Exploring intermolecular contacts in multi-substituted benzaldehyde derivatives: X-ray,Hirshfeld surface and lattice energy analyses

Crystal structures of six benzaldehyde derivatives (1–6) have been determined and their supramolecular networks were established by an X-ray crystallographic study. The study has shown that the compounds are linked by various intermolecular interactions such as weak C–H⋯O hydrogen bonding, and C–H⋯π, π–π and halogen bonding interactions which consolidate and strengthen the formation of these molecular assemblies. The carbonyl group generates diverse synthons in 1–6via intermolecular C–H⋯O hydrogen bonds. An interplay of C–H⋯O hydrogen bonds, and C–H⋯π and π–π stacking interactions facilitates the formation of multi-dimensional supramolecular networks. Crystal packings in 4 and 5 are further generated by type I halogen⋯halogen bonding interactions. The differences in crystal packing are represented by variation of substitution positions in the compounds. Structure 3 is isomorphous with 4 but there are subtle differences in their crystal packing. The nature of intermolecular contacts in the structures has been studied through the Hirshfeld surfaces and two-dimensional fingerprint plots which serve as a comparison in constructing different supramolecular networks. The intermolecular interaction energies are quantified utilizing theorectical calculations for the title compounds and various analogous structures retrieved from the Cambridge Structural Database (CSD). Also intermolecular interactions for the molecular pairs are exctrated from respective crystal structures. Essentially, there are some invariant and variable intermolecular contacts realized between different groups in all six structures. The ab initio DFT total lattice energy (E_Tot) calculations showed a direct correlation with thermal strengths of the title compounds.

We report here crystal packing, and Hirshfeld surface and Lattice energy analyses of six new multi-substituted benzaldehyde derivatives for the first time.     

Polymorphism of Au11(PR3)7Cl3 clusters: understanding C–H⋯π interaction and C–H⋯Cl–C van der Waals interaction on cluster assembly by surface modification

The C–H⋯π interaction and the C–H⋯Cl–C van der Waals interaction play a crucial role in the crystallization of nanoclusters. In this paper, we present an example of a crystal system transformation of Au₁₁(PR₃)₇Cl₃ from monoclinic (M) to trigonal (T) by surface modification. Atomically-resolved gold nanoclusters containing tris(4-chlorophenyl)phosphine and chloride ligands were synthesized and determined to be Au₁₁(p-ClPPh₃)₇Cl₃ (p-ClPPh₃ = tris(4-chlorophenyl)phosphine) by X-ray crystallography. Crystal data demonstrated that the C–H⋯Cl–C interaction is dominant in a trigonal crystal system of Au₁₁(p-ClPPh₃)₇Cl₃ with a R$\bar{3}$ space group. However, the C–H⋯π interaction is the major driving force to form a monoclinic crystal system of Au₁₁(PPh₃)₇Cl₃ (PPh₃ = triphenylphosphine) with a P2(1)/n space group. Moreover, UV-vis absorption spectra and X-ray photoelectron spectra reveal that the electronic structure of the Au₁₁(p-ClPPh₃)₇Cl₃ nanocluster is greatly influenced by p-ClPPh₃. This work provides critical implications for the crystallization of metal nanoclusters, as well as a better understanding of the non-covalent interaction on the nanocluster assembly and the crystal engineering by surface modification.

C–H⋯π interactions and C–H⋯Cl–C van der Waals interactions are dominant in the crystallization of Au₁₁(PR₃)₇Cl₃ clusters, resulting in a crystal system transformation.     

Quantitative analysis of hydrogen and chalcogen bonds in two pyrimidine-5-carbonitrile derivatives,potential DHFR inhibitors: an integrated crystallographic and theoretical study

Two potential bioactive pyrimidine-5-carbonitrile derivatives have been synthesized and characterized by spectroscopic techniques (¹H and ¹³C-NMR) and the three dimensional structures were elucidated by single crystal X-ray diffraction at low temperature (160 K). In both structures, the molecular conformation is locked by an intramolecular C–H⋯C interaction involving the cyano and CH of the thiophene and phenyl rings. The intermolecular interactions were analyzed in a qualitative manner based on the Hirshfeld surface and 2D-fingerprint plots. The results suggest that the phenyl and thiophene moieties have an effect on the crystal packing. For instance, the chalcogen bonds are only preferred in the thiophene derivative. However, both structures uses a common N–H⋯O hydrogen bond motif. Moreover, the structures of 1 and 2 display 1D isostructurality and molecular chains stabilize by intermolecular N–H⋯O and N–H⋯N hydrogen bonds. The nature and extent of different non-covalent interactions were further characterized by the topological parameters derived from the quantum theory of atoms-in-molecules approach. This analysis indicates that apart from N–H⋯O hydrogen bonds, other non-covalent interactions are closed-shell in nature. A strong and linear N–H⋯O hydrogen bond shows intermediate bonding character between shared and closed-shell interactions. The molecular docking analysis suggests that both compounds display potential inhibitory effect against the dihydrofolate reductase (DHFR) enzyme from humans and Staphylococcus aureus.

Qualitative and quantitative analyses of hydrogen and chalcogen bonds in two pyrimidine-5-carbonitrile derivatives are described.     

Role of O–H⋯O/S conventional hydrogen bonds in considerable Csp2–H blue-shift in the binary systems of acetaldehyde and thioacetaldehyde with substituted carboxylic and thiocarboxylic acids

Stable binary complexes of RCZOH⋯CH₃CHZ (R = CH₃, H, F; Z = O, S) are due to contributions from the O–H⋯O/S and C_sp²–H⋯O/S hydrogen bonds. The strength of C_sp²/O–H⋯O is 1.5 to 2 times greater than that of the C_sp²/O–H⋯S bond. The substitution of H(C_sp²) of HCZOH by CH₃ causes a decrease in complex stability, while the opposite trend occurs for the F atom. A very large red shift of the O–H stretching frequency in O–H⋯O/S bonds was observed. A surprising C_sp²–H blue shift up to 104.5 cm⁻¹ was observed for the first time. It is found that the presence of O–H⋯O/S hydrogen bonds and a decisive role of intramolecular hyperconjugation interactions in the complex cause a significant blue shift of the C_sp²–H covalent bonds. A striking role of O compared to the S atom in determining the blue shift of C_sp²–H stretching vibration and stability of binary complexes is proposed. The obtained results show that the ratio of deprotonation enthalpy and proton affinity could be considered as an index for the classification of the non-conventional hydrogen bond. SAPT2+ results show that the strength of RCSOH⋯CH₃CHS complexes is dominated by electrostatic and induction energies, while a larger contribution to the stability of remaining complexes is detected for the electrostatic component.

The presence of O–H⋯O/S conventional hydrogen bonds in the complex governs a significant blue shift of Csp_²–H bonds.     

Interplay of π-stacking and inter-stacking interactions in two-component crystals of neutral closed-shell aromatic compounds: periodic DFT study

This paper bridges the gap between high-level ab initio computations of gas-phase models of 1 : 1 arene–arene complexes and calculations of the two-component (binary) organic crystals using atom–atom potentials. The studied crystals consist of electron-rich and electron-deficient compounds, which form infinite stacks (columns) of heterodimers. The sublimation enthalpy of crystals has been evaluated by DFT periodic calculations, while intermolecular interactions have been characterized by Bader analysis of the periodic electronic density. The consideration of aromatic compounds without a dipole moment makes it possible to reveal the contribution of quadrupole–quadrupole interactions to the π-stacking energy. These interactions are significant for heterodimers formed by arenes with more than 2 rings, with absolute values of the traceless quadrupole moment (Q_zz) larger than 10 D Å. The further aggregation of neighboring stacks is due to the C–H⋯F interactions in arene/perfluoroarene crystals. In crystals consisting of arene and an electron-deficient compound such as pyromellitic dianhydride, aggregation occurs due to the C–H⋯O interactions. The C–H⋯F and C–H⋯O inter-stacking interactions make the main contribution to the sublimation enthalpy, which exceeds 150 kJ mol⁻¹ for the two-component crystals formed by arenes with more than 2 rings.

The interplay of π-stacking and inter-stacking interactions in two-component organic crystals without conventional hydrogen bonds.     

Synthesis,intermolecular interactions and biological activities of two new organic–inorganic hybrids C6H10N2,2Br and C6H10N2,2Cl·H2O

A slow evaporation method has permitted the crystallization of two novel crystals of (2-aminomethyl)pyridindiumdihalide C₆H₁₀N₂,2Br (1) and C₆H₁₀N₂,2Cl·H₂O (2). The structures of the prepared compounds (1) and (2) were elucidated by single-crystal X-ray diffraction which revealed that they crystallize, respectively, with triclinic and monoclinic symmetries. Their crystal packing was stabilized by non-covalent interactions, including N–H⋯Br, C–H⋯Br, N–H⋯Cl, O–H⋯Cl and N–H⋯O hydrogen bonds. 3-D Hirshfeld surface analysis followed by 2-D fingerprint schemes gives insights into the intermolecular interactions in the crystalline structure. Furthermore, the FT-IR spectroscopy of these two compounds was carried out. The synthesized products were also screened for in vitro antioxidant and antimicrobial activities, which reveals their favourable antioxidant activities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) as well as the discolouration of β-carotene.

A slow evaporation method has permitted the crystallization of two novel crystals of (2-aminomethyl)pyridindiumdihalide C₆H₁₀N₂,2Br (1) and C₆H₁₀N₂,2Cl·H₂O (2).     

Structure and surface analyses of a newly synthesized acyl thiourea derivative along with its in silico and in vitro investigations for RNR,DNA binding,urease inhibition and radical scavenging activities

N-((4-Acetylphenyl)carbamothioyl)-2,4-dichlorobenzamide (4) was synthesized by the treatment of 2,4-dichlorobenzoyl chloride with potassium thiocyanate in a 1 : 1 molar ratio in dry acetone to afford the 2,4-dichlorobenzoyl isothiocyanate in situ which on reaction with acetyl aniline furnished (4) in good yield and high purity. The compound was confirmed by FTIR, ¹H-NMR, and ¹³C-NMR and single crystal X-ray diffraction studies. The planar rings were situated at a dihedral angle of 33.32(6)°. The molecules, forming S(6) ring motifs with the intramolecular N–H⋯O hydrogen bonds, were linked through intermolecular C–H⋯O and N–H⋯S hydrogen bonds, enclosing R₂²(8) ring motifs, into infinite double chains along [101]. C–H⋯π and π⋯π interactions with an inter-centroid distance of 3.694 (1) Å helped to consolidate a three-dimensional architecture. Hirshfeld surface (HS) analysis further indicated that the most important contributions for the crystal packing were from H⋯C/C⋯H (20.9%), H⋯H (20.5%), H⋯Cl/Cl⋯H (19.4%), H⋯O/O⋯H (13.8%) and H⋯S/S⋯H (8.9%) interactions. Thus C–H⋯π (ring), π⋯π, van der Waals interactions and hydrogen bonding played the major roles in the crystal packing. The electronic structure and computed DFT (density functional theory) parameters identified the reactivity profile of compound (4). In silico binding of (4) with RNA indicated the formation of a stable protein–ligand complex via hydrogen bonding, while DNA docking studies inferred (4) as a potent groove binder. The experimentally observed hypochromic change (57.2%) in the UV-visible spectrum of (4) in the presence of varying DNA concentrations together with the evaluated binding parameters (K_b; 7.9 × 10⁴ M⁻¹, ΔG; −28.42 kJ mol⁻¹) indicated spontaneous interaction of (4) with DNA via groove binding and hence supported the findings obtained through docking analysis. This compound also showed excellent urease inhibition activity in both in silico and vitro studies with an IC₅₀ value of 0.0389 ± 0.0017 μM. However, the radical scavenging efficiency of (4) was found to be modest in comparison to vitamin C.

A new acyl thiourea derivative was explored for its binding interaction with RNR and DNA and for excellent urease inhibition activity.     

Synthesis and characterization of a mononuclear zinc(ii) Schiff base complex: on the importance of C–H⋯π interactions

A zinc(ii) complex, [ZnL(H₂O)]·H₂O {H₂L = 2,2′-[(2,2-dimethyl-1,3-propanediyl)bis(nitrilomethylidyne)]bis[6-ethoxyphenol]} has been synthesized and characterized by UV-vis and IR spectroscopy. The structure of the complex has been confirmed by X-ray crystallography and the noncovalent interactions characterized using Hirshfeld surface analysis. In addition to the conventional H-bonds involving the Zn-coordinated and non-coordinated water molecules, interesting C–H⋯π interactions between the H-atoms belonging to aliphatic part of the ligand (2,2-dimethyl-1,3-propanediyl) and the Zn-coordinated aromatic rings are established. These interactions have been studied using DFT calculations (PBE0-D3/def2-TZVP) and characterized using molecular electrostatic potential (MEP) surfaces and the noncovalent interaction (NCI) plot index analyses.

The strength of the C–H⋯π interaction in the solid state of [ZnL(H₂O)]·H₂O has been evaluated using DFT calculations and also analysed using the MEP surface and NCI plot index computational tool.     

Understanding the effects of vicinal carbon substituents and configuration on organofluorine hydrogen-bonding interaction

An investigation of C–F⋯H–O hydrogen bonds in the complexes CH_nXCH_nF⋯H₂O (n = 0, 1, 2; X = H, F, Cl, Br) was performed at the MP2/aug-cc-pVTZ level. We found that the electron-withdrawing halogen substituents on the vicinal carbon cause the fluorine atom, participating in the hydrogen bond formation, to be less negatively charged. Thus, the halogen groups weaken the strength of organofluorine hydrogen bond by inductive effect. The position of the substituents on the vicinal carbon affects the strength of the C–F⋯H–O interaction. Compared with that in other isomers, the electron withdrawing substituent in 1-fluoro-ethane with stagger conformation as well as in 1-fluoro-ethene with trans configuration much weakens the interaction of C–F⋯H–O due to the hyperconjugative interaction between σ_(C–F) and . By analogy, the electron-donating ones could largely strengthen it. We found that there is a good linear relationship between electron density at the BCP of F⋯H and Wiberg bond indexes (WBI) as well as between natural bond-bond polarizability (NBBP) and WBI, which indicates that the magnitude of NBBP and WBI could be a good indicator of the hydrogen bond strength.

The vicinal substituents, with gauche/stagger isomer in CH₂XCH₂F and cis/trans isomer in CHXCHF, affect the interaction of C(spⁿ)–F⋯H–O organofluorine hydrogen bonds differently.     

Host–guest modes and supramolecular frameworks of complexes of tetramethyl cucurbit[6]uril with 4-chloroaniline and 4,4′-diaminostilbene

Since the first reportal on decamethylcucurbit[5]uril (Me₁₀Q[5]) in 1992, substituted cucurbit[n]urils have attracted considerable research interest. In this study, the host–guest modes between the tetramethyl cucurbit[6]uril (TMeQ[6]) as a host and 4-chloroaniline and 4,4′-diaminostilbene (G1 and G2) as guests were investigated by single-crystal X-ray diffraction, NMR, ITC, UV-Vis spectrum, and MALDI-TOF mass spectrometry analyses. The experimental results showed that TMeQ[6] formed a 1 : 1 inclusion compound with G1, and the carbonyl portal of TMeQ[6] formed a 1 : 1 self-assembly with G2. Further, multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H⋯π interactions, ion–dipole interactions, and dipole–dipole interactions).

Two TMeQ[6]-based multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H... π interactions, ion–dipole interactions, and dipole–dipole interactions).     

Green synthesis,structural analysis and anticancer activity of dihydropyrimidinone derivatives

In this study, for the first time, we have used Citrus macroptera juice to synthesize dihydropyrimidine (DHPM) derivatives via the Biginelli reaction, which showed better yield, shorter reaction time, and did not require an organic solvent for the reaction. A series of DHPM derivatives were synthesized, and characterized, and structural analysis was achieved through SCXRD & Hirshfeld surface analysis. We observed that these synthesized dihydropyrimidine (DHPM) derivatives showed C–H⋯π, C–H⋯O, C–H⋯N, C–H⋯C, lone pair⋯π, π⋯π, etc. interactions. We also performed in silico studies for their inhibitory activities against human kinesin Eg5 enzyme, and the cytotoxic activity of the synthesized compounds was carried out against A549 lung adenocarcinoma cells. In silico analysis demonstrated that compounds with a chloro-group at the 3- or 4-position in the substituted ring of DHPM showed higher binding affinity for the human kinesin Eg5 enzyme (−7.9 kcal mol⁻¹) than the standard drug monastrol (−7.8 kcal mol⁻¹). Furthermore, in vitro cellular studies revealed that compounds with a chloro-group at the 3- or 4-position in the substituted ring of DHPM induced significant cell death in human A549 lung adenocarcinoma cells. This result indicates that a deactivating group (chlorine) at the 3- or 4-position in the substituted ring of DHPM might be a promising anticancer drug candidate for treating different types of cancers, particularly cancer of the lung.

Green synthesis, study and development of new potent dihydropyrimidinone analogues as anti-cancer drugs.     

Pressure-induced phase transition of 4-aminobenzonitrile: the formation and enhancement of N–H⋯N weak hydrogen bonds

A reversible pressure-induced structural phase transition of 4-aminobenzonitrile was found at about 0.3 GPa by conducting in situ high-pressure synchrotron angle-dispersive X-ray diffraction (ADXRD) experiments. The discontinuous changes of Raman modes at 0.2 GPa confirmed the occurrence of phase transition. In situ high-pressure Raman spectra indicated that the molecular arrangement and intermolecular interactions changed abruptly. The process of this phase transition continued up to about 1.0 GPa. When the pressure reached 1.1 GPa, the initial N–H⋯N interaction transformed into a new weak hydrogen bond, which was enhanced by further compression. The ab initio calculations and Hirshfeld surfaces were used to illustrate the above views. This study gives an example that demonstrates that the pressure can induce the formation of hydrogen bonds, which contributes to the development of supramolecular chemistry.

The initial N–H⋯N interactions in 4-aminobenzonitrile crystals are enhanced and changed into weak hydrogen bonds by high pressure.     

Synthesis,solid state self-assembly driven by antiparallel π⋯π stacking and {⋯H–C–C–F}2 dimer synthons,and in vitro acetyl cholinesterase inhibition activity of phenoxy pendant isatins

A series of novel phenoxy pendant isatins PI1–12 have been synthesized in excellent yields by a simple nucleophilic substitution reaction involving isatins and 1-(2-bromoethoxy)-4-substituted benzenes, and characterized by their FT-IR, ¹H NMR, ¹³C NMR and GC-MS data, and in the case of PI4 by its single crystal X-ray analysis. The solid-state structure of PI4 showed an intriguing and unique 1D-supramolecular chain-based self-assembled structure, the driving force of which is mainly the strong antiparallel π⋯π stacking and {⋯H–C–C–F}₂ dimer synthons. This compound not only highlights the potential of the isatin moiety in forming strong antiparallel π⋯π stacking interactions but also provides a platform to have considerable insight into the nature, strength and directionality of much debated π–π and C–H⋯F–C interactions. The in vitro biological studies revealed that three phenoxy pendant isatins PI1, PI2 and PI4 are highly potent inhibitors of acetylcholinesterase enzyme with IC₅₀ values of 0.52 ± 0.073 μg ml⁻¹, 0.72 ± 0.012 μg ml⁻¹ and 0.68 ± 0.011 μg ml⁻¹, respectively, showing comparable activity to the standard drug, donepezil (IC₅₀ = 0.73 ± 0.015 μg ml⁻¹). A simple and efficient synthesis of phenoxy pendant isatins PI1–12 from inexpensive and commercially available starting materials, and their high potential of acetyl cholinesterase inhibition provide an attractive opportunity to find more effective medication for Alzheimer''s disease (AD).

The phenoxy pendant isatins were observed to be highly potent inhibitors of acetylcholinesterase. In addition, the solid-state structure of a phenoxy pendant isatin showed an intriguing 1D-supramolecular self-assembled structure.     

Solvent-driven structural topology involving energetically significant intra- and intermolecular chelate ring contacts and anticancer activities of Cu(ii) phenanthroline complexes involving benzoates: experimental and theoretical studies

Two new coordination solids [Cu₂(μ²-Bz)₄(CH₃OH)₂][Cu₂(η²-Bz)₂(phen)₂(H₂O)₂]·(NO₃)₂ (1) and [Cu(phen)(H₂O)(Bz)(η²-Bz)] (2) (phen = 1,10-phenanthroline; Bz = benzoate) have been synthesized and characterized using elemental analysis, TGA, spectroscopic (IR, UV-vis-NIR and ESR) and single crystal X-ray diffraction techniques. Change of the solvent from methanol to DMF results in changes in the architectures that are triggered by a change from square pyramidal to octahedral coordination at the divalent metal centers for complexes 1 and 2 respectively. The structural topology of the complexes is established by the interplay of strong O–H⋯O and weak C–H⋯O, C–H⋯C, π–π stacking interactions. Unconventional parallel intramolecular and anti-parallel intermolecular contacts involving the chelate rings (CR) also stabilize the structures. The energetic analyses of the structures evidence that the parallel arrangement is energetically favoured which is likely due to the presence of the Cu⋯Cu cuprophilic interaction in 1 that is not established in 2. Compound 1 exhibits the highest antibacterial activity against Rhizobium leguminosarum among the tested cultures. In vitro cytotoxicity and apoptosis studies were carried out for compounds 1 and 2 on malignant Dalton''s lymphoma cell line (DL). Both compounds showed a significant effect on the decrease in cell viability as compared to a control, while compound 2 induced remarkable cytotoxicity towards DL cells. Treatment also showed the appearance of membrane blebbing, chromatin condensation and fragmented nuclei which are typical characteristic features of apoptotic cell death. Furthermore, a docking study revealed that both compounds docked in the active sites of all the cancer target proteins under study. Moreover, SAR analysis revealed that oxygen and nitrogen atoms of compound 1 and the oxygen atoms of compound 2 are crucial for biological activities.

Solvent driven structural topology and in vitro anticancer evaluation of two new Cu(ii) complexes considering cytotoxicity, apoptosis and molecular docking.     

Comparative investigation of interactions of hydrogen,halogen and tetrel bond donors with electron-rich and electron-deficient π-systems

Recently, noncovalent interactions in complexes and crystals have attracted considerable interest. The current study was thus designed to gain a better understanding of three seminal types of noncovalent interactions, namely: hydrogen, halogen and tetrel interactions with π-systems. This study was performed on three models of Lewis acids: X₃–C–H, F₃–C–X and F–T–F₃ (where X = F, Cl, Br and I; and T = C, Si, Ge and Sn) and three π-systems as Lewis bases: benzene (BZN), 1,3,5-trifluorobenzene (TFB) and hexafluorobenzene (HFB). Quantum mechanical calculations, including geometrical optimization, molecular electrostatic potential (MEP), maximum positive electrostatic potential (V_s,max), Point-of-Charge (PoC), potential energy surface (PES), quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) calculations, were carried out at the MP2/aug cc-pVDZ level of theory. The binding energies were additionally benchmarked at the CCSD(T)/CBS level. The results showed that: (i) the binding energies of the X₃–C–H⋯π-system complexes were unexpectedly inversely correlated with the V_s,max values on the hydrogen atom but directly correlated with the X atomic sizes; (ii) the binding energies for the F₃–C–X⋯π-system and F–T–F₃⋯π-system complexes were correlated with the σ-hole magnitudes of the X and T atoms, respectively; and (iii) for the F₃–C–F⋯π-system complexes, the binding energy was as strong as the π-system was electron-deficient, indicating the dominating nucleophilic character of the fluorine atom. NCI analysis showed that the unexpected trend of X₃–C–H⋯π-system binding energies could be attributed to additional attractive interactions between the X atoms in the X₃–C–H molecule and the carbon atoms of the π-system. Furthermore, the I₃–Sn–H molecule was employed as a case study of hydrogen, halogen and tetrel interactions with π-systems. It was found that hydrogen and halogen interactions of the I₃–Sn–H molecule correlated with the electron-richness of the π-system. In contrast, tetrel interactions correlated with the electron deficiency of the π-system.

Three seminal types of noncovalent interaction, namely: hydrogen, halogen and tetrel interactions with π-systems, were investigated using quantum mechanical calculations.     

Hydrogen bonds-triggered differential extraction efficiencies for bifenthrin by three polymeric ionic liquids with varying anions based on FT-IR spectroscopy

Herein, we fabricated three imidazolium-based polymeric ionic liquids (PILs) with different anions (P[VEIM]BF₄, P[VEIM]PF₆ and P[VEIM]Br), and analyzed their differential extraction efficiencies for bifenthrin through H-bonding induced effects. Three PILs all presented an irregular block structure with rough surface and lower specific-surface area (SSA, 11.2–18.7 m² g⁻¹) than carbon-based nanomaterials. They formed hydrogen bonds with free-water molecules in the lattice of PILs, including C_2,4,5–H⋯O–H, Br⋯H–O–H⋯Br, O–H⋯Br, C_2,4,5–H⋯F–P, P–F⋯H–O–H⋯F–P, C_2,4,5–H⋯F–B and B–F⋯H–O–H⋯F–B. After extraction, the O–H stretching-vibration peak was prominently intensified, whereas the C–H bond varied slightly concomitant with reduced B–F and P–F vibration. Theoretically, the C–H vibration should become more intense in the C_4,5–H⋯H₂O and C₂–H⋯H₂O bonds after extraction in contrast to before extraction. These contrary spectral changes demonstrated that the hydrogen bonds between cations in the PILs and free-water molecules were broken after extraction, yielding the H-bonding occurrence between bifenthrin and H–O–H in the lattice. As a time indicator for the free-water binding and releasing process, the highest slope for the plot of I_t/I₀ against time implied that the shortest time was required for P[VEIM]PF₆ to reach an adsorption equilibrium. Overall, the strong hydrophobicity, small SSA and electrostatic-repulsion force for P[VEIM]PF₆ are all not conducive to its efficient adsorption. Beyond our anticipation, P[VEIM]PF₆ provided the highest extraction recovery for bifenthrin up to 92.4% among three PILs. Therefore, these data lead us to posit that the above high efficiency results from the strongest H-bonding effect between P[VEIM]PF₆ and bifenthrin. These findings promote our deep understanding of PILs-triggered differential efficiency through a H-bonding induced effect.

Herein, we fabricated three imidazolium-based polymeric ionic liquids (PILs) with different anions (P[VEIM]BF₄, P[VEIM]PF₆ and P[VEIM]Br), and analyzed their differential extraction efficiencies for bifenthrin through H-bonding induced effects.     

Importance of water and intramolecular interaction governs substantial blue shift of Csp2–H stretching frequency in complexes between chalcogenoaldehydes and water

Geometrical structure, stability and cooperativity, and contribution of hydrogen bonds to the stability of complexes between chalcogenoaldehydes and water were thoroughly investigated using quantum chemical methods. The stability of the complexes increases significantly when one or more H₂O molecules are added to the binary system, whereas it decreases sharply going from O to S, Se, or Te substitution. The O–H⋯O H-bond is twice as stable as C_sp²–H⋯O and O–H⋯S/Se/Te H-bonds. It is found that a considerable blue-shift of C_sp²–H stretching frequency in the C_sp²–H⋯O H-bond is mainly determined by an addition of water into the complexes along with the low polarity of the C_sp²–H covalent bond in formaldehyde and acetaldehyde. The C_sp²–H stretching frequency shift as a function of net second hyperconjugative energy for the σ*(C_sp²–H) antibonding orbital is observed. Remarkably, a considerable C_sp²–H blue shift of 109 cm⁻¹ has been reported for the first time. Upon the addition of H₂O into the binary systems, halogenated complexes witness a decreasing magnitude of the C_sp²–H stretching frequency blue-shift in the C_sp²–H⋯O H-bond, whereas CH₃-substituted complexes experience the opposite trend.

The considerable blue shift of C_sp²–H stretching frequency.