A non-empirical molecular orbital study of valence tautomers of C2H3N

The valence tautomers of C₂H₃N have been examined by non-empirical molecular orbital calculations using two split-valence shell basis sets. All geometries were fully optimized using the 4–31G basis set and these structures were then used in 6–31G basis set calculations. The order of stability of the three possible cyclic isomers is 1-azirine > cyclic carbene > 2-azirine. The profiles for conversion of vinylmethylene into cyclopropene, vinylnitrene into 1-arizine, and iminomethylene into 2-azirine have all been shown to have barriers.     

Valence of D5h C50 fullerene

The energetic and electronic properties of D5h C50 before and after passivation by H or Cl are investigated using first-principle computational method of density functuional theory with generalized gradient approximation and local density approximation functionals. The results show that H or Cl addition can lead to energetic stabilization. Additions also increase the highest occupied molecular orbit-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of C50 fullerides and make them chemically more stable. In the series of C50H2m (m = 0 approximately 7), the Saturn-shaped D5h C50H10 has the largest HOMO-LUMO gap, which suggests that such a structure of C50H10 is a "magic-number" stable one of C50 adducts, and ten is a pseudovalence or effective valence of C50 fullerene pseudoatom. This point also is supported by the energetic properties of C50H2m series such as binding energies, etc. A minimal energy reaction pathway is constructed to get C50H10 and C50H14. Some useful experience for determining the favorable addition sites was summarized. A simple steric method is developed to predict the effective valences of classical fullerenes.     

The dianion of 5-cyanoiminotetrazoline: C2N62-

Several salts (alkali, Pd(NH(3))(3), and (i)PrNH(2)) of 5-cyanoiminotetrazoline (C(2)N(6)(2-), 5-cyanoiminotetrazolinediide, CIT) were investigated. A full characterization by means of X-ray, Raman, NMR techniques, mass spectrometry, and elemental analysis is presented for the (i)()PrNH(2) (4), Cs (5), and Pd(NH(3))(3) (6) salts. The CIT dianion represents a nitrogen-rich binary CN dianion, and 5 forms monoclinic crystals (a = 7.345(2) Angstroms, b = 9.505(2) Angstroms, c = 10.198(2) Angstroms, beta = 92.12(3) degrees, space group P2(1)/n, Z = 4). DSC and in situ temperature-dependent X-ray diffraction measurements of the cesium salt 5 revealed an astonishing thermal stability accompanied by a reversible phase transition from the low-temperature alpha modification to the metastable beta modification at 253 degrees C. Above the melting point (334 degrees C), the cesium salt decomposes yielding cesium azide and cesium dicyanamide, which decomposes under further heating under release of nitrogen. The reaction of Cs(2)CIT with SO(2) resulted in the surprising formation of a new cesium salt with the 5-cyaniminotetrazoline-1-sulfonate dianion (Cs(2)CITSO(3).SO(2) (7)). 7 crystallizes in the monoclinic space group P2(1) with one SO(2) solvent molecule (a = 8.0080(2) Angstroms, b = 8.0183(2) Angstroms, c = 9.8986(3) Angstroms, beta = 108.619(1) degrees, Z = 2). The structure and bonding of the 10pi dianion are discussed on the basis B3LYP/aug-cc-pvTZ computations (MO, NBO), and the three-dimensional array of the cesium salts with respect to the Cs(delta) (+)-N(delta)(-) in 5 compared to the Cs(delta)(+)-N(delta)(-) and Cs(delta)(+)-O(delta)(-) in 7 is discussed. Due to the expected rich bonding modes of the CIT anions, the coordination chemistry with palladium was also studied, yielding monoclinic crystals of [Pd(CIT)(NH(3))(3)].H(2)O (6, a = 7.988(2) Angstroms, b = 8.375(2) Angstroms, c = 13.541(3) Angstroms, beta = 104.56 degrees, space group P2(1)/n, Z = 4). In the solid state, the complex is composed of dimers, showing two agostic interactions and an unusual close interplanar pi-pi stacking of the tetrazole moiety of the CIT ligand.     

Ring contraction during the 6pi-electrocyclisation of naphthopyran valence tautomers

The thermal and photochemical ring-opening of spiro(3H-naphtho[2,1-b]pyran-3,9'-thioxanthene-10,10-dioxide) results in the facile ring-contraction to 9-(naphtho[2,1-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide . Similar behaviour is displayed by the isomeric spiro(2H-naphtho[1,2-b]pyran-2,9'-thioxanthene-10,10-dioxide) affording 9-(naphtho[1,2-b]furan-2-yl)-9H-thioxanthene-10,10-dioxide , though more severe reaction conditions were required. The comparative ease of this rearrangement for the isomers and was rationalised on the basis of the relative isomer populations of the ring-opened naphthopyrans. The rearrangement of simple mono- and bis-methylsulfonylphenyl substituted photochromic naphthopyrans , was examined; the former failed to rearrange whereas the latter could be induced to rearrange only under prolonged UV irradiation. The photochromism of diastereoisomerically pure sulfoxides derived from the oxidation of spiro(3H-naphtho[2,1-b]pyran-3,9'-thioxanthene) and spiro(2H-naphtho[1,2-b]pyran-2,9'-thioxanthene) resulted in conversion to the most thermodynamically stable trans-isomer in each case.     

Ab initio molecular dynamics studies of tetrasulfur. Dynamics coupling the C2v open and D2h closed forms of S4

Ab initio molecular dynamics (AIMD) simulations were performed on the closed D(2h) and open C(2v) isomers of tetrasulfur. After a careful calibration of the electronic structure method, the calculations were done using the BPW91/aug-cc-pVTZ method. This combination of method/basis set adequately reproduces the relative benchmark CCSD(T) energy difference [Matus, M.; Dixon, D.; Peterson, K. A.; Harkless, J. A. W.; Francisco, J. S. J. Chem. Phys. 2007, 127, 174305] between these two isomers and, crucially, the fact that the D(2h) structure is a transition state linking two equivalent (mirror images) C(2v) isomers. The trajectories show that the symmetric open C(2v) isomers interconvert when passing through the D(2h) closed transition state structure and that, unlike tetraoxygen, no three-dimensional structures arise. The dynamic vibrational analysis yields peaks in good agreement with the static CCSD(T) harmonic frequencies and explains higher peaks as overtones, thus showing that unlike previous AIMD DFT-based approaches, carefully calibrated exchange-correlation functionals can produce reliable molecular dynamics results for complex PESs as the one corresponding to the lowest singlet of S(4).     

A systematic search for the valence structures of the tetradecahydrotetradecaborate dianion

A systematic search has been used to find all the allowed valence structures of the D_6d bicapped hexagonal antiprismatic BH₁₄²⁻closo-boron hydride dianion. From the number of allowed valence structures (72), a valence state index (VSI) equal to 0.0773 can be deduced for the tetradecahydrotetradecaborate dianion, that is compared to those of the parent B_nH_n²⁻ derivatives (n = 6–12).     

Selective synthesis of the C3v isomer of C60h18

[chemical structure: see text]. C60H18 has been produced by hydrogenation of C60 at 100 bar H2 pressure and 673 K for 10 h. We have investigated the crude material without any purification by use of 1H NMR, 13C NMR, and IR spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. We show that the crude material consists of 95% of the C3v isomer of C60H18.     

Calcium croconate and calcium oxalato-croconate complexes with 2D and 3D crystal structures

Two novel complexes of calcium croconate Ca(μ₃-C₅O₅)(H₂O)₃ (I) and calcium oxalato-croconate Ca₂(μ₄-C₅O₅)(μ₆-C₂O₄)(H₂O) (II) have been synthesized by soft chemical routes and their crystal structures have been solved from single-crystal data. Croconates I and II crystallize in orthorhombic space groups Pbca and Pnma, respectively. Their crystal structures evidence the versatile character of the croconate anion in the framework design. The calcium croconate I displays a 2D structure with corrugated sheets formed by croconate dianions and eightfold coordinated calcium atoms within [Ca₂O₁₄] dimers. The sheets develop eight-member apertures made of four dimers and four croconate dianions. The structure of II displays a 3D open-framework built from layers connected to each other by croconate dianions. This arrangement generates rectangular cavities free of water molecules. Seven- and eightfold coordinated calcium atoms with oxalate dianions constitute the layers. In both structures, the connecting modes of croconates are unusual. The thermal behaviour study has demonstrated that II is stable until 380 °C.     

Stabilization of NH tautomers of quinolines by osmium and ruthenium

Complexes OsH2Cl2(PiPr3)2 and RuH2Cl2(PiPr3)2 promote the tautomerization of quinoline and 8-methylquinoline to NH tautomers, which lie about 44 kcal.mol-1 above the usual CH tautomers. The NH tautomers are stabilized by coordination to the metal center and by means of a Cl...HN interaction. As a consequence, the six-coordinate elongated dihydrogen complexes OsCl2{kappa-C2-(HNC9H5R)}(eta2-H2)(PiPr3)2, the five-coordinate derivatives RuCl2{kappa-C2-(HNC9H5R)}(PiPr3)2, and the six-coordinate dihydrogen compounds RuCl2{kappa-C2-(HNC9H5R)}(eta2-H2)(PiPr3)2 (R = H, Me) have been isolated and characterized.     

Theoretical Studies on Electronic Structures and Spectra for C80^n （D5d,C2v） Singlet

1INTRODUCTIONC80iscalledthemissingfullereneduetoitsinstabilityinkineticsandlowerLUMO-HOMOenergygap[1],aswellasthelowerabundanceintheexperimentandthedifficultyinsynthesis[1~5].However,thestableexistenceofcomplexLa2@-C80[2]stimulatestheresearchinterestinionsofC80.Zhang[3]performedtheoreticalstudiesonthestabi-lityandNMRspectraforC80isomers.Nakao[4]cal-culatedtheLUMO-HOMOenergygapofC80byusingabinitiomolecularorbital.Hennrich[5]syn-thesizedC80(D5)fromfullerenesootextractionbydHPLC.…     

First infrared spectroscopic detection of the monobridged diboranyl radical (B2H5, C2v) and its D5-isotopomer in low-temperature diborane ices

With the use of a surface-scattering machine, layers of 27+/-4 nm diborane (B2H6) frosts were irradiated at 10 K and 10(-10) Torr with energetic electrons. The electrons induce a unimolecular decomposition of the diborane molecules and lead to boron-hydrogen bond rupture processes. Here, we report the first infrared spectroscopic detection of the monobridged diboranyl radical (B2H5, C2v) via the nu8 mode at 1033 cm(-1). The infrared assignment of the B2H5 isomer was verified by conducting experiments with diborane-d6 (B2D6). Under identical experimental conditions, the monobridged B2D5 isomer was observed via the nu6(1154 cm(-1)), nu8(823 cm(-1)), and nu5(1307 cm(-1)) absorptions. These data can be utilized in future spectroscopic studies of chemical vapor deposition processes to allow an identification of the monobridged diboranyl isomer in real time via infrared spectroscopy.     

Relativistic symmetry orbitals for the double groups C2v,C∞v,D∞h,and Oh

Relativistic symmetry orbitals are given for molecular LCAO calculations for the double groups: C_2v, C_∞v, D_∞h, and O_h (6-fold) coordination. The atomic orbitals used in the LCAO are of the four component form. A discussion of the comparison between nonre ativistic and relativistic molecular eigenvalues is presented.     

Photochromic and thermochromic spiropyrans. 11. Calculation of the stabilities of the valence tautomers of spiropyrans

A method was developed for the estimation of the relative stabilities of spirocyclic and merocyanine structures of spiropyrans on the basis of the Pariser-Farr-Pople method in , parametrization with a corresponding estimate of the energy of formation of the spiro node. The results of the calculations are in satisfactory agreement with the experimental data and the results of calculation by the MINDO/3 method.See [1] for communication 10.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 177–184, February, 1980.     

Planar D 2h B26H8, D 2h B26H8 2+, and C 2h B26H6: Building Blocks of Stable Boron Sheets with Twin-Hexagonal Holes

The most stable mono-layer boron sheets were predicted to have both the isolated hexagonal hole and the twin-hexagonal hole. Previous investigations indicate that planar B₁₈H _n ^q (n = 3–6, q = n ? 4) are the building blocks of boron sheets with isolated hexagonal holes. Extensive DFT investigations performed in this work show that D _2h B₂₆H₈, D _2h B₂₆H₈ ²⁺, and C ₂ B₂₆H₆, may serve as the building blocks of boron sheets with twin-hexagonal holes. These bicyclic clusters possess planar or quasi-planar geometries at B3LYP/6-311+G(d,p) level, with 16, 14, and 14 delocalized π electrons, respectively. Detailed analyses indicate that they are overall aromatic in nature, with the formation of islands of both σ and π aromaticity. They are analogous to D _2h C₁₆H₁₄ and D _2h C₁₆H₁₄ ²⁺ in π bonding patterns, respectively, but fundamentally different from the latter in σ-bonding. Remarkably, all of them appear to be energetically the lowest-lying isomers obtained, which are promising targets for future gas phase syntheses. These hydroboron clusters, together with B₁₈H _n ^q clusters, establish the molecular basis for modeling the short-range structures, nucleation, and growth processes of monolayer boron sheets. The results obtained in this work enrich the chemistry of boron hydride clusters and expand the analogy relationship between hydroborons and hydrocarbons.