Single Bond Lengths Research Articles

Crystal structure of nitridobis(tri-methyl-silanolato)[1,1,1-trimethyl-N-(tri-methyl-sil-yl)silanaminato]molybdenum(VI).

In the title compound, [Mo(C6H18NSi2)(C3H9OSi)2N], the Mo(VI) cation is located on a mirror plane and is coordinated by a nitride anion, a 1,1,1-trimethyl-N-(tri-methyl-sil-yl)silanaminate anion and two tri-methyl-silanolate anions in a distorted tetra-hedral geometry; the N atom and two Si atoms of the 1,1,1-trimethyl-N-(tri-methyl-sil-yl)silanaminato anionic ligand are also located on the mirror plane. The MoN bond length of 1.633 (6) Å is much shorter than the Mo-N single-bond length of 1.934 (7) Å. No hydrogen bonding is observed in the crystal structure.

The Solitary Isomer of C60 H18 Is Proven to Have a C3v Crown Shape: Crystal Structure Determination and Synthesis of Its Triruthenium Cluster Complex.

Analytically pure C60 H18 is obtained by a Ru3 cluster complexation and decomplexation method. The crystal structure of C60 H18 consists of one flattened hemisphere, to which all 18 hydrogen atoms are symmetrically bonded, and one curved hemisphere akin to C60 . A benzenoid ring in the flattened hemisphere is isolated from the residual π systems by a belt composed of sp(3) -hybridized CH units. The average out-of-plane distances for carbon atoms attached to the benzenoid ring (0.14 Å) is substantially larger than that found in C60 F18 (0.06 Å). Several long C(sp(3) )C(sp(3) ) single bond lengths [1.61(3)-1.65(3) Å] are observed for C60 H18 . The reaction of [Ru3 (CO)12 ] and C60 H18 produces [Ru3 (CO)9 (μ3 -η(2) ,η(2) ,η(2) -C60 H18 )] (1), where the Ru3 triangle is regiospecifically linked to the hexagon opposite to the benzenoid ring. Compound 1 is the first transition metal complex of a polyhydrofullerene (fullerane). C60 H18 and 1 have been characterized by (1) H and (13) C NMR, UV/Vis, and mass spectroscopies. The HOMO-LUMO gap of C60 H18 is evaluated to be 1.51 V by cyclic voltammetry.

Cascade of High-Pressure Transitions of Claudetite II and the First Polar Phase of Arsenic(III) Oxide

Claudetite II, one of the three known As2O3 polymorphs, has been studied by single-crystal synchrotron X-ray diffraction up to 21 GPa. Three new As2O3 polymorphs, all structurally related to claudetite II, are formed through a sequence of single-crystal-to-single-crystal phase transitions: the ambient pressure claudetite IIα (monoclinic space group P21/n, Z = 4) transforms at 2 GPa continuously to phase IIα′ (P21/a, Z = 8), at 6 GPa to phase IIα″ (P21/a, Z = 24), and at 11 GPa it transforms discontinuously to phase IIβ (P21, Z = 4). The experimentally observed phases α–α″ are centrosymmetric, whereas phase β is polar. A significant hysteresis on decompression skips the α″ phase and only α′ phase is formed before the ambient pressure α polymorph is recovered. The transitions and compression of claudetite II preserve its structure of 2D polymeric As2O3 layers; however, the intersheet As···As distances are compressed at 21 GPa to about 2.9 A, only 0.5 A more than the As–As single bond length. Previous DFT mo...

Crystal structure of the cage derivative penta-cyclo-[5.4.0.0(2,6).0(3,10).0(5,9)]undeca-8,11-dione ethyl-ene di-thio-ketal.

The title penta-cyclo-undecane cage derivative, C13H14OS2, was identified during a thio-ketalization reaction. The reaction selectively gave the title compound and the product corresponding to bis-ketal was not formed. The title compound exhibits unusual Csp (3)-Csp (3) single bond lengths ranging from 1.495 (3) to 1.581 (2) and strained bond angles as small as 89.29 (12) and as large as 115.11 (11)°.

Silicon-based counterpart of alpha-graphyne

Abstract We present the first principles density functional calculations of electronic structure and energetics of silicon-based counterpart of α-graphyne, labeled as α-silicyne. Both LDA and GGA functionals are applied for exchange–correlation potentials. We show that graphyne-like silicon in 2D buckled structure (equilibrium buckling δ z ≅ 0.73 and Δ z ≅ 1.45 A ) has ≈ 2.33 eV and ≈ 1.96 eV lower energies than planar geometry for GGA and LDA functionals, respectively. The single and triple bond lengths of silicon are consistent with previously reported values. As a different case from graphyne, which is semimetallic, the electronic band structures of buckled α-silicyne do not show Dirac fermion indicating a metallic nature. The metallic character of the system is largely determined by p-electronic states of the triple bonded silicon atoms.

Electronegativity effects and single covalent bond lengths of molecules in the gas phase.

This paper discusses in detail the calculation of internuclear distances of heteronuclear single bond covalent molecules in the gaseous state. It reviews briefly the effect of electronegativity in covalent bond length. A set of single bond covalent radii and electronegativity values are proposed. Covalent bond lengths calculated by an adapted form of a simple expression (which calculated internuclear separation of different Group 1 and Group 2 crystalline salts to a remarkable degree of accuracy) show very good agreement with observed values. A small number of bond lengths with double bonds as well as bond lengths in the crystalline state are calculated using the same expression and when compared with observed values also give good agreement. This work shows that covalent radii are not additive and that radii in the crystalline state are different from those in the gaseous state. The results also show that electronegativity is a major influence on covalent bond lengths and the set of electronegativity scale and covalent radii proposed in this work can be used to calculate covalent bond lengths in different environments that have not yet been experimentally measured.

Validation and time step determination of discrete element modeling of flexible fibers

In this paper, a flexible fiber model, based on the Discrete Element Method (DEM) and the bonded-particle model by Potyondy and Cundall (International Journal of Rock Mechanics & Mining Sciences 41 (2004) 1329–1364), is comprehensively examined by considering the cases of the bending, stretching, and twisting of a fiber under static loads and dynamic vibrations. The numerical simulation results are in good agreement with the analytical predictions from elastic thin beam theories. In addition, a time step criterion is discussed and proposed in order to ensure numerical stability and obtain correct dynamic behaviors of fibers. It is found that the time step should be less than the time it takes for an axial extensional/compressional wave to travel a single bond length.

The Synthesis, X-ray Structure Analysis, and Photoisomerization Assessment of the Acyclic Triazenes 4-[(E)-2-(biphenyl-4-yl)diazenyl]-morpholine and 1,3-Bis(biphenyl-4-yl)triazene

The acyclic triazenes 4-[(E)-2-(biphenyl-4-yl)diazenyl]-morpholine (1) and 1,3-bis(biphenyl-4-yl)triazene (2) were prepared and their X-ray crystal structures determined. Compound 1 crystallized in the monoclinic space group P21/c with a = 29.153 (5) A, b = 6.0444 (14) A, c = 7.5997 (15) A, and β = 96.03 (1)°. Compound 2 crystallized as the 1/4 cyclohexane solvate in the triclinic space group P $$\bar{1}$$ with a = 10.3228 (10) A, b = 13.4541 (14) A, c = 15.4323 (15) A, α = 87.158 (4)°, β = 76.030 (4)° and γ = 71.492 (5)°. The N–N double bond in 1 and 2 adopted an (E)-configuration and had bond angles that ranged from 112.19 (9)° to 114.01 (13)°, which deviated from optimal trigonal planar geometry by 6°–8°. A degree of π-conjugation across the acyclic triazene moieties in compounds 1 and 2 was indicated by N–N double and single bond lengths that were respectively longer and shorter than the literature values for these types of bonds. The room temperature electronic absorption spectra of 1 and 2 in various solvents were both dominated by an intense band above 300 nm that was assigned to a combination of π → π* and n → π* transitions. Compounds 1 and 2 in acetonitrile and methanol solution were found to undergo trans → cis photoisomerization. The magnitudes of trans → cis rate constants were rationalized in terms of the degree of solvent stabilization of the dipolar resonance hybrid structure of the acyclic triazene subunits in 1 and 2. Irradiation of chloroform solutions of 1 and 2 caused trans → cis photoisomerization and radical decomposition to occur. The X-ray structures of compounds 1 and 2 were determined and their photoisomerization kinetics explored.

Cs3UP2S8, a Coordination Polymer Containing the Unprecedented [U=S]2+ Sulfidouranium(2+) Moiety

AbstractAlthough terminal chalcogeno ligands are well known for the group 5 and 6 transition metals, they are highly unusual for the oxophilic group 4 metals and unknown so far for the lanthanides or actinides. Cs3UP2S8, is the first actinide compound containing a terminal M=S group. It was synthesized by reacting uranium metal, Cs2S, S, and P2S5 in a 4:1:8:3 ratio at 700 °C in an eutectic LiCl/CsCl mixture. The crystal structure was determined by single‐crystal X‐ray diffraction techniques. Cs3UP2S8 crystallizes in the rhombohedral space group R$\bar{3}$ [a = 15.5217(8) Å; c = 35.132(2) Å, V = 8305.0(8) Å3, Z = 18]. The crystal structure is based on a tetrahedral network type, wherein the uranium atoms are coordinated by a unusual sulfido moiety and thiophosphate groups in a pseudo‐tetrahedral fashion. The U=S distance of 2.635(3) Å observed in the sulfide moiety is approx. 0.2 Å shorter than the average U–S single bond length, indicating a double‐bond type character.

Isolated large π systems in pyrene–fluorene derivatives for intramolecular through-space interaction in organic semiconductors

In order to give an insight of the special spectra of isolated π systems, a series of pyrene–fluorene derivatives, with conjugated or non-conjugated pyrene groups, were systematically studied. Besides absorption of non-conjugated pyrene itself and main conjugation chain, all the pyrene-non-conjugated large conjugated materials show a characteristic sharp absorption peak at ∼352nm. Through systematical investigation, this special absorption peak was attributed to the intramolecular through-space interaction between the two isolated large π systems. Such interaction could also be defined as π – π hyperconjugation. And from quantum calculation, this intramolecular interaction does shorten the length of single bond. Through systematical research, the condition of this intramolecular through-space interaction is proved to be that the non-conjugated pyrene must have projection on fluorene plane. And then this effect is applied to explain the improved injection ability of the materials by bringing out one simple hopping model.

Bond strengths of New Carbon-nitride-Related material C2N2(CH2)

A new carbon-nitride-related material C2N2(CH2) nanopletelet was synthesized by subjecting a precursor C3N4HxOy+Au in a laser-heating diamond anvil cell (LHDAC) to the pressure of 40 GPa and the temperature of 1200-2000 K. The synthesized C2N2(CH2) was accordingly found to be an orthorhombic unit cell of the space group Cmc21 with lattice constants a = 7.625Å, b = 4.490Å, and c = 4.047Å. The bulk modulus B0 was determined to be B0 = 258 ± 3.4 GPa, only the 60 % that of the diamond. C2N2(CH2) consists of the tetrahedrally coordinated C with three C-N single bond and the one C-C single bond, and the bridging carbon with the C-CH2-C bond. The C-N single bond length of the tetrahedron ranges from 1.444 to 1.503 Å. This bond length is close to the C-N single bond of 1.447 to 1.458 Å in the superhard β-C3N4. The compressibility of the C-N and C-C single bond of C2N2(CH2) ranges from 0.976 to 0.982 with the pressure of 30 GPa. These values are very close to the compressibility of the C-N and C-C single bond of 0.978 to 0.982 in β-C3N4, cubic-C3N4, and diamond.

Theoretical study of the COLin complexes: Interaction between carbon monoxide and lithium clusters of different sizes

A theoretical study was carried out about the complexes composed of carbon monoxide and small lithium clusters, namely COLi2, COLi4, COLi6, COLi8, COLi5+, and COLi7+. The complexation of carbon monoxide with Li2 is found to be endothermic and not spontaneous. As for Li4 and Li5+, they can only reduce CO to single bond length. By comparison with the N2Lin complexes where a minimum of eight lithium atoms are needed to cleave the triple bonded nitrogen completely, the Lin cluster behaves more efficiently in activating the CO molecule because the Li6 cluster is sufficient to cleave the CO triple bond in a highly exothermic way. Besides, the degree of reduction of CO gradually increases with Lin becoming larger, and the Li7+ and Li8 clusters can cleave the CO triple bond to greater extent than Li6 does. Due to the ability of lithium clusters to cleave the NN and CO triple bonds in effective ways, they offer a promising approach to activate other strong chemical bonds.

Non-fused polyaromatic hydrocarbons: interactions of aromatic and antiaromatic rings through a CC bond

The interaction of the moieties of benzene, cyclobutadiene, cyclopentadinyl anion, and the cyclopent- adianide cation upon each other and upon a CC bond connecting pairs of these rings is investigated computa- tionally. The resulting non-fused bicycles include biphenyl, phenylcyclobutadiene, phenylcyclopentadienylium, phe- nylcyclopentadienide, pentafulvalene, cyclobutadienyl- cyclopentadienylium, cyclobutadienyl-cyclopentadienide, and bicyclobutadiene. The relative stability and aromaticity are assessed from hydrogenation energies, aromatic sta- bilization energies, ring separation energies, nucleus-inde- pendent chemical-shift, harmonic oscillator model of aromaticity, and natural bond orbital analysis. Calculations are performed with density functional theory (B3LYP) and Moller-Plesset perturbation theory of second order (MP2). Enthalpy quantities are also determined by G3. When both rings are aromatic in character, the bridging bond is mostly r in character. When one or both of the rings is antiaro- matic, the bridging bond has significant p character. Sys- tems with contrasting aromaticities have CC bridging bonds of lengths between CC single bond lengths and CC double bond lengths and where the systems were charged, the charge is evenly distributed between the rings.

Periodic DFT study of adsorption of nitroamine molecule on α-Al2O3(0 0 1) surface

The adsorption of NH2NO2 molecule on the Al2O3(001) surface were investigated by the generalized gradient approximation (GGA) of density functional theory (DFT). The calculations employ a supercell model represented with 2×2 of periodic boundary conditions. The strong attractive forces between NH2NO2 molecule and Al2O3 induce obvious change of the NH2NO2 and Al2O3 structure. Although the NH2NO2 molecule does not decompose, AlO bonds partially decompose and some OO bonds form, whose bond lengths are intervenient between OO double bond length and OO single bond length. The largest adsorption energy is −453.8kcalmol−1. By the adsorption energy and the change with structure of NH2NO2 and Al2O3, it can be concluded that aluminized explosive of NH2NO2 keeps high reactivity even if the aluminum is oxidized to form a film of the alumina. This finding can make clear the activated aluminum as a stored energy source for propellants and the good performance of aluminized explosives. The energies of DOS for N and O atoms of the NH2NO2 molecule match with those of Al atoms, and AlO or AlN bond forms easily at the corresponding energies range. The DOS projections on the N, O and Al atoms occur with obvious shift of peaks, which infers energy bands become broad and the interactions of chemical bonds are strengthened.

Chlorido[1-phenyl-3-(2,3,5,6-tetramethylbenzyl)benzimidazol-2-ylidene]silver(I)

In the title compound, [AgCl(C24H24N2)], the terminal phenyl and tetra­methyl­benzene rings [which form a dihedral angle of 87.92 (14)°] make dihedral angles of 59.59 (11) and 83.19 (12)° with respect to the central benzimidazole ring system. The Ag—C and Ag—Cl single-bond lengths are 2.087 (3) and 2.3267 (9) Å. The C—Ag—Cl bond angle is 172.84 (7)°. C—H⋯π inter­actions contribute to the stabilization of the crystal structure. A very weak π–π stacking inter­action between adjacent tetra­methyl­benzene rings [centroid–centroid distance = 4.0610 (18) Å] is also observed.

Fitting EXAFS data using molecular dynamics outputs and a histogram approach

The estimation of metal nanoparticle diameter by analysis of extended x-ray absorption fine structure (EXAFS) data from coordination numbers is nontrivial, particularly for particles 5 nm in diameter, for which the undercoordination of surface atoms becomes an increasingly significant contribution to the average coordination number. These undercoordinated atoms have increased degrees of freedom over those within the core of the particle, which results in an increase in the degree of structural disorder with decreasing particle size. This increase in disorder, however, is not accounted for by the standard means of EXAFS analysis, where each coordination shell is fitted with a single bond length and disorder term. In addition, the surface atoms of nanoparticles have been observed to undergo a greater contraction than those in the core, further increasing the range of bond distances. Failure to account for this structural change results in an increased disorder being measured, and therefore, a lower apparent coordination number and corresponding particle size are found. Here, we employ molecular dynamics (MD) simulations for a range of nanoparticle sizes to determine each of the nearest neighbor bond lengths, which were then binned into a histogram to construct a radial distribution function (RDF). Each bin from the histogram was considered to be a single scattering path and subsequently used in fitting the EXAFS data obtained for a series of carbon-supported platinum nanoparticles. These MD-based fits are compared with those obtained using a standard fitting model using Artemis and the standard model with the inclusion of higher cumulants, which has previously been used to account for the non-Gaussian distribution of neighboring atoms around the absorber. The results from all three fitting methods were converted to particle sizes and compared with those obtained from transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements. We find that the use of molecular dynamics simulations resulted in an improved fit over both the standard and cumulant models, in terms of both quality of fit and correlation with the known average particle size.

5-Sulfanylidene-2H,5H-1,3-dithiolo[4,5-d][1,3]dithiol-2-one

The title mol­ecule, C4OS5, is essentially planar, with an r.m.s. deviation of 0.032 (3) Å. All the C—S single bonds are shorter than the standard Csp 3—S single-bond length, showing the π-conjugated nature of the molecule. In the crystal, molecules lie parallel to one another and pack in columns along the a axis. Short inter­molecular S⋯S contacts [3.314 (3), 3.482 (2) and 3.501 (2) Å] are observed between the columns. The angle between the two mol­ecular dipole moments in the unit cell is 39.3 (1)° and the macro-polarization vector is along the [1 0 − 1.41] direction. As a result of the high polarization and π-conjugation of the structure, the crystalline powder exhibits a second harmonic generating intensity, which is as strong as that of the urea standard powder crystals, when irradiated by a 1053 nm laser beam. The diffraction space of the crystal showed a nonmerohedral twinning.

Synthesis and Characterization of an Amidinate-Stabilized Siladithiocarboxylate and Its Germanium(II) Complex

The synthesis and characterization of the amidinate-stabilized potassium siladithiocarboxylate [{LSi(S)2}K(THF)2]2 (2, L = PhC(NBut)2) are described. Compound 2 was synthesized by the reaction of [LSiCl] (1) with two equivalents of elemental sulfur and KC8 in THF. X-ray crystallography and DFT calculations show that the Si–S bond lengths in 2 are intermediate between the Si═S double and Si–S single bond lengths. There is a weak electronic delocalization along the “Si(S)2” skeleton. Compound 2 underwent a salt elimination reaction with GeCl2·dioxane to form [{LSi(S)2}2Ge:] (3), which contains two “LSi(S)2–” moieties chelating to the germanium(II) atom in an anisobidentate manner.

3,4-Bis(4-bromophenyl)-N-phenylmaleimide

In the title mol­ecule, C22H13Br2NO2, the three benzene rings are arranged in a propeller-like fashion around the central malemide ring, making dihedral angles of 48.2 (4), 30.2 (4) and 34.8 (4)° with the malemide ring. The C—C single-bond lengths connecting benzene groups and maleimide are significantly shorter [C—C = 1.468 (9) and 1.478 (9) Å] than a typical Csp 3—Csp 3 single bond, indicating partial conjugation between the benzene and the mal­eimide. A weak non­classical C—H⋯O hydrogen bond helps to stabilize the crystal structure.

Excitation energy calculation of conjugated hydrocarbons: A new Pariser–Parr–Pople model parameterization approaching CASPT2 accuracy

A new parameterization for the Pariser-Parr-Pople (PPP) model for conjugated hydrocarbons is proposed in this work. The distance-dependence of PPP parameters are obtained from CASPT2 ground state and low-lying excited state energies of ethylene and its cation at various C-C single bond lengths and are fitted to a set of carefully chosen mathematical functions. Our new PPP model is applied to the calculation of vertical singlet-triplet energy gaps and the excitation energies for low-lying π→π(*) valence excitations in various π-conjugated molecules. Results with the new PPP model are consistently better than the standard PPP model in use. It often surpasses density functional theory and single-reference excited state methods such as configuration interaction singles or time-dependent density functional theory in terms of its accuracy and agrees reasonably well with high-level theories or experiments.