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Theoretical investigations of the interactions between carbon monoxide (CO) and bromopentafluorobenzene (C6F5Br) have been carried out at both M06-2X/6-311++G(2d,2p) and M06-2X/aug-cc-pVTZ levels of theory. Because both C and O atom-ends of CO show negative electrostatic potential, they can favorably interact with the positive electrostatic potential generated by the σ-hole of Br and the π-hole of the aromatic ring of C6F5Br, yielding four different dimers and trimers. Their structures, spectroscopy and nature were systematically studied. The competition between the interactions involving the σ-hole of the Br atom and the π-hole of C6F5Br with the C and O atom-ends of CO was illustrated for the dimers and trimers, and meanwhile, the cooperativity between the two components of the trimers was elaborated. In addition, the experimental FT-IR and fluorescence spectra were measured for C6F5Br and the mixed C6F5Br and CO system without and with the solvent of hexane to gain information on the formation of molecular complexes between C6F5Br and CO. The results presented in this work are beneficial for the understanding of the competition and cooperativity of σ- and π-hole intermolecular interactions. [ABSTRACT FROM AUTHOR]

The tin-oxo cage ([R12Sn12O14(OH)6]2+) is an excellent photoresist candidate in extreme ultraviolet lithography (EUVL). Photoionization that leads to plenty of photoelectrons and secondary electrons is an inevitable process upon irradiation by EUV light. The secondary electrons could cause electron blur and decrease the resolution of the photoresist. The utilization and improvement are limited owing to its poorly understood fundamental chemical process, such as exposure to EUV. In this study, the property of complexes (bare cage, binary complexes, and ternary complexes) formed by the combination of the cage and different counterions (methanesulfonate, tosylate, and triflate) was explored using density functional theory (DFT). Extended transition state-nature orbital of chemical valence (ETS-NOCV), charge decomposition analysis (CDA), and atomic dipole moment corrected Hirshfeld (ADCH) atomic charge analyses were carried out to characterize the interaction process (including ionization, electron attachment, and cleavage of the carbon–tin bond) and inherent mechanism. The number and species of counterions are closely associated with ionization and electron attachment; however, they show an inconspicuous effect on the carbon–tin bond energy. Meanwhile, tin free radical could be the reactivity site of ionization (and electron affinity). The activity of radical species is affected by counterions; this could be attributed to the changes in the charge density by diverse counterions, which could be an important factor in why the counterion affects the pattern. In addition, a superb linearity between the ADCH of tin free radical and IP/AP was found, which indicate that the atomic charge could be a simple and reliable substitution of complicated calculation for IP (or AP) to screen suitable counterions and improve the resolution of photoresist. [ABSTRACT FROM AUTHOR]

Substituent size and isomerization play an important role in the polymorphism of 2-(naphthalen-n-ylamino)-benzoic acids (n = 1, 2; 2-NBAs) as each of the two previously investigated 2-NBAs was found to be polymorphic, while their parent compound fenamic acid (FA) has only one form discovered. 2-(Naphthalen-1-ylamino)-nicotinic acid (1) and 2-(naphthalen-2-ylamino)-nicotinic acid (2) (2-NNA) are isosteric compounds of 2-NBAs, and 2-(2,3-dimethyl-phenylamino)-nicotinic acid (3) and 2-(3,4-dimethyl-phenylamino)-nicotinic acid (4) are 2-NNA analogues with similar substitution patterns. All four compounds are clonixin analogues. The polymorphism of these four compounds was investigated. One solvent-free form (1-A) and one hydrate (1-H) were discovered for 1, three forms (2-I, 2-II, and 2-III) were obtained for 2, and one form was found for 3 and 4. The four systems were characterized by single-crystal XRD (SCXRD) and powder XRD (PXRD), and structural properties were compared among the crystals of the four compounds, their isosteres, and other related analogues. The phase behavior of the four systems was studied with differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) was used to investigate the dehydration of 1-H. Computational studies such as stable conformer search, π–π interaction energy calculation, and non-covalent interaction (NCI) analysis were performed to shed light on the rise of polymorphism, and the relative contribution of various intermolecular interactions to the overall stability of the crystals. The study confirmed the effect of substituent size, thus the consequent π–π interactions, on the hydrate formation of compound 1 and polymorphism of compound 2. [ABSTRACT FROM AUTHOR]

First principles investigation and Hirshfeld surface analysis of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystals have been carried out. The geometrical and electronic structures of TATB molecules in the crystal and gas phases were compared. The Hirshfeld surface analysis of the TATB crystal structure shows that the intermolecular H⋯O interactions make important contributions in stabilizing the TATB crystal, while other intermolecular H⋯N and H⋯C interactions, O⋯O, N⋯O, C⋯O, and C⋯N close contacts also make contributions. QTAIM analyses of the intermolecular interactions in the molecular pairs confirm the presence of these intermolecular interactions based on Hirshfeld surface analyses, indicating that these intermolecular interactions play important roles in the crystal. The reason why the TATB crystal adopts a high energy conformer in which the NO2 and NH2 groups are coplanar with the benzene ring is elaborated. The cooperativity between hydrogen bonding and π⋯π interactions in the TATB crystal is verified and illustrated. [ABSTRACT FROM AUTHOR]

Cu2O-based composites for photocatalysis have been extensively explored owing to their promising application in solving environmental and energy problems. At present, the research on photocatalysis is focused on improving the photocatalytic performance of materials. It has been reported that adjusting the morphology and size of Cu2O can effectively improve its photocatalytic property. However, photocorrosion is still an inevitable problem, which hinders the application of Cu2O in photocatalysis. The strategies of constructing heterogeneous nanostructures and ion doping can significantly improve the light stability, light absorption capacity and separation efficiency of electron–hole pairs. Cu2O-based composites exhibit superior performances in degrading organic matter, producing hydrogen, reducing CO2 and sterilization. Therefore, the construction of multi-materials will be one of the future directions in their photocatalytic application. This review summarizes the recent strategies for enhancing the photocatalytic activity of Cu2O by analyzing different Cu2O-based photocatalysts, and the charge transfer pathway is further discussed in detail. Finally, several opportunities and challenges in the field of photocatalysis are illustrated. [ABSTRACT FROM AUTHOR]

Monoalkylation of aniline can be readily achieved using trichloroacetimidate as an alkylating agent and a Brønsted acid, such as (±)-camphorsulfonic acid, as a catalyst. In this study, systematic theoretical calculations were performed to understand the reaction mechanism for the monoalkylation of 2,5-dichloroaniline with trichloroacetimidate catalyzed by (±)-camphorsulfonic acid; moreover, the judgement about whether the reaction takes place via an SN1 or SN2 mechanism was elaborated. The two possible proton-transfer reaction mechanisms proposed herein based on the experimental results were investigated; moreover, another two possible reaction mechanisms involving the activation of both 2,5-dichloroaniline and trichloroacetimidate by (±)-camphorsulfonic acid via dual hydrogen-bonding activation modes were evaluated. The calculated results suggest that the reaction between 2,5-dichloroaniline and trichloroacetimidate catalyzed by (±)-camphorsulfonic acid preferentially occurs through the SN1 mechanism based on the dual hydrogen-bonding activation modes. [ABSTRACT FROM AUTHOR]

Triethylene diamine (DABCO) has the characteristic of being hydrophilic and exhibits a color change in air because its N atom can interact with H2O and CO2. To understand these phenomena, herein, theoretical calculations on the intermolecular interactions between DABCO and H2O (or CO2) were carried out at the M06-2X/aug-cc-pVDZ level without and with the counterpoise method, and single-point calculations at the CCSD(T)/aug-cc-pVDZ level were also performed. The electron donating ability of DABCO was revealed by the molecular surface electrostatic potential and Fukui function. The driving forces for the formation of a dimer and trimer were uncovered by EDA analyses. Because DABCO can interact with both H2O and CO2, the formation of hydrogen bonds and tetrel bonds is competitive, and meanwhile, DABCO can interact with H2O and CO2 simultaneously, so the hydrogen bond and tetrel bond can coexist and cooperate with each other. The hydrogen bond and tetrel bond in the dimers and trimers were proven and analyzed by NCI and QTAIM. The results presented here will provide useful insight in understanding the hydrophilic characteristic and the color change of DABCO. [ABSTRACT FROM AUTHOR]

Bromo- and iodo-pentafluorobenzene (C6F5X, X = Br, I) exhibit intriguing σ- and π-hole characters, which are able to accept electrons, whereas furan (C4H4O) and thiophene (C4H4S) are able to donate electrons because of their electron-rich atoms and groups (i.e., the O atom and π-ring in C4H4O and the π-ring in C4H4S). Theoretical investigations of intermolecular interactions in these systems (i.e., C4H4O and C6F5Br, C4H4S and C6F5Br, C4H4O and C6F5I, and C4H4S and C6F5I) have been carried out at the M06-2X/aug-cc-pVDZ and wB97-XD/aug-cc-pVDZ levels with and without the counterpoise method, together with single-point calculations at the CCSD(T)/aug-cc-pVDZ level. For the system of C4H4O and C6F5X (X = Br, I), five different dimers, namely, I–V and I′–V′, which are connected by σ-hole…n, σ-hole…π and π-hole…π bonds, were found. Moreover, for the system of C4H4S and C6F5Br, four different dimers, namely, VI–IX, which are connected by σ-hole…π and π-hole…π bonds, were found. However, five dimers, namely, VI′–X′, were found for the system of C4H4S and C6F5I, which are connected by σ-hole…π, π-hole…π and σ-hole…n bonds. The driving forces for the formation of these dimers were revealed by EDA analyses. NCI, QTAIM and NBO analyses were employed to prove the existence of intermolecular interactions in these dimers and to elucidate their nature. The results presented here will be insightful for the study of other intermolecular systems that involve σ- and π-holes. [ABSTRACT FROM AUTHOR]

Prototype lanthanide metal–organic frameworks (LnMOFs), Ln(BTC) (Ln = Eu and Tb; BTC = benzene-1,3,5-tricarboxylate), have been considered as luminescent sensors for detecting toxic anions, while their neutral pore structures have limited the entrance and encapsulation of anions to produce highly anion-responsive photoluminescence (PL). To facilitate anions to enter the pore space of Ln(BTC), a one-pot synthesis method was proposed in which BTC was partially replaced with its structural analogue L·BF4 (H3L·BF4 = 2,4,6-tricarboxy-1-methylpyridinium tetrafluoroborate) which consists of an anion affinity site of cationic methylpyridinium. Compared to the original Ln(BTC), the co-doped cationic framework Eu0.05Tb0.95-BTC0.9L0.1 is highly sensitive for detecting different toxic anions by tuning the energy absorption of organic chromophores, the energy transfer efficiency to Ln3+ ions and the energy allocation between different Ln3+ ions in the PL spectra. We demonstrated that the Eu0.05Tb0.95-BTC0.9L0.1 PL sensor has the capability of decoding various toxic anions with a clearly differentiable and unique emission intensity ratio of 5D4→7F5 (Tb3+, 545 nm) to 5D0→7F2 (Eu3+, 618 nm) transitions (ITb/IEu). Compared to Ln(BTC), the co-doped Eu0.05Tb0.95-BTC0.9L0.1 presents self-calibrating, high distinguishable and stable PL signals for detecting toxic anions. [ABSTRACT FROM AUTHOR]

Two molecules with different conformations appear in the asymmetric unit of fenamic acid crystal (Z′ = 2). The two conformations have higher energies, and they dimerize via asymmetric O–H…O hydrogen bonds. For the predicted crystal (Z′ = 1), the symmetric O–H…O hydrogen bonds form between the lower energy conformers. Quantum mechanical calculations were carried out to elaborate the existence of higher energy conformers and their special arrangements. The asymmetric O–H…O hydrogen bonds in the crystal (Z′ = 2) are even stronger than the symmetric O–H…O hydrogen bonds in the predicted crystal (Z′ = 1), which is an important reason that the crystal with Z′ = 2 is observed. Additionally, intricate intermolecular interactions, that is, many adjacent molecules interacting with the substituted and unsubstituted benzene groups of higher energy conformers, also come into play, and these interactions cooperate and stabilize the conformers. A comparison of these intermolecular interactions in the crystal (Z′ = 2) with those in the predicted crystal (Z′ = 1) was made. The potential factors holding the two higher energy conformers together as a packing motif have been discussed in detail. We expect that the results could shed light on the understanding of the origin of the Z′ = 2 structure and other higher Z′ structures. [ABSTRACT FROM AUTHOR]