Search Results (12)

Two single-crystal X-ray structure determinations of 2-aminopyrimidinium hydrogen tri oxofluorophosphate, (C₄H₆N₃)⁺·(HFO₃P)⁻, (I), and bis(2-aminopyrimidinium) trioxofluorophosphate, 2(C₄H₆N₃)⁺·(FO₃P)²⁻, (II), as well as their vibration spectra (FTIR on powder samples and the Raman spectra on unoriented single crystals) with a detailed assignment of vibrational modes are reported. The structure (I) consists of one independent 2-aminopyrimidinium cation and one hydrogen trioxofluorophosphate anion, while (II) consists of two symmetry independent 2-aminopyrimidinium cations and one trioxofluorophosphate anion. In (I), there is an O-H···O hydrogen bond of a moderate strength. A pair of these hydrogen bonds is situated about the symmetry centre and involved in the graph set motif R²₂(8). There are also N-H···O hydrogen bonds of a moderate strength, which are present in both structures while being involved in the graph set motifs R²₂(8), too. In addition, the N-H···O hydrogen bonds form R³₄(10) graph set motifs in (II). The latter motifs form ribbons which propagate parallel to the unit-cell axis a. In both structures, there are present π···π-electron ring interactions into which the primary amine groups are involved. In both structures, there are also present weak C-H···N hydrogen bonds with participation of the non-protonated ring N-atoms. The fluorine participates in the C-H···F hydrogen bonds in both title structures. The P-F distances are normal in both anions. The structure (I) differs from the known structure of 2-aminopyrimidinium hydrogen phosphite, the compositional isomer, though the main hydrogen bonds show similar geometry in both structures. The crystal of (I) was twinned. Full article

As part of a systematic study on the structures of the mixed halide isothiocyanates, Sn^IIHal(NCS), their single crystals were grown and structurally characterized. For Hal = F (1), the SnClF structure type was confirmed, while with Hal = Cl (2), Br (3), and I (4), there are three isostructural compounds of a new structure type, and for Hal = Cl (5), there is a second modification of a third structure type. These structure types have been described with respect to the composition and coordination geometry of the first, second, and van der Waals crust coordination spheres and their dependence on the halogen size and thiocyanate binding modes. With respect to the first coordination spheres, all three structure types constitute one-dimensional coordination polymers. In 1, “ladder”-type double chains result from μ₃-bridging fluorine atoms, and in 2–4, single-chains built up from μ₂-halogen atoms are pairwise “zipper”-like interconnected via κ²NS-bridging NCS ligands, which manage the halogen-linked chain assembly in the double chains of 5. Based on the octet rule, short atom distances are interpreted in terms of 2c-2e and various (symmetrical, quasi-symmetrical, and asymmetrical) kinds of 3c-4e bonds. Weak contacts, the topology of which suggests the extension of the latter bonding concept, are identified as electron-deficient, bifurcated tetrel bonds. Full article

This study reports the synthesis and characterization of a novel thiolate-bridged heteroleptic dinuclear silver(I) complex, [Ag(μ-C₆F₅S)(dppbz)]₂, incorporating o-bis(diphenylphosphino)benzene (dppbz). The complex was synthesized in high yield via the reaction of silver(I) oxide with pentafluorothiophenol and dppbz. Single crystal X-ray diffraction analysis revealed a distorted tetrahedral structure with an Ag₂S₂ core, where each Ag atom is coordinated by dppbz. The Ag…Ag distance (3.2652(3) Å) suggests weak argentophilic interaction. Notably, an uncommon intermolecular fluorine-fluorine contact is observed, likely stabilized by intermolecular hydrogen bonding stabilizing the structure. The complex shows weak luminescence under UV radiation with an emission maximum at 514 nm. Full article

Three halo-substituted phenyl-quinazolinone derivatives were prepared and structurally characterized [1 = 3-(4-chlorophenyl)-6-iodo-2-methylquinazolin-4(3H)-one, 2 = 6-iodo-3-(4-methoxyphenyl)-2-methylquinazolin-4(3H)-one, and 3 = 7-chloro-2-methyl-3-[4-(trifluoromethoxy)phenyl]quinazolin-4(3H)-one)] in order to explore the relationship between structure and melting point in this group of compounds. Depending on the compound, molecules are interconnected by weak π∙∙∙π interactions, have I···Cl or Cl···Cl halogen bonding, or primarily form C–H∙∙∙N, C–H∙∙∙O, and π∙∙∙π interactions (no halogen bonding). The presence of the OCF₃ group leads to interactions between fluorine atoms that are shorter than the sum of the van der Waals radius for fluorine, suggesting that these interactions contribute to the overall lattice energy. The sequence of melting points cannot be fully explained by intermolecular interactions present in the solid state (enthalpy factor). To address this, a concept related to entropy called the functional group rotation influence, which relates to a decrease in fusion entropy caused by the rotational freedom of polyatomic groups, was introduced. Analysis of previously synthesized 3-phenylquinazolinones showed that the compounds with the highest melting point are the quinazoline-substituted and phenyl-nitro-substituted ones. Among halo-phenyl-substituted compounds, the melting point follows the sequence ortho < meta < para. Regarding the halogen atom type, the order of melting points is Cl ≈ Br > F > I for enantiopure and Br > I ≈ Cl > F for racemic compounds. Also, the melting point order correlates to halogen bond energy (I > Br > Cl > F) only when the geometry and energy of these interactions are favorable. Full article

Many cite the strength of C–F bonds for the poor microbial biodegradability of polyfluorinated organic compounds (PFCs). However, commercial PFCs almost invariably contain more functionality than fluorine. The additional functionality provides a weak entry point for reactions that activate C–F bonds and lead to their eventual cleavage. This metabolic activation strategy is common in microbial biodegradation pathways and is observed with aromatic hydrocarbons, chlorinated compounds, phosphonates and many other compounds. Initial metabolic activation precedes critical bond breakage and assimilation of nutrients. A similar strategy with commercial PFCs proceeds via initial attack at the non-fluorinated functionalities: sulfonates, carboxylates, chlorines, phenyl rings, or phosphonates. Metabolic transformation of these non-fluorinated groups can activate the C–F bonds, allowing more facile cleavage than a direct attack on the C–F bonds. Given that virtually all compounds denoted as “PFAS” are not perfluorinated and are not alkanes, it is posited here that considering their individual chemical classes is more useful for both chemical and microbiological considerations of their fate. Full article

Fluorine is a common substituent in medicinal chemistry and is found in up to 50% of the most profitable drugs. In this study, a statistical analysis of the nature, geometry, and frequency of hydrogen bonds (HBs) formed between the aromatic and aliphatic C–F groups of small molecules and biological targets found in the Protein Data Bank (PDB) repository was presented. Interaction energies were calculated for those complexes using three different approaches. The obtained results indicated that the interaction energy of F-containing HBs is determined by the donor–acceptor distance and not by the angles. Moreover, no significant relationship between the energies of HBs with fluorine and the donor type was found, implying that fluorine is a weak HB acceptor for all types of HB donors. However, the statistical analysis of the PDB repository revealed that the most populated geometric parameters of HBs did not match the calculated energetic optima. In a nutshell, HBs containing fluorine are forced to form due to the stronger ligand–receptor neighboring interactions, which make fluorine the “donor’s last resort”. Full article

Physical hydrogels are supramolecular materials obtained by self-assembly of small molecules called gelators. Aromatic amino acids and small peptides containing aromatic rings are good candidates as gelators due to their ability to form weak bonds as π-π interactions and hydrogen bonds between NH and CO of the peptide chain. In this paper we show our results in the preparation of a transparent hydrogel that was obtained by self-assembly of a fluorine-containing dipeptide that relies on the additional formation of halogen bonds due to the fluorine atoms contained in the dipeptide. We used Boc-D-F₂Phe-L-Oxd-OH (F₂Phe = 3,4-difluorophenylalainine; Oxd = 4-methyl-5-carboxy-oxazolidin-2-one) that formed a strong and transparent hydrogel in 0.5% w/w concentration at pH = 4.2. The formation of a hydrogel made of unnatural fluorinated amino acids may be of great interest in the evaluation of patients with parkinsonian syndromes and may be used for controlled release. Full article

High-level quantum-chemical computations (G4MP2) are carried out in the study of complexes featuring tetrel bonding between the carbon atom in the carbenoid CB₁₁H₁₁—obtained by hydride removal in the C-H bond of the known closo-monocarbadodecaborate anion CB₁₁H₁₂⁽⁻⁾ and acting as Lewis acid (LA)—and Lewis bases (LB) of different type; the electron donor groups in the tetrel bond feature carbon, nitrogen, oxygen, fluorine, silicon, phosphorus, sulfur, and chlorine atomic centres in neutral molecules as well as anions H⁽⁻⁾, OH⁽⁻⁾, and F⁽⁻⁾. The empty radial 2p_r vacant orbital on the carbon centre in CB₁₁H₁₁, which corresponds to the LUMO, acts as a Lewis acid or electron attractor, as shown by the molecular electrostatic potential (MEP) and electron localization function (ELF). The thermochemistry and topological analysis of the complexes {CB₁₁H₁₁:LB} are comprehensively analysed and classified according to shared or closed-shell interactions. ELF analysis shows that the tetrel C⋯X bond ranges from very polarised bonds, as in H₁₁B₁₁C:F⁽⁻⁾ to very weak interactions as in H₁₁B₁₁C⋯FH and H₁₁B₁₁C⋯O=C=O. Full article

The 3:2 Charge Transfer (CT) co-crystal (Perylene)₃(TCNQF₁)₂ is grown by the Physical Vapor Transport (PVT) method, and characterized structurally and spectroscopically. Infrared analysis of the charge sensitive modes reveals a low degree of charge transfer (less than 0.1) between donor and acceptor molecules. The crystal is isostructural to the other 3:2 CT crystals formed by Perylene with TCNQF₂ and TCNQF₄, whereas such stoichiometry and packing is not known for the CT crystals with non-fluorinated TCNQ. The analysis of the isostructural family of 3:2 Perylene–TCNQF_x (x = 1,2,4) co-crystal put in evidence the role of weak F^…HC bonding in stabilizing this type of structure Full article

The peculiarities of interatomic interactions formed by fluorine atoms were studied in four tosylate derivatives p-CH₃C₆H₄OSO₂CH₂CF₂CF₃ and p-CH₃C₆H₄OSO₂CH₂(CF₂)_nCHF₂ (n = 1, 5, 7) using X-ray diffraction and quantum chemical calculations. Compounds p-CH₃C₆H₄OSO₂CH₂(CF₂)_nCHF₂ (n = 1, 5) were crystallized in several polymorph modifications. Analysis of intermolecular bonding was carried out using QTAIM approach and energy partitioning. All compounds are characterized by crystal packing of similar type and the contribution of intermolecular interactions formed by fluorine atoms to lattice energy is raised along with the increase of their amount. The energy of intra- and intermolecular F…F interactions is varied in range 0.5–13.0 kJ/mol. Total contribution of F…F interactions to lattice energy does not exceed 40%. Crystal structures of studied compounds are stabilized mainly by C-H…O and C-H…F weak hydrogen bonds. The analysis of intermolecular interactions and lattice energies in polymorphs of p-CH₃C₆H₄OSO₂CH₂(CF₂)_nCHF₂ (n = 1, 5) has shown that most stabilized are characterized by the least contribution of F…F interactions. Full article

Can two sites of positive electrostatic potential localized on the outer surfaces of two halogen atoms (and especially fluorine) in different molecular domains attract each other to form a non-covalent engagement? The answer, perhaps counterintuitive, is yes as shown here using the electronic structures and binding energies of the interactions for a series of 22 binary complexes formed between identical or different atomic domains in similar or related halogen-substituted molecules containing fluorine. These were obtained using various computational approaches, including density functional and ab initio first-principles theories with M06-2X, RHF, MP2 and CCSD(T). The physical chemistry of non-covalent bonding interactions in these complexes was explored using both Quantum Theory of Atoms in Molecules and Symmetry Adapted Perturbation Theories. The surface reactivity of the 17 monomers was examined using the Molecular Electrostatic Surface Potential approach. We have demonstrated inter alia that the dispersion term, the significance of which is not always appreciated, which emerges either from an energy decomposition analysis, or from a correlated calculation, plays a structure-determining role, although other contributions arising from electrostatic, exchange-repulsion and polarization effects are also important. The 0.0010 a.u. isodensity envelope, often used for mapping the electrostatic potential is found to provide incorrect information about the complete nature of the surface reactive sites on some of the isolated monomers, and can lead to a misinterpretation of the results obtained. Full article

The channel fluorine implantation (CFI) process was integrated with the Si₃N₄ contact etch stop layer (SiN CESL) uniaxial-strained n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) with the hafnium oxide/silicon oxynitride (HfO₂/SiON) gate stack. The SiN CESL process clearly improves basic electrical performance, due to induced uniaxial tensile strain within the channel. However, further integrating of the CFI process with the SiN CESL-strained nMOSFET exhibits nearly identical transconductance, subthreshold swing, drain current, gate leakage and breakdown voltage, which indicates that the strain effect is not affected by the fluorine incorporation. Moreover, hydrogen will diffuse toward the interface during the SiN deposition, then passivate dangling bonds to form weak Si-H bonds, which is detrimental for channel hot electron stress (CHES). Before hydrogen diffusion, fluorine can be used to terminate oxygen vacancies and dangling bonds, which can create stronger Hf-F and Si-F bonds to resist consequent stress. Accordingly, the reliability of constant voltage stress (CVS) and CHES for the SiN CESL uniaxial-strained nMOSFET can be further improved by the fluorinated HfO₂/SiON using the CFI process. Nevertheless, the nMOSFET with either the SiN CESL or CFI process exhibits less charge detrapping, which means that a greater part of stress-induced charges would remain in the gate stack after nitrogen (SiN CESL) or fluorine (CFI) incorporation. Full article