Bond Lenghts Research Articles

Microscopic investigation of the strain distribution in InGaAs/GaAs quantum well structures grown by molecular beam epitaxy

Extended X-ray absorption fine structure in the glancing angle geometry has been used to study the strain accomodation in quantum well structures of In x Ga 1- x As⧸GaAs ( x<0.25). The results show that a number of Ga-As bond lenghts are stretched. Indeed, two Ga-As bonds distances coexists: 2.45 ± 0.01 Å and 2.64 ± 0.02 Å, which correspond to the Ga-As and In-As bond distances in the binary compounds GaAs and InAs, respectively. This result is independent of the In molar fraction in the strained alloy layers.

Catena-[Cd{μ-S(CH2)3NHMe2}Br2

The title complex, catena-poly[dibromocadmium-μ-3-dimethylamino-1-propanethiolato], contains polymeric chains of alternating Cd and S atoms with Cd-S bond lenght of 2.515(3) and 2.520(3) A. Distorted tetrahedral coordination of Cd [with a wide S-Cd-S angle of 126.95(5) o ] is completed by two Br ligands [Cd-Br 2.5834(15) and 2.6400(14) A]. The longer Cd-Br bond is to a Br atom involved in inter-chain hydrogen bonding with the ammonium group of a mercaptoamine ligand of an adjacent chain, to give two-dimensional sheets

Electronic structure and bonding in the metallocarbohedrene Ti8C12.

Total-energy and electronic-structure calculations are presented for a recently proposed dodecahedral cluster of eight titanium and twelve carbon atoms. The calculations were done using density-functional theory and a recently developed cluster full-potential linear muffin-tin orbital method which is suited to arbitrary geometries and permits direct evaluation of the forces. As in the ${\mathrm{C}}_{60}$ molecule, the atoms form a spherical grahitelike shell with a threefold coordination at all sites. The C-C and Ti-C bond lenghts are calculated to be of 2.63 and 3.76 bohrs, respectively, and the binding energy is 6.6 eV per atom. The bonding mechanism is quite different from that which stabilizes the graphite crystal or the ${\mathrm{C}}_{60}$ molecule.

Structures of 1-cyano-2,2-bis(methylthio)vinyl N,N-dimethyldithiocarbamate (2) and 1,2,2-tris(methylthio)vinyl N,N-dimethyldithiocarbamate (3)

The N,N-dimethyldithiocarbamate moiety in both title compounds is planar. The C5-N1 bond lenghts are 1.332 and 1.327 A.

Stereoelectronic effect of the trimethylsilyl substituent upon carbon-oxygen bond lengths at the .beta. position: some structural studies

Results of low-temperature (130 K) crystal structure analyses for seven β-trimethylsilyl-substituted cyclo hexylnitrobenzoate esters are reported. For those molecules (three) with the Si-C and C-O bonds antiperiplanar the C-O bond lenghts are increased by 0.014 A av (Δ/σ min=2.9) compared with that in the silicon-free analogue. For those molecules (four) with the Si-C and C-O bonds gauche no such systematic lengthening of the C-O bonds is observed

Exploring the conformation space of cycloalkanes by linearized embedding

AbstractLinearized embedding is a variant on the usual distance geometry methods for finding atomic Cartesian coordinates given constraints on interatomic distances. Instead of dealing primarily with the matrix of interatomic distances, linearized embedding concentrates on properties of the metric matrix, the matrix of inner products between pairs of vectors defining local coordinate systems within the molecule. Here, the approach is used to explore the full conformation space allowed to small cyclic alkanes, given the constraint of exact bond lenghts and bond angles. Useful general tools developed along the way are expressions for rotation matrices in any number of dimensions and a generalization of spherical coordinates to any number of dimensions. Analytical results give some novel views of the conformation spaces of cyclopropane, cyclobutane, cyclopentane, and eyclohexane. A combination of numerical and analytical approaches gives the most comprehensive description to date of the cycloheptane conformation space with fixed bond lengths and angles. In this representation, the pseudorotation paths of cyclohexane and cycloheptane are closed curved lines on the surfaces of spheres.

LEED crystallographic studies for the Cu(110)-(2 × 3)-N surface structure

An initial multiple-scattering analysis of LEED intensities has been performed for the Cu(100)-type top-layer reconstructions. The best R-factor analysis supports neither simple N overlayer models nor models with Cu(100)-type top-layer reconstructions. The best correspondence between calculated and experimental intensities appears with models where every other 〈001〉 row is missing, similar to that observed for the Cu(110)-(2 × 1)-O surface. The favoured surface structure has N atoms chemisorbed on long-bridge sites such that chains of (Cu aNCu bNCu a) x create a surface analogous to the ideal Cu 3N(110) sur face, except that every third N atom is missing from the surface chains. There is evidence that lateral displacement of copper atoms from the ideal positions leads to two different NCu surface bond lengths with values near 1.83 and 1.90 Å. Each N atom also bonds to two Cu atoms in the second layer with equal bond lenghts of about 1.88 Å.

Computations of point defect energies in YBa 2Cu 3O 6.5

The atomistic simulation technique has been employed to compute point defect energies in YBa 2Cu 3O 6.5. Potentials employed earlier for YBa 2Cu 3O 7 and more recent modifications are employed. The dominant oxygen ion defect is predicted to be of the Frenkel type in comparison to Schottky types. This result is similar to previous behavior found in YBa 2Cu 3O 7 and YBa 2Cu 4O 8. Point defects involving cations are predicted to be less likely except for Cu + that can form at an interstitial site in the Y plane. The potentials are used to demonstrate a dependence of internal bond lenghts upon copper-oxygen hole concentration which is similar to experimental determinations. Realistic values for the energy of oxygen intercalation are derived with these potentials.

IR, Multinuclear‐NMR, and Structural Studies on [WH(CO)2(NO)(PR3)2]: cis‐Influence of Phosphorus Ligands on Hydride Character

AbstractA thorough IR and 1H‐, 13C‐, 31P‐, 183W‐NMR spectroscopic, and X‐ray structural study was carried out on complexes of the type trans, trans‐[WH(CO)2(NO)(PR3)2], (R = Et, Me, Ph, i‐PrO, MeO, and PhO). Linear correlations could be found between Tolman's parameter X and v(CO), v(WH), v(NO), δ(13C) (CO), as well as 1n(k), k being the H/D exchange rate constant for the hydride in CD3OD. The 1J(183W,31P), 2J(31P,1H), and 2J(31P,13C) as well as the 1J(183W,1H) values are related to the electronegativity of the R groups on the phosphorus ligands. This is also indicated by EHT calculations of s‐orbital populations of appropiate W model complexes. The X‐ray structures of [WH(CO)2(NO)(PR3)2] (R = Me, Ph, and MeO) were determined. Minor differences were observed in the WP bond lenghts and in the PWP and CWC angles. No obvious relationship between X‐ray data and spectroscopic parameters could be found. All three structures reveal a bending of both the CO and PR3 ligands towards the hydride atom. The total octahedral distortion is remarkably constant (25.6, 29.4, and 27.0° tilt, respectively), although the ligands individually are very different. This is attributed to redistribution of π‐electron density between CO and PR3 groups toward the central W‐atom in the three complexes.

The synthesis of several new cyclopentadienyl-ruthenium t-butyl thiol complexes

The air-sensitive complexes [CpRu(L)(L′)(HSBu t)]PF 6 (L = L′ = PPh(OMe) 2, PPh 2OMe, P(OMe) 3; L = PPh 3, L′ = CO, P(OMe) 3) are prepared by heating methanol solutions of CpRu(L)(L′)Cl, HSBu t, and NH 4PF 6. The cyclopentadienyl-ruthenium thiol complexes oxidized in air to form paramagnetic complexes, one of which, [CpRu(PPh 2OMe) 2SBu t]PF 6, was isolated and characterized by a single crystal x-ray diffraction study. Crystals are monoclinic with space group P2 1/ c, a = 12.8070(25), b = 14.3160(36) c = 20.1768(50) Å, β = 97.841(18)°, and Z = 4. Data were refined to R = 0.0452 (6248 reflections). The RuS(1) bond length was 2.274(1) Å and the RuP bond lenghts were 2.298(1) and 2.291(1) Å. The synthesis of CpRu(CO)(PPh 3)SBu t is also reported.

An Unusual sandwich-type nickel oxide-siloxanolate complex {[PhSiO]} 6 (μ 4-O) 2 (μ 3-O) 4[Ni 8(μ 3-0) 2](μ 3-O) 4(μ 4-O) 2 [PhSiO] 6}·14n-BuOH·10H 2O·2Me 2CO. Synthesis and crystal structure

An X-ray crystal study of the nickel oxide-siloxanolate complex {[PhSiO] 6(μ 4-O) 2(μ 3-O) 4[Ni 8(μ 3O) 2] (μ 3-O) 4(μ 4-O) 2[PhSiO] 6}·14n-BuOH·10H 2O·2MeCO (I or Ia without noncoordinating solvate molecules) having a cage structure has been carried out. The complex studied was prepared by the interaction of NiCl 2 with the product of the reaction of phenylsilsesquioxane (PhSiO 1.5) n with NaOH. The polynuclear cage-like centrosymmetric molecule Ia has a sandwich-type structure. The inner two-dimensional nickel oxide fragment Ni 8o 2(μ-O) 12 2 = Ni 8O 8 is structurally identical to a fragment of the NiO crystal layer which is one Ni atom thick and parallel to the (111) plane. All Ni atoms have oxygen atoms in an octahedral coordination (oxide, silanolate, molecules of water, butanol and acetone). The O atoms of the nickel oxide layer have both trigonal pyramidal (μ 3-O) and distorted tetrahedral (μ 4-O) coordination. The nickel oxide layer is bonded by NiOSi bridges through silanolate O atoms with two outer 12-membered hexasiloxane (SiO) 6 cycles (sandwich “caps”) with an almost ideal crown conformation. Some of the butanol and H 2O crystallosolvate molecules do not coordinate the Ni atoms being included in the cavities between Ia molecules. The NiO bond lenghts are 2.006–2.159 Å, while the average SiO(Si) and SiO(Ni) bond lengths are 1.637 and 1.618 Å, respectively.

Synthese von Cp(CO) 2 MnTCNE aus [Cp(CO) 2MnXPh] n (X = S, Se, Te; n = 1,2); Festkörperstruktur und Magnetismus

Cp(CO) 2MnTCNE ( 1) which was first reported by M. Herberhold et al., has been obtained from the reaction of [Cp(CO) 2MnXPh] n (X = S, n = 1; X = Se, Te, n = 2) with TCNE. The synthesis of the relevant organometallic sulfur, selenium and tellurium derivatives is described. An X-ray diffraction study of the TCNE compound reveals that two Cp(CO) 2MnNCC(CN)C(CN) 2 ( 1) molecules form centrosymmetric dimers containing a coordinated centrosymmetric (TCNE) 2 x− pair. The bond lenghts, the v(CN) spectra and a solid state magnetism of μ eff = 1.1 μ B (293 K) are all consistent with this structural finding.

Iridium carbonyl clusters: VIII. The crystal structure of (η 5-C 5H 5) 2W 2Ir 2(CO) 4 (μ-CO) 2(μ 3-CPh)(μ 3-η 3-C 3Ph 3), a “60-electron” cluster with a triangulated rhomboidal W 2Ir 2 skeleton

The reaction of (η 5-C 5H 5) 2W 2Ir 2(CO) 10 with PhCCPh has previous been shown to produce, inter alia, a complex of stoichioetry (η 5-C 5H 5) 2W 2Ir 2(CO) 6(PhCCPh) 2. This is shown here to be the dimetalloallyl-benzylidyne complex (η 5-C 5H 5) 2W 2Ir 2-(CO) 4(φ-CO) 2 (μ 3-CPh)(μ 3-η 3-C 3Ph 3), which crystallizes in the centrosymemtric monoclinic space group P2 1/ c (No. 14) with a 14.253(9), b 15.629(4), c 18.731(4) Å, β 96.86(4)°, V 4143(3) Å 3 and Z = 4. Diffractio data were collected with a Syntex P2 1 automated four-circle diffractometer (Mo- K α radiation, 2θ 4.5–45.0°). Substantial crystal decomposition was observed, but the structure was solved and refined to R 8.5% for all 4887 data ( R 5.8% for those 3395 data with | F o| > 3σ(| F o|)). The complex, although a “60-electron” cluster, has a triangulated rhomboidal skeleton (dihedral angle 170.33°) with W(1) and Ir(1) as the bridgehead atoms. Metalmetal distances show some irregularities and there are two “semi-bridging” carbonyl ligands, possibly as a result of the formally “electron-poor” environment of Ir(1). Metalmetal bond lenghts are W(1)W(2) 3.080(1), Ir(1)Ir(2), 2.720(1), W(2)Ir(1) 2.665(1), W(1)Ir(1) 2.723(2) and W(1)Ir(2) 2.852(2) Å. The μ 3-benzylidyne fragment is linked to W(1), W(2) and Ir(1), while the μ 3-η 3-C 3Ph 3 ligand is σ-bonded to W(1) and Ir(1) and is π-bonded (η 3 mode) to Ir(2). The μ 3-CPh and μ 3-η 3-C 3Ph 3 ligands lie on the same surface of the close-to-planar W 2Ir 2 cluster.

Structural correlations and vibrational spectra of molten and glassy GeSe 2

Using an effective interionic interaction the properties of vitreous and molten GeSe 2 are investigated by molecular dynamics method (MD). The effective interaction includes steric repulsion, Coulomb interactions due to charge transfer, and charge-dipole interaction due to large electronic polarizability of anions. Calculations are carried out on systems consisting of 648 and 5184 particles. Results for partial pair distribution functions, static structure factors, distribution of bond angles, and vibrational density of states are calculated at various temperatures in the molten and glassy states. Short range order in both glassy and molten states is dominated by Ge(Se 1 2 ) 4 tetrahedra and Ge-Se, Se-Se and Ge-Ge bond lenghts are found to be 2.35, 3.75 and 4.30 Å, respectively. The static structure factor exhibits the first sharp diffraction peak (FSDP), a characteristics of intermediate range order in chalcogenide glasses, as well as all the other peaks observed in X-ray and neutron diffraction measurements. We have also calculated the anomalous temperature dependence of the first sharp difraction peak. From a detailed analysis of partial distribution functions we determine that Ge-Ge correlations around 10 Å and Ge-Se correlations around 6 Å are responsible for the FSDP. The calculated vibrational density of states in the glass shows peaks at 8.0, 10.8, 26.4, 34.4 and 37.2 meV, which are all in good agreement with inelastic neutron scattering experiments. In addition, the companion line ( A 1c) of the symmetric breathing mode A 1 (26.4 meV) is identified with a feature at 27.8 meV in the density of states. Raman scattering studies also find the companion line to be ∼ 1.5 meV higher than the symmetric breathing mode.

Thermal and IR spectroscopic characterization of Kamotoïte

Kamotoïte-(Y), a new uranyl and rare earth carbonate, has been studied by thermal treatment. The mineral has also been characterized by IR spectroscopy and the presence of the bidentate binding of carbonate to uranyl ion has been confirmed. Likewise, the U-O bond lenght in the uranyl group can be estimated by IR measurements.

Comparative stereochemical studies of Ph 3SnL complexes (L = 1-carbodithioato vs. 1-carbothioato ligand). Crystal structures of [Ph 3Sn(S.CS.N(CH 2) 5] and [Ph 3Sn(S.CO.N(CH 2) 4O)

Single crystal X-ray structure determinations have been carried out on [Ph 3Sn(S.CS.N(CH 2) 5)] ( 1) and [Ph 3Sn(S.CO.N(CH 2) 4O)] ( 2) (the latter the first organotin(IV) complex of the monothiocarbamate ligand) and the results compared with those recently reported for [PH 3Sn(S.CS.N(CH 2) 4)] ( 3) in order to throw light on details of the variations in the Sn environment and their possible causes. The crystal of compounds 1 and 2 are monoclinic, P2 1/ c, Z = 4. For 1 a 10.009(5), b 15.959(7), c 15.831(6) Å, β 115.79(3)°; R was 0.026 for N o = 2224 ‘observed’ reflections. For 2, a 15.16(1), b 9.560(7), c 18.47(2) Å, β 125.05(5)°; R = 0.031 for N o = 2642. The overall molecular structures are similar, and similar to those of 3, with wide but parallel variations in CSnC (≈ 102–120°) and SSnC angles (≈91–120°). In 1 the SnS bond lengths are 2.481(2), 2.919(2) Å, while in 2 the SnS,O bond lenghts are 2.446(2), 2.809(4) Å, the longer distances in each case being associated with considerable double bond character in the adjacent CS,O linkage (1.678(4), 1.243(6) Å).

Synthesis and molecular structure of the dimagnetic trigonal-bipyrimidal cluster (π-MeC 5H 4) 5V 5(μ 3-S) 6

The reaction of (MeC 5H 4) 2V with HSCMe 3 in boiling heptane leads together with the previously described tetranuclear cluster Cp 4V 4(μ 3-S0 4 (I) (Cp = η-CH 3C 5H 4) to the diamagnetic pentanuclear cluster Cp 5V 5(μ 3-S) 6 (II). The structure of II was confirmed by an X-ray study. The crystals of II are triclinic, a 9.9071(9), b 10.2952(9), c 16.9685(16) Å, α 94.062(7), β 90.399(7), λ 64.145(6)°, V 1553.0(4) Å 3, space group P 1 . The metal framework of the cluster is in the form of a trigonal bipyramid with average V eqV ax and V eqV eq bond lenghts of 3.062(2) and 3.206(2) Å, respectively. The μ 3-bridge sulphur atoms are situated over the faces of the bipyramid at average V eqS and V axS bond lengths of 2.396(2) and 2.226(2) Å, respectively, forming also intramolecular S⋯S contacts of 2.8 Å.

Bicyclische lithium-t-butylaminofluorsilane, moleküle mit zwei- und vierfachkoordinierten lithium

Dimeric lithium-t-butylamino-di-t-butylfluorosilane, [(CMe 3) 2SiFLiNCMe 3] 2, adds one molecule of THF per dimer when crystallized from THF. A bicyclic compound is obtained with fourfold [F 2Li(THF)N] and twofold [NLiN] coordinated lithium. The Si(1)N(1) bond lenght in the six-membered ring has the lenght expected for a ▪bond and is 5.4 pm shorter than the Si(2)N(2) bond of the four-membered ring. The 7Li and the solid state 13C NMR spectra confirm the asymmetry of the molecule. NMR spectra in solution show an equilibration of the H, C, F and Si atoms, a feature which is consistent with fluctuation of Li(1)N(1) and Li(1)N(2) bonds. The THF adduct of lithiated t-butylamino-bis(methyltrimethylsilylamino)-fluorosilane exhibits similar NMR effects.

Structures and phase transitions in piperazinium hexachlorometallates, (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn. A X‐ray diffraction and 35Cl NQR study

AbstractCrystal structures and the nature of the chemical bond in piperazinium hexachlorometallates (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn, were studied by X‐ray diffraction and 35Cl NQR spectroscopy. Piperazinium hexachlorostannate trihydrate shows a solid‐solid phase transition at Tc = 256 K. A disorder of the piperazinium ring and of one of the three water molecules appears in the high temperature phase (space group D122h‐Pnnm, a = 1147.5 pm, b = 959.9 pm, c = 719.4 pm, Z = 2). The disorder affects the 35Cl NQR spectrum. The low temperature phase of (C4H12N2)[SnCl6] · 3H2O reveals two 35Cl NQR lines, whereas in the high temperature phase only one resonance line was observed besides the existence of two crystallographically different chlorine atoms in the unit cell. — Piperazinium hexachlorotellurate crystallizes with space group D162h‐Pnma (a = 1398.5 pm, b = 1203.1 pm, c = 822.2 pm, Z = 4). The TeCl6 octahedra is strongly distorted, with the Te‐Cl bond lenghts differing by about 15%. This distortion is reflected in the 35Cl NQR spectra; the resonance lines are spread over a wide frequency range. — The crystal structure of piperazinium hexachloroplatinate (space group C32h‐C2/m, a = 1016.0 pm, b = 1184.7 pm, c = 695.2 pm, β = 130.227°, Z = 2) shows only small distortions in the PtCl6 octahedra. The two line 35Cl NQR spectrum at lower temperature is in agreement with the crystal structure. — Piperazinium hexachloroplumbate reveals a three 35Cl NQR lines at lower temperature. At Tc = 310 K a phase transition occurs and a one line 35Cl NQR spectrum appears. A hysteresis, about 5 K wide, is connected with the transition.

Trimethylphophinecobalt(I) complexes: crystal and molecular structure of [Co(CO) 2(PMe 3) 3]BPh 4

Crystals of dicarbonyltris)trimethylphophine)cobalt(I) tetraphenylborate belong to the monoclinic space group P2 1/ c with a 10.135(4), b 12.630(4), c 29.35(1) Å, β 106.11(3)° and Z = 4. The structure was refined on 2969 nonzero Cu-K α reflections to R = 0.043. The unit-cell contains discrete BPh 4 − anions and [Co(CO) 2(PMe 3) 3 + cations. The coordination geometry of the cation lies roughly halfway between a trigonal bipyramid (with equatorial CO ligands) and a square pyramid (with trans basal CO ligands), defining an intermediate configuration along the interconversion pathway in the Berry process. The Co-P distance (2.246 Å) to the unique PMe 3 ligand (apical in the square pyramid or equatorial in the trigonal bipyramid) is longer than the other two (2.209 and 2.211 Å). The CoCO bond lenghts are 1.740 and 1.766 Å. the v(CO) infrared bands indicate that the same geometry is retained in CH 2Cl 2 and acetone.