Isomer stability and bond-breaking energies of N8C8H8 cages

Molecules consisting entirely or predominantly of nitrogen have been extensively investigated for their potential as high-energy density materials (HEDM). Such molecules react to produce N2 and large amounts of energy, but many such molecules are too unstable for practical applications. In the present study, cage isomers of N8C8H8 are studied using theoretical calculations to determine the structural features that lead to the most stable cages and determine the energetics of dissociation for the various isomers. The isomers are evaluated for thermodynamic (isomer vs isomer) stability and kinetic (with respect to dissociation) stability. Density functional theory (B3LYP), perturbation theory (MP2), and coupled-cluster theory [CCSD(T)] are employed, in conjunction with the cc-pVDZ basis set of Dunning. Trends in isomer stability and dissociation energies are calculated and discussed.     

Contrast of Bonding and Characters for C6, B3N3, C6H6 and B3N3H6 Molecules

Through integrative consideration of NICS, MO, MOC and NBO, we precisely investigated delocalization and bonding characters of C₆, C₆H₆, B₃N₃ and B₃N₃H₆ molecules. Firstly, we originally discovered and testified that C₆ cluster was sp² hybridization. Negative NICS values in 0 and 1 Å indicated that C₆ had δ and Π aromaticity. Secondly, B₃N₃ with sp² hybridization had obvious δ aromaticity. Finally, WBI values approved that there were delocalization in C₆, C₆H₆ and B₃N₃ molecules, but B₃N₃H₆ structure did not have delocalization with the WBI 1.0. Moreover, total WBI values of carbon, boron and nitrogen atoms were four, three and three, respectively. Namely, the electrons of B₃N₃H₆ and B₃N₃ were localized in nitrogen atoms and they did not form delocalized bonding. In a word, bonding characters of carbon, boron and nitrogen atoms were dissimilar although the molecules composed of carbon, boron and nitrogen were regarded as isoelectronic structures.     

Synthesis and Structure of Melamium Bromide C6N11H10Br and Melamium Iodide C6N11H10I

Melamium bromide and melamium iodide were synthesized from dicyandiamide in the presence of ammonium halides in evacuated Duran glass ampoules at temperatures of 450 °C. The crystal structures of both compounds were obtained from single‐crystal X‐ray diffraction. Melamium bromide C₆N₁₁H₁₀Br crystallizes in space group P2₁/n [no. 14, a = 7.0500(5), b = 28.7096(18), c = 10.8783(8) Å, β = 96.060(2)°, Z = 8, wR₂ = 0.2231] and exhibits a layer‐like arrangement of melamium ions, wherein both planar as well as twisted molecular structures of the cations occur. Melamium iodide C₆N₁₁H₁₀I crystallizes in space group P2₁/c [no. 14, a = 6.8569(3), b = 11.9949(6), c = 14.0932(6) Å, β = 97.613(2)°, Z = 4, wR₂ = 0.0654], however in a structure completely different from the one of melamium bromide. The melamium iodide structure is comprised of stacks of planar melamium ions that form complex, hydrogen‐bonded network layers with iodide ions within the layers. Both compounds were further characterized by FTIR spectroscopy, mass spectrometry, and elemental analyses. Melamium bromide and melamium iodide could be obtained as air stable and colorless crystals. Samples are crystallographically phase pure as shown by Rietveld refinement.     

Geometry and stability of fullerene cages: C24 to C70

The electronic structures and geometries of all even carbon fullerenes were investigated theoretically using density functional theory (DFT) at the B3LYP/6‐31G* level. Based on geometries, energies, and aromaticities, the potential relationship between geometry factors and stability has been investigated systematically. The extra stability of C₆₀ has been confirmed by the shorter average bond length, smaller angle strain, widest energy gap, larger binding energy, and dissociation energy. Furthermore, C₃₂ and C₅₀ are predicted to have higher aromaticity due to larger negative nucleus independent chemical shift (NICS) values, whereas C₆₀ displays a weak aromaticity. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Stability of N18C6H6: triangular versus hexagonal structure

Large nitrogen cage molecules Nx have been previously shown to prefer elongated, cylindrical structures with triangular caps versus more spherical structures composed entirely of pentagons and hexagons. It was argued that this preference derived from the electronic properties of the nitrogen atoms, including the lone pairs. In the current study, the same structural comparison is carried out, with the substitution of C-H-bonding groups for six of the nitrogens. Various substitution patterns on the cylindrical (triangular) and spherical (hexagonal) frameworks are examined. Isomers of N18C6H6 are studied by theoretical calculations to determine the relative stability of triangular versus hexagonal structures, as well as the stability effects of the substitution patterns on each framework. Hartree-Fock theory, density functional theory (PBE1PBE), and perturbation theory (MP2) are employed, in conjunction with the correlation-consistent basis sets of Dunning. Stability trends within each class of molecules and between the two classes of molecules are calculated and discussed.     

Novel products from C6H5 + C6H6/C6H5 reactions

To date only one product, biphenyl, has been reported to be produced from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions. In this study, we have investigated some unique products of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via both experimental observation and theoretical modeling. In the experimental study, gas-phase reaction products produced from the pyrolysis of selected aromatics and aromatic/acetylene mixtures were detected by an in situ technique, vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometry (TOFMS). The mass spectra revealed a remarkable correlation in mass peaks at m/z = 154 {C(12)H(10) (biphenyl)} and m/z = 152 {C(12)H(8) (?)}. It also demonstrated an unexpected correlation among the HACA (hydrogen abstraction and acetylene addition) products at m/z = 78, 102, 128, 152, and 176. The analysis of formation routes of products suggested the contribution of some other isomers in addition to a well-known candidate, acenaphthylene, in the mass peak at m/z = 152 (C(12)H(8)). Considering the difficulties of identifying the contributing isomers from an observed mass number peak, quantum chemical calculations for the above-mentioned reactions were performed. As a result, cyclopenta[a]indene, as-indacene, s-indacene, biphenylene, acenaphthylene, and naphthalene appeared as novel products, produced from the possible channels of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions rather than from their previously reported formation pathways. The most notable point is the production of acenaphthylene and naphthalene from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via the PAC (phenyl addition-cyclization) mechanism because, until now, both of them have been thought to be formed via the HACA routes. In this way, this study has paved the way for exploring alternative paths for other inefficient HACA routes using the PAC mechanism.     

C3N6H6(H3BO3)2的合成及晶体结构

以三聚氰胺和硼酸为原料在水溶液中反应合成出了一种新的BCN化合物先驱体C3N6H6(H3BO3)2。XRD表征结果表明三聚氰胺和硼酸的最佳配比为1∶3(物质的量比)。用单晶X-射线衍射分析法测定了该化合物的晶体结构。该化合物属单斜晶系,空间群为P21/C,晶胞参数为a=0.3597(7)nm,b=2.0105(4)nm,c=1.4112(3)nm,α=90,°β=92.07(3),°γ=90,°V=1.0199(3)nm3,Z=4,D c=1.627g.cm-3,μ(MoKα)=0.144mm-1,F(000)=520。晶体结构经全矩阵最小二乘法修正,最终可靠因子R1=0.0519,wR2=0.1361。该化合物是由C3N6H6分子和H3BO3分子通过氢键加合组装形成的三维超分子结构化合物。     

The Crystal Structures of Two No–Metal Tricyanomelaminates: Diammonium Tricyanomelaminate Dihydrate [NH4]2[C6N9H] · 2 H2O and Dimelaminium Tricyanomelaminate Melamine Dihydrate [C3N6H7]2[C6N9H] · C3N6H6 · 2 H2O

Diammonium tricyanomelaminate dihydrate [NH₄]₂[C₆N₉H] · 2 H₂O ( 1 ) and dimelaminium tricyanomelaminate melamine dihydrate [C₃N₆H₇]₂[C₆N₉H] · C₃N₆H₆ · 2 H₂O ( 2 ) were obtained by metathesis reactions from Na₃[C₆N₉] in aqueous solution and characterized by single‐crystal X‐ray diffraction and ¹⁵N solid‐state NMR spectroscopy ( 1 ). Both salts contain mono‐protonated tricyanomelaminate (TCM) anions and crystallize as dihydrates. Considering charge balance requirements, the crystal structure of 1 (C2/c, a = 3181.8(6) pm, b = 360.01(7) pm, c = 2190.4(4) pm, β = 112.39(3)°, V = 2319.9(8) 10⁶ · pm³) can best be described by assuming a random distribution of an ammonium ion – crystal water pair over two energetically similar sites. Apart from two melaminium cations, 2 (P2₁/c, a = 674.7(5) pm, b = 1123.6(5) pm, c = 3400.2(5) pm, β = 95.398(5), V = 2566(2) 10⁶ · pm³) contains one neutral melamine per formula unit acting as an additional “solvent” molecule and yielding a donor‐acceptor type of π–stacking interaction.     

The new thioantimonate(V) (C3H10N)[NiSbS4(C6H18N4)]

Turquoise crystals of the title salt, propyl­ammonium di‐μ‐thio‐1:2κ⁴S‐di­thio‐2κ²S‐tris(2‐amino­ethyl)­amine‐1κ⁴N‐anti­mony(V)­nickel(II), (C₃H₁₀N)[NiSbS₄(C₆H₁₈N₄)] or [PAH][Ni(tren)SbS₄] [where tren is tris(2‐amino­ethyl)­amine and PA is propyl­amine], were synthesized under solvothermal conditions by reacting [Ni(tren)₂]Cl₂, Sb and S in a solution of PA. The Ni^II ion is octahedrally surrounded by four N atoms of the tetradentate tren mol­ecule and by two S atoms of the tetrahedral [Sb^VS₄]^3? anion, thus forming the anionic [Ni(tren)SbS₄]^? part of the compound. Charge balance is achieved through the PAH⁺ cation. An extended intermolecular hydrogen‐bonding network is observed between the anion and the cation.     

Synthesis and Crystal Structure of [VO2（C17H11N3O2） ] [VO （C4H13N3）（C6H5N3O） ]（C2H5OH）

The reaction of VO（acac）2 with 2-hydroxyl-1-naphthaldehyde isonicotinyl hydrazone and amines （ethylenediamine or diethylenetriamine） in CH3OH yields crystals of novel vanadium compounds characterized by IR, NMR spectroscopic methods and X-ray single-crystal structure determination. Two different vanadium units exist in the crystal cell of [VO2（C17H11N3O2）][VO- （C4H13N3）（C6H5N3O）]（C2H5OH） which crystallizes in the triclinic system, space group P1 with a = 8.0104（17）, b = 13.898（3）, c = 14.955（3）A, α = 89.103（4）, β = 79.551（4）, γ = 78.352（4）°, V = 1603.3（6）A^3, Mr = 723.54, Dc = 1.499 g/cm^3, Z = 2, λ（MoKα） = 0.71073 ]A,μ= 0.644 mm^-1, F（000） = 748, the final R = 0.0547 and wR = 0.0997 for 8920 observed reflections with I 〉 2σ（I）. According to structure analysis, two different molecules are arranged in the lattice and the two vanadium atoms adopt octahedral and square pyramidal coordination geometries, respectively. The interactions between DNA and vanadium complexes have been investigated by UV-Vis absorption spectro- photometry.