CN Moieties Research Articles

Uncovering excited state behaviours associated with electron-withdrawing CN and electron-donating TPA moieties on SAA derivatives: a theoretical study

Inspired by the excellent photochemical characteristics exhibited by salicylaldehyde azine (SAA) derivatives, our current endeavour primarily revolves around delving into the intricacies of photo-induced excited state reactions for its electron-donating and electron-withdrawing moieties derivatives (i.e. CN-SAA-CN, CN-SAA-TPA and TPA-SAA-TPA). Our simulations reveal push–pull-substituted-dependent photoexcitation that could significantly affect excited state intramolecular proton transfer (ESIPT) reaction for SAA derivatives. Constructing potential energy surfaces (PESs), we unveil the ultrafast ESIPT mechanism due to the low potential barriers. Additionally, by comparing the differences of barriers among CN-SAA-CN, CN-SAA-TPA and TPA-SAA-TPA, we present regulative manner for SAA derivatives by substituting electron-donating and electron-withdrawing moieties. We sincerely anticipate that the modulation of push–pull substitutions on excited state behaviours will pave the way for ground-breaking advancements in luminescent materials.

Protonation of apolar species: From Cl2H+ to (E)-NCCHCHCNH+ through computational investigations

Radioastronomy is a powerful tool for the discovery of molecules in space but it requires molecular species to be polar. The observation of apolar species can be however enabled by protonation, which occurs from reaction with the abundant H3+ ion whenever the proton affinity of the species under consideration is greater than that of H2. This property can be easily investigated by computational chemistry and, in this work, it has been used to asses the potential protonation of simple homo diatomics, such as Cl2, P2, and Si2, as well as apolar species containing two equivalent CN moieties, such as diisocyanogen (CNNC) and (E)-1,2-dicyanoethene. Quantum chemistry has also been exploited to investigate the mechanisms of three protonation reactions of H3+ with Cl2, P2, and CNNC. To support laboratory measurements and astronomical observations of the resulting transient species, their rotational spectroscopic parameters were accurately computed together with fundamental vibrational frequencies. For this purpose, we have employed CCSD(T)-based computational methodologies, which provide equilibrium structures with errors smaller than 0.001 Å and 0.1° for bond distances and angles, respectively. Such an accuracy is expected to lead to rotational constants predicted, in relative terms, with uncertainties better than 0.2%. Instead, the expected accuracy on vibrational frequencies is ∼10 cm−1, thus being well suited to guide band assignments.

Rational design of modified donor-acceptor functionalized graphitic carbon nitride structures with tailored optoelectronic and textural features for visible light-assisted H2O2 production

In this study, we tried to design novel structures of graphitic carbon nitride (GCN) by tuning the quantity of their structural NHx (x = 1, 2) and CN moieties via a facile NaBH4-assisted calcination of supramolecular assemblies of cyanuric acid and melamine (CM complex). These functional groups with different electron affinities would act as donor-acceptor (D-A) motifs in the obtained GCN conjugated polymer, constructing a simple analogy of a biomimetic D-A system. Consequently, the structurally modified sample (DCN) exhibited an extended electronic delocalization, and enhanced exciton dissociation owing to formation of the internal electric field in the molecular scale. Further, employing the CM complex endows the structures with an improved surface area and unique coral-like morphology. As a result, the modified sample showed a remarkable photocatalytic H2O2 production rate of 351 µmol h−1 g−1, which is much higher than that of 158 µmol h−1 g−1 for the pristine sample (CN).

Amphiphilic cyclodextrins: Dimerization and diazepam binding explored by molecular dynamics simulations

Amphiphilic cyclodextrins spontaneously aggregate to form different supramolecular assemblies with potential applications in drug release. Herein, we employ extended molecular dynamics simulations in order to characterize the structure and dynamics in explicit solvent of several amphiphilic derivatives of the β-cyclodextrin (β-CD) molecule, with aliphatic chains ester-bound to the wide rim of the hydrophobic cavity. We also study the binding properties considering a typical guest (diazepam) and the dimerization of these macrocyclic systems, assessing the relative stability of the complexes by means of end-point free energy methods. Different lengths (C4, C10, and C14 atoms) are considered for the alkyl side chains included in the amphiphilic β-CD-Cn molecules. According to the simulations, the length of these Cn moieties determines the complexing and aggregation capabilities of the β-CD-Cn systems. Compared to the native β-CD, the alkyl side chains in the β-CD-Cn molecules destabilize the inclusion complexes with diazepam and hinder the access of guest molecules to the hydrophobic cavity. In turn, dimerization is favored in the largest amphiphilic derivatives associated to the hydrophobic interaction between the Cn fragments.

High-rate aqueous zinc-organic battery achieved by lowering HOMO/LUMO of organic cathode

Despite the development of quinone as the potential cathode material for Zn-organic batteries, there are undesired behaviors for the rate and cycling performances. To achieve high-performance Zn-organic batteries, intentional organic molecular design and a deep understanding of the mechanism of Zn-organic batteries are highly essential. Herein, strong electron-withdrawing and conjugating groups (-CN) were introduced to lower the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy on an aromatic Schiff base (Hexaazatrinnphthalene, denoted as HATN). With such a decoration, HATN-3CN exhibits an outstanding rate capacity with retention of 60.7% of the initial capacity at 400 times the initial current density and long cycle life of over 5800 cycles. Besides, the charge storage mechanism was systematically investigated through experiments and density functional theory calculation, showing that CN moieties are the active site for the storage of H+/Zn2+. This strategy and insight provided by molecular orbital theory and kinetics-controlled process offer a feasible pathway of molecular-level design for constructing high-performance Zn-organic batteries.

Improved Access to Organo-Soluble Di- and Tetrafluoridochlorate(I)/(III) Salts.

A facile one‐pot gram‐scale synthesis of tetraalkylammonium tetrafluoridochlorate(III) [cat][ClF4] ([cat]=[NEt3Me]+, [NEt4]+) is described. An acetonitrile solution of the corresponding alkylammonium chloride salt is fluorinated with diluted fluorine at low temperatures. The reaction proceeds via the [ClF2]− anion which is structurally characterized for the first time. The potential application of [ClF4]− salts as fluorinating agents is evaluated by the reaction with diphenyl disulfide, Ph2S2, to pentafluorosulfanyl benzene, PhSF5. The CN moieties in acetonitrile and [B(CN)4]− are transferred in CF3 groups. Exposure of carbon monoxide, CO, leads to the formation of carbonyl fluoride, COF2, and elemental gold is dissolved under the formation of tetrafluoridoaurate [AuF4]−.

Boosting the bifunctional oxygen electrocatalytic performance of atomically dispersed Fe site via atomic Ni neighboring

Atomically dispersed metal-nitrogen-carbon complexes on carbon supports have drawn tremendous attention in the electrocatalysis fields. Herein, we managed the synthesis of atomically dispersed binary NixFe100-x-NC (x = 0–100) materials with tunable Ni/Fe ratios and investigated their underneath synergy effects for the enhancement of oxygen reduction (ORR) and oxygen evolution reactions (OER). EXAFS revealed the abundant presence of Ni(N3)-Fe(N3)-Cn moieties in Ni66Fe34-NC sample. XPS fine scans indicated deep synergy of dual-site Ni/Fe that favored more charge localized over Ni/Fe sites. Electrochemical measurments showed that the Ni66Fe34-NC delivered a very high ORR half-wave potential (E1/2) of 0.85 V and a low OER overpotential of 467 mV at ∼10 mA cm−2 (Ej=10). The Fe site with Ni neighboring, as suggested by DFT simulations and in-situ Raman, was the responsible site for both ORR and OER. Furthermore, the Ni66Fe34-NC-assembled Zn-air battery afforded large specific power density and extraordinary cycling stability.

Amino hydroxyapatite/chitosan hybrids reticulated with glutaraldehyde at different pH values and their use for diclofenac removal

Diclofenac sodium (DS) is an emergent pollutant, and among the methods investigated for its removal, adsorption is the most widely utilized technique. Hydroxyapatite and chitosan are biomaterials often used for adsorption. However, both biomaterials are limited due to their low chemical stability in an acidic medium; furthermore, pure hydroxyapatite interacts poorly with diclofenac. In this work, hydroxyapatite was organofunctionalized with 3-aminopropyltrimethoxysilane and further used to obtain amino hydroxyapatite /chitosan hybrids by crosslinking with glutaraldehyde at pH 3, 4, 5, and 6. X-ray diffraction patterns indicated the preservation of the hydroxyapatite phase under all pH conditions. Based on the control reaction of the amino hydroxyapatite with glutaraldehyde and its further reduction in sodium borohydride, the formation of CN moieties was highlighted as the main interaction mechanism between the aldehyde and amino groups. Therefore, crosslinking with glutaraldehyde was evaluated by infrared, Raman spectroscopy, and 13C NMR techniques; the results suggested contributions of imine formation and hydrogen bonding. The hybrid obtained at pH 3 exhibited an enhanced adsorption capacity of 125 mg g−1 at 15 min. The synergy between amino hydroxyapatite and chitosan crosslinked by glutaraldehyde was demonstrated.

Phase-mediated robust interfacial electron-coupling over core-shell Co@carbon towards superior overall water splitting

The development of bifunctional electrocatalysts is an appealing yet challenging task for renewable energy conversion. Herein, taking core-shell structure as an example, we propose a “phase mediation” strategy to boost electronic synergism on hydrogen and oxygen evolution reaction (HER/OER). Through precisely tuning the cobalt cores from face-centered-cubic (fcc) to hexagonal (hcp) structure, the electrocatalytic overpotentials of Co@NC for both HER and OER are reduced by ∼100 mV, and lower than those of most other carbon-based electrocatalysts yet reported. Operando SR-FTIR measurements uncover key intermediates of *H and *OO bonding to N and C sites of CN moieties in hcp-Co@NC during the HER and OER processes, respectively, suggesting the adjacent CN moieties as synergistic active sites. In addition, atomic-level characterizations combined with theoretical calculations reveal robust interfacial metal-ligand coordination and electron injection effect within hcp-Co@NC. This promotes the delocalization of electronic structure of the NC shell, greatly accelerating overall water splitting.

Highly Sensitive and Exceptionally Wide Dynamic Range Detection of Ammonia Gas by Indium Hexacyanoferrate Nanoparticles Using FTIR Spectroscopy.

Ammonia gas is useful but caustic; thus, its concentration is monitored depending on applications. We prepared indium hexacyanoferrate nanoparticles (InHCF-NPs, HCF = [FeII(CN)6]4-) with average diameter around 8 nm by simple reaction at room temperature between In cations and HCF anions, and we found the unique functionality of InHCF-NPs which were capable of highly sensitive (16 ppb) and exceptionally wide range (190000, 16 ppb -0.3%) detection of ammonia gas within 6 min by IR measurements. Slope changes of the IR peak ratio of adsorbed ammonium over CN moieties in the InHCF framework indicated a good log-log linear correlation along gas concentrations, in which a wide dynamic range over 105 was realized for the first time in the field of ammonia gas detection.

Directing the amount of CNTs in CuO–CNT catalysts for enhanced adsorption-oriented visible-light-responsive photodegradation of p-chloroaniline

Copper oxide (CuO, 10–90wt%) was loaded onto carbon nanotubes (CNTs) by electrosynthesis method. The catalysts (CuO/CNT) were characterized by XRD, nitrogen adsorption–desorption, ESR, FTIR, Raman, and XPS spectroscopy. The results indicated that a lower amount of CuO was dispersed well on the CNT, while higher loading was agglomerated, producing large-size crystallites, hence resulting in lower specific surface area. Adsorption studies revealed that the isotherms are fitted well with the Langmuir model. Moreover, the n value that was obtained from Freundlich model indicated that adsorption process is chemisorption. Photodegradation of p-chloroaniline (PCA) under visible light irradiation demonstrated that the 50wt% CuO/CNT catalyst gave the highest degradation (97%). It was concluded that CN moieties of PCA were chemisorbed on the catalyst prior to photodegradation, while the CuOC bonds, surface defects and oxygen vacancies were the main active site in enhancing the subsequent photodegradation. The kinetics of photodegradation were correlated with pseudo-first-order model, verifying the surface reaction was the controlling step. Remarkable mineralization results of PCA were attained by TOC (89.1%) and BOD5 (50.7%). It was also evidenced that the catalyst has a good potential toward degradation of various endocrine disruption compounds.

Vibrational frequencies of hydrogenated silicon carbonitride: A DFT study

Due to their good chemical and thermal inertness, SiCxNy:H films are suitable for a variety of applications in electronic, tribology, optic, photovoltaic and more recently gas separation membranes. For these applications, film evolution can be attractively probed by FTIR spectroscopy. In this work, a systematic quantum mechanical study of the vibrational modes position in the pattern of a-SiCxNy(O):H is presented. Vibrational frequencies of SiC, SiN, CN, SiH, CH and NH moieties have been calculated at DFT/B3LYP level of theory using the 6-311++G(3df,3pd) basis set. Characteristic absorption domains have been compared with FTIR data from the literature. In particular, DFT calculations provide guidelines to discriminate SiH from CN stretching bands, which are calculated to lie below and above ~2230cm−1, respectively. As an example, the oxidation of a microwave PECVD SiCxNy:H films during ageing was evidenced in this work through the progressive increase of SiO stretching band (~1040cm−1). The simultaneous decay of the band centered at 2170cm−1 was attributed to the vanishing of SiH bond upon oxidation. This example illustrates that unambiguous band assignment is required to provide a molecular description of the ageing process, which is in turn required to optimize the material composition and stability. Results of these calculations will be helpful to identify both the chemical moieties and their environment in future investigations on a-SiCxNy:H materials but also on materials containing additional elements such as B- or O-doped SiCN-based systems.

Supramolecular Two-Dimensional Network Mediated via Sulfur’s σ-Holes in a Conducting Molecular Crystal: Effects of Its Rigidity on Physical Properties and Structural Transition

This study reveals that noncovalent intermolecular interactions mediated by σ-holes on sulfur atoms can function as an efficient tool to design and construct a novel supramolecular motif, and that these noncovalent bonds are rigid enough to regulate the displacement of molecules at the structural transition. A novel two-dimensional cation···anion supramolecular structure via sulfur’s σ-holes was constructed in a functional molecular crystal, (ethyl-4-bromothiazolium)2[Pt(mnt)2]3 (mnt = maleonitriledithiolato). The unit cell contained two crystallographically independent anions A and B. Electrostatic σ-hole bonds were detected between σ-holes on sulfur in the cation and lone pairs of −CN moieties in B, while A did not form such S···N σ-hole bonds. This salt exhibited a structural transition at ca. 150 K, in which B did not show apparent displacement, while A shifted along the anion’s stacking direction. This shift enhanced trimerization of the anion in the low-temperature phase, leading to the enhanced ant...

Novel 3,4-methylenedioxyde-6-X-benzaldehyde-thiosemicarbazones: Synthesis and antileishmanial effects against Leishmania amazonensis

A series of eleven 3,4-methylenedioxyde-6-X-benzaldehyde-thiosemicarbazones (16–27) was synthesised as part of a study to search for potential new drugs with a leishmanicidal effect. The thiosemicarbazones, ten of which are new compounds, were prepared in good yields (85–98%) by the reaction of 3,4-methylenedioxyde-6-benzaldehydes (6-X-piperonal), previously synthesised for this work by several methodologies, and thiosemicarbazide in ethanol with a few drops of H2SO4. These compounds were evaluated against Leishmania amazonensis promastigotes, and derivatives where X = I (22) and X = CN (23) moieties showed impressive results, having IC50 = 20.74 μM and 16.40 μM, respectively. The intracellular amastigotes assays showed IC50 = 22.00 μM (22) and 17.00 μM (23), and selectivity index >5.7 and >7.4, respectively, with a lower toxicity compared to pentamidine (positive control, SI = 4.5). The results obtained from the preliminary QSAR study indicated the hydrophobicity (log P) as a fundamental parameter for the 2D-QSAR linear model. A molecular docking study demonstrated that both compounds interact with flavin mononucleotide (FMN), important binding site of NO synthase.

Charge Transfer and Energy Level Alignment at the Interface between Cyclopentene-Modified Si(001) and Tetracyanoquinodimethane

We examine how the electronic structure (via synchrotron radiation XPS, UPS, and NEXAFS) and the molecular orientation (via NEXAFS) of a strong acceptor molecule, tetracyanoquinodimethane (TCNQ), change as a function of thickness when it is deposited on the cyclopentene-covered Si(001)-2×1 substrate. XPS shows that the monomolecular cyclopentene layer acts as an efficient chemical protective barrier. All spectroscopies indicate that anionic TCNQ is formed at (sub)monolayer coverage. However, the transfer should only concern those CN moieties pointing toward the Silicon surface. At higher thicknesses, neutral TCNQ is observed. We do not observe the upward bending of the silicon bands associated with electron transfer from the substrate to the acceptor molecular that one would expect for an unpinned Fermi level interface. In fact, donor levels are likely created within the cyclopentene layer or at its interface with silicon. The formation of TCNQ– is associated with a strong increase in the work function. The attained value (∼5.7 eV) is independent of the work function of the cyclopentene-modified Si(001) surface (that varies with Si doping), in agreement with the integral charge transfer model. Therefore, ultrathin layers of TCNQ can be used to improve the hole-injection properties of this alkene-modified silicon surface.

Graphene based all-solid-state supercapacitors with ionic liquid incorporated polyacrylonitrile electrolyte

Herein, we report, the fabrication of a mechanically stable, flexible graphene based all-solid-state supercapacitor with ionic liquid incorporated polyacrylonitrile (PAN/[BMIM][TFSI]) electrolyte for electric vehicles (EVs). The PAN/[BMIM][TFSI] electrolyte shows high ionic conductivity (2.42 mS/cm at 28 °C) with high thermal stability. Solid-like layered phase of ionic liquid is observed on the surface of pores of PAN membrane along with liquid phase which made it possible to hold 400 wt% of mobile phase. This phase formation is facilitated by the ionic interaction of CN moieties with the electrolyte ions. A supercapacitor device, comprised PAN/[BMIM][TFSI] electrolyte and graphene as electrode, is fabricated and the performance is demonstrated. Several parameters of the device, like, energy storage and discharge capacity, internal power dissipation, operating temperature, safe operation and mechanical stability, meet the requirements of future EVs. In addition, a good cyclic stability is observed even after 1000 cycles.

Self-assembled Pd-dicyanobiphenyl multilayer films and their application in electrocatalytic oxidation of methanol in alkaline medium

Through the layer-by-layer technology, (Pd/dcbp)n (dcbp=4,4′-dicyanobiphenyl) multilayer films were prepared by alternately immersing quartz slide pre-coated with poly(ethylenimine) layer in PdCl2 and dcbp aqueous solutions. (Pd/dcbp)n multilayers were characterized by UV–vis spectra, atomic force image and X-ray photoelectron spectroscopy (XPS). UV–vis spectra showed that the fabrication of (Pd/dcbp)n multilayers depends on the coordination interaction between palladium ions and CN moieties. The results of XPS analysis show that mixed zero-valent and divalent Pd coexist in (Pd/dcbp)n multilayers. During the self-assembly process, Pd ions within the multilayers are in situ reduced by weak reducibility of the ligand bpcn. Transmission electron microscopy further demonstrated that Pd nanoparticles within multilayers were highly dispersed and uniform. The electrode modified with Pd/dcbp multilayer films showed electrocatalytic activity toward methanol oxidation in alkaline medium.

Stability and Spectroscopic Properties of Singly and Doubly Charged Anions

Using density functional theory and hybrid B3LYP exchange-correlation energy functional we have studied the structure, stability, and spectroscopic properties of singly and doubly charged anions composed of simple metal atoms (Na, Mg, Al) decorated with halogens such as Cl and pseudohalogens such as CN. Since pseudohalogens mimic the chemistry of halogen atoms, our objective is to see if pseudohalogens can also form superhalogens much as halogens do and if the critical size for a doubly charged anion depends upon the ligand. The electron affinities of MCl(n) (M = Na, Mg, Al) exceed the value of Cl for n ≥ (k + 1), where k is the normal valence of the metal atom. However, for M(CN)(n) complexes this is only true when n = k + 1. In addition, while the electron affinities and vertical detachment energies of MCl(n) complexes are close to each other, they are markedly different when Cl is replaced by pseudohalogen, CN. The origin of these anomalous results is found to be due to the large binding energy of cyanogen, (NCCN) molecule. Because of the tendency of CN molecules to dimerize, the ground state geometries of the neutral and anionic M(CN)(n) complexes are very different when their number exceed the normal valence of the metal atom. While our calculations support the conclusion of Skurski and co-workers that pseudohalogens can form the building blocks of superhalogens, we show that there is a limitation on the number of CN moieties where this is true. Equally important, we find large differences between the ground state geometries of the neutral and anionic M(CN)(n) complexes for n ≥ (k + 2) which could play an important role in interpreting future experimental data on M(CN)(n) complexes. This is because the electron affinity defined as the energy difference between the ground states of the anion and neutral can be very different from the adiabatic detachment energy defined as the energy difference between the ground state of the anion and its structurally similar neutral isomer.

Ordered bimetallic coordination networks featuring rare earth and silver cations

Three lanthanide complexes of the ditopic ligand 3-cyanopentane-2,4-dionate (acacCN) have been synthesized and structurally characterized. Longer intermolecular contacts result in ninefold coordination of the cation in Ce(acacCN)(3)(H(2)O)(2), whereas mononuclear complexes of the same stoichiometry with coordination number eight are obtained for the smaller Eu(III) and Yb(III) cations. Reaction of these labile compounds with AgPF(6) leads to re-organization of the coordination sphere of the rare earth cations: neutral extended structures are formed in which the peripheric -CN moieties of Ln(acacCN)(4) anions coordinate to silver cations. The initially formed heterometallic networks show additional coordination of water or inclusion of solvent molecules; three different structure types, two of them as isomorphous pairs, have been characterized. In the case of Eu(III) and Yb(III), these solids are instable when stored in their mother liquor and undergo a slow aging process, finally resulting in phase pure stable and solvent-free 3D networks Ln(acacCN)(4)Ag.

Au(CN)n Complexes: Superhalogens with Pseudohalogen as Building Blocks

Electron affinity (EA) is one of the most important factors that govern reactivity of atoms and molecules. Chlorine, with the highest electron affinity (3.6 eV) of all elements in the periodic table, is a classic example of reactive elements. Over past thirty years, much research has been done to expand the scope of molecules with electron affinities even larger than that of Cl. These molecules, called superhalogens, have the general formula MX(n+1) where M is a metal atom, X is a halogen atom, and n is the valency of the metal. In this paper we explore the potential of pseudohalogens such as CN, which mimic the chemistry of halogens, to serve as building blocks of new superhalogens. Using calculations based on density functional theory, we show that when a central Au atom is surrounded by CN moieties, superhalogens can be created with electron detachment energies as high as 8.4 eV. However, there is a stark contrast between the stability of these superhalogens and that of conventional AuF(n) superhalogens. Whereas AuF(n) complexes are stable up to n = 5 for neutrals and n = 6 for anions, Au(CN)(n) complexes (with CN moieties attached individually) are metastable beyond n = 1 for neutrals and n = 3 for anions. We investigate the nature and origin of these differences. In addition, we elucidate important distinctions between electron affinity (EA) and adiabatic detachment energy (ADE), two terms that are often used synonymously in literature.