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Fluoronitrogens are strongly related to high-energy density materials. Fluoropentazole (

A vital issue for the fixation and conversion of CO2 into useful chemical products is to find effective catalysts. In this work, in order to develop more effective and diverse catalysts, we implemented the first computational screening study (at M06-2X//B3LYP level) on the cycloaddition of CO2 with aziridines under eighteen metal-substituted HKUST-1 MOFs and tetrabutylammonium bromide (TBAB) as a co-catalyst. For all considered catalytic systems, the ring-opening of aziridine is calculated to be the rate-determining step. Up to 11 M-HKUST-1 systems, i.e., Rh (31.87 kcal mol−1), Y (31.02), Sc (30.50), V (30.02), Tc (29.90), Cd (29.80), Ti (29.32), Mn (29.05), Zn (28.29), Fe (27.85) and Zr (25.09), possess lower ring-opening barrier heights than the original Cu-HKUST-1 (32.90), indicative of their superior catalytic ability to the original Cu-HKUST-1 in theory. With the lowest ring-opening barrier, Zr-HKUST-1 is strongly advocated for future synthetic and catalytic studies.

The more-than-one-century-old arylpentazoles can only be used in situ in generating the pentazole anion due to their unfavourable kinetic stability. We successfully increased the N2-leaving barrier to reach hitherto the highest value of 40.83 kcal mol-1 at the CBS-QB3 level via a newly proposed co-stabilization method, making the broader applications of arylpentazoles feasible.

It was revealed in recent experimental studies that metal–organic frameworks (MOFs) show very attractive activities for the catalytic CO2 cycloaddition with aziridines in cooperation with tetrabuty...

The global minimum of XMg4Y− (X = Si, Ge; Y = In, Tl) and SiMg3In2 contains a planar pentacoordinate atom of group 14 other than carbon. Its design is based on the “localization” approach, replacing one or two peripheral atoms in XMg52− by more electronegative ones. This change diminishes the repulsion and leads to stronger covalent X–Y bonds, stabilizing the planar pentacoordinate atom species.

The design and characterization of the heteronuclear group 14 C[triple bond, length as m-dash]E (E = Si, Ge, Sn, Pb) triple bonds have attracted intensive interest in the past few decades. In the current work, utilizing the advantages of N-heterocyclic carbenes (NHCs) and Lewis acid-base pair strategy, we theoretically designed a new class of compounds III-1, i.e., (NHCAR)C[triple bond, length as m-dash]E(Al(C6F5)3). Quantum chemical calculations showed that these singlet compounds possess very favourable isomerization, fragmentation and dimerization stabilities at the B3LYP/def2-TZVPP//B3LYP/def2-SVP level. The calculated bond lengths of CE in III-1 are 1.63 A for Si, 1.70 A for Ge, 1.91 A for Sn and 2.01 A for Pb, respectively, which are close to or even shorter than the known C[triple bond, length as m-dash]E bond lengths. In addition, the significant Mayer bond order values, two orthogonal π orbitals and one σ orbital between the C and E atoms also indicate the characteristics of triple bonds. Based on several bonding analyses, strong delocalization is found to exist between the C[triple bond, length as m-dash]E core and NHCAR forming a weak C[double bond, length as m-dash]C double bond. Hence, such obtained C[triple bond, length as m-dash]E species also can be described by their resonace structures as cunmulene analogs. In all, III-1 proposed here not only presents a universal C[triple bond, length as m-dash]E motif for all the heavier group 14 elements, but also provides a new strategy for the design and synthesis of heteronuclear group 14 triple bonds in the future.

For over 100 years, known bent CC compounds have been limited to those with organic (I) and all-carbon (II) scaffoldings. Here, we computationally report a novel type (III) of bent CC compound, i.e., C2Al4F6-01, which is the energetically global minimum isomer and bears an inorganic–metallic scaffolding and unexpected click reactivity.

We present a global planar pentacoordinate carbon (ppC) featuring a hitherto unreported σ–σ diradical characteristic. Using the multi-reference approach combined with the CCSD(T)/aug-cc-pVTZ method, the ppC C3Li3− was found to be an intriguing triplet ground state, in which the unpaired density is mostly located at three Li ligands. Chemical bonding analysis reveals that the 2pz π electrons of C3Li3− are fully located at the C3 ring formed by C–C multiple bonds, in contrast to the perfect 2pz π-delocalization found in the well-known ppCs.

In cluster studies, the isoelectronic replacement strategy has been successfully used to introduce new elements into a known structure while maintaining the desired topology. The well-known penta-atomic 18 valence electron (ve) species CAl42- and its Al- /Si or Al/Si+ isoelectronically replaced clusters CAl3 Si- , CAl2 Si2 , CAlSi3- , and CSi42+ , all possess the same anti-van't Hoff/Le Bel skeletons, that is, nontraditional planar tetracoordinate carbon (ptC) structure. In this article, however, we found that such isoelectronic replacement between Si and Al does not work for the 16ve-CAl4 with the traditional van't Hoff/Le Bel tetrahedral carbon (thC) and its isoelectronic derivatives CAl3 X (X = Ga/In/Tl). At the level of CCSD(T)/def2-QZVP//B3LYP/def2-QZVP, none of the global minima of the 16ve mono-Si-containing clusters CAl2 SiX+ (X = Al/Ga/In/Tl) maintains thC as the parent CAl4 does. Instead, X = Al/Ga globally favors an unusual ptC structure that has one long C─X distance yet with significant bond index value, and X = In/Tl prefers the planar tricoordinate carbon. The frustrated formation of thC in these clusters is ascribed to the CSi bonding that prefers a planar fashion. Inclusion of chloride ion would further stabilize the ptC of CAl2 SiAl+ and CAl2 SiGa+ . The unexpectedly disclosed CAl2 SiAl+ and CAl2 SiGa+ represent the first type of 16ve-cationic ptCs with multiple bonds. © 2019 Wiley Periodicals, Inc.

Of the pentanitrogen cation (N

For the 22 year-old pentanitrogen cation N5+ (01), we surprisingly found that the previously reported transition states (TSs) do not correspond to N2-extrusion. We located the real N2-extrusion TS, which can well reconcile the hitherto remaining inconsistency between the gas-phase and salt-like forms of 01 both in structure and energetics.

The exhaustive exploration of the potential energy surfaces of CE2M2 (E = Si-Pb, M = Li, and Na) revealed seven global minima containing a planar tetracoordinate carbon (ptC). The design was based on a π-localization strategy, resulting in a ptC embedded in a linear or a bent allene-type E=C=E motif. The magnetic response showed a σ-aromaticity in the bent E=C=E fragments. The bonding analysis indicated that the ptCs form C-E covalent bonds and C-M electrostatic interactions.

Developing high-performance catalysts for the chemical fixation of CO2 into epoxides remains an ongoing hot yet challenging issue in the field of catalysis. Metal–organic frameworks (MOFs) represent an attractive type of catalyst candidate for this reaction due to their remarkable properties including large surface area, high stability, open channels, and permanent porosity. Although the Cu-HKUST-1 MOF has recently been shown to exhibit good activity towards CO2 fixation, and a series of other isostructural analogues, i.e., M-HKUST-1 (M = Mo, Cr, Fe, Ru and Zn), have even been synthesized, there is no theoretical investigation on CO2 cycloaddition catalyzed by both the parent and metal-substituted HKUST-1, to the best of our knowledge. In this work, with the attempt to design powerful catalysts, we computationally screened a series of M-HKUST-1 systems (M = Mo, Cr, Ti, Cu, W, Sc, Fe, Ru, Zn, Cd, and V) in the presence of quaternary ammonium salts (TBAX, X = F, Cl, Br, and I) for catalytic activity toward the synthesis of cyclic carbonates from propylene oxide (PO) and CO2. Of these, several M-HKUST-1 systems (M = Cr, W, Fe, Zn, and Cd) were predicted to exceed the performance of the original Cu-HKUST-1 reported experimentally for CO2 chemical conversion based on the rate-limiting energy barrier. In particular, W-HKUST-1 was predicted to be the most promising catalyst within the screened M-HKUST-1 series. In addition, for Cu-HKUST-1, the catalyst system containing Br− is more efficient than the one containing F−, Cl− and I−. The proton attachment energy of the X− anion is a suitable descriptor for screening promising co-catalytic materials for the specific reaction. The present computational investigation would greatly enrich the CO2–PO reaction catalyzed by M-HKUST-1/TBAX, and provide a valuable guideline for the design of more powerful MOFs/IL catalysts.

Metal cyanide/isocyanide and hydrometal cyanide/isocyanide compounds are key metal-carriers in interstellar space. Lighter group 14 elements (X = C/Si/Ge) cyanides/isocyanides and hydrocyanides/hydroisocyanides have been studied theoretically and experimentally. However, no reports are available on the analogues of tin (Sn) and lead (Pb). In this work, we carried out the first theoretical study on the structures and stabilities of [X,C,N] and [H,X,C,N] (X = Sn/Pb) at the CCSD(T)/def2-QZVPP//B3LYP/def2-QZVPP level. Comparisons were made with the lower analogues (X = C/Si/Ge) concerning the structural, energetic and bonding properties. Significantly different from that of c-C2N, a dative-bonded valence structure of c-XCN for heavier X was revealed for the first time, which can account for the rather worse kinetic stability of cyclic [X,C,N] for heavier X = Si/Ge. A unique kind of agostic bonding was found within three isomers of [H,Pb,C,N], whereas it is absent for X = C/Si/Ge/Sn. The computed structural and spectroscopic data could aid future laboratory and astrophysical detection of the [X,C,N] and [H,X,C,N] (X = Sn/Pb) isomers.

Porous conjugated polymers offer enormous potential for energy storage because of the combined features of pores and extended π-conjugated structures. However, the drawbacks such as low pore volumes and insolubilities of micro- and mesoporous conjugated polymers restrict the loading of electroactive materials and thus energy storage performance. Herein, we report the synthesis of iron-doped macroporous conjugated polymers for hosting sulfur as the cathode of high-performance lithium–sulfur (Li–S) batteries. The macroporous conjugated polymers are synthesized via in situ growth of poly(3-hexylthiophene) (P3HT) from reduced graphene oxide (RGO) sheets, followed by gelation of the composite (RGO-g-P3HT) in p-xylene and freeze-drying. The network structures of the macroporous materials can be readily tuned by controlling the chain length of P3HT grafted to RGO sheets. The large pore volumes of the macroporous RGO-g-P3HT materials (ca. 34 cm3 g–1) make them excellent frameworks for hosting sulfur as cathodes o...

The fixation of CO2 with epoxides catalyzed by metal-organic frameworks (MOFs) has been the ongoing hot topic investigated extensively in experiment throughout the years. Recent experimental studies have revealed that the MIL-101(Cr) can effectively catalyze the cycloaddition conversion of CO2 with the aid of the tetrabutylammonium bromide(TBAB). However, the mechanistic details remain largely unraveled. In this work, we undertook a detailed DFT study on the cycloaddition reaction catalyzed by the binary system MIL-101/TBAB in comparison with the non-catalyzed, MIL-101-catalyzed alone and TBAB-catalyzed alone reactions. The three-step route involving the consecutive ring-opening of PO (propylene oxide), insertion of carbon dioxide, and ring-closure of cyclic carbonate was found to be kinetically more favorable than the two-step route (ring-opening of PO and ring-closure of cyclic carbonate). Based on the rate-determining activation energy barrier, the cycloaddition of CO2 to PO proceeds in a much easier way in the presence of MIL-101/TBAB (18.11 kcal mol−1) than the non-catalyzed (57.67 kcal mol−1), MIL-101-catalyzed (46.89 kcal mol−1) and TBAB-catalyzed (26.86 kcal mol−1) alone reactions. The computational findings can satisfactorily explain the available experimental observations, enabling a molecular-level understanding of congener catalysts for organic carbonate production as well as the rational design of more powerful MOF-orientated catalysts.

Despite their high theoretical capacity, the practical commercialization of lithium-sulfur batteries have continued to face obstacles of low cycle stability and low efficiency, which stem from the dissolution and diffusion of lithium polysulfides intermediates in the electrolyte. Here, by means of comprehensive density functional theory computations, we exploited the potentials of the experimentally available metal-nitrogen/graphene as the anchoring material for high-performance Li-S batteries. Our results revealed that Cr-, Mn-, Fe-, Co-, and Cu-nitrogen/graphenes exhibit optimal interaction with soluble lithium polysulfides due to the synergistic effects between the metal and N atoms, which not only effectively traps the soluble lithium polysulfides to suppress the shuttle effects, but also well keeps their cyclic structures intact. Especially, the electronic properties of metal-nitrogen/graphenes are well preserved, and the computed voltages of discharge processes are larger than those of the well-established nitrogen-doped graphenes. Thus, the metal-nitrogen/graphene could present a kind of quite promising anchoring material for lithium sulfur battery cathodes to suppress the lithium polysulfides shuttle effect.

A vital issue for the fixation and conversion of CO

The design and characterization of the heteronuclear group 14 C[triple bond, length as m-dash]E (E = Si, Ge, Sn, Pb) triple bonds have attracted intensive interest in the past few decades. In the current work, utilizing the advantages of N-heterocyclic carbenes (NHCs) and Lewis acid-base pair strategy, we theoretically designed a new class of compounds III-1, i.e., (NHCAR)C[triple bond, length as m-dash]E(Al(C6F5)3). Quantum chemical calculations showed that these singlet compounds possess very favourable isomerization, fragmentation and dimerization stabilities at the B3LYP/def2-TZVPP//B3LYP/def2-SVP level. The calculated bond lengths of CE in III-1 are 1.63 Å for Si, 1.70 Å for Ge, 1.91 Å for Sn and 2.01 Å for Pb, respectively, which are close to or even shorter than the known C[triple bond, length as m-dash]E bond lengths. In addition, the significant Mayer bond order values, two orthogonal π orbitals and one σ orbital between the C and E atoms also indicate the characteristics of triple bonds. Based on several bonding analyses, strong delocalization is found to exist between the C[triple bond, length as m-dash]E core and NHCAR forming a weak C[double bond, length as m-dash]C double bond. Hence, such obtained C[triple bond, length as m-dash]E species also can be described by their resonace structures as cunmulene analogs. In all, III-1 proposed here not only presents a universal C[triple bond, length as m-dash]E motif for all the heavier group 14 elements, but also provides a new strategy for the design and synthesis of heteronuclear group 14 triple bonds in the future.

The design of planar tetracoordinate carbon (ptC) has always been a challenge due to its unique bonding mode that necessitates the perfect balance between the carbon center and surrounding ligands both electronically and mechanically. A unique type of 18-valence-electron (18ve) template, i.e., CAl42-, has been found to be very effective in designing various novel 18ve-species upon skeletal substitution. In this work, we showed that though ptC is not the global structure for the parent 16ve-CAl4, suitable skeletal substitution can allow for a series of global minimum ptC species. Theoretical calculations at the level of CCSD(T)/def2-QZVP//B3LYP/def2-QZVP for 35 carbon-group 13 systems with 16-ve, i.e., CXaYbZcKd (X, Y, Z, K = Al/Ga/In/Tl; 0 ≤ a, b, c, d ≤ 4, a + b + c + d = 4), showed that 9 systems (CAl3Tl, CGa3Tl, CGa2Tl2, CAl2GaTl, CAl2InTl, CGa2InTl, CAlGa2Tl, CGa2InTl and CAlGaInTl) possess global minimum ptC and 2 systems (CAl3In and CAl2Tl2) have quasi-GM ptC. Except for CAl3Tl and CAl3In, all the ptCs were predicted for the first time. All these stable ptC structures have the same skeleton and can be described as the same ionic sub-structure, i.e., [A-]B+. This study not only enriches 16ve-ptC, but also directly demonstrates that utilizing an ionic strategy, non-ptC CAl4 also can be used as a template to extend the ptC family.

As a perpetual chemical curiosity, planar tetracoordinate carbon (ptC) that violates the traditional tetrahedral carbon (thC) has made enormous achievements. In particular, the 18-valence-electron (18ve) counting rule has been found to be very effective in predicting ptC structures, as in CX42- (X = Al/Ga/In/Tl). By contrast, the corresponding neutral CX4 with 16ve each takes the thC form like methane. Herein, we report a mono-substituted neutral 16ve-CAl3X (X = Al/Ga/In/Tl). Our theoretical results showed that the competition between thC and ptC can be well tuned upon variation of X, and for X = In and Tl, the ptC structure becomes isoenergetic to and even more stable than thC, respectively. Thus, a low-lying ptC can be achieved in the 16ve-CAl3X set without acquiring additional electrons. This unintuitive result can be ascribed to the increased energetic preference of the ionic sub-structure [CAl3-]X+ from X = Al to Tl. We thus predict the first penta-atomic ptC species with 16ve, and the ionic strategy presented in this work is expected to promote novel designs of ptC molecules.

Metal–metal double-π bonding in s-block metals has not been reported until now. The octahedral clusters of Be2(μ2-X)4 only possessing degenerate Be–Be double-π bonds were first achieved by an innovative concerted electron-donating strategy from the vertical plane of the Be–Be midpoint using four s1-type electron-donating ligands. Moreover, this novel strategy is universal and independent of electronegativity. Three typical clusters were discussed herein including Be2(BeF)4, Be2Li4 and Be2Cu4. Especially, WBIBe–Be in Be2Li4 reached up to 1.96. The significant π-bonding character was confirmed by various bond analysis strategies.

Contrasting the big family of the planar tetracoordinate carbon (ptC), species featuring the planar tetracoordinate heavier group element M (ptM) have been largely limited. Effective structural fra...