Diboryne Nanostructures Stabilized by Multitopic N-Heterocyclic

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

pubs.acs.org/IC

Diboryne Nanostructures Stabilized by Multitopic N‑Heterocyclic Carbenes: A Computational Study Felipe Fantuzzi, Caroline B. Coutinho, Ricardo R. Oliveira, and Marco Antonio Chaer Nascimento* Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-909, Brazil S Supporting Information *

ABSTRACT: Different families of nanomaterials produced from the stabilization of diboryne (BB) units by multitopic N-heterocyclic carbenes (NHCs), such as nanowires, nanorings, and nanotents, were studied by computational methods. Density functional theory calculations with and without periodic boundary conditions were applied to estimate the dependence of the electronic and thermochemical properties of different diboryne macromolecules with respect to the nature of the bridging ligand. Our results show that all diboryne nanostructures studied herein are viable candidates for synthesis. The Janus-type multitopic naphthobis(imidazolylidene) (5), anthrobis(imidazolylidene) (10), and pyracenetetrakis(imidazolylidene) (16) compounds are the best candidates for generating diboryne nanowires. A path to covalent organic frameworks, nanocages, and nanotubes from the optimized diboryne nanostructures is also described. Rather than just scientific curiosity, diboryne nanostructures emerge as interesting targets for the synthesis of main-group nanomaterials.

■

prepared by Zhou et al. in a low-temperature matrix.16 The results suggested that both systems present a BB bond, in which all valence electrons of the boron atoms are being used to make this peculiar bonding. Inspired by the theoretical predictions, Braunschweig et al. developed a route to synthesize the first ambient-temperature stable L:B2:L diboryne compound.17 The strategy adopted by the authors involved the reduction of a molecule with a preformed B−B bond. A total of 2 equiv of an NHC ligand was added to a B2Br4 molecule, which was then reduced to NHC: (Br)BB(Br):NHC or NHC:BB:NHC with either 2 or 4 equiv of a tetrahydrofuran solution of sodium naphthalenide, [Na(C10H8)]. In further studies, the authors replaced the NHC by a CAAC and showed that the nature of the ligand could impart a cumulene-like character to the C−B2−C moiety.18 Concerning the reactivity of the NHC-stabilized diboryne, it was found that it could perform multielectron reductions, being able to reductively link up to four CO molecules to form a bis(boralactone)19 and five chalcogens to form sulfur- and selenium-bridged cyclic compounds.20 A highly strained B2Te ring cation was also found for the reaction of diboryne with 1,2diphenylditelluride.21 These results, together with theoretical and NMR analyses, give support to the triple character of the B−B bond in diboryne.22,23 Although the vast majority of known NHCs are monodentate ligands, a number of multitopic NHCs has recently been synthesized. In terms of coordination with Lewis acidic species, these multidentate molecules can act as chelating,

INTRODUCTION The chemistry of low-valent main-group elements has been experiencing an extraordinary active period in the past decade. This revolution is based on the application of N-heterocyclic carbenes (NHCs) to stabilize highly reactive main-group species, previously unreachable from the synthetic point of view.1−4 The major concept behind this new chemistry is that these ligands are capable of making donor−acceptor bonds, acting as kinetically stable and bystander Lewis bases. It was the pioneer work of Robinson and co-workers that paved the way for the use of NHCs in this type of approach. The authors reported, as early as 1995 and 1997, the synthesis and molecular structure of cyclogallenes5 and digallyne,6 exotic gallium molecules stabilized by sterically demanding mterphenyl ligands. Around a decade later, Bertrand showed that P4 could aggregate into a NHC:P12:NHC compound7 or stay as a tetramer if a cyclic (alkyl)(amine)carbene (CAAC) is used as the ligand.8 Robinson reported the synthesis of a L:SiCl4 adduct, which could be reduced by KC8 to form a disilene L:Si2:L compound.9 Using a stronger dimagnesium(I) reducing agent, Jones, Frenking, and co-workers were able to synthesize the L:Ge2:L10 and L:Sn2:L analogues.11 The lightest homologue of the group, L:C2:L, was theoretically predicted by Dutton and Wilson12 and synthesized independently by Roesky et al.13 and Bertrand et al.14 using CAAC ligands. In 2011, Frenking and co-workers predicted that L:E2:L (E = B−In), analogues of the NHC-stabilized disilene species, could also be formed.15 However, while for E = Al−In a typical antiperiplanar arrangement of the ligands was found, a linear structure with a very short B−B distance (1.47 Å) was obtained for L:B2:L. A related OC:B2:CO molecule had earlier been © XXXX American Chemical Society

Received: January 12, 2018

A

DOI: 10.1021/acs.inorgchem.8b00089 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 1. NHC ligands studied herein. The IY abbreviation stands for imidazolylidene. Throughout this work, the ligands 2 and 3 are also mentioned as bis(IY) and :BIY:, respectively.

pincer, tripodal, or bridging ligands.24−35 Several multitopic NHCs ranging up to four carbenes have been theoretically proposed based on Clar’s aromatic sextet theory.26 Key structural properties for the generation of stable multitopic architectures were identified, which could allow the design of new topologies for NHC-based complexes and covalent frameworks. In a recent work developed by our group,36 we have shown that 1D diboryne nanowires of the type (:L:B2)n:L: could be formed by using the Janus-type benzobis(imidazolylidene) [:BIY:, 3], a known multitopic NHC,37,38 as the ligand. Herein, we apply density functional theory (DFT) calculations with and without periodic boundary conditions (PBCs) to estimate the dependence of the electronic and thermochemical properties of diboryne nanowires on the nature of the multitopic NHC and to explore the structural diversity of diboryne nanostructures, such as nanorings and nanotents. Finally, the generation of covalent organic frameworks (COFs), nanocages, and nanotubes from the optimized diboryne structures is discussed. The L ligands comprise the NHC species shown in Figure 1. The fusion of two imidazolylidene (IY, 1) rings at the C−C bond leads to bis(imidazolylidene) [bis(IY), 2], the simplest multitopic NHC generated by structure 1. Although 2 has not been reported to date, the fully hydrogenated analogue of 2, as well as its bis(carbene)iridium complex, were recently synthesized and characterized by Peris and co-workers.39 Structure 1 can also be fused with benzenoid moieties, and this process could lead to a vast diversity of multiple-ring multitopic carbenes. Because 1 presents six π electrons, such as

the benzenoid rings, the resulting multitopic carbenes could be classified as analogues to Clar’s benzenoid aromatic hydrocarbons.26 The simplest benzenoid-fused bis(imidazolylidene)s are structures 3 and 4, in which a benzene ring is the spacer between two NHC rings. The Janus-type :BIY: (3) was synthesized by Bielawski et al.37,38 and presents the NHC rings oppositely connected to the benzo group in a linear fashion, leading to an anthracene analogue. On the other hand, in structure 4, the rings are bent, and the resulting multitopic carbene could be compared to phenanthrene. Other linear and bent bis(NHCs) analogous to fused benzenoids were also studied, such as structures 5−11. The ligands 5−9 are different isomers analogous to the C18H12 system, namely tetracene (5), benz[a]anthracene (6), benzo[c]phenanthrene (7), chrysene (8), and triphenylene (9). In turn, structures 10 and 11 are analogous to the C22H14 system, in which 10 is related to pentacene, and 11 is the bis(NHC) akin to dibenzo[a,h]anthracene. In the case of polycyclic benzenoids, it is known that the bent structures are more stable than the straight ones, an effect usually attributed to a more efficient bonding in the π-electron system of the kinked molecules.40 However, for the multitopic NHC analogues, the trend is the opposite.26 The ligand 12 is composed of two NHCs joined together by a pair of formal single bonds, analogous to the strained biphenylene molecule. Structures 13 and 14 are respectively the Janus-type quinobis(imidazolylidene) and oxanthrobis(imidazolylidene) molecules, recently synthesized by Bielawski B


Article

Inorganic Chemistry

Figure 2. Selected :L:B2:L:-optimized structures.

et al.25,41 The pyracenebis(imidazolylidene) compound 15, on the other hand, was synthesized by Peris and co-workers in 2012.42 Finally, two tetrakis(NHC) ligands were also included in this work. Structure 16 is a multitopic NHC generated from the annulation of IY rings into the aromatic terminals of 15. On the other hand, structure 17 is a tetraannulated derivative of phthalocyanine, a macrocyclic compound.

■

Using PBCs, DFT calculations were performed with the PBE functional for some representative species. Geometry optimizations without any restrictions were performed for the diboryne nanowires 3, 5, 12, 14, and 16, for the nanorings 18 and 19, and for structures 26− 28. The energy cutoff of the plane-wave basis set was set to 400 eV with the projector-augmented-wave approximation,43 a value that is recommended by Vienna ab initio simulation package (VASP) for main-group elements. Integration over the first Brillouin zone was done using the Monkhorst−Pack method44 with a 3 × 1 × 1 k-point mesh for all nanowires, 1 × 1 × 1 for the structures 27 and 28, and at the Γ point for 18, 19, and 26. These values were chosen to be as dense as possible because of the large dimensions of the systems studied herein. All non-PBC calculations were performed using Jaguar 7.9,45 while the PBC calculations were performed with the VASP 5.3 program.46 Ligands 16 and 17 have nonequivalent carbene units, which could give rise to different nanowires depending on which carbene is being used for interaction with the diboryne moiety. Eventually, the synthesis of materials based on these multitopic NHCs could lead to the formation of undesired byproducts or isomers. In spite of such problems, we decided to proceed with the calculations related to these ligands, to verify how the nanowires based on such tetrakis(NHC) ligands would compare in terms of energy and structure with the bis(NHC)s 2−15. For the materials obtained with such ligands, only the isomers with the lowest energies are described herein. Finally, it is important to mention that the steric hindrance provided by the pendant groups at the NHC nitrogen atoms plays an important role in stabilization of the diboryne core. In fact, alkylated aryls, such as diisopropylphenyl and mesityl, are the smallest groups that are routinely used as substituents in NHCs. However, because of computational limitations, in all calculations, these groups are replaced by methyl groups for ligands 1−15 and by hydrogen atoms in 16 and 17. This means that the energies obtained in this work do not account for such stabilizing effects and are underestimated. Such values should be used, therefore, as a lower level for the final stabilization energies of the compounds.

COMPUTATIONAL DETAILS

Geometry optimizations and Hessian calculations at the DFT level without PBCs were performed for several (L:B2)n:L nanostructures, such as nanowires, nanorings, and nanotents. The nanowires and nanotents consist of systems of up to 120 atoms, and calculations were performed using B3LYP as the DFT functional and the Pople triple-ζ quality basis set with polarization functions, 6-311G**. The choice of the functional was made after the results of preliminary tests on the performance of different DFT functionals with respect to the energetic and structural properties, which are available in the Supporting Information (SI) file. On the other hand, the nanorings were optimized at the B3LYP level using the Pople double-ζ basis set with polarization functions, 6-31G**. The optimized systems were also used as building blocks for designing supramolecular structures, such as nanocages, nanotubes, and COFs. The propensity of NHCs to form diboryne nanowires was evaluated by calculating the enthalpy (H) at 298 K of two isodesmic reactions: Reaction 1 (ΔH1)

IY:B2:IY + 2:L: → :L:B2:L: + 2:IY

(1)

Reaction 2 (ΔH2)

:BIY:(B2:BIY:)2 + 3:L: → :L:(B2:L:)2 + 3:BIY:

(2)

where reaction (1) gives the tendency of the :L: ligand to form a stable :L:B2:L: system in comparison to the IY:B2:IY compound, as synthesized by Braunschweig et al.17 On the other hand, reaction (2) estimates the propensity of the L ligand to form a :L:(B2:L:)2 nanowire, relative to 3 [:BIY:(B2:BIY:)2] as a reference stable system. Because :L:(B 2 :L:) 2 compounds have not been obtained experimentally to the present date, we have chosen the system in which L = :BIY: (3) is the reference state for reaction (2). This choice is based on the fact that this is the only system of the :L:(B2:L:)2 type already proposed before in the literature.36 The Gibbs free energies of both reactions (ΔG1 and ΔG2), which gives the spontaneity of forming the nanowire by isodesmic processes, were also computed. A similar approach to the calculation of diboryne nanotents was used and will be discussed in detail further on.

■

RESULTS AND DISCUSSION Diboryne Nanowires. Figure 2 shows some optimized :L:B2:L: structures obtained in this work. In all cases, a geometry corresponding to the minimum energy containing a diboryne unit stabilized by two bis(NHC)s was found. Moreover, the main geometrical features of the triply bonded boron dimers described herein are in agreement with previous studies of analogous systems.17,36 The B−B bond distances, for example, range from 1.454 to 1.467 Å (see Table 1), which C


Article

Inorganic Chemistry

Table 1. Enthalpies (HL and HLBBL, hartree), B−B Internuclear Distances (RB−B, Å), Enthalpies of Reaction (ΔH1 and ΔH2, kcal mol−1), and Gibbs Free Energies of Reaction (ΔG1 and ΔG2, kcal mol−1) for the Formation of Diboryne Nanowires Stabilized by NHC Bridging Ligands at 298 K ligand

HL

HLBBL

RB−Ba

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16d 17

−304.7412 −530.8777 −684.5519 −684.5434 −838.1777 −838.1760 −838.1551 −838.1733 −838.1586 −991.7986 −991.7966 −606.9623 −833.8316 −1064.8435 −990.5352 −1128.5508 −2572.9576

−659.1849 −1111.4588 −1418.8209 −1418.7990 −1726.0779 −1726.0690 −1726.0283 −1726.0597 −1726.0253 −2033.3237 −2033.3052 −1263.6379 −1717.3725 −2179.4029 −2030.7787 −2306.8285 −5195.6343

1.454 1.454 1.458 1.455 1.462 1.458 1.461 1.456 1.456 1.463 1.455 1.460 1.460 1.458 1.455 1.467 1.460

RB−B(PBCs)

1.468 1.469

1.470, 1.471 1.467, 1.469 1.471, 1.472

ΔH1b

ΔH2b

ΔG1c

ΔG2c

0.0 −0.5 −9.1 −6.1 −12.5 −9.1 −9.8 −6.6 −3.5 −15.0 −5.9 −6.7 −4.3 −8.4 −3.6 −15.3 −10.4

12.1 0.0 5.0 −7.7 −2.4 −3.3 3.2 8.2 −12.8 4.4 0.7 7.5 −0.8 7.1 −13.9

0.0 3.4 1.1 4.7 −0.9 2.4 −0.2 4.1 5.8 −2.3 5.3 −1.3 5.3 3.6 −5.9 −5.4 2.1

13.8 0.0 8.3 −1.9 7.2 2.4 11.9 15.9 −1.1 13.8 5.2 12.5 10.2 −1.7 −7.3

RB−B is related to the L:B2:L structures without PBCs. bReaction (1): IY:B2:IY + 2:L: → :L:B2:L: + 2:IY. cReaction (2): :BIY:(B2:BIY:)2 + 3:L: → :L:(B2:L:)2 + 3:BIY:. dCoordination through the naphthalene units.

a

Table 1 also shows a comparison of the electronic and thermochemical properties of diboryne nanowires with regard to the nature of the multitopic NHCs, by making use of the isodesmic reactions described in reactions (1) and (2). The results suggest that all multitopic NHCs described in this work should form stable :L:B2:L: systems. Ligands 5, 10, 16, and 17 are the ones for which ΔH1 is more negative than that for 1 by more than 10 kcal mol−1. Among the studied molecules, the most stable :L:B2:L: species should be formed by the pyracenetetrakis ligand 16. Upon a comparison of the isomeric ligands 5−9, it is possible to see that the all-linear isomer 5, analogous to tetracene, is both the most stable L species and the one for which ΔH1 and ΔG1 are the most negative. In general, among the different isomers of a certain NHC group, the more stable the isomer is, the more stable the species :L:B2:L: will be. The exception among the C18H12 analogous NHCs is 7. The formation of the NHC-stabilized diboryne somewhat compensates for the strain energy of 7 due to steric repulsion of the IY rings. This extrastabilization is ultimately responsible for making the isomer a potential target for the synthesis of NHC-stabilized diborynes. The ΔH1 and ΔG1 values can also be evaluated with respect to the size of the linear benzenoid chain. By a comparison of 2, 3, 5, and 10, it is possible to see that the stability increases with the size of the chain. Moreover, the energy difference along the series is not constant. The results indicate that a plateau of stability should be reached for a certain number of rings. The influence of the oxygen functional groups is another aspect to be analyzed. A comparison of 3 and 13 indicates that replacement of the benzenoid ring by a benzoquinone group does not contribute to an increase of the stability of the diboryne species, as well as substitution of a benzenoid ring (10) by a 1,4-dioxin group (14). In contrast to ΔH1, most of the ΔH2 values are positive, which illustrates that oligomeric :L:(B2:L:)n units are inherently more difficult to produce than their basic units. In fact, only six ligands (5, 6, 7, 10, 14, and 16) have negative ΔH2 values, whereas four (5, 10, 15, and 16) have negative ΔG2 values. By a

suggests that the B2 dimers are connected by triple bonds. A dihedral angle of ∼90° between the NHC ligands, a common trend of these NHC sandwich molecules, is also found for all structures. Finally, a linear CBBC skeleton between the carbene centers and the B2 unit was verified for the entire set of systems. The results indicate that multitopic NHCs are capable of forming stable diboryne structures. Figure 3 shows some optimized (:L:B2)2:L: structures obtained in this work. In all cases, a minimum-energy geometry

Figure 3. Selected (:L:B2)2:L:-optimized structures.

was found. Moreover, regardless of the multitopic carbene used, a linear CBBC skeleton is found for all diboryne centers. The results indicate that bis(NHC)-stabilized nanowires, composed of multiple units of a monomeric :L:B2:L: moiety, could be formed. D


Article

Inorganic Chemistry

Figure 4. Some examples of NHC-stabilized diboryne nanorings.

comparison of ΔH1 and ΔH2, it is possible to see that the energy trend among the ligands is practically the same for both reactions. The ligand 2, for instance, has the least negative ΔH1 value (−0.5 kcal mol−1) and the highest ΔH2 (12.1 kcal mol−1). Analogously, ligand 16 has the highest negative ΔH1 (−15.3 kcal mol−1) and ΔH2 (−13.9 kcal mol−1) values. By including entropic factors, this trend is less evident. Nevertheless, the ΔG values suggest that ligands 5, 10, and 16 are the most prominent among the ligands to form stable diboryne nanowires. Concerning PBC calculations, in all cases optimized 1D nanowires were obtained. Although the B−B distances with PBCs are greater than the respective non-PCB results by ∼0.01 Å, this difference is small enough to still suggest NHCstabilized triply bonded boron dimers. The fact that the periodic structures did not collapse during optimization is more evidence that diboryne nanowires are experimentally achievable. Diboryne Nanorings. The formation of cyclic biopolymers, such as protein,47 DNA48 and RNA49 nanorings, is among the most important self-assembly processes. This type of complex organization, however, is not just present in biomaterials. Martel and co-workers have shown that singlewalled carbon nanotubes can be tailored to generate nanoring structures.50 In addition, the spontaneous growth of polarization-induced nanorings has been obtained for zinc oxide by the cyclization of single-crystal nanobelts.51 Rectangular nanorings have also been observed through the oriented attachment of PbSe nanocrystals.52 Other widely studied macrocycles are hydrocarbon nanorings, such as [n]paraphenyleneacetylene (or [n]CPPA),53 and porphyrin-like materials.54−56 The topological characteristics of multitopic NHC ligands 16 and 17 could be used to generate stable diboryne nanorings. Figure 4 shows some of the nanorings that could be formed from the interaction of 16 with B2 units. Compound 18 is a nanoring composed of six diboryne units, [(NHC)6(B2)6], in a chairlike conformation and Ci symmetry. As in the previous cases, a linear CBBC skeleton was observed. The B−B bond

distances are in the around 1.465 and 1.475 Å, slightly greater than the range values of the :L:B2:L: molecules. Adjacent NHCs present a dihedral angle of 90°, like that for the diboryne nanowires. The 19 nanoring is composed of eight NHCstabilized diboryne units, [(NHC)8(B2)8]. Because of the similarity between the geometrical properties of both classes of 1D nanoclusters, it is reasonable to consider the diboryne nanorings as potential synthetic targets in the condensed phase. The nanorings 18 and 19 were also obtained at the PBC level of calculation. The B−B bond distances are 1.476, 1.477, and 1.481 Å for 18 and 1.477 and 1.484 Å for 19. As in the case of nanowires, the bond distances are also slightly greater than the non-PBC B3LYP results but still compatible with BB bond internuclear distances. The interaction of two 19 structures could give rise to compounds 20 and 21. Unfortunately, because of size limitations, it was not possible to properly optimize both structures in the levels of calculation used in this work. However, because they are formed by optimized and stable constituents, it is still possible to infer some qualitative properties of such species. In compound 20, two rectangular [(NHC)8(B2)8] structures analogous to 19 are connected by two central NHCs in a ladder-type fashion. In this supramolecular architecture, the 19-like moieties are connected by an 18-like structure. The system, therefore, represents a case in which both 18 and 19 nanorings are functioning as building blocks for the construction of complex macrostructures. Compound 21 is the [2]catenane isomer of 20, composed of two interlocked 19 structures. Catenanes have been attracting the chemistry community for a long time57 because of their structural, topological, and electronic properties.58 Even a single catenane in a polymer chain can drastically affect the solid-state properties of a macromolecular compound.59 Therefore, the presence of such a macrocycle in a polymeric matrix could impart singular electronic, optical, and mechanical properties to a diboryne nanomaterial. Diboryne Nanotents. Concave nanostructures, or nanotents, represent another important class of supramolecular moieties, especially for host−guest chemistry. An efficient E


Article

Inorganic Chemistry

Figure 5. Enthalpies of reaction following reactions (3) and (4) for diboryne nanotents, (CNC)n (n = 4−10).

separation and purification of C60+ from fullerite, for example, was observed after treatment with host concave molecules, such as calix[n]arenes, calix[4]resorcinarenes, and cyclotriveratrylenes.53 The implantation of argon atoms beneath single layers of hexagonal boron nitride and graphene on a substrate has been successfully achieved, leading to stable nanotents.60,61 Inorganic alloy nanotents, such as PtPd and RhZn, have also been produced by the usage of doping agents to induce structural transformations during the crystal growth of noblemetal nanoparticles.62,63 These nanotents could ultimately lead to both reactive and selective organic transformations, such as the hydrogenation of phthalimides.63 The diboryne nanotents described in this work were designed as follows. Initially, different multitopic fused NHC heads with (CNC)n stoichiometries (n = 4−10) were optimized. Then, different nanotents were generated by linking B2:(NHC) tails to each one of the carbene units. In all cases, the NHC used in the tail was the ligand 1. The subsequent notation was used to label the nanotent (CNC)n[B2(NHC)]m, in which n indicates the number of carbene moieties in the head and m indicates the number of tails linked to them. A measure of the preference for the head−tail linkage is given by the enthalpy difference of the following reaction:

(CNC)n [B2(NHC)]m − 1 + (NHC)2 B2 → (CNC)n [B2(NHC)]m + NHC

(3)

in which 1 ≤ m ≤ n. It is important to mention that the (CNC)4 head did not converge as a tetracarbene cluster. On the other hand, complete hydrogenation of the four carbene centers has generated a minimum structure with a (CNCH2)4 stoichiometry (see Figure 5). In this case, the following reaction was used to verify the preference for the formation of the nanotent: (CNC)4 (H 2)5 − m [B2(NHC)]m − 1 + (NHC)2 B2 → (CNC)4 (H 2)4 − m [B2(NHC)]m + (NHC)H 2

(4)

in which 1 ≤ m ≤ 4. The number of π electrons composing the base of the multitopic NHC influences the geometric and thermodynamic characteristics of the system. While the (CNC)4 head presents four π electrons in a nonplanar base, (CNC)6 is composed of a planar hexagon ring base with equivalent C−C bonds, six π electrons, and C6v symmetry, properties that are usually related to aromaticity. However, no calculation concerning the chemical structure of such a system, based on molecular orbitals or modern valence bonds, has been F


Article

Inorganic Chemistry

ment.71 Encapsulation of a native protein into a giant welldefined self-assembled functional nanocage made by synthetic organic ligands and palladium(II) metal ions has also been achieved in the last years.72 In turn, single-walled carbon nanotubes can be produced by rolling a graphene sheet around itself along different directions.73 As in the case of nanocages, different binary compounds have also been studied as the basic unit of a tubular material, such as boron nitride,74 berylium oxide,75 lithium fluoride,76 and silicon carbide.70 Potential applications of such kinds of materials range from gas sensors and hydrogen storage to microelectronics, solar cell components, and tissue engineering. COFs are porous crystalline organic polymers, whose monomeric units are kept together by strong covalent bonds. These structures can present one (1D), two (2D), or three (3D) dimensions. In 2005, Yaghi and co-workers developed the first 2D COFs from dehydration reactions of the 1,4benzeneboronic acid with itself (COF-1) or with hexahydroxytriphenylene (COF-5).77 The first synthesis of 3D COFs is also attributed to Yaghi and co-workers, developed in 2007.78 The main advantages of COFs in comparison to inorganic zeolites and metal−organic frameworks are low density, high surface area, controlled porous size, and a versatile combination of building blocks, giving rise to different materials.79 Figure 7 shows examples of diborynes nanocages, nanotubes, and COFs that could be formed from the junction of the

made so far. From the authors’ point of view, this is another case in which six monoelectronic eigenstates are interfering among themselves, leading ultimately to a six-center sixelectron π chemical bond, such as benzene.64,65 However, the chemical bonding of this fused NHC structure should be studied in more detail and will be the focus of a future work. Figure 5 shows the ΔH values for the production of nanotents according to reactions (3) and (4). For (CNCH2)4, it is possible to see that all head−tail linkages are endothermic, with ΔH values that range from 25 to 35 kcal mol −1. On the other hand, for all other cases, it was found that the formation of the nanotent is exothermic. For example, the formation of (CNC)6[B2(NHC)] from (CNC)6 and B2(NHC)2 is −35.9 kcal mol−1. As the number of B2(NHC) units attached to carbene atoms of the hexagon-base head increases, ΔH becomes less negative, leveling at −13.8 kcal mol−1 with the attachment of five units. In the case of (CNC)8, it was only possible to link from one to five B2(NHC) units. All attempts to obtain optimized nanotent structures with six or more units attached to (CNC)8 have failed, leading to stationary points with one or more imaginary frequencies whose values were significantly higher than the ones usually attributed to numerical errors.45 The ΔH values ranged from −40.6 to −12.5 kcal mol−1, similar to the range of values related to the formation of (CNC)10[B2(NHC)]m nanotents. For the decagon-base head, ΔH linearly increases from m = 1 to 6. After that, the addition of B2(NHC) groups does not significantly alter the ΔH values. The molecular structures of selected optimized nanotents can be visualized in Figure 6.

Figure 7. Some examples of diboryne nanomaterials constructed from structures 18 and 19.

Figure 6. Some examples of NHC-stabilized diboryne nanotents.

structures that were discussed in previous sections of this work. The structures were optimized at the PBE level using planewave basis set and, except for 26, PBCs. The nanocage 26 is made of two 18 nanorings. The B−B distances are in the range of 1.467−1.472 Å, and the estimated internal diameter is about 20 Å. In turn, the stacking of multiple units of the nanoring 19 along the axis perpendicular to the plane of the ring could produce the nanotube 27. The B−B bond profile of 27 is the same as that of 19. The estimated internal diameters are 27 and 28 Å for the lateral units and 35 Å for the diagonal section.

Diboryne Nanocages, Nanotubes, and COFs. Since the discovery of fullerene by Kroto and co-workers,66 the search for analogous cagelike structures has been the focus of intense research. Nanocages composed of binary compounds, such as boron nitride,67 zinc sulfide,68 zinc oxide69 and silicon carbide,70 have already been successfully described in the literature. Noble-metal nanocages, which possess hollow interiors and porous walls, were satisfactorily used in biomedical applications, such as cancer diagnosis and treatG


Article

Inorganic Chemistry Therefore, the spatial diffusion of ions and small molecules throughout the tube would be possible. Finally, structure 28 is an example of a optimized COF that could be formed from the 3D propagation of diboryne units stabilized by the ligand 16. As in the previous cases, a linear CBBC bonding motif is observed around the boron dimers throughout the whole structure. However, the B−B bond lengths are in the range of 1.508−1.553 Å, significantly higher than the typical BB bond length. This result suggests that 3D propagation of diboryne nanowires could impart a cumulenic profile to the walls of such boron-containing COFs. The estimated internal cage volume is about 23.5 nm3, which is large enough for molecule encapsulation, thus suggesting the viability of such material as a molecule storage system.

■

tests on the performance of different DFT with respect to energetic and structural as well as the energy and Cartesian of all optimized structures studied herein

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +55 (21) 3938 7563. Fax: +55 (21) 3938 7265. ORCID

Felipe Fantuzzi: 0000-0002-8200-8262 Ricardo R. Oliveira: 0000-0001-9472-3899 Marco Antonio Chaer Nascimento: 0000-0002-5655-0576

■

CONCLUSIONS In this work, periodic and nonperiodic DFT calculations were used to explore the molecular diversity of NHC-stabilized diboryne nanomaterials, such as nanowires, nanorings, nanotents, nanotubes, and nanocages. We have found that all families of diboryne materials studied herein are potential targets for experimental studies. For the nanowires, both PBC and non-PBC calculations indicate that in all cases the boron atoms are linked by triple bonds, and the structural properties of the monomer are maintained throughout the nanowire. The thermochemical results indicate that the naphthobis(imidazolylidene) (5), anthrobis(imidazolylidene) (10) and pyracenetetrakis(imidazolylidene) (16) ligands are the best candidates for generating stable diboryne nanowires. By a comparison of the different NHC isomers, it was shown that, in general, the more stable the isomer is, the more suitable it will be for generating diboryne nanowires. In terms of the size of the linear benzenoid chain, the tendency of generating nanowires increases with the size of the linear chain. On the other hand, the replacement of a benzene ring by benzoquinone or dioxin groups does not contribute to an increase in the stability of the nanowire. Nanorings are also viable candidates as promising diboryne materials, once cyclic nanomaterials containing six and eight diboryne units stabilized by multitopic NHCs were successfully characterized as minimum-energy structures. These macrocycles could be tailored to generate supramolecular structures, such as nanotubes, nanocages, and COFs with pore sizes of ∼30 Å. Diboryne concave nanostructures, or nanotents, were also investigated in this work. It is shown that, while all diboryne linkages on a (CNCH 2 ) 4 head are endothermic, the (CNCH2)6, (CNCH2)8, and (CNCH2)10 heads could give rise to stable NHC-stabilized diboryne nanotents. In summary, we suggest that diboryne nanomaterials are viable candidates for synthesis, with applications that could range from optoelectronics to molecular storage. The authors hope that this study will encourage experimentalists to synthesize novel nanomaterials based on NHC-stabilized diboryne units.

■

Preliminary functionals properties, coordinates (PDF)

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank CNPq, FAPERJ, CAPES, and INOMAT for financial support.

■

REFERENCES

(1) Wang, Y.; Robinson, G. H. N-Heterocyclic Carbene-Main-Group Chemistry: A Rapidly Evolving Field. Inorg. Chem. 2014, 53, 11815− 11832. (2) Braunschweig, H.; Dewhurst, R. D. Boron-Boron Multiple Bonding: From Charged to Neutral and Back Again. Organometallics 2014, 33, 6271−6277. (3) Frenking, G.; Hermann, M.; Andrada, D. M.; Holzmann, N. Donor-Acceptor Bonding in Novel Low-Coordinated Compounds of Boron and Group-14 Atoms C-Sn. Chem. Soc. Rev. 2016, 45, 1129− 1144. (4) Würtemberger-Pietsch, S.; Radius, U.; Marder, T. B. 25 Years of N-Heterocyclic Carbenes: Activation of Both Main-Group ElementElement Bonds and NHCs Themselves. Dalton Trans. 2016, 45, 5880−5895. (5) Li, X.-W.; Pennington, W. T.; Robinson, G. H. Metallic System with Aromatic Character. Synthesis and Molecular Structure of Na2[[(2,4,6-Me3C6H2)2C6H3]Ga]3 The First Cyclogallane. J. Am. Chem. Soc. 1995, 117, 7578−7579. (6) Su, J.; Li, X. W.; Crittendon, R. C.; Robinson, G. H. How Short is a -Ga⋮Ga- Triple Bond? Synthesis and Molecular Structure of Na2[Mes*2C6H3-Ga⋮Ga-C6H3Mes*2] (Mes* = 2,4,6-i-Pr3C6H2): The First Gallyne. J. Am. Chem. Soc. 1997, 119, 5471−5472. (7) Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G. NHC-Mediated Aggregation of P4: Isolation of a P12 Cluster. J. Am. Chem. Soc. 2007, 129, 14180−14181. (8) Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G. Carbene Activation of P4 and Subsequent Derivatization. Angew. Chem., Int. Ed. 2007, 46, 7052−7055. (9) Wang, Y.; Xie, Y.; Wei, P.; King, R. B.; Schaefer, H. F.; Schleyer, P. v. R.; Robinson, G. H. A Stable Silicon(0) Compound with a SiSi Double Bond. Science 2008, 321, 1069−1071. (10) Sidiropoulos, A.; Jones, C.; Stasch, A.; Klein, S.; Frenking, G. NHeterocyclic Carbene Stabilized Digermanium(0). Angew. Chem., Int. Ed. 2009, 48, 9701−9704. (11) Jones, C.; Sidiropoulos, A.; Holzmann, N.; Frenking, G.; Stasch, A. An N-Heterocyclic Carbene Adduct of Diatomic Tin,:SnSn: Chem. Commun. 2012, 48, 9855. (12) Dutton, J. L.; Wilson, D. J. D. Lewis Base Stabilized Dicarbon: Predictions from Theory. Angew. Chem., Int. Ed. 2012, 51, 1477−1480. (13) Li, Y.; Mondal, K. C.; Samuel, P. P.; Zhu, H.; Orben, C. M.; Panneerselvam, S.; Dittrich, B.; Schwederski, B.; Kaim, W.; Mondal, T.; Koley, D.; Roesky, H. W. C4 Cumulene and the Corresponding

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00089. H


Article

Inorganic Chemistry Air-Stable Radical Cation and Dication. Angew. Chem., Int. Ed. 2014, 53, 4168−4172. (14) Jin, L.; Melaimi, M.; Liu, L.; Bertrand, G. Singlet Carbenes as Mimics for Transition Metals: Synthesis of an Air Stable Organic Mixed Valence Compound [M2(C2)+; M = Cyclic(Alkyl)(Amino)Carbene]. Org. Chem. Front. 2014, 1, 351. (15) Holzmann, N.; Stasch, A.; Jones, C.; Frenking, G. Structures and Stabilities of Group 13 Adducts [(NHC)(EX3)] and [(NHC)2(E2Xn)] (EB to In; X = H, Cl; N = 4, 2, 0; NHCN-Heterocyclic Carbene) and the Search for Hydrogen Storage Systems: A Theoretical Study. Chem. - Eur. J. 2011, 17, 13517−13525. (16) Zhou, M.; Tsumori, N.; Andrews, L.; Xu, Q. Infrared Spectra of BCO, B(CO)2, and OCBBCO in Solid Argon. J. Phys. Chem. A 2003, 107, 2458−2463. (17) Braunschweig, H.; Dewhurst, R. D.; Hammond, K.; Mies, J.; Radacki, K.; Vargas, A. Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond. Science 2012, 336, 1420−1422. (18) Böhnke, J.; Braunschweig, H.; Ewing, W. C.; Hörl, C.; Kramer, T.; Krummenacher, I.; Mies, J.; Vargas, A. Diborabutatriene: An Electron-Deficient Cumulene. Angew. Chem., Int. Ed. 2014, 53, 9082− 9085. (19) Braunschweig, H.; Dellermann, T.; Dewhurst, R. D.; Ewing, W. C.; Hammond, K.; Jimenez-Halla, J. O. C.; Kramer, T.; Krummenacher, I.; Mies, J.; Phukan, A. K.; Vargas, A. Metal-Free Binding and Coupling of Carbon Monoxide at a Boron-Boron Triple Bond. Nat. Chem. 2013, 5, 1025−1028. (20) Braunschweig, H.; Dellermann, T.; Ewing, W. C.; Kramer, T.; Schneider, C.; Ullrich, S. Reductive Insertion of Elemental Chalcogens into Boron-Boron Multiple Bonds. Angew. Chem., Int. Ed. 2015, 54, 10271−10275. (21) Braunschweig, H.; Constantinidis, P.; Dellermann, T.; Ewing, W. C.; Fischer, I.; Hess, M.; Knight, F. R.; Rempel, A.; Schneider, C.; Ullrich, S.; Vargas, A.; Woollins, J. D. Highly Strained Heterocycles Constructed from Boron-Boron Multiple Bonds and Heavy Chalcogens. Angew. Chem., Int. Ed. 2016, 55, 5606−5609. (22) Holzmann, N.; Hermann, M.; Frenking, G. The Boron-Boron Triple Bond in NHC→B≡B←NHC. Chem. Sci. 2015, 6, 4089−4094. (23) Böhnke, J.; Braunschweig, H.; Constantinidis, P.; Dellermann, T.; Ewing, W. C.; Fischer, I.; Hammond, K.; Hupp, F.; Mies, J.; Schmitt, H. C.; Vargas, A. Experimental Assessment of the Strengths of B-B Triple Bonds. J. Am. Chem. Soc. 2015, 137, 1766−1769. (24) Jahnke, M. C.; Ekkehardt Hahn, F. In N-Heterocyclic Carbenes: From Laboratory Curiosity to Efficient Synthetic Tools; Diez-Gonzalez, S., Ed.; Royal Society of Chemistry: Cambridge, U.K., 2011; Chapter 1, pp 1−41. (25) Neilson, B. M.; Tennyson, A. G.; Bielawski, C. W. Advances in bis(N-Heterocyclic Carbene) Chemistry: New Classes of Structurally Dynamic Materials. J. Phys. Org. Chem. 2012, 25, 531−543. (26) Suresh, C. H.; Ajitha, M. J. DFT Prediction of Multitopic NHeterocyclic Carbenes using Clar’s Aromatic Sextet Theory. J. Org. Chem. 2013, 78, 3918−3924. (27) Wang, Y.-T.; Chang, M.-T.; Lee, G.-H.; Peng, S.-M.; Chiu, C.W. Planar tris-N-Heterocyclic Carbenes. Chem. Commun. 2013, 49, 7258. (28) Schick, S.; Pape, T.; Hahn, F. E. Coordination Chemistry of Bidentate bis(NHC) Ligands with Two Different NHC Donors. Organometallics 2014, 33, 4035−4041. (29) Tapu, D.; McCarty, Z.; McMillen, C. A Stable Janus bis(maloNHC) and its Zwitterionic Coinage Metal Complexes. Chem. Commun. 2014, 50, 4725−4728. (30) Deck, E.; Reiter, K.; Klopper, W.; Breher, F. A Dinuclear Gold(I) Bis(Carbene) Complex Based on a Ditopic Cyclic (Aryl)(Amino)Carbene Framework. Z. Anorg. Allg. Chem. 2016, 642, 1320− 1328. (31) Bertermann, R.; Braunschweig, H.; Celik, M. A.; Dellermann, T.; Kelch, H. Cyclisation of Biscarbenoids - a Novel Mode of Cyclobutadiene Stabilisation. Chem. Commun. 2016, 52, 13249− 13252.

(32) González-Sebastián, L.; Chaplin, A. B. Synthesis and Complexes of Imidazolinylidene-Based CCC Pincer Ligands. Inorg. Chim. Acta 2017, 460, 22. (33) Hickey, A. K.; Lee, W.-T.; Chen, C.-H.; Pink, M.; Smith, J. M. A Bidentate Carbene Ligand Stabilizes a Low-Coordinate Iron(0) Carbonyl Complex. Organometallics 2016, 35, 3069−3073. (34) Martinez, G. E.; Ocampo, C.; Park, Y. J.; Fout, A. R. Accessing Pincer bis(Carbene) Ni(IV) Complexes from Ni(II) via Halogen and Halogen Surrogates. J. Am. Chem. Soc. 2016, 138, 4290−4293. (35) Iwasaki, H.; Yamada, Y.; Ishikawa, R.; Koga, Y.; Matsubara, K. Isolation and Structures of 1,2,3-Triazole-Derived Mesoionic Biscarbenes with Bulky Aromatic Groups. Eur. J. Org. Chem. 2016, 2016, 1651−1654. (36) Fantuzzi, F.; Chaer Nascimento, M. A. Prediction of BoronBoron Triple-Bond Polymers Stabilized by Janus-Type bis(NHeterocyclic) Carbenes. Chem. - Eur. J. 2015, 21, 7814−7819. (37) Khramov, D. M.; Boydston, A. J.; Bielawski, C. W. Synthesis and Study of Janus bis(Carbene)s and their Transition-Metal Complexes. Angew. Chem., Int. Ed. 2006, 45, 6186−6189. (38) Boydston, A. J.; Bielawski, C. W. Bis(Imidazolylidene)s as Modular Building Blocks for Monomeric and Macromolecular Organometallic Materials. Dalton Trans. 2006, 4073−4077. (39) Prades, A.; Poyatos, M.; Mata, J. A.; Peris, E. Double CH Bond Activation of C(sp3)H2 Groups for the Preparation of Complexes with Back-to-Back Bisimidazolinylidenes. Angew. Chem., Int. Ed. 2011, 50, 7666−7669. (40) Poater, J.; Visser, R.; Solà, M.; Bickelhaupt, F. M. Polycyclic Benzenoids: Why Kinked is More Stable than Straight. J. Org. Chem. 2007, 72, 1134−1142. (41) Tennyson, A. G.; Ono, R. J.; Hudnall, T. W.; Khramov, D. M.; Er, J. A. V.; Kamplain, J. W.; Lynch, V. M.; Sessler, J. L.; Bielawski, C. W. Quinobis(Imidazolylidene): Synthesis and Study of an ElectronConfigurable bis(N-Heterocyclic Carbene) and its Bimetallic Complexes. Chem. - Eur. J. 2010, 16, 304−315. (42) Prades, A.; Peris, E.; Alcarazo, M. Pyracenebis(Imidazolylidene): A New Janus-Type Biscarbene and Its Coordination to Rhodium and Iridium. Organometallics 2012, 31, 4623−4626. (43) Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953. (44) Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, 5188. (45) Bochevarov, A. D.; Harder, E.; Hughes, T. F.; Greenwood, J. R.; Braden, D. A.; Philipp, D. M.; Rinaldo, D.; Halls, M. D.; Zhang, J.; Friesner, R. A. Jaguar: A High-Performance Quantum Chemistry Software Program with Strengths in Life and Materials Sciences. Int. J. Quantum Chem. 2013, 113, 2110−2142. (46) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations using a Plane-Wave Basis Set. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169−11186. (47) Bai, Y.; Luo, Q.; Zhang, W.; Miao, L.; Xu, J.; Li, H.; Liu, J. Highly Ordered Protein Nanorings Designed by Accurate Control of Glutathione S-Transferase Self-Assembly. J. Am. Chem. Soc. 2013, 135, 10966−10969. (48) Roller, E.-M.; Khorashad, L. K.; Fedoruk, M.; Schreiber, R.; Govorov, A. O.; Liedl, T. DNA-Assembled Nanoparticle Rings Exhibit Electric and Magnetic Resonances at Visible Frequencies. Nano Lett. 2015, 15, 1368−1373. (49) Yingling, Y. G.; Shapiro, B. A. Computational Design of an RNA Hexagonal Nanoring and an RNA Nanotube. Nano Lett. 2007, 7, 2328−2334. (50) Martel, R.; Shea, H. R.; Avouris, P. Rings of Single-Walled Carbon Nanotubes. Nature 1999, 398, 299−299. (51) Kong, X. Y.; Wang, Z. L. Spontaneous Polarization-Induced Nanohelixes, Nanosprings, and Nanorings of Piezoelectric Nanobelts. Nano Lett. 2003, 3, 1625−1631. (52) Cho, K.-S.; Talapin, D. V.; Gaschler, W.; Murray, C. B. Designing PbSe Nanowires and Nanorings through Oriented Attachment of Nanoparticles. J. Am. Chem. Soc. 2005, 127, 7140−7147. I


Article

Inorganic Chemistry (53) Kawase, T.; Kurata, H. Ball-, Bowl-, and Belt-Shaped Conjugated Systems and Their Complexing Abilities: Exploration of the Concave-Convex π-π Interaction. Chem. Rev. 2006, 106, 5250− 5273. (54) Sprafke, J. K.; et al. Belt-Shaped π-Systems: Relating Geometry to Electronic Structure in a Six-Porphyrin Nanoring. J. Am. Chem. Soc. 2011, 133, 17262−17273. (55) Jiang, H.-W.; Tanaka, T.; Mori, H.; Park, K. H.; Kim, D.; Osuka, A. Cyclic 2,12-Porphyrinylene Nanorings as a Porphyrin Analogue of Cycloparaphenylenes. J. Am. Chem. Soc. 2015, 137, 2219−2222. (56) Favereau, L.; Cnossen, A.; Kelber, J. B.; Gong, J. Q.; Oetterli, R. M.; Cremers, J.; Herz, L. M.; Anderson, H. L. Six-Coordinate Zinc Porphyrins for Template-Directed Synthesis of Spiro-Fused Nanorings. J. Am. Chem. Soc. 2015, 137, 14256−14259. (57) Amabilino, D. B.; Stoddart, J. F. Interlocked and Intertwined Structures and Superstructures. Chem. Rev. 1995, 95, 2725−2828. (58) Collier, C. P. A [2]Catenane-Based Solid State Electronically Reconfigurable Switch. Science 2000, 289, 1172−1175. (59) Ahamed, B. N.; van Velthem, P.; Robeyns, K.; Fustin, C.-A. Influence of a Single Catenane on the Solid-State Properties of Mechanically Linked Polymers. ACS Macro Lett. 2017, 6, 468−472. (60) Cun, H.; Iannuzzi, M.; Hemmi, A.; Osterwalder, J.; Greber, T. Implantation Length and Thermal Stability of Interstitial Ar Atoms in Boron Nitride Nanotents. ACS Nano 2014, 8, 1014−1021. (61) Cun, H.; Iannuzzi, M.; Hemmi, A.; Osterwalder, J.; Greber, T. Ar Implantation Beneath Graphene on Ru(0001): Nanotents and ”Can-Opener” Effect. Surf. Sci. 2015, 634, 95−102. (62) Park, J.; Oh, A.; Baik, H.; Choi, Y. S.; Kwon, S. J.; Lee, K. One Pot Synthesis of Nanoscale Phase-Segregated PdPt Nanoarchitectures via Unusual Pt-Doping Induced Structural Reorganization of a Pd Nanosheet into a PdPt Nanotent. Nanoscale 2014, 6, 10551. (63) Lee, K. W.; Park, J.; Lee, H.; Yoon, D.; Baik, H.; Haam, S.; Sohn, J.-H.; Lee, K. Morphological Evolution of 2D Rh Nanoplates to 3D Rh Concave Nanotents, Hierarchically Stacked Nanoframes, and Hierarchical Dendrites. Nanoscale 2015, 7, 3460−3465. (64) Cardozo, T. M.; Fantuzzi, F.; Nascimento, M. A. C. The NonCovalent Nature of the Molecular Structure of the Benzene Molecule. Phys. Chem. Chem. Phys. 2014, 16, 11024−30. (65) Fantuzzi, F.; de Sousa, D. W. O.; Nascimento, M. A. C. The Nature of the Chemical Bond from a Quantum Mechanical Interference Perspective. ChemistrySelect 2017, 2, 604−619. (66) Kroto, H. W.; Heath, J. R.; O’Brien, S. C.; Curl, R. F.; Smalley, R. E. C60: Buckminsterfullerene. Nature 1985, 318, 162−163. (67) Golberg, D.; Bando, Y.; Stéphan, O.; Kurashima, K. Octahedral Boron Nitride Fullerenes Formed by Electron Beam Irradiation. Appl. Phys. Lett. 1998, 73, 2441−2443. (68) Zhang, X.; Zhao, M.; He, T.; Li, W.; Lin, X.; Wang, Z.; Xi, Z.; Liu, X.; Xia, Y. Theoretical Models of ZnS Nanoclusters and Nanotubes: First-Principles Calculations. Solid State Commun. 2008, 147, 165−168. (69) Zhao, Y.; Truhlar, D. G. Size-Selective Supramolecular Chemistry in a Hydrocarbon Nanoring. J. Am. Chem. Soc. 2007, 129, 8440−8442. (70) Zhao, M.; Xia, Y.; Mei, L. Silicon Carbide Nanocages and Nanotubes: Analogs of Carbon Fullerenes and Nanotubes or Not? J. Comput. Theor. Nanosci. 2012, 9, 1999−2007. (71) Skrabalak, S. E.; Chen, J.; Sun, Y.; Lu, X.; Au, L.; Cobley, C. M.; Xia, Y. Gold Nanocages: Synthesis, Properties, and Applications. Acc. Chem. Res. 2008, 41, 1587−1595. (72) Fujita, D.; Suzuki, K.; Sato, S.; Yagi-Utsumi, M.; Yamaguchi, Y.; Mizuno, N.; Kumasaka, T.; Takata, M.; Noda, M.; Uchiyama, S.; Kato, K.; Fujita, M. Protein Encapsulation Within Synthetic Molecular Hosts. Nat. Commun. 2012, 3, 1093. (73) Tasis, D.; Tagmatarchis, N.; Bianco, A.; Prato, M. Chemistry of Carbon Nanotubes. Chem. Rev. 2006, 106, 1105−1136. (74) Chopra, N.; Luyken, R.; Cherrey, K.; Crespi, V.; Cohen, M.; Louie, S.; Zettl, A. Boron Nitride Nanotubes. Science 1995, 269, 966− 967.

(75) Baima, J.; Erba, A.; Rérat, M.; Orlando, R.; Dovesi, R. Beryllium Oxide Nanotubes and their Connection to the Flat Monolayer. J. Phys. Chem. C 2013, 117, 12864−12872. (76) Fernandez-Lima, F. A.; Henkes, A. V.; da Silveira, E. F.; Nascimento, M. A. C. Alkali Halide Nanotubes: Structure and Stability. J. Phys. Chem. C 2012, 116, 4965−4969. (77) Côté, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks. Science 2005, 310, 1166−1170. (78) El-Kaderi, H. M.; Hunt, J. R.; Mendoza-Cortes, J. L.; Cote, A. P.; Taylor, R. E.; O’Keeffe, M.; Yaghi, O. M. Designed Synthesis of 3D Covalent Organic Frameworks. Science 2007, 316, 268−272. (79) Ding, S.-Y.; Wang, W. Covalent Organic Frameworks (COFs): From Design to Applications. Chem. Soc. Rev. 2013, 42, 548−568.

J


Diboryne Nanostructures Stabilized by Multitopic N-Heterocyclic

Recommend Documents