Dispersion-corrected density functional theory (DFT) calculations were employed to investigate stable structures of triiodobenzenes (BzI3) inside an armchair (m,m) carbon nanotube (m = 7–9), denoted ...by n × BzI3@(m,m), where n is the number of guests (n = 1–4). Three BzI3 isomers were considered: 1,3,5-, 1,2,4-, and 1,2,3-BzI3. DFT calculations found that nanotube confinement has an impact on n × BzI3@(m,m) structures, featuring guest orientation, positioning, and alignment. Then, we estimated a threshold value of the diameter of a tube containing BzI3 monomer in a certain orientation without repulsive host–guest interactions (D threshold). To represent the degree of nanotube confinement in 1 × BzI3@(m,m), we obtained ΔD small values by subtracting the smallest limit of D threshold of the guest from the host–tube diameter (D). Negative ΔD small values indicate strong confinement, and positive values less (much larger) than 1.0 Å indicate medium (weak) confinement. The strong and medium confinement in n × BzI3@(m,m) form a linear alignment of guests in parallel orientation with the smallest D threshold value. Reflecting from the different degrees of nanotube confinement, various types of intermolecular interactions operate. DFT calculations found that I–I intermolecular interactions are key in enhancing the second-order nonlinear optical properties of n × BzI3@(m,m). As a result, n × 1,2,4-BzI3@(8,8) with medium nanotube confinement has the most significant hyperpolarizability.
Complex salts composed of cationic Au(
i
) and anionic Cu(
i
) species were synthesized by utilizing bis(diphenylarsino)methane (dpam) and bis(diphenylphosphino)methane (dppm) ligands. The discrete ...tetranuclear complexes were obtained as crystals, and the four-metal chain, Cu Au Au Cu, was linked through homo- and hetero-metallophilic interactions. Three crystal polymorphs were obtained for the dpam- and dppm-complexes, depending on the recrystallization solvent. All the crystals exhibited intense phosphorescence (quantum yields up to 0.97) at room temperature, and the emission color of each crystal was significantly different. The crystals could be interconverted by exposure to solvent vapor, and this was accompanied by a drastic change in the emission color.
Discrete complex salts having Au···Au and Au···Cu interactions were obtained as three crystalline polymorphs exhibiting various emission colors with high efficiency. Solvent vapor caused crystal-to-crystal transition, changing the emission color.
The behavior of alkyl guest radicals inside carbon nanotube hosts with different diameters is analyzed using density functional theory (DFT) calculations. Here the inner alkyl radicals are assumed to ...be formed by decomposition of their precursors, which had been incorporated into the tubes. DFT calculations show that inner alkyl radicals prefer to exist separately from the nanotube wall (separate form) rather than forming an inner covalent bond with the wall (bound form). Keeping a radical apart from the inner wall is more likely for a more bulky radical inside a smaller diameter tube. A key to the preference for the separate forms over the bound forms is that the bound forms gain a weak attraction due to the formation of a bond with the inner wall. The weak attraction, ascribed to the inertness of the inner surface, is counteracted by destabilization due to deformations of a tube and radical induced by guest-host coupling. The energy balance argument illuminates that the inertness of the inner wall makes an alkyl radical species remain alive inside a tube and retain its reactivity. These findings can help us to understand experimental results where chemical reactions inside a tube proceed after guests are activated.
Dispersion-corrected density functional theory (DFT) calculations examined energetically preferable hybrid structures between 13cycloparaphenylene (13CPP) and an armchair (m,m) tube (5 ≤ m ≤ 9). ...Tube-in-ring and ring-on-tube structures, denoted by (m,m)@13CPP and 13CPP–(m,m), respectively, were considered. DFT-based energy-decomposition analyses revealed that the key factors determining the stability of the hybrid structures are attractive long-range interactions between 13CPP and the (m,m) tube and the energy penalty required for the deformation of 13CPP. The long-range interactions in (m,m)@13CPP become more significant with an increase in the tube diameter. The 13CPP deformation in (m,m)@13CPP varies with the degree of deviation between the radius difference between 13CPP and a tube (Δr) and the van der Waal contact distance between two carbon atoms (3.35 Å). Accordingly, the stability of (m,m)@13CPP depends on the tube diameter. Particularly, (8,8)@13CPP, whose Δr is close to 3.35 Å, is highly stabilized among (m,m)@13CPP because of a negligible energy penalty for the 13CPP deformation. In contrast, the stability of 13CPP–(m,m) is less sensitive to the tube-diameter, and their attractive long-range interactions are weaker than those in (m,m)@13CPP. Consequently, a tube-in-ring structure whose radius difference is close to 3.35 Å is the most preferable among hybrid structures between 13CPP and an (m,m) tube.
A practical arsenic halogenation of 9-arsafluorene, which can be safely and easily prepared from a cyclooligoarsine, was developed by using halogen sources such as iodine and iodine monochloride. The ...in situ prepared 9-halogeno-9-arsafluorenes reacted with various nucleophiles to provide 9-arsafluorene derivatives. The functional groups affected their emission properties in the solid state through changes in the packing structure. To estimate the reaction mechanism of the halogenation, density functional theory calculations were employed; the molecular behaviors of oxidative addition and reductive elimination on the arsenic atom were elucidated. Furthermore, the present reaction was applied to a structure other than 9-arsafluorene as well.
Dispersion-corrected DFT calculations were performed to investigate energetically stable structures of a Li+ cation solvated by some PC molecules inside an AB-stacked graphene bilayer (2G) with a ...variant interlayer spacing (L ranging from 5 to 8 Å), denoted by PC n –Li+@2G(L), where n is the number of PC molecules (1 ≤ n ≤ 3). The 2G(L) structures model slit-type pore geometries of microporous carbons, where the interlayer spacing corresponds to their pore width. DFT calculations found L- and n-dependences of stabilized PC n –Li+@2G(L) structures due to different degrees of CH−π and cation−π interactions between a graphene bilayer host and a PC n –Li+ guest. Since the interlayer space of 2G(L) at L = 6 Å is the smallest limit that can accommodate a single PC molecule, the restricted interlayer space can be utilized to selectively stabilize a PC1–Li+ structure due to attractive cation−π interactions and negligible CH−π interactions. Within a larger interlayer space of graphene bilayers (L ≥ 7 Å), attractive cation−π and CH−π interactions between the host and guests are significant for stabilizing inner PC n –Li+ structures (n ≥ 3). Similar structural preferences can be found in the solvated state of Na+ cations within the interlayer space of 2G(L) at L = 6 Å. By using the distance of a Li+ cation from a carbon layer in the PC n –Li+@2G(L) structures compared with that in the optimized PC4–Li+ structure on a graphene monolayer (1G) as a model of external and macroporous carbons, the capacitances of PC n –Li+@2G(L) structures relative to that of PC4–Li+ structure on 1G were approximately estimated. The estimated capacitance of the PC1–Li+ structure stabilized inside 2G(L) at L = 6 Å is almost twice as large as that in PC4–Li+ on the 1G structure. Accordingly, the DFT calculations revealed that the confinement of PC n –Li+ structures within microporous carbons whose pore size is around 6 Å significantly enhances the capacitance relative to those in external or macroporous carbons due to the selective formation of the significantly desolated Li+ cations.
We propose theoretically that the reactivity of O2-bound Cu-ZSM-5 toward methane is enhanced by the presence of one water molecule near a dinuclear copper site inside a 10-membered ring of the ...zeolite cavity. The current study employed density functional theory (DFT) calculations with the B3LYP functional to elucidate reaction intermediates during dioxygen activation by Cu-ZSM-5 in the presence of one water molecule attached to a dicopper site. The initial event is the formation of a hydroperoxo species bridged by the dicopper site via an H atom transfer from an attached water to the bound dioxygen. After the formation of the intermediate, the hydroperoxo O–O bond is completely cleaved to form radical oxygen containing intermediates, such as a Cu–O–Cu species bound by two OH groups (HO–Cu–O–Cu–OH), as well as a copper oxyl group containing intermediate (HO–Cu–OH–CuO). The radical oxygen containing intermediates can cleave a methane C–H bond in a homolytic fashion. Examining the barrier for the C–H bond activation obtained from DFT calculations, we found that the two types of intermediates have the power to more effectively cleave methane C–H bonds than the Cu–O–Cu intermediate that has been proposed to be formed in the absence of a water molecule. The current DFT findings propose that O2-bound Cu-ZSM-5 in the presence of one water molecule is a potential candidate for catalysts desired for methane to methanol conversion under mild conditions. Recently, techniques for controlling the number of water molecules near the active site of a ZSM-5 zeolite have been developed, and therefore the DFT findings should stimulate experimental efforts for constructing catalysts for direct methane hydroxylation.
A platinum diiodide complex with 9-pentafluorophenyl-9-arsafluorene formed a porous molecular crystal (PMC) or a non-porous molecular crystal (n-PMC), depending on the recrystallization solvents. ...Vapor exposure can cause reversible crystal-to-crystal transition between the PMC and the n-PMC. The PMC exhibits open-close switching of porosity as well as on-off switching of luminescence.
Fluorinated porous molecular crystals (PMCs) were fabricated from platinum(
ii
) dihalide complexes with 9-pentafluorophenyl-9-arsafluorene. The diiodide complex formed a PMC exhibiting open-close switching of porosity as well as on-off switching of luminescence.
Density functional theory (DFT) calculations were employed to investigate the energetics of carbon dioxide migration within hydrated or anhydrous graphene oxides (GOs). When anhydrous GO structures ...contain a carbon dioxide molecule, the carbon dioxide interacts repulsively with the GO layers to increase the interlayer spacing. The repulsive electrostatic interactions are reduced by the insertion of water molecules into CO2-containing GO structures due to the occurrence of attractive water-layer interactions through hydrogen bonding. Consequently, the interlayer spacings in CO2-containing hydrated structures are shortened compared with those in the anhydrous structures. The results indicate that the intercalated water molecules have the ability to connect the GO layers in the presence of carbon dioxide. Furthermore, the DFT calculations indicated that the GO interlayer spacings, which are influenced by the intercalation of water molecules, control carbon dioxide migration within the GO layers. The importance of the interlayer spacings on the migration of carbon dioxide arises from the occurrence of repulsive interactions between CO2 and oxygen-containing groups attached on the graphene sheets. When the GO interlayer spacings are short due to the presence of intercalated water molecules, the repulsive interactions between carbon dioxide and the GO layers are strong enough to prevent CO2 from migrating from its original position. Such repulsive interactions do not occur during the migration of CO2 within anhydrous GO structures because of the relatively longer interlayer spacing. Accordingly, CO2 migrates within anhydrous GO with a less significant barrier, indicating that carbon dioxide molecules are easily released from the GO.
Dibenzoarsacrowns have been synthesized as a novel class of heteroatom-fused crown ethers. The dibenzoarsacrowns can size-selectively capture alkali metal cations, and the arsenic atoms ...chemoselectively coordinated to gold(
i
) chloride (AuCl) due to the soft Lewis acid-base interaction. It is notable that the AuCl complex of 21-dibenzoarsacrown-7 further encapsulated Na
+
with the enhanced association constant from bare 21-dibenzoarsacrown-7. The positive allosteric effect was studied computationally.
A series of dibenzoarsacrowns were synthesized through a practical protocol. As and O preferentially coordinated to soft and hard cations, respectively. Positive allosteric effect was observed when coordinated to Au and Na cations.
