The regium bonds are primarily dominated by electrostatic interaction, accompanied by moderate contribution from polarization. Linear relationships were identified between the electrostatic energies and the local most positive potentials over the Au atom, as well as between the polarization energies and the amount of charge transfer. Most of the π-hole regium bonds in the AuL3(NCC6H4X)⋯LB complexes exhibit the characters of closed shell noncovalent interactions. In the polymers (AuCl3(NCC6H4Y))n, weak face-to-face π-π stacking interactions are also present, in addition to regium bonds. The trimers displayed a slightly negative cooperativity in comparison to the dimers.

Spectroscopic identification of the ammonia-mercapto radical complex.

The elusive hydrogen-bonded radical complex (˙SH⋯NH3) consisting of ammonia (NH3) and a mercapto radical (˙SH) has been generated through the 193 nm laser photolysis of the molecular complex between NH3 and hydrogen sulfide (H2S) in solid Ar- and N2-matrixes at 10 K. The identification of ˙SH⋯NH3 with matrix-isolation IR spectroscopy and UV-vis spectroscopy is supported by 15N- and D-isotope labeling experiments and quantum chemical calculations at the B3LYP-D3(BJ)/6-311++G(3df,3pd) level of theory. In line with a large red shift of -172.2 cm-1 for the frequency of the S-H stretching mode observed in ˙SH⋯NH3 (cf. free ˙SH), the radical ˙SH acts as a hydrogen donor, and NH3 acts as an acceptor. According to the calculations at the CCSD(T)/aug-cc-pVTZ level, the SH⋯N bonded structure ˙SH⋯NH3 (binding energy De = 3.9 kcal mol-1) is more stable than the isomeric amidogen radical complex HSH⋯˙NH2 (De = 2.8 kcal mol-1) by 16.6 kcal mol-1. This is in sharp contrast to the photochemistry of the closely related HOH⋯NH3 complex, since the water-amidogen radical complex HOH⋯˙NH2 (De = 5.1 kcal mol-1) was generated under similar photolysis conditions, whereas the ammonia-hydroxyl radical complex ˙OH⋯NH3 (De = 7.9 kcal mol-1) is higher in energy by 9.3 kcal mol-1.

The intermolecular interactions of ammonia with chlorine and bromine oxides: a theoretical study.

The role of halogen oxides is substantial in the stratosphere, especially for ozone depletion. It is important to make clear the interaction of halogen oxides with other gaseous molecules. This work performed quantum chemical calculations to investigate the intermolecular interactions between XmOn (X = Cl or Br, m, n = 1 or 2) and ammonia. The chlorine and bromine oxides selected in this paper include typical halogen oxides which can influence the atmospheric processes. For each complex, two different types of interactions, halogen and hydrogen bonds were identified. A π-hole interaction was also found in the XO2···NH3 complex. The interaction energy implies that the strength of the halogen bond is far more stronger than the hydrogen bond. A prominent difference exists between the halogen oxides of singlet or doublet state, which can be ascribed to the electron spin density distribution. The nature of the intermolecular interactions was identified by an independent gradient model based on Hirshfeld partition (IGMH) analysis. Symmetry-adapted perturbation theory (SAPT) calculation indicates that electrostatic interaction dominates the halogen-bonded complex, and hydrogen bond is driven by electrostatic interaction and dispersion.

Computational investigation of the conformer selective complexes of 1,2,3,4-tetrahydroisoquinoline: Ammonia (THIQ: NH3) in S0

Three low-energy conformations are identified in 1,2,3,4-tetrahydroisoquinoline (THIQ): NH3 complexes. The lone pairs on N atoms strongly affects the conformational landscape. Both density functional theory (DFT) and MP2 levels of computations yield consistent results. Multiple PESs corresponding to different types of hydrogen bonds are drawn to account for all possible complexes. Ten complexes are identified. The global minimum contains a strong N-H⋅⋅⋅N and a weak N-H⋅⋅⋅π hydrogen bonds where NH3 is an H bond acceptor. In the remaining two complexes ammonia acts as a donor. All the low-energy complexes which can show intermolecular proton transfer were studied in detail although none shows PT with a single NH3 molecule. The intermolecular vibrational modes are critically analyzed and the relative shifts in the characteristic modes of ammonia are explained. Types and sites for H-bonding can be ascertained from the vibrational analyses. Changes in molecular electrostatic potentials (MEP) on complex formation are explained and confirm our computational results. We suggest further experiments to confirm our key observations.

Radiation-induced transformation of the C2H2⋯NH3 complex in cryogenic media: Identification of C2H2⋯NH2∙ complex and evidence of cold synthetic routes

Acetylene and ammonia are important constituents of the interstellar medium, and their coupled chemistry induced by high-energy radiation may be responsible for the formation of a variety of prebiotically important organic-nitrogen compounds. In this work, we first comprehensively characterized the vibrational spectrum of the 1:1 C2H2⋯NH3 complex obtained by deposition of the C2H2/NH3/Ng (Ng = Ar, Kr, or Xe) gaseous mixtures at 5K using Fourier transform infrared spectroscopy and ab initio calculations at the CCSD(T)/L2a_3 level of theory and examined its radiation-induced transformations. The parent complex adopts a C3v symmetric top molecular structure with C2H2 acting as a proton donor. The x-ray-induced transformations of this complex result in the formation of the C2H2⋯NH2 ∙ complex and various CN-containing species (CH2CNH, CH3NC, CH2NCH, CH2NC∙, CCN∙, and CNC∙). The radical-molecule complex was identified based on comparison of experimental data with the results of the UCCSD(T)/L2a_3 computations. It is characterized by distinct features in the region of acetylene CHasym str mode, red-shifted from the corresponding absorptions of non-complexed acetylene by -72.9, -70.4, and -60.6cm-1 for Ar, Kr, and Xe, respectively. Additionally, in krypton and xenon matrices, the blue-shifted features in the CHasym bend region of acetylene were observed, which can be also tentatively attributed to the C2H2⋯NH2 ∙ complex. The extrapolated to the complete basis set limit unrestricted coupled cluster method with single and double, and perturbative triple excitations binding energy of the C2H2⋯NH2 ∙ complex (including zero-point vibration energy correction) is lower than that of the C2H2⋯NH3 complex (1.90 and 2.51kcal mol-1, respectively). We believe that the C2H2⋯NH2 ∙ complex may be an important intermediate in cold synthetic astrochemistry.

Enhancement of xanthate adsorption on lead-modified and sulfurized smithsonite surface in the presence of ammonia

The contribution of ammonia to the sulfurization of Cu and Zn oxide minerals has been widely investigated, but the practical role of ammonia in the xanthate adsorption that directly determines the flotation of minerals has not been clearly confirmed. In this work, the promotion performance of NH3·H2O for xanthate adsorption onto the smithsonite surface was visually exhibited through adsorption density detection and the relating adsorption mechanism was revealed in terms of adsorption behavior and structure. Ultraviolet–visible spectroscopy and infrared spectroscopy tests showed that NH3·H2O treatment significantly increased the adsorption density of xanthate, with an increasing value of approximately 0.52 mg/m2 on the smithsonite surface at the initial xanthate concentration of 300 mg/L. With NH3·H2O treatment, the zeta potential of smithsonite particles increased, which was attributed to the chemisorption of Zn–NH3 complex cations on the mineral surface; such increased potential enhenced the proximity and adsorption probability for xanthate anions on the mineral surface through electrostatic attraction. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analysis indicated that Pb–xanthate was the main xanthate product chemisorbed onto the Pb-modified and sulfurized smithsonite surface; NH3·H2O effectively increased the number of Pb sites on the surface and facilitated the transformation of the Pb(II)–S state to the Pb(II) xanthate state, resulting in an increase of Pb–xanthate content on smithsonite surface. Thus, NH3·H2O improved the hydrophobicity and increased the flotation recovery of smithsonite by approximately 10% in the Pb ion-modified sulfurization–xanthate system.

VUV photoabsorption of thermally processed carbon disulfide and ammonia ice mixtures – Implications for icy objects in the solar system

Many icy bodies in the solar system have been found to contain a rich mixture of simple molecules on their surfaces. Similarly, comets are now known to be a reservoir of molecules ranging from water to amides. The processing of planetary/cometary ices leads to the synthesis of more complex molecules some of which may be the harbingers of life. Carbon disulphide (CS2) and ammonia (NH3) are known to be present on many icy satellites and comets. Reactions involving CS2 and NH3 may lead to the formation of larger molecules that are stable under space conditions. In this paper we present temperature dependent VUV spectra of pure CS2 in the ice phase, and of CS2 and NH3 ices deposited as (i) layered, and (ii) mixed ices at 10 K and warmed to higher temperatures until their sublimation. Pure CS2 ice is found to have a broad absorption in the VUV region, which is unique for a small molecule in the ice phase. In layered and mixed ices, the molecules tend to affect the phase change and sublimation temperature of each other and also leave behind a form of CS2−NH3 complex after thermal annealing. This study of CS2-NH3 ice systems in layered and mixed configurations would support the detection of these species/complexes in mixed molecular ices analogous to that on planetary and cometary surfaces.

σ‐Hole Interactions of Tetrahedral Group IV–VIII Lewis Acid Centers with Lewis Bases: A Comparative Study

AbstractIn the current study, σ‐hole interactions of group IV–VIII element‐containing molecules in tetrahedral geometry with Lewis bases were comparatively scrutinized. The FSiF3, OPF3, NSF3, FClO3, and OArO3 molecules were devoted as Lewis acid centers to interact with NH3 and NCH Lewis bases. According to the results, the most significant σ‐hole interactions were ascribed to the FSiF3⋅⋅⋅ and FClO3⋅⋅⋅Lewis base complexes with interaction energy up to –29.74 kcal mol−1 in the case of the FSiF3⋅⋅⋅NH3 complex. Symmetry‐adapted perturbation theory‐based energy decomposition analysis (SAPT‐EDA) demonstrated that the electrostatic energy (Eelst) was the most prevalent force dominating the explored interactions, while the exchange energies exhibited unfavorable contribution. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) results emphasized the closed‐shell nature for all the investigated complexes except FSiF3⋅⋅⋅NH3 complex that demonstrated a covalent nature. Crucially, the utilization of the positively‐ and negatively‐directed external electric field (EEF) led to amelioration and debilitation of the strength of the studied interactions, respectively. The present findings provide knowledge essential to further expanded applications in the fields pertinent to materials science and crystal engineering.

The Copper Chemical Garden as a Low Cost and Efficient Material for Breaking Down Air Pollution by Gaseous Ammonia

AbstractChemical garden (CG) from copper(II) sulfate, nitrate and chloride (CG CuSO4, CG Cu(NO3)2, CG CuCl2) were grown, and characterized from the structural and compositional point of view by using scanning electron microscopy, X‐ray powder diffraction, elemental analysis, thermogravimetric analysis coupled with mass spectrometry, and DR (diffuse reflectance) UV‐Vis‐NIR spectroscopy. The main crystalline phases, controlled by the anion of the starting salt, were brochantite and kobyashevite for CG CuSO4, gerhardtite, rouaite and anthonyite for CG Cu(NO3)2, and atacamite for CG CuCl2. The materials were then exposed to ammonia vapors to test the effectiveness of their entrapping property. All materials proved to be very efficient and rapid in the uptake of ammonia, which invariably results in the formation of a Cu(II)/NH3 complex. However, after a few tens of minutes, CG Cu(NO3)2 and CG CuCl2 release water and get wet, thereby resulting unsuitable for applications. Only CG CuSO4 remains dry for at least 25 hours. This makes it a valid candidate for building devices for trapping ammonia, and possibly other gases capable of interacting with Cu(II). The entrapment of ammonia by this material was also characterized by 1H and 29Si MAS‐NMR XAS spectroscopies.

Electrostatics Explains the Reverse Lewis Acidity of BH3 and Boron Trihalides: Infrared Intensities and a Relative Energy Gradient (REG) Analysis of IQA Energies.

The reaction path for the formation of BX3–NH3 (X = H, F, Cl, Br) complexes was divided into two processes: (i) rehybridization of the acid while adopting a pyramidal geometry, and (ii) the complex formation from the pyramidal geometries of the acid and base. The interacting quantum atom (IQA) method was used to investigate the Lewis acidity trend of these compounds. This topological analysis suggests that the boron–halogen bond exhibits a considerable degree of ionicity. A relative energy gradient (REG) analysis on IQA energies indicates that the acid–base complex formation is highly dependent on electrostatic energy. With increasing halogen electronegativity, a higher degree of ionicity of the B–X is observed, causing an increase in the absolute value of X and B charges. This increases not only the attractive electrostatic energy between the acid and base but also enhances the repulsive energy. The latter is the main factor behind the acidity trend exhibited by trihalides. Changes in geometry are relevant only for complexes where BH3 acts as an acid, where lower steric hindrance facilitates the adoption of the pyramidal geometry observed in the complex. The CCTDP analysis shows that infrared intensities of BX3–NH3 are determined mostly by the atomic charges and not by the charge transfer or polarization. The opposite is observed in covalent analogues.

Sensing Mechanism of H2O, NH3, and O2 on the Stability-Improved Cs2Pb(SCN)2Br2 Surface: A Quantum Dynamics Investigation.

Although the perovskite sensing materials have shown high sensitivity and ideal selectivity toward neutral, oxidative, or reductive gases, their structural instability hampers the practical application. To exploit perovskite-based gas-sensing materials with improved stability and decent sensitivity, three adsorption complexes of H2O, NH3, and O2 on the Cs2Pb(SCN)2Br2 surface are built by doping Br– and Cs+ in the parent (CH3NH3)2Pb(SCN)2I2 structure and submitted to quantum dynamics simulations. Changes in the semiconductor material geometric structures during these dynamic processes are analyzed and adsorption ability and charge transfer between Cs2Pb(SCN)2Br2 and the gas molecules are explored so as to further establish a correlation between the geometrical structure variations and the charge transfer. By comparing with the previous CH3NH3PbI3 and (CH3NH3)2Pb(SCN)2I2 adsorption systems, we propose the key factors that enhance the stability of perovskite structures in different atmospheres. The current work is expected to provide clues for developing innovative perovskite sensing materials or for constructing reasonable sensing mechanisms.