Axial Chlorine Research Articles

The Rivalry between Intramolecular Tetrel Bonds and Intermolecular Hydrogen Bonds in (O-Si) Chelates of N-Silylmethylamides and -ureas. A Theoretical Study.

The comparison of the results of theoretical calculations of (O-Si) chelates of N-silylmethylated amides and ureas with the axial chlorine or fluorine atom at silicon to the data of X-ray analysis of related compounds revealed the formation of covalent O-Si tetrel bonds (TB) or noncovalent O⋅⋅⋅Si tetrel bonds (NTB). The nature of the formed tetrel bond depends on the substituents at silicon and the polarity of the medium. The competition between the intramolecular TB and intermolecular hydrogen bonds (HB) with proton donors depends on the center of basicity involved in the formation of HB, which could be either oxygen or halogen. The hydrogen bonding can result in changing the nature of the tetrel bonds from covalent to noncovalent and vice versa by varying their lengths and energies. The O-Si bond energies estimated by QTAIM analysis of N-[(chlorodimethylsilyl)methyl]-N-methylacetamide and its H-complexes vary within the range of 7.2 and 12 kcal/mol in gas and solution, respectively, and correlate with the O-Si bond lengths.

Axial Chlorine Induced Electron Delocalization in Atomically Dispersed FeN4 Electrocatalyst for Oxygen Reduction Reaction with Improved Hydrogen Peroxide Tolerance.

Atomically dispersed iron sites on nitrogen-doped carbon (Fe-NC) are the most active Pt-group-metal-free catalysts for oxygen reduction reaction (ORR). However, due to oxidative corrosion and the Fenton reaction, Fe-NC catalysts are insufficiently active and stable. Herein, w e demonstrated that the axial Cl-modified Fe-NC (Cl-Fe-NC) electrocatalyst is active and stable for the ORR in acidic conditions with high H2 O2 tolerance. The Cl-Fe-NC exhibits excellent ORR activity, with a high half-wave potential (E1/2 ) of 0.82V versus a reversible hydrogen electrode (RHE), comparable to Pt/C (E1/2 = 0.85V versus RHE) and better than Fe-NC (E1/2 = 0.79V versus RHE). X-ray absorption spectroscopy analysis confirms that chlorine is axially integrated into the FeN4. More interestingly, compared to Fe-NC, the Fenton reaction is markedly suppressed in Cl-Fe-NC. In situ electrochemical impedance spectroscopy reveals that Cl-Fe-NC provides efficient electron transfer and faster reaction kinetics than Fe-NC. Density functional theory calculations reveal that incorporating Cl into FeN4 can drive the electron density delocalization of the FeN4 site, leading to a moderate adsorption free energy of OH* (∆GOH* ), d-band center, and a high onset potential, and promotes the direct four-electron-transfer ORR with weak H2 O2 binding ability compared to Cl-free FeN4, indicating superior intrinsic ORR activity.

Axial chlorine coordinated iron-nitrogen-carbon single-atom catalysts for efficient electrochemical CO2 reduction

Iron-nitrogen-carbon single-atom catalysts (Fe-N-C SACs) are promising low-cost catalysts for electrochemical CO2 reduction reaction (CO2RR) to achieve carbon neutrality. However, their relatively low selectivity and activity are related to the strong binding of reaction intermediates (e.g., CO*) on single Fe atoms. Here, combining experimental and theoretical studies, we show that introducing axial chlorine (Cl) atom can modulate the electronic structure of Fe atoms in catalytically active FeN4 sites, which facilitates the desorption of CO* and inhibits the adsorption of H*, resulting in improved activity and selectivity in CO2RR. The Cl modified Fe-N-C SAC embedded in nitrogen-doped carbon nanosheets (FeN4Cl/NC) was synthesized in two steps: pyrolyzing Fe-loaded two-dimensional zeolite imidazole framework nanosheets and low-temperature incubation in hydrochloric acid solution. X-ray absorption spectroscopy results reveal that most atomically dispersed Fe atoms are coordinated with one axial Cl atom at 2.26 Å and four N atoms at 2.02 Å. The optimized FeN4Cl/NC exhibits a CO Faradaic efficiency of 90.5%, a high current density of 10.8 mA cm−2 at a low overpotential of 490 mV, and a high turnover frequency of 1566 h−1, one of the best among recently reported Fe-based CO2RR catalysts. FeN4Cl/NC was further applied as a bifunctional catalyst to construct rechargeable zinc-CO2 batteries, delivering a power density of 0.545 mW cm−2 with excellent stability over 15 h. Tailoring the coordination environment of metal atoms in M-N-C SACs by introducing axial atoms may be further extended as an efficient general approach to design advanced catalysts for various electrochemical applications, such as fuel cells, nitrogen fixation, and lithium-sulfur batteries.

Highly Scalable Conversion of Blood Protoporphyrin to Efficient Electrocatalyst for CO2‐to‐CO Conversion

AbstractElectrochemical CO2 reduction to valuable chemicals represents a green and sustainable approach to close the anthropogenic carbon cycle, but has been impeded by low efficiency and high cost of electrocatalysts. Here, a cost‐effective hybrid catalyst consisting of hemin (chloroprotoporphyrin IX iron(III)), a product recovered from bovine blood, adsorbed onto commercial Vulcan carbon is reported. Upon heat treatment, this material shows significantly improved activity and selectivity for CO2 reduction in water while exhibiting good stability for more than 10 h. The heat treatment leads to consecutive removal of the axial chlorine atom and decomposition of the iron porphyrin ring, restructuring to form atomic Fe sites. The optimized hybrid catalyst obtained at 900 °C shows near‐unity selectivity for reduction of CO2 to CO at a small overpotential of 310 mV. The insight into transformation of adsorbed Fe complexes into single Fe atoms upon heat treatment provides guidance for development of single atom catalysts.

Redox and Photophysical Properties of Four Subphthalocyanines Containing Ferrocenylcarboxylic Acid as Axial Ligands.

Four new ferrocenylsubphthalocyanines Y-BSubPc, with ferrocenylcarboxylic acid YH = Fc-CH2-CH2-COOH (1) or Fc-CH═CH-COOH (2) in the axial Y position, were synthesized with a 40% yield. The axial ferrocenylcarboxylic acid moiety did not have a significant influence on the position of the Q bands maxima of the UV/vis spectra of the ferrocenylsubphthalocyanines or on the 1H NMR position of the ring proton peaks of Y-BSubPc(H12) or on the 19F NMR position of the ring F peaks of YSubPc(F12), relative to their respective parent compounds Cl-BSubPc(H12) 3 and Cl-BSubPc(F12) 4, containing axial chlorine. Very weak metal-to-ligand-charge-transfer bands (MLCT) in the near-IR region were observed. An electrochemical study utilizing cyclic voltammetry showed that electronic communication exists between ferrocene on the axial ferrocenylcarboxylic acid and the π-electrons of the macrocycle of the ferrocenylsubphthalocyanine (Fc(CH2)2COO)-BSubPc(H)12,5, (Fc(CH)2COO)-BSubPc(H)12, 6, (Fc(CH2)2COO)-BSubPc(F)12, 7, and (Fc(CH)2COO)-BSubPc(F)12, 8. The Fe group of the ferrocenyl-containing axial ligand is involved in the first reversible oxidation process, followed by a second oxidation localized on the subphthalocyanine ligand. The fluorine ring substituents in SubPcs 7 and 8 caused the ferrocenyl oxidation to shift more positive by ca. 0.1 V, compared to SubPcs 5 and 6 without fluorine. Density functional theory (DFT) calculations provided further insight into the properties of these novel ferrocenylsubphthalocyanines. The neutral species of SubPcs 5-8 have LUMOs with mainly π-ring character and HOMOs with mainly iron-d character, confirming ring-based reduction, metal-based Fe(II) to Fe(III) oxidation, as well as weak MLCT in the near-IR region. Further DFT optimization of the cation (oxidized) species was essential to verify the second ring-based oxidation.

Electron Density Redistribution in the System GeCl4←O=C[N(CH3)2]2 upon Coordination Bond Formation

Quantum-chemical calculations of the system Cl4Ge←O=C[N(CH3)2]2 with full geometry optimization were performed by RHF/6-31G(d) and MP2/6-31G(d) methods. The calculations took into account that the Ge–Cl axial bond and the O=C bond are not at one line, as opposed to the previous belief. The MP2/6-31G(d) calculations of this system were also performed for various distances between coordination centers, and for GeCl4 and O=C[N(CH3)2]2 molecules, with full geometry optimization. The results of the calculations were used to quantify electron density redistribution in the system upon coordination bond formation. The electron density of chlorine atoms, especially, of the axial chlorine atom, was shown to increase upon coordination bond formation due to its transfer from the ligand hydrogen atoms and Ge–Cl bond polarization. The partial negative charge of the oxygen atom and the positive charge of the carbonyl carbon atom increase in association.

Structural features of SnCl4–ortho-dimethoxybenzene complexes as derived from ab initio computations

Computations for the possible structures of SnCl4–ortho-dimethoxybenzene complexes and initial components have been performed by MP2/LANL2DZ method. Computation results have been compared with experimental data of 35Cl nuclear quadrupole resonance. cis-Octahedral structure of the complex through the coordination of both oxygen atoms has been confirmed. This complex differs considerably from the majority of studied tetrachlorostannane complexes of cis-octahedral structure in terms of the ratios of axial and equatorial Sn–Cl bond distances, p σ electron density, and 35Cl NQR frequencies for axial and equatorial chlorine atoms.

Chloride Ion Erosion in Concrete under Sustained Axial Pressure

As one of the leading causes of influencing the durability of concrete structure, reinforcement corrosion has been a central issue. Erosion of chloride ions on the concrete structure is influenced by many factors. This is not only concerned with its own structural properties, but also to its environment, to withstand the load and other factors. This article has carried on an experiment which researches on the rules of chloride ion penetration in the sustained axial compression after different corrosive time, when the concrete is corroded under the joint action of axial compression load and chlorine salt circulation. The results prove that, with the increase of Intensity of load and the cycle time of chlorine salt, the number of Chloride ion ingress in concrete continues to increase. The experimental results may provide a reference to the durability design of concrete in chloride environment.

Mechanism and selectivity of methyl and phenyl migrations in hypervalent silylated iminoquinones.

Chlorosilanes R(X)(Y)SiCl (R = Me, Ph; X, Y = Me, Ph, Cl) have been reported to react with Pb(ONO(Q))2 (ONO(Q) = 3,5-di-tert-butyl-1,2-quinone-(3,5-di-tert-butyl-2-oxy-1-phenyl)imine) to give five-coordinate (X)(Y)Si(ON[R]O), in which the R group has migrated from silicon to nitrogen. This migration is intramolecular, as confirmed by the lack of crossover between (CH3)3SiCl and (CD3)3SiCl in their reaction with Pb(ONO(Q))2. Reaction of PhSiMeCl2 takes place with high kinetic stereoselectivity to produce isomer Ph(Cl)Si(ON[Me]O) in which the phenyl is axial in the trigonal bipyramid, which subsequently isomerizes to the thermodynamic isomer with axial chlorine. This indicates that migration takes place preferentially from the stereoisomer of the octahedral intermediate, κ(3)-Ph(CH3)(Cl)Si(ONO(Q)), in which the phenyl and methyl groups are mutually trans, indicating that the observed complete selectivity for methyl over phenyl migration is due to intrinsic differences in migratory aptitude. DFT calculations suggest that migration takes place from this isomer not because it undergoes migration faster than other possible stereoisomers, but because it is formed most rapidly, and migration occurs faster than isomerization.

SubPc-ZnPorphyrin conjugates – Synthesis, characterization and properties

A set of SubPc-Porphyrin dyads and triads have been synthesized by the nucleophilic substitution reaction of hydroxyl-containing meso-substituted porphyrins and a good electron acceptor, dodecafluorosubphthalocyanine. Acid-catalyzed condensation of p-hydroxybenzaldehyde and the corresponding dipyrromethane, followed by zinc metallation, afforded the appropriate metalloporphyrins. Subsequent nucleophilic substitution occurred between the porphyrin and the axial chlorine atom of the subphthalocyanine when reacted in a sealed tube at 180 °C. The structures of all the synthesized compounds were characterized by 1H NMR, 13C NMR and mass spectroscopy. The photophysical and electrochemical studies have also been performed by using UV–Vis, fluorescence spectroscopy and cyclic voltammetry experiments.

Theoretical Investigation into the Mechanism of 3′-dGMP Oxidation by [PtIVCl4(dach)

The mechanism for the oxidation of 3'-dGMP by [PtCl(4)(dach)] (dach = diaminocyclohexane) in the presence of [PtCl(2)(dach)] has been investigated using density functional theory. We find that the initial complexation, i.e., the formation of [PtCl(3)(dach)(3'-dGMP)], is greatly assisted by the reaction of the encounter pair [PtCl(2)(dach)···3'-dGMP] with [PtCl(4)(dach)], leading to migration of an axial chlorine ligand from platinum(IV) to platinum(II). A dinuclear platinum(II)/platinum(IV) intermediate could not be found, but the reaction is predicted to pass through a platinum(III)/platinum(III) transition structure. A cyclization process, i.e., C8-O bond formation, from [PtCl(3)(dach)(3'-dGMP)] occurs through an intriguing phosphate-water-assisted deprotonation reaction, analogous to the opposite of a proton shuttle mechanism. Followed by this, the guanine moiety is oxidized via dissociation of the Pt(IV)-Cl(ax) bond, and the cyclic ether product is finally formed after deprotonation. We have provided rationalizations, including molecular orbital explanations, for the key steps in the process. Our results help to explain the effect of [PtCl(4)(dach)] on the complexation step and the effect of a strong hydroxide base on the cyclization reaction. The overall reaction cycle is intricate and involves autocatalysis by a platinum(II) species.

Density Functional Theory Studies on the Oxidation of 5′-dGMP and 5′-dAMP by a Platinum(IV) Complex

Density functional theory has been used to investigate the oxidation of a guanine nucleotide by platinum(IV), a process that can be important in the degradation of DNA. For the first time, we have provided a comprehensive mechanism for all of the steps in this process. A number of intermediates are predicted to occur but with short lifetimes that would make them difficult to observe experimentally. A key step in the mechanism is electron transfer from guanine to platinum(IV), and we show that this is driven by the loss of a chloride ligand from the platinum complex after nucleophilic attack of 5'-phosphate to C8 of guanine. We have investigated several different initial platinum(IV) guanine adducts and shown that the adduct formed from replacement of an axial chlorine ligand in the platinum(IV) complex undergoes oxidation more easily. We have studied adenine versus guanine adducts, and our results show that oxidation of the former is more difficult because of disruption of the aromatic π system that occurs during the process. Finally, our results show that the acidic hydrolysis step to form the final oxidized product occurs readily via an initial protonation of N7 of the guanine.

Ab initio Calculation of the stereoelectronic structure of 1-(1-trichlorogermylethyl)-pyrrolidin-2-one*

RHF/6-31G(d) and MP2/6-31G(d) calculations were carried out to study the stereoelectronic structure of 1-(1-trichlorogermylethyl)pyrrolidin-2-one with a pentacoordinated germanium atom. These results were compared with the X-ray diffraction structural analysis data. Upon formation of the Ge ← O coordination bond in this molecule, the electron density of all the atoms of the coordination polyhedron of the germanium atom, including the oxygen atom, increases, especially the axial chlorine atom, while the electron density of the germanium, nitrogen, and carbonyl group carbon atoms decreases. Different polarization of all three valence p-orbitals of each Cl atom of this molecule was established. 35Cl nuclear quadrupole resonance spectrum parameters were evaluated. The molecule also has stable form, in which the germanium atom is tetracoordinated. The total energy of this form is 2.7 kcal/mol higher than for the structure with a pentacoordinated germanium atom.

Quantum-chemical study of chlorophosphoranes: I. Structure of the (C6H5)2PCl3 molecule in gaseous and crystalline states

The quantum-chemical calculations of the (C6H5)2PCl3 molecule were performed by the methods RHF/6-31G(d) and MP2/6-31G(d) with complete and partial optimization of its geometry. The results of calculations were used for evaluating the NQR frequencies of 35Cl and the parameters of asymmetry of the of electric field gradient on the 35Cl nuclei of this molecule. According to the results of calculations with the partial optimization of geometry and to the experimental data of 35Cl NQR the bond lengths were found of central atom P in the solid state of this compound. The mutual influence of its axial and equatorial bonds was studied. It is shown that in chlorophosphoranes the 35Cl NQR frequencies of the axial and equatorial chlorine atoms decrease with the decrease in the bond lengths of phosphorus atom.

Quantum-chemical study of chlorophosphoranes: III. Structure of the molecules of the series (X,X′) a P(Cl3) e . Mutual influence of axial and equatorial substituents

Quantum-chemical calculations by the methods RHF/6-31G(d) and MR2/6-31G(d) of a series of chlorophosphoranes (X,X′)aP(Cl3)e with complete optimization of their geometry were performed. The results of the calculations were used to estimate 35Cl NQR frequencies and asymmetry parameters of the electric field gradient at the 35Cl nuclei of these molecules. From the results of calculations using RHF/6-31G(d) method with partial geometry optimization and experimental data on 35Cl NQR the lengths of the bonds of central P atom of the compounds in solid state were found. Mutual influence of axial and equatorial substituents was revealed. As in other chlorophosphoranes, the decrease in the length of axial or equatorial P-Cl bonds leads to the decrease in NQR frequencies of axial and equatorial chlorine atoms, respectively.

Quantum-chemical study of chlorophosphoranes: II. Structure of molecules of (Cl2) a P(Cl n X3−n ) e series, and mutual influence of axial and equatorial substituents

The quantum-chemical calculations by the methods RHF/6-31G(d) and MP2/6-31G(d) of chlorophosphoranes of a series (Cl2)aP(ClnX3−n)e with complete and partial optimization of their geometry were performed. The results of calculations were used for evaluation of the frequencies of 35Cl NQR and the asymmetry parameters of the electric field gradient on the 35Cl nuclei of these molecules. According to the results of calculations with the partial geometry optimization and the experimental data on 35Cl NQR the bond lengths of central atom P in the solid state of the corresponding compounds were used. A substantial change in the NQR frequencies of the axial chlorine atoms and a weak change in the frequencies of the equatorial ones at a change in the number of the latter was explained.

Deprotection, Tethering, and Activation of a One-Legged Metalloporphyrin on a Chemically Active Metal Surface: NEXAFS, Synchrotron XPS, and STM Study of [SAc]P−Mn(III)Cl on Ag(100)

The structural and reactive properties of the acetyl-protected "one-legged" manganese porphyrin [SAc]P-Mn(III)Cl on Ag(100) have been studied by NEXAFS, synchrotron XPS and STM. Spontaneous surface-mediated deprotection occurs at 300 K accompanied by spreading of the resulting thio-tethered porphyrin across the metal surface. Loss of the axial chlorine ligand occurs at 498 K, without any demetalation of the macrocycle, leaving the Mn center in a low co-ordination state. At low coverages the macrocycle is markedly tilted toward the silver surface, as is the phenyl group that forms part of the tethering "leg". In the monolayer region a striking transition occurs whereby the molecule rolls over, preserving the tilt angle of the phenyl group, strongly increasing that of the macrocycle, decreasing the apparent height of the molecule and decreasing its footprint, thus enabling closer packing. These findings are in marked contrast with those previously reported for the corresponding more rigidly bound four-legged porphyrin [ Turner , M. , Vaughan , O. P. H. , Kyriakou , G. , Watson , D. J. , Scherer , L. J. , Davidson , G. J. E. , Sanders , J. K. M. and Lambert , R. M. J. Am. Chem. Soc. 2009 , 131 , 1910 ] suggesting that the physicochemical properties and potential applications of these versatile systems should be strongly dependent on the mode of tethering to the surface.

Deprotection, Tethering, and Activation of a Catalytically Active Metalloporphyrin to a Chemically Active Metal Surface: [SAc]4P−Mn(III)Cl on Ag(100)

The adsorption and subsequent thermal chemistry of the acetyl-protected manganese porphyrin, [SAc](4)P-Mn(III)Cl on Ag(100) have been studied by high resolution XPS and temperature-programmed desorption. The deprotection event, leading to formation of the covalently bound thioporphyrin, has been characterized and the conditions necessary for removal of the axial chlorine ligand have been determined, thus establishing a methodology for creating tethered activated species that could serve as catalytic sites for delicate oxidation reactions. Surface-mediated acetyl deprotection occurs at 298 K, at which temperature porphyrin diffusion is limited. At temperatures above approximately 425 K porphyrin desorption, diffusion and deprotection occur and at >470 K the axial chlorine is removed.

Zerovalent Iron Nanoparticles for Treatment of Ground Water Contaminated by Hexachlorocyclohexanes

Ground water and aquifer samples from a site contaminated by hexachlorocyclohexanes (HCHs; C(6)H(6)Cl(6)) were exposed to nanoscale iron particles to evaluate the technology as a potential remediation method. The summed concentration of the HCH isomers in ground water was approximately 5.16 micromol L(-1) (1500 microg L(-1)). Batch experiments with 2.2 to 27.0 g L(-1) iron nanoparticles showed that more than 95% of the HCHs were removed from solution within 48 h. Using a pseudo first-order kinetics model, the HCH isomers were removed in accordance with the trend gamma congruent with alpha > beta > delta. This seems to be correlated with the orientation (axial vs. equatorial) of the chlorine atoms lost in the dihaloelimination steps. Although the reactivity of the HCH isomers has been investigated in the classical organic chemistry literature, the present study was the first in the environmental remediation arena. The rate of removal is directly correlated to the number of axial chlorines. The observed rate constant varied from 0.04 to 0.65 h(-1), and the rate constant normalized to the iron surface area concentration ranged from 5.4 x 10(-4) to 8.8 x 10(-4) L m(-2) h(-1). Post-test extractions of the reactor contents detected little HCH remaining in solution or on the iron surfaces, reinforcing the contention that reaction rather than sorption was the operative mechanism for the HCH removal. Together with previously published work on a wide variety of chlorinated organic solvents, this work further demonstrates the potential of zerovalent iron nanoparticles for treatment and remediation of persistent organic pollutants.

35Cl, 93Nb, 181Ta, and 121Sb NQR in Cl5MV · OPCl3 (MV = Nb, Ta, Sb, or P) Complexes

The behavior of 35Cl NQR spectra in Cl5M · OPCl3 complexes is affected by the nature of the metal center and the distortion of its surrounding geometry. In all cases considered, the 35Cl NQR frequencies in the OPCl3 fragment shift toward higher frequencies upon complex formation, whereas the frequencies of axial chlorine atoms in the Cl5M group in the phosphorus and antimony complexes lie below those for the equatorial atoms, and in the niobium and tantalum complexes, the frequencies of the axial atoms are higher than those of the equatorial ones.