HF Complex Research Articles

Development of Group IV Metal Complexes Bearing Thioether-Amido Ligands with Enhanced High-Temperature Catalytic Performance toward Olefin Copolymerization.

The development of homogeneous metal catalysts with both high activity and exceptional thermal stability is crucial for the efficient synthesis of polyolefin elastomers (POEs) through solution-phase olefin polymerization. In this study, a series of Hf (Hf1-Hf5), Zr (Zr1), and Ti (Ti1) complexes featuring thioether-amido ligands were synthesized and carefully characterized using advanced techniques such as 1H and 13C NMR spectroscopy as well as single-crystal X-ray diffraction analysis for Hf4 and Hf5. The results revealed that the catalytic activity and 1-octene incorporation efficiency of these metal complexes followed the trend Hf > Zr > Ti, underscoring the significant impact of the metal center on catalytic performance. Furthermore, the choice of ligands was found to play a critical role in dictating the catalytic properties, with ligands bearing less steric hindrance on the sulfur atom proving to be more favorable for copolymerization reactions. Notably, the Hf complex Hf1, featuring a methyl group on the sulfur atom, displayed exceptional catalytic activity as high as 21,060 kg(polymer)·mol-1(Hf)·h-1 toward ethylene/1-octene copolymerization at 120 °C and produced POE with a high molecular weight (Mw = 6.3 × 104 g·mol-1), relatively narrow distribution (Đ = 2.4), and high incorporation of 1-octene (34.1 mol %). This study demonstrates the potential of tailored ligand design in developing efficient metal catalysts for the production of high-value-added POEs.

Zirconium and Hafnium Complexes Bearing Tridentate ONN-Ligands: Extremely High Activity toward Ethylene (Co)Polymerization.

The pursuit of high-performance catalysts in the realm of polyolefins is a constant goal. In this study, a range of zirconium (1-ZrCl3, 2-ZrCl3, 3-ZrCl4, 12-Zr) and hafnium (1-HfCl3, 12-Hf) complexes featuring phenoxy-imine-amine ONN-ligands (2,6-R2-C6H3-NH-C6H4-N═CH-C6H2-3,5-tBu2-OH; 1-L: R = H; 2-L: R = F; 3-L: R = iPr) were synthesized and characterized using NMR spectroscopy, as well as single-crystal X-ray diffraction for 2-ZrCl3, 3-ZrCl4, and 12-Zr. These Zr and Hf complexes exhibited remarkable efficiency for ethylene homopolymerization and copolymerization with 1-octene when paired with MAO as the cocatalyst. Notably, the Zr complexes outperformed the Hf complexes with the same ligand, underscoring the substantial impact of the metal center on catalytic performance. The substituents and coordination modes of the ligands also exerted significant influence on the catalytic behavior, affecting both the activity and properties of the resulting polymers. Particularly noteworthy was the exceptional activity of 1-ZrCl3, achieving activity as high as 6.30 × 108 g(PE)·mol-1(Zr)·h-1 for ethylene homopolymerization and generating bi- or multimodal distribution polyethylene. The activation of 1-ZrCl3 by 5 or 20 equiv of d-MAO afforded a dinuclear Zr complex bridged by two chlorides (μ-Cl2-(1-ZrCl2)2), which was analyzed and confirmed by in situ 1H NMR spectroscopy and single-crystal X-ray diffraction.

New Data on the Reactions of Zirconium and Hafnium Tetrachlorides with Aliphatic Acids

The reaction of ZrCl4 or HfCl4 with excess 2-methylpropanoic acid when boiling under reflux has been studied. The formation of polynuclear Zr and Hf complexes of the composition M2O(i-C3H7CO2)6 during prolonged reflux of the reaction mixtures was found. The complexes are very sensitive to hydrolysis, forming hexanuclear [M6(O)4(OH)4(i-C3H7CO2)12]. The reactions have a general character for aliphatic acids and can be used as an alternative to the known methods for the synthesis of polynuclear carboxylate clusters of Group 4 metals. The crystal and molecular structures of previously undescribed {[Hf6(μ3-O)4(μ3-OH)4(i-C3H7CO2)12(H2O)]·3i-C3H7COOH} have been determined. The molecular structure is a completely asymmetric hexanuclear cluster containing six Hf(IV) atoms united by a 4:4 μ3-O/OH system of bridges, and stabilized by twelve 2-methylpropanoate ligands, eight of which are bidentate bridging, three are chelating, and one is monodentate. The crystal structure of the complex includes three independent solvating 2-methylpropanoic acid molecules. The obtained IR spectroscopy data make it possible to determine the type of complexes in the reaction mixture. The results of the study may be useful for improving the catalytic systems for ethylene oligomerization.

The Extraction Mechanism of Zirconium and Hafnium in the MIBK-HSCN System

The extraction of zirconium (Zr) and hafnium (Hf) in methyl isobutyl ketone (MIBK)—thiocyanic acid (HSCN) system has been widely used in the production of nuclear-grade zirconium and hafnium in industry, while the extraction mechanism was not adequately studied. In this study, the extraction and stripping equilibrium of Zr and Hf in the MIBK-HSCN system was studied. The results showed that elevated HCl concentration can increase the distribution ratio of SCN− and decrease that of Zr/Hf in organic phase. In the stripping process, HCl concentration and the Organic/Aqueous (O/A) phase ratio played important roles. The mechanism of the extraction reaction was discussed by considering the stoichiometric relationship of possible reaction equations and corresponding equilibrium constants. The results indicated that SCN− could be extracted into MIBK as HSCN·MIBK. Meanwhile, SCN− could also be extracted into MIBK by complexing with metal (Zr or Hf). The molar ratios of MIBK to the complexes of Zr and Hf have been found to be 5.34 and 5.03, respectively. With the increase in the initial concentration of HCl in the aqueous phase, the complexation molar ratios of SCN− to Zr and Hf increased first and then decreased, and so do the extraction equilibrium constants, which might be due to the extraction competition of HSCN and metal complexes.

Polymer‐Derived Ceramic Coatings with Excellent Thermal Cycling Stability

In the present work, transition metal‐containing preceramic silicon polymers were synthesized via chemical modification of a commercially available organopolysilazane with Hf and Ta amido complexes as well as with borane dimethyl sulfide complex. The incorporation of transition metals into the polymer structure, their influence on ceramization and processability were thoroughly investigated. Moreover, the prepared preceramics were coated onto silicon wafers via spin coating and converted into crack‐free, amorphous SiHfTa(B)CN‐based ceramic coatings with excellent adhesion to the substrate. The composition of the ceramic coatings was investigated via X‐ray photoelectron spectroscopy (XPS) and their high‐temperature behavior was studied via oxidation tests performed at 1100 °C. Moreover, a thermal cycling procedure to temperatures above 1250 °C with rapid heating and cooling rates (i.e., in the range of 100–120 K s−1) was applied to the ceramic coating, which showed no damage even after ten thermal cycles, indicating their outstanding performance and their potential for use as environmental barrier coatings at high temperatures.

Synthesis and spectral properties of mixed-ligand Zr and Hf phthalocyanine complexes with out-of-plane coordinated alkylamino-β-ketoenolate chromophores and decanoate

The development of novel materials based on modification of phthalocyanines is promising for various applications in science, medicine and technology. Here mixed-ligand Zr and Hf phthalocyanine complexes with out-of-plane coordinated alkylamino-β-ketoenolate chromophores and decanoate were synthesized for the first time. Complexes were obtained by one stage reaction of bis(decanoato)zirconium and hafnium phthalocyanines with alkylamino-β-ketoenols that resulted in replacement of only one decanoate ligand with the alkylamino-β-ketoenol. Therefore, mixed-ligand Zr and Hf complexes with two chromophore systems (phthalocyanine and alkylamino-β-ketoenol) were synthesized by using four different alkylamino-β-ketoenols, and their structural characterizations were carried out by using some spectroscopic methods: 1H NMR, UV–Vis, IR and MALDI TOF MS. In the UV–Vis spectra of the obtained complexes, the absorption bands characteristic for phthalocyanine system were observed along with additional absorption band of out-of-plane ligand (in the region 440–480 nm). The fluorescence spectra of investigated compounds are characterized by a maximum at about 690 nm, which corresponds to the emission of the phthalocyanine macrocycle, while the emission of alkylamino-β-ketoenol ligand is not observed.

Investigations of the reaction mechanism of sodium with hydrogen fluoride to form sodium fluoride and the adsorption of hydrogen fluoride on sodium fluoride monomer and tetramer.

The reaction between Na and HF is a typical harpooning reaction which is of great interest due to its significance in understanding the elementary chemical reaction kinetics. This work aims to investigate the detailed reaction mechanisms of sodium with hydrogen fluoride and the adsorption of HF on the resultant NaF as well as the (NaF)4 tetramer. The results suggest that the reaction between Na and HF leads to the formation of sodium fluoride salt NaF and hydrogen gas. Na interacts with HF to form a complex HF···Na, and then the approaching of F atom of HF to Na results in a transition state H···F···Na. Accompanied by the broken of H-F bond, the bond forms between F and Na atoms as NaF, then the product NaF is yielded due to the removal of H atom. The resultant NaF can further form (NaF)4 tetramer. The interaction of NaF with HF leads to the complex NaF···HF; the form I as well as II of (NaF)4 can interact with HF to produce two complexes (i.e., (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF), but the form III of (NaF)4 can interact with HF to produce only one complex (NaF)4(III)···HF. These complexes were explored in terms of noncovalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. NCI analyses confirm the existences of attractive interactions in the complexes HF···Na, NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF. QTAIM analyses suggest that the F···Na interaction forms in the HF···Na complex while the F···H hydrogen bonds form in NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF complexes. Natural bond orbital (NBO) analyses were also applied to analyze the intermolecular donor-acceptor orbital interactions in these complexes. These results would provide valuable insight into the chemical reaction of Na and HF and the adsorption interaction between sodium fluoride salt and HF. The calculations were carried out at the M06-L/6-311++G(2d,2p) level of theory which were performed using the Gaussian16 program. Intrinsic reaction coordinate (IRC) calculations were carried out at the same level of theory to confirm that the obtained transition state was true. The molecular surface electrostatic potential (MSEP) was employed to understand how the complex forms. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) analysis was used to know the topology parameters at bond critical points (BCPs) and intermolecular interactions in the complex and intermediate. The topology parameters and the BCP plots were obtained by the Multiwfn software.

Synthesis of dinuclear pyridyl-amido hafnium and zirconium complexes toward olefin polymerization with unexpected stereospecificity and ultra-high molecular weight capability

Dinuclear syn-Hf2 exerts an unexpected stereospecificity toward propylene polymerization and affords ultra-high molecular weight atactic polypropylene as a thermoplastic elastomer.

Polarized metal-metal multiple bonding and reactivity of phosphinoamide-bridged heterobimetallic group IV/cobalt compounds.

Heterobimetallic complexes are studied for their ability to mimic biological systems as well as active sites in heterogeneous catalysts. While specific interest in early/late heterobimetallic systems has fluctuated, they serve as important models to fundamentally understand metal-metal bonding. Specifically, the polarized metal-metal multiple bonds formed in highly reduced early/late heterobimetallic complexes exemplify how each metal modulates the electronic environment and reactivity of the complex as a whole. In this Perspective, we chronicle the development of phosphinoamide-supported group IV/cobalt heterobimetallic complexes. This combination of metals allows access to a low valent Co-I center, which performs a rich variety of bond activation reactions when coupled with the pendent Lewis acidic metal center. Conversely, the low valent late transition metal is also observed to act as an electron reservoir, allowing for redox processes to occur at the d0 group IV metal site. Most of the bond activation reactions carried out by phosphinoamide-bridged M/Co-I (M = Ti, Zr, Hf) complexes are facilitated by cleavage of metal-metal multiple bonds, which serve as readily accessible electron reservoirs. Comparative studies in which both the number of buttressing ligands as well as the identity of the early metal were varied to give a library of heterobimetallic complexes are summarized, providing a thorough understanding of the reactivity of M/Co-I heterobimetallic systems.

The state of Zr and Hf in chloride hydrothermal fluids from in situ X-ray absorption spectroscopy

In order to quantify the hydrothermal mobility of Zr and Hf in chloride fluids we performed an investigation of the speciation of these metals by means of in situ X-ray absorption spectroscopy (XAS). The experiments included registration of Zr K-edge X-ray absorption near edge structure/extended X-ray absorption fine structure (XANES/EXAFS), and Hf L1-edge (XANES) and Hf L3-edge (EXAFS) spectra. The capillary method, when the experimental solution together with baddeleyite ZrO2(cr) or HfO2(cr) is sealed inside a silica glass capillary, was used. The spectra were recorded between 320 °C/600 bar and 480 °C/2200 bar (Zr) and at 370 °C/2100 bar (Hf) after the stationary solubility of the solid phase was attained. The aqueous fluid composition varied from 3.8 m HCl to 3.5 m HCl/3.2 m CsCl and 3.3 m HCl/2.2 m NaCl (Zr), and was set to 7.7 m HCl in the case of Hf. The composition of the dominant complexes was determined by means of EXAFS fitting and theoretical XANES modeling as ZrCl3(OH)2−/ ZrCl5(H2O)− and HfCl4OH−/ HfCl5(H2O)−. In Zr complexes the metal-to-ligand distances varied between 2.10 ± 0.06 Å - 2.16 ± 0.06 Å (OH−), 2.22 ± 0.03 Å - 2.32 ± 0.07 Å (OH2), and 2.46 ± 0.02 Å - 2.49 ± 0.02 Å (Cl−) depending on the fluid PT-compositional parameters. In Hf-bearing species the average HfO distance is 2.07 ± 0.12 Å, and the HfCl distance is 2.43 ± 0.03 Å. Both the distances are slightly shorter compared to the interatomic distances in Zr complexes. Higher number of Cl ligands and shorter metal-to-ligand distance determined for Hf complexes mean higher affinity of Hf to oxygen-bearing ligands and chloride ion, which can result in separation of Zr and Hf in hydrothermal processes. Reactions of the dissolution of Zr- and Hf-bearing minerals imply that both ionic associate HCl(aq) and ion Cl− are necessary for the formation of the negatively charged complexes. The region, that best satisfy these conditions, is located between ca. 300 and 450 °C. At higher temperature the neutral Zr/Hf-OH-Cl complexes can support the hydrothermal mobility of these metals. The complexation mechanisms determined for Zr and Hf demonstrate that deep chloride fluids can play an important role in mobilization and separation of these metals in subduction zones and in the fluid-rock interaction processes.

Investigation of the H2CO···HF complex in gas phase by the help of FTIR spectroscopy and computational methods

High-resolution infrared absorption spectra of the H2CO···HF complex and its monomers are recorded in gas phase in C=O and C−H regions by means of Bruker HR 125 spectrometer recorded with a resolution of 0.05 cm−1. Upon the complexation in the HF stretching band of complex the asymmetrical shape was not observed due to weak interaction between C=O and C−H stretching of the H2CO···HF complex. Quantum-chemical calculations are performed in mp2//6-311++g(3df, 3pd) approximation and calculated geometrical, energetic, and spectral parameters of the complex.

Fluorocyclisation of Oximes to Isoxazolines Through I(I)/I(III) Catalysis

AbstractA regioselective fluorocyclisation of β,γ‐unsaturated oximes through I(I)/I(III) catalysis is disclosed to generate 5‐fluoromethylated isoxazolines. The transformation leverages p‐iodotoluene as an inexpensive catalyst, Selectfluor® as the terminal oxidant and an amine⋅HF complex (1 : 7.5) as both the fluoride and Brønsted acid source. The λ3‐iodane p‐TolIF2, which is generated in situ, engages the pendant alkene of the substrate to facilitate a cyclisation/fluorination sequence. A range of 5‐fluoromethyl isoxazolines can be generated using this method, including aliphatic and aromatic systems (up to 56 % yield). Single crystal X‐ray analysis of a representative example reveals a conformation that is consistent with the stereoelectronic gauche effect between the exocyclic C(sp3)−F bond and the C(sp3)−O of the isoxazoline (ϕOCCF=−62.0°).

INTERACTION OF HAFNIUM(IV) WITH 6,7-DIHYDROXY‑4-CARBOXYL‑2- PHENYLBENZOPYRYLLIUM SALTS IN BINARY SYSTEMS AND IN THE PRESENCE OF CATIONIC SURFACTANTS

In the current study, the peculiarities of the complexation of Hafnium(IV) with 6,7-dihyroxy‑4-carboxyl‑2-phenylbenzopyrylium salts (CDC) in binary systems and in the presence of cationic surfactants (Surf) were studied. The CDC was synthesized by condensation of pyrogallol A with benzoylpyruvic acid in an acetic acid medium in the presence of perchloric acid. To obtain KDC bromide and chloride, the synthesis was carried out in the presence of bromide acid or by sparging of dry hydrogen chloride, respectively. Using classical spectrophotometric methods of molar ratios and Bent-French, it was found that at pH 2.5 in binary system one complex with stoichiometry Hf(IV): CDC1:2 was formed. Molar absorptivity coefficient was calculated for Hf(IV) complex with CDC and it was equal 3,9⸱104. It was shown that in the presence of cetylpyridinium chloride or cetyltrimetrylammonium bromide complexes with a molar ratio of Hf(IV): CDC: Surf = 1:2:2 were formed. It is noted that the complexes were formed within 10–15 minutes, and the absorbance of the solutions remains constant for at least 2 hours. It was established that the nature of the anion, which is part of the reagent, does not significantly affect the characteristics of the analytical form. It is shown that in the presence of cationic surfactants, the optimal pH of complex formation shifts to a more acidic region. In addition, the introduction of cationic surfactants leads to a batachromic shift of the absorption band by 10–15 nm and an increase in the molar absorptivity to 5.8⸱104 and 6.4⸱104 when cetylpyridinium chloride or cetyltrimetrylammonium bromide were used respectively. It is noted that the found analytical forms can be used as a basis for the development of combined spectroscopic methods for determining trace amounts of Hafnium(IV).

Synthesis and X-ray structure analysis of cytotoxic heptacoordinated Salan hafnium(IV) complexes stabilized with 2,6-dipicolinic acid

Four novel Salan Hf(IV) complexes stabilized by 2,6-dipicolinic acid (Dipic) were synthesized and characterized by 1H, 13C NMR and X-ray diffraction spectroscopy. These Hf(IV)bis-chelates could be obtained in good to excellent yields (88%–91%) and demonstrated rather good stability in aqueous media and on silica gel. [L2Hf(IV)Dipic4-H,Cl] containing steric bulk L2 were stable in about 10% H2O (H2O/THF (v/v)), however, [L1Hf(IV)Dipic4-H,Cl] with non-steric L1 could slowly dissociate and release nontoxic L1. [L1–2Hf(IV)Dipic4-Cl] showed excellent anti-tumoral activity in the range of cisplatin (Hela S3: IC50 = 3.5 ± 0.4 μM, Hep G2: IC50 = 11.2 ± 2.1 μM). In addition, the cellular uptake and apoptosis investigation of [L1Hf(IV)Dipic4-Cl] suggested a fast cellular uptake process against Hela S3 cells with an almost exclusive induced apoptosis cell death path.

The Importance of Electrostatics and Polarization for Noncovalent Interactions: Ionic Hydrogen Bonds vs Ionic Halogen Bonds

A series of 26 hydrogen-bonded complexes between Br− and halogen, oxygen and sulfur hydrogen-bond (HB) donors is investigated at the M06-2X/6–311 + G(2df,2p) level of theory. Analysis using a model in which Br− is replaced by a point charge shows that the interaction energy ({Delta E}_{Int}) of the complexes is accurately reproduced by the scaled interaction energy with the point charge ({Delta E}_{Int}^{PC}).This is demonstrated by {Delta E}_{Int}=0.86{Delta E}_{Int}^{PC} with a correlation coefficient, R2 =0.999. The only outlier is (Br-H-Br)−, which generally is classified as a strong charge-transfer complex with covalent character rather than a HB complex. {Delta E}_{Int}^{PC} can be divided rigorously into an electrostatic contribution ({Delta E}_{ES}^{PC}) and a polarization contribution ({Delta E}_{Pol}^{PC}).Within the set of HB complexes investigated, the former varies between -7.2 and -32.7 kcal mol−1, whereas the latter varies between -1.6 and -11.5 kcal mol−1. Compared to our previous study of halogen-bonded (XB) complexes between Br− and C–Br XB donors, the electrostatic contribution is generally stronger and the polarization contribution is generally weaker in the HB complexes. However, for both types of bonding, the variation in interaction strength can be reproduced accurately without invoking a charge-transfer term. For the Br−···HF complex, the importance of charge penetration on the variation of the interaction energy with intermolecular distance is investigated. It is shown that the repulsive character of {Delta E}_{Int} at short distances in this complex to a large extent can be attributed to charge penetration.

Cyclopropene activation via I(I)/I(III) catalysis: Proof of principle and application in direct tetrafluorination

Preliminary validation of cyclopropene activation by an I(I)/I(III) catalysis manifold is disclosed to enable the direct tetrafluorination of 3,3-diarylcyclopropenes. This transformation occurs through the in situ generation of ArI(III)F2, with inexpensive iodobenzene, amine·HF complexes and Selectfluor® serving as catalyst, fluoride source and oxidant, respectively. Leveraging this approach, it has been possible to generate four C(sp3)-F bonds in a single operation (up to 44%). A Hammett study revealed that the reaction has a very narrow tolerance window with respect to the p-substituent of the aryl groups. Through a process of reaction deconstruction, a mechanism involving two discrete catalytic processes is proposed. Whereas the first cycle results in the ring opening fluorination of the 3,3-diarylcyclopropene, the second proceeds via a fluorination/phenonium ion rearrangement to liberate a tetrafluorinated diarylethane. This study adds hypervalent iodine catalysis to the plenum of strategies that facilitate cyclopropene activation.

Exploration of the СH3CN…HF complex in the gas phase with high-resolution FTIR spectroscopy and computational methods

This paper presents a comprehensive study of the IR absorption spectrum of the СH3CN … HF complex in the gas phase, including computation methods. The high resolution IR absorption spectra of the gaseous mixtures of the title complex were recorded in the region of 4000–2000 cm−1 at a resolution from 0.1 to 0.005 cm−1 with a Bruker IFS-120 HR vacuum Fourier-transform infrared spectrometer. The formation mechanism of the ν(HF) stretching band contour was explained. By utilizing DFT quantum chemical calculations we determined the equilibrium configuration and the geometric parameters, the harmonic vibrational frequencies, the dipole moments, and the binding energies of the СH3CN … HF complex in the mp2//311++G(3df,3pd) approximation. The three 3 D potential energy surfaces of the complex were evaluated, and the constructed graphs allowed us to reveal a link between the structural changes and the potential energies of the СH3CN … HF complex.

Anion-exchange Experiment of Zr, Hf, and Th in HNO3 and Quantum Chemical Study on the Nitrate Complexes toward Chemical Research on Element 104, Rf

ABSTRACT Anion-exchange behavior of Zr, Hf, and Th in nitric acid was investigated to determine suitable experimental conditions for the experiment of element 104, rutherfordium (Rf) and to obtain comparative data for discussion of nitrate complexes of Rf. Anion-exchange reactions in a Adogen 464/HNO3 system was found to reach equilibrium within 60 s, suggesting that the reaction system is suitable for the experiment of 261Rf having a half-life of 68 s. We also studied the electronic states of Zr, Hf, and Th nitrate complexes by quantum chemical calculations. The calculation results support the experimental results that Th4+ forms stable anionic complexes such as [Th(NO3)6]2− with a large coordination number of 12, while Zr4+ and Hf4+ do not.

Computational mechanistic insights into hafnium catalyzed CO2 activation and reduction

In this study, we present the reaction mechanisms for CO2 activation and reduction reactions using hafnium complex as a frustrated Lewis pair catalyst investigated using density functional theory (DFT) calculations. CO2 activation reactions with different oxidation states of the catalyst were explored. The energy barriers for CO2 activation with oxidised, single-electron reduced and two-electron reduced catalyst were calculated to be 17.18, 14.46 and 15.73 kcal/mol, respectively. The mechanisms of CO2 reduction to CO and HCOO- upon addition of HCl as a proton source were also studied. The activation energies to release CO and HCOO- from the hafnium complex were calculated to be 9.05 and 75.34 kcal/mol, respectively. The results indicated that formate formation is unlikely. The overall analysis of the reaction mechanisms shows that the studied Hf complex effectively activates CO2 and can also potentially reduce the activated CO2 to CO.

Radiation-induced transformations of difluoromethane in noble gas matrices

Difluoromethane (CH2F2) is considered as an ecologically friendly alternative to conventionally used chlorofluorocarbons for various applications. Being photochemically inert in the broad UV range, this molecule can be decomposed only through the action of hard vacuum UV or ionizing radiation, while the corresponding mechanisms are poorly studied. In this work we report the results of model investigations of the X-ray induced decomposition of isolated CH2F2 in solid noble gas matrices at 6 K. The radiation-chemical yields of difluoromethane were found to decrease from 1.3 to 0.1 molecule/100 eV with decreasing the ionization energy of matrix (from Ne to Xe), which indicates significance of the “hot” ionic channels. Difluorocarbene (CF2) was detected as one of the principal radiolysis products in all the matrices, whereas the CHF⋯HF complex was detected in Ne, Ar, and Kr. Annealing of the irradiated samples results in thermally induced reactions of trapped H and F atoms yielding a number of various species, including the noble gas compounds. The radiolysis mechanism, nature of matrix effects and possible implications for atmospheric chemistry are discussed.