Substituent Effects on Cl···N, S···N, and P···N Noncovalent Bonds

Balancing interlayer spacing, pore structures and conductivity endows hard carbon with high capacity for rechargeable aluminum batteries

As a key configuration, hard carbon (HC) is widely regarded as a promising cathode for rechargeable aluminum batteries (RABs), because of its enlarged interlayer spacing and well-developed pore structures. However, the trade-off between the pore structure, interlayer spacing and conductivity easily leads to an unsatisfactory electrochemical performance in terms of capacity and cycling stability. Hence, N-doped hard carbon (P-M) is synthesized at a relatively low temperature (700 °C) and anion intercalation associated with the energy storage process is investigated. The results demonstrate that the introduction of a N-doping agent not only expands the layer spacing and creates rich pore structures, but also boosts the conductivity. Compared with HC without N-doping, the expanded interlayer spacing in P-M can increase ion storage ability, and the rich pore channels contribute to electron transfer. Besides, compared with HC annealed at a higher temperature (900 °C), the enhanced conductivity in P-M is conducive to accelerating ion diffusion. Benefiting from these structure merits, the optimized P-M cathode delivers a high capacity (323 mA h g-1 at 500 mA g-1) and a prolonged cycle lifespan over 1000 cycles at 1 A g-1 retaining 109 mA h g-1. This work can provide a guidance for developing other high-performance hard carbon cathodes.

Factors contributing to halogen bond strength and stretch or contraction of internal covalent bond

The halogen bond formed by a series of Lewis acids TF₃X (T = C, Si, Ge, Sn, Pb; X = Cl, Br, I) with NH₃ is studied by quantum chemical calculations. The interaction energy is closely mimicked by the depth of the σ-hole on the X atom as well as the full electrostatic energy. There is a first trend by which the hole is deepened if the T atom to which X is attached becomes more electron-withdrawing: C > Si > Ge > Sn > Pb. On the other hand, larger more polarizable T atoms are better able to transmit the electron-withdrawing power of the F substituents. The combination of these two opposing factors leaves PbF₃X forming the strongest XBs, followed by CF₃X, with SiF₃X engaging in the weakest bonds. The charge transfer from the NH₃ lone pair into the σ*(TX) antibonding orbital tends to elongate the covalent TX bond, and this force is largest for the heavier X and T atoms. On the other hand, the contraction of this bond deepens the σ-hole at the X atom, which would enhance both the electrostatic component and the full interaction energy. This bond-shortening effect is greatest for the lighter X atoms. The combination of these two opposing forces leaves the T-X bond contracting for X = Cl and Br, but lengthening for I.

Metal Coordination Enhances Chalcogen Bonds: CSD Survey and Theoretical Calculations

In this study the ability of metal coordinated Chalcogen (Ch) atoms to undergo Chalcogen bonding (ChB) interactions has been evaluated at the PBE0-D3/def2-TZVP level of theory. An initial CSD (Cambridge Structural Database) inspection revealed the presence of square planar Pd/Pt coordination complexes where divalent Ch atoms (Se/Te) were used as ligands. Interestingly, the coordination to the metal center enhanced the σ-hole donor ability of the Ch atom, which participates in ChBs with neighboring units present in the X-ray crystal structure, therefore dictating the solid state architecture. The X-ray analyses were complemented with a computational study (PBE0-D3/def2-TZVP level of theory), which shed light into the strength and directionality of the ChBs studied herein. Owing to the new possibilities that metal coordination offers to enhance or modulate the σ-hole donor ability of Chs, we believe that the findings presented herein are of remarkable importance for supramolecular chemists as well as for those scientists working in the field of solid state chemistry.

Enhancing chalcogen bonding by metal coordination

This manuscript shows that chalcogen bonding (ChB) interaction is enhanced by the coordination of the chalcogen atom to metal centers, as evidenced using DFT calculations (PBE0-D3/def2-TZVP level of theory). X-ray...

Highly Efficient Removal of Neonicotinoid Insecticides by Thioether-Based (Multivariate) Metal-Organic Frameworks

Circumventing the impact of agrochemicals on aquatic environments has become a necessity for health and ecological reasons. Herein, we report the use of a family of five eco-friendly water-stable isoreticular metal-organic frameworks (MOFs), prepared from amino acids, as adsorbents for the removal of neonicotinoid insecticides (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid) from water. Among them, the three MOFs containing thioether-based residues show remarkable removal efficiency. In particular, the novel multivariate MOF {Sr^IICu^II₆[(S,S)-methox]_1.5[(S,S)-Mecysmox]_1.50(OH)₂(H₂O)}·36H₂O (5), featuring narrow functional channels decorated with both -CH₂SCH₃ and -CH₂CH₂SCH₃ thioalkyl chains-from l-methionine and l-methylcysteine amino acid-derived ligands, respectively-stands out and exhibits the higher removal efficiency, being capable to capture 100% of acetamiprid and thiacloprid in a single capture step under dynamic solid-phase extraction conditions-less than 30 s. Such unusual combination of outstanding efficiency, high stability in environmental conditions, and low-cost straightforward synthesis in 5 places this material among the most attractive adsorbents reported for the removal of this type of contaminants.

Relative Strengths of a Pnicogen and a Tetrel Bond and Their Mutual Effects upon One Another

The ability of the T and Z atoms of TR₃ZR₂ to engage in a noncovalent interaction with NH₃ is assessed by DFT calculations, where the T atom refers to C, Si, and Ge; Z = As, Sb, and P; and substituents R = H and F. In most instances, the tetrel bond (TB) is both stronger and shorter than the pnicogen bond (ZB). These two bond strengths can be equalized, or preference shifted to the ZB, if F substituents are placed on the Z and H on the T atoms. Employing C as the T atom results in a very weak TB, with the ZB clearly favored energetically. The simultaneous formation of both TB and ZB weakens both, particularly the latter, but both bonds survive intact. Geometric and spectroscopic perturbations of the subunits reflect the two types of noncovalent bonds.

Nitrogen as a pnicogen?: evidence for π-hole driven novel pnicogen bonding interactions in nitromethane-ammonia aggregates using matrix isolation infrared spectroscopy and ab initio computations

The role of nitrogen, the first member of the pnicogen group, as an electron donor in hypervalent non-covalent interactions has been established long ago, while observation of its electron accepting capability is still elusive experimentally, and remains quite intriguing, conceptually. In the light of minimal computational exploration of this novel class of pnicogen bonding so far, the present work provides experimental proof with unprecedented clarity, for the existence of N(acceptor)N(donor) interaction using the model nitromethane (NM) molecule with ammonia (AM) as a Lewis base in NM-AM aggregates. The NM-AM dimer, in which the nitrogen atom of NM (as a unique pnicogen) accepts electrons from AM (the traditional electron donor), was synthesized at low temperatures under isolated conditions within inert gas matrixes and was characterized using infrared spectroscopy. The experimental generation of the NM-AM dimer stabilized via NN interaction has strong corroboration from ab initio calculations. Furthermore, confirmation regarding the directional prevalence of this NN interaction over C-HN and N-HO hydrogen bonding is elucidated quantitatively by quantum theory of atoms in molecules (QTAIM), electrostatic potential mapping (ESP), natural bond orbital (NBO), non-covalent interaction (NCI) and energy decomposition (ED) analyses. The present study also allows the extension of σ-hole/π-hole driven interactions to the atoms of the second period, in spite of their low polarizability.

Participation of S and Se in hydrogen and chalcogen bonds

The heavier chalcogen atoms S, Se, and Te can each participate in a range of different noncovalent interactions. They can serve as both proton donor and acceptor in H-bonds. Each atom can also act as electron acceptor in a chalcogen bond.

Highly stretchable and strong poly(butylene maleate) elastomers via metal–ligand interactions

The search for advanced elastomers with simultaneously high strength, high stretchability and reprocessability remains a challenging task.

Dominance of unique Pπ phosphorus bonding with π donors: evidence using matrix isolation infrared spectroscopy and computational methodology

Albeit the first account of hypervalentπ interactions has been reported with halogenπ interactions, the feasibility of their extension to other hypervalent atoms as possible Lewis acids is still open. In this work, the role of phosphorus as an acceptor from the π electron cloud (Pπ pnicogen or phosphorus bonding) in PCl3-C2H2 and PCl3-C2H4 heterodimers is explored, by combining matrix isolation infrared spectroscopy with ab initio and DFT computational methodologies. The respective potential energy surfaces of the PCl3-C2H2 and PCl3-C2H4 heterodimers reveal unique minima stabilized by a concert of reasonably strong to weak interactions, of which Pπ phosphorus bonding was energetically dominant. Heterodimers, trimers and tetramers bound primarily by this unique phosphorus bond were generated at low temperatures. The dominance of phosphorus bonding in the PCl3-C2H2 and PCl3-C2H4 heterodimers over other interactions (such as Hπ, HCl, HP, Clπ and lone pair-π interactions) was confirmed and substantiated using extended quantum theory of atoms in molecules, natural bond orbital, electrostatic potential mapping and energy decomposition analyses. The following inferences in correlation with results from non-covalent-interaction analysis offer a complete understanding of the nature of the Pπ phosphorus bonding interactions. The significance of electrostatic forces kinetically favoring the formation of phosphorus bonded heterodimers, in addition to thermodynamic stabilization, is demonstrated experimentally.

Theoretical Investigation of Cyano-Chalcogen Dimers and Their Importance in Molecular Recognition

In this manuscript the different noncovalent interactions established between (HYCN)₂ dimers (Y=S, Se and Te) have been studied at the MP2 and CCSD(T) level of theory. Several homodimers have been taken into account, highlighting the capacity of these compounds to act both as electron donor and acceptor. The main properties studied were geometries, binding energy (E_b ), and molecular electrostatic potential (MEP). Given the wide application of chalcogen bonds, and more specifically of cyano-chalcogen moieties in molecular recognition, natural bond orbital (NBO), "atoms-in-molecules" (AIM), and electron density shift (EDS) analysis were also used to analyse the different noncovalent interactions upon complexation. The presence of hydrogen, chalcogen and dipole-dipole interactions was confirmed and their implications on molecular recognition were analysed.

Differential Binding of Tetrel-Bonding Bipodal Receptors to Monatomic and Polyatomic Anions

Previous work has demonstrated that a bidentate receptor containing a pair of Sn atoms can engage in very strong interactions with halide ions via tetrel bonds. The question that is addressed here concerns the possibility that a receptor of this type might be designed that would preferentially bind a polyatomic over a monatomic anion since the former might better span the distance between the two Sn atoms. The binding of Cl⁻ was thus compared to that of HCOO⁻, HSO₄⁻, and H₂PO₄⁻ with a wide variety of bidentate receptors. A pair of SnFH₂ groups, as strong tetrel-binding agents, were first added to a phenyl ring in ortho, meta, and para arrangements. These same groups were also added in 1,3 and 1,4 positions of an aliphatic cyclohexyl ring. The tetrel-bonding groups were placed at the termini of (-C≡C-)_n (n = 1,2) extending arms so as to further separate the two Sn atoms. Finally, the Sn atoms were incorporated directly into an eight-membered ring, rather than as appendages. The ordering of the binding energetics follows the HCO₂⁻ > Cl⁻ > H₂PO₄⁻ > HSO₄⁻ general pattern, with some variations in selected systems. The tetrel bonding is strong enough that in most cases, it engenders internal deformations within the receptors that allow them to engage in bidentate bonding, even for the monatomic chloride, which mutes any effects of a long Sn···Sn distance within the receptor.

Elusive hypervalent phosphorus⋯π interactions: evidence for paradigm transformation from hydrogen to phosphorus bonding at low temperatures

A paradigm transformation from hydrogen to phosphorus bonding is found to depend on the proton affinity of the interacting π-systems.

On the capability of metal–halogen groups to participate in halogen bonds

Halogens in a M–X bond are inhibited from forming a halogen bond but can do so in certain circumstances, with or without a σ-hole.

Comparative Strengths of Tetrel, Pnicogen, Chalcogen, and Halogen Bonds and Contributing Factors

Ab initio calculations are employed to assess the relative strengths of various noncovalent bonds. Tetrel, pnicogen, chalcogen, and halogen atoms are represented by third-row atoms Ge, As, Se, and Br, respectively. Each atom was placed in a series of molecular bonding situations, beginning with all H atoms, then progressing to methyl substitutions, and F substituents placed in various locations around the central atom. Each Lewis acid was allowed to engage in a complex with NH₃ as a common nucleophile, and the strength and other aspects of the dimer were assessed. In the context of fully hydrogenated acids, the strengths of the various bonds varied in the pattern of chalcogen > halogen > pnicogen ≈ tetrel. Methyl substitution weakened all bonds, but not in a uniform manner, resulting in a greatly weakened halogen bond. Fluorosubstitution strengthened the interactions, increasing its effect as the number of F atoms rises. The effect was strongest when the F atom lay directly opposite the base, resulting in a halogen > chalcogen > pnicogen > tetrel order of bond strength. Replacing third-row atoms by their second-row counterparts weakened the bonds, but not uniformly. Tetrel bonds were weakest for the fully hydrogenated acids and surpassed pnicogen bonds when F had been added to the acid.

A Computational Study of Chalcogen-containing H2 X…YF and (CH3 )2 X…YF (X=O, S, Se; Y=F, Cl, H) and Pnicogen-containing H3 X'…YF and (CH3 )3 X'…YF (X'=N, P, As) Complexes

A computational study was undertaken for the model complexes H₂ X…YF and (CH₃ )₂ X…YF (X=O, S, Se; Y=F, Cl, H), and H₃ X'…YF and (CH₃ )₃ X'…YF (X'=N, P, As), at the MP2/6-311++G(d,p) level of theory. For H₂ X…YF and H₃ X'…YF, noncovalent interactions dominate the binding in order of increasing YF dipole moment, except for H₃ As…F₂ , and possibly H₃ As…ClF. However, for the methyl-substituted complexes (CH₃ )₂ X…YF and (CH₃ )₃ X'…YF the binding is especially strong for the complexes containing F₂ , implying significant chemical bonding between the interacting molecules. The relative stability of these complexes can be rationalized by the difference in the electronegativity of the X or X' and Y atoms.

The intrinsic strength of the halogen bond: electrostatic and covalent contributions described by coupled cluster theory

36 halogen-bonded complexes YXAR_m (X: F, Cl, Br; Y: donor group; AR_m acceptor group) have been investigated at the CCSD(T)/aug-cc-pVTZ level of theory. Binding energies, geometries, NBO charges, charge transfer, dipole moments, electrostatic potential, electron and energy density distributions, difference density distributions, vibrational frequencies, local stretching and bending force constants, and relative bond strength orders n have been calculated and used to order the halogen bonds according to their intrinsic strength. Halogen bonding is found to arise from electrostatic and strong covalent contributions. It can be strengthened by H-bonding or lone pair delocalization. The covalent character of a halogen bond increases in the way 3c-4e (three-center-four-electron) bonding becomes possible. One can characterize halogen bonds by their percentage of 3c-4e bonding. FCl-phosphine complexes can form relatively strong halogen bonds provided electronegative substituents increase the covalent contributions in form of 3c-4e halogen bonding. Binding energies between 1 and 45 kcal mol^-1 are calculated, which reflects the large variety in halogen bonding.

Pentavalent phosphorus as a unique phosphorus donor in POCl3 homodimer and POCl3–H2O heterodimer: matrix isolation infrared spectroscopic and computational studies

Phosphorus, an important element among the pnicogen group, opens up avenues for experimental and computational explorations of its interaction in a variety of compounds.

The Many Facets of Chalcogen Bonding: Described by Vibrational Spectroscopy

A diverse set of 100 chalcogen-bonded complexes comprising neutral, cationic, anionic, divalent, and double bonded chalcogens has been investigated using ωB97X-D/aug-cc-pVTZ to determine geometries, binding energies, electron and energy density distributions, difference density distributions, vibrational frequencies, local stretching force constants, and associated bond strength orders. The accuracy of ωB97X-D was accessed by CCSD(T)/aug-cc-pVTZ calculations of a subset of 12 complexes and by the CCSD(T)/aug-cc-pVTZ //ωB97X-D binding energies of 95 complexes. Most of the weak chalcogen bonds can be rationalized on the basis of electrostatic contributions, but as the bond becomes stronger, covalent contributions can assume a primary role in the strength and geometry of the complexes. Covalency in chalcogen bonds involves the charge transfer from a lone pair orbital of a Lewis base into the σ* orbital of a divalent chalcogen or a π* orbital of a double bonded chalcogen. We describe for the first time a symmetric chalcogen-bonded homodimer stabilized by a charge transfer from a lone pair orbital into a π* orbital. New polymeric materials based on chalcogen bonds should take advantage of the extra stabilization granted by multiple chalcogen bonds, as is shown for 1,2,5-telluradiazole dimers.

Modulating of the pnicogen-bonding by a H⋯π interaction: An ab initio study

An ab initio study of the cooperativity in XH₂P⋯NCH⋯Z and XH₂P⋯CNH⋯Z complexes (X=F, Cl, Br, CN, NC; Z=C₂H₂,C₆H₆) connected by pnicogen-bonding and H⋯π interactions is carried out by means of MP2 computational method. A detailed analysis of the structures, interaction energies and bonding properties is performed on these systems. For each set of the complexes considered, a favorable cooperativity is observed, especially in X=F and CN complexes. However, for a given X or Z, the amount of cooperativity effects in XH₂P⋯CNH⋯Z complexes are more important than XH₂P⋯NCH⋯Z counterparts. Besides, the influence of a H⋯π interaction on a P⋯N (C) bond is more pronounced than that of a P⋯N (C) bond on a H⋯π bond. The quantum theory of atoms in molecules shows that ternary complexes have increased electron densities at their bond critical points relative to the corresponding binary systems. The results also indicate that the strength of the P⋯N(C) and H⋯π interactions increases in the presence of the solvent.

Quantitative Assessment of Halogen Bonding Utilizing Vibrational Spectroscopy

A total of 202 halogen-bonded complexes have been studied using a dual-level approach: ωB97XD/aug-cc-pVTZ was used to determine geometries, natural bond order charges, charge transfer, dipole moments, electron and energy density distributions, vibrational frequencies, local stretching force constants, and relative bond strength orders n. The accuracy of these calculations was checked for a subset of complexes at the CCSD(T)/aug-cc-pVTZ level of theory. Apart from this, all binding energies were verified at the CCSD(T) level. A total of 10 different electronic effects have been identified that contribute to halogen bonding and explain the variation in its intrinsic strength. Strong halogen bonds are found for systems with three-center-four-electron (3c-4e) bonding such as chlorine donors in interaction with substituted phosphines. If halogen bonding is supported by hydrogen bonding, genuine 3c-4e bonding can be realized. Perfluorinated diiodobenzenes form relatively strong halogen bonds with alkylamines as they gain stability due to increased electrostatic interactions.

The mutual influence of Y···N and H···H interactions in XHY···NCH···HM complexes (X = F, Cl, Br; Y = S, Se; M = Li, Na, BeH, MgH): tuning of the chalcogen bond by dihydrogen bond interaction

The equilibrium structures, interaction energies, and bonding properties of ternary XHY···NCH···HM complexes are studied by ab initio calculations, where X = F, Cl, Br, Y = S, Se, and M = Li, Na, BeH, MgH. The ab initio calculations are carried out at the MP2/aug-cc-pVTZ level. The results indicate that all optimized Y···N and H···H binding distances in the ternary complexes are smaller than the corresponding values in the binary systems. The calculated cooperative energies (Ecoop) are between −0.20 kcal/mol in BrHS···NCH···HBeH and −3.29 kcal/mol in FHSe···NCH···HNa. For a given Y and M, the estimated Ecoop values increase as X = F > Cl > Br. In addition, the selenium-bonded complexes exibit larger Ecoop values than those of the sulfur-bonded counterparts. The cooperativity between Y···N and H···H interactions is further analyzed by quantum theory of atoms in molecules and natural bond orbital methods. Cooperative effects make an increase in the J(Y–N) and J(H–H) spin–spin coupling constants of the ternary complexes with respect to the binary systems.

The influence of intramolecular sulfur-lone pair interactions on small-molecule drug design and receptor binding

Sulfur-lone pair interactions are important conformational control elements in sulfur-containing heterocycles that abound in pharmaceuticals, natural products, agrochemicals, polymers and other important classes of organic molecules. Nonetheless, the role of intramolecular sulfur-lone pair interactions in the binding of small molecules to receptors is often overlooked. Here we analyze the magnitudes and origins of these interactions for a variety of biologically relevant small molecules using quantum chemical and automated docking calculations. In most cases examined in this study, the lowest energy conformation of the small molecule displays a sulfur-lone pair close contact. However, docking studies, both published and new, often predict that conformations without sulfur-lone pair contacts have the best binding affinity for their respective receptors. This is a serious problem. Since many of these predicted bound conformations are not actually energetically accessible, pursuing design (e.g., drug design) around these binding modes necessarily will lead, serendipity aside, to dead end designs. Our results constitute a caution that one best not neglect these interactions when predicting the binding affinities of potential ligands (drugs or not) for hosts (enzymes, receptors, DNA, RNA, synthetic hosts). Moreover, a better understanding and awareness of sulfur-lone pair interactions should facilitate the rational modulation of host-guest interactions involving sulfur-containing molecules.

Structures of Trichloromethyl Thiocyanate, CCl3 SCN, in Gaseous and Crystalline State

Trichloromethyl thiocyanate, CCl3 SCN, was structurally studied in both the gas and crystal phases by means of gas electron diffraction (GED) and single-crystal X-ray diffraction (XRD), respectively. Both experimental studies and quantum chemical calculations indicate a staggered orientation of the CCl3 group relative to the SCN group. This conclusion is supported by the similarity of the C-SCN bond length to that of the anti-structure of CH2 ClSCN (Berrueta Martínez et al. Phys. Chem. Chem. Phys. 2015, 17, 15805-15812). Bond lengths and angles are similar for gas and crystal CCl3 SCN structures; however, the crystal structure presents different intermolecular interactions. These include halogen and chalcogen type interactions, the geometry of which was studied. Characteristic C-Y⋅⋅⋅N angles (Y=Cl or S) close to 180° provide evidence for typical σ-hole interactions along the halogen/chalcogen-carbon bond in N⋅⋅⋅Cl and N⋅⋅⋅S, intermolecular units.

Building a Better Halide Receptor: Optimum Choice of Spacer, Binding Unit, and Halosubstitution

Quantum calculations are used to measure the binding of halides to a number of bipodal dicationic receptors, constructed as a pair of binding units separated by a spacer group. A number of variations are studied. A H atom on each binding unit (imidazolium or triazolium) is replaced by Br or I. Benzene, thiophene, carbazole, and dimethylnaphthalene are considered as spacer groups. Each receptor is paired with halides F(-) , Cl(-) , Br(-) , and I(-) . Substitution with I on the binding unit yields a large enhancement of binding, as much as 13 orders of magnitude; a much smaller increase occurs for substitution with Br. Imidazolium is a more effective binding agent than is triazolium. Benzene and dimethylnaphthalene represent the best spacers, followed by thiophene and carbazole. F(-) binds much more strongly than do the other halides, which obey the order Cl(-) >Br(-) >I(-) .

Influence of the protonation of pyridine nitrogen on pnicogen bonding: competition and cooperativity

Ab initio MP2/aug-cc-pVTZ calculations were performed to investigate the pnicogen-bonded complexes of PyZX₂ (Py = pyridine, Z = P and As, X = H and F) and their protonated analogues.

Weak interactions within nitryl halide heterodimers

Nitryl halides (XNO₂, X = F, Cl, Br and I) are versatile molecules that exhibit several types of interactions within XNO₂:YNO₂ heterodimers mainly governed by dispersion.

Modulating intramolecular P⋯N pnictogen interactions

The strength of P⋯N intramolecular pnictogen interactions can be modulated, enhanced or diminished upon substitution of different electron withdrawing or donor groups.