Bond Lenghts Research Articles

Solid state structure and reactivity in solution. II. The crystal and molecular structure of (2,2,7,7-tetramethyl-3,6-dithiaoctane)-tetracarbonylchromium(0)

The crystal and molecular structure of the title compound, (DTO)Cr(CO) 4, has been determined by single-crystal X-ray diffraction techniques. The crystals are monoclinic, a = 9.583(4), b = 13.399(5) and c = 14.809(8) Å, β = 101.62(4)°, space group P2 1/n, d (calc. z = 4) = 1.32 g/cm 3. The structure was solved by MULTAN and refined by full-matrix least-squares methods to R = 0.05 using 2274 reflections measured on a four circle diffractometer with Mo-Kα radiation. The coordination about the central chromium atom is a distorted octahedron, the greatest deviations from ideal geometry being the angle S1CrS2, 80.6(1)°, and the angle between the two mutually trans carbonyls, 169.8(2)°. Mean metal-ligand bond lenghts are CrS = 2.437(1), CrC( cis) = 1.863(5) and CrC( trans) = 1.820(5) Å. The influence of the two bulky t-butyl substituents, bonded to S, on the octahedral geometry about Cr, and the possible influence of this molecular distortion on the reactivity of the complex via displacement of the chelating ligand by Lewis bases are discussed.

Vibrational spectra and normal coordinate analysis of CF 3 compounds : XXXIV. The bis(trifluoromethyl)difluoroborate anion: X-ray structure of Cs[(CF 3) 2BF 2

The 10B and 11B IR and Raman spectra of the [(CF 3) 2BF 2] − anion are reported, assigned, and used to determine a quadratic local symmetry force field via a normal coordinate analysis. The crystal structure of Cs[(CF 3) 2BF 2] ( P2 1/ m, a 5.958(1), b 7.628(1), c 8.2997(9) Å, β 100.50(1)°, Z = 2, d c 2.863 g cm −3 has been determined by X-ray diffractometry. The most important force constants are f(BC) 3.68 × 10 2, f(BF) 4.17 × 10 2 and f(CF) 4.85 × 10 2 N/m, the respective mean bond lenghts being 1.618, 1.391 and 1.353 Å. The FBF and CBC bond angles are 108.1(4) and 113.6(5)°, respectively. Apparently because of Cs⋯F(B, C) interactions, one BC bond has a staggered and the other an eclipsed conformation in the solid state.

The choice of the inversion coordinate and the geometry of formaldehyde in the A1 A2 excited electronic state

The semi-rigid inversion hamiltonian is used to fit the rotation-inversion energy separations of formaldehyde in the A1 A2 excited electronic state. In the model the HCH angle is a function of the inversion coordinate which is defined as an angle between the CO bond and the HCH plane. It is noticed that the CO and CH bond lenghts calculated, here are different from those obtained whithin the rigid approach.

Kristall-und molekülstrukturen zweier modifikationen de hexaphenyldigermylsulfids (C 6H 5) 3GeSGe(C 6H 5) 3

en Two differnt crystal modifications of hexaphenyldigermanium sulfide (C 6H 5GeSGe(C 6H 5) 3 (I and II were obtained by crystallization from hot benzene/methanol or form ethanol at 20°C. Single crystal X-ray structural analyses for both I (low temperature data at −130°C) and II (at 20°C) (I, R = 0.046; II, R = 0.048) were performed. I is monoclinic, P2 1/c, with a = 11.020(3), b = 15.473(3), c 18.606(3) »,π = 106.92(2)°, Z = 4; II is orthorhombic, P2 12 12 1, with a = 2.617(2), b = 17.345(3), c = 18.408(3) », Z = 4. The molecules have different conformeric structures with respect to a rotation of the (C 6H 6) 3Ge groups around the Ge bonds with very similar bond lenghts and angles. Bond data for I(II) are: GeS 2.212(1) and 2.261(1) » (2.227(2) and 2.240(2) »); GeC 1.933(4) ⋯ 1.971(4), mean 1.945(5) » (1.931(7)⋯1.954(7), mean 1.943(4) »); GeSGe 111.2(1)° (110.7(1)°). The Ge bond lenghts are comparable to those in thiogermanates and do not indicate significant π-bond contributions.

Enhancement of diamagnetic susceptibility in amorphous semiconductors

We have used a localized bond-orbital model to calculate the magnetic susceptibility x of a model elemental semiconductor in the amorphous phase. The amorphous state has been approximated by disorder in the bond angles only; the bond lenghts have been assumed to be unchanged from their crystalline values. To calculate x dia and x para, the dia- and paramagnetic parts of x associated with the valence band electrons, a representation in which the bond-orbitals orbitals at each site are orthogonal, is used. We find that in going from the crystalline to the amorphous phase; (i) the magnitude of x dia does not always increase which is in contrast to some earlier theoretical results and; (ii) x para is reduced if a certain average energy denominator increases or remains unchanged. We argue that for Ge and Si, the diamagnetic enhancement in going from the crystalline to the amorphous phase is likely to be large as seen experimentally.

Cis-trans-Isomere von Diazadiphosphetidin-Derivaten: Fünf Kristall- und Molekülstrukturen / Cis-trans Isomers of Diazadiphosphetidine Derivatives: Five Crystal and Molecular Structures

Abstract The crystal structures of the compounds [R3CP(X)NR]2(R= CH3; X=S, Te for cis isomers and X= lone pair, S, Te for trans isomers) (2-6) were determined from single crystal X-ray data. The four-membered P-N rings in the cis isomers 2 and 3 show significant deviations from planarity attributed to steric overcrowding in the molecules.The trans isomers 4-6 are planar. The P-N bond lenghts (mean values for 2-6:171.4, 170, 171.6, 169.2 and 168.3 pm)in the cis isomers are not significantly different from the corresponding lengths in the trans isomers 5 and 6.

Lattice constants and force constants for iron, nickel, and copper from orbital energies added to pairwise atomic repulsions in cluster models

A theory combining electrostatic forces and one-electron molecular orbital energies is used to determine the bulk lattice and nearest neighbor stretching force constants for α-Fe using 9- and 15-atom models. While 13-atom clusters do not produce bulk bond lenghts for bcc, Ni and Cu, 9-atom bcc clusters produce close estimates.

Synthesis and molecular structure of niobocene trimethylacetate and its π-complex with diphenylacetylene

Niobocene trimethylacetate Cp 2Nb(OOCCMe 3) (I) does not react with usual n-donors (pyridine and triphenylphosphine), but readily adds a π-acceptor molecule of diphenylacetylene (tolane) in benzene to form Cp 2Nb(OOCCMe 3)(π-Ph 2C 2) · 0.5 C 6H 6 (II). The structures of the diamagnetic complexes I and II have been determined by an X-ray diffraction study. These molecules represent wedge-like sandwiches wit dihedral angles between cyclopentadienyl ligands equal to 44.4 and 50.7°, and average NbC distances of 2.39 and 2.44 Å, respectively. The bisector plane of I contains the chelate trimethylacetate group (NbO bond lenghts 2.23 and 2.24 Å) and that of II contains the coordinated tolane molecule and the oxygen atom of the terminal trimethylacetate ligand (NbO 2.16, NbC 2.18 and 2.19, CC 1.29 Å, PhCC angles 141 and 146°). An unusually large splitting of OCO stretching frequencies is observed in the IR spectrum of I (1652−1305 = 347 cm −1). Structural characteristics of the coordinated CC triple bond in II are similar to those found in Cp(π-Ph 4C 4)Nb(CO)(π-Ph 2C 2) studied earlier. The role played by the Nb III lone pair in I and II is discussed.

Force constants and equilibrium geometries in H 2O 2 and other small molecules containing an OH group

General harmonic ab initio and semi-empirical force fields have been established for hydrogen peroxide and hypofluorous acid. Previous experimental force fields for H2O2 are unreliable due to the lack of sufficient experimental data for gaseous H2O2 and isotopic derivates.Harmonic and some anharmonic force constants are compared in a series of XOH compounds with X standing for H, H3C, H2N, HO and F. In this sequence,the OH stretching force constant frr decreases while the XOH bending force constant increases. There is a noticeable opposite trend for fRα (increasing) and fRα (decreasing) with the sum fRα + frα being almost constant. This effect maybe simulated by a simple model. The stretch-stretch coupling constant frR is always small and negative.The calculated OH bond lenghts are in very good agreement with available experimental values and support the previously assumed value of 0.965 A for H2O2. Bond angles are reproduced within an accuracy of 1 to 2 degrees.

Crystallographic studies of some transuranic trihalides: 239PuCl 3, 244CmBr 3, 249BkBr 3 and 249CfBr 3

Single-crystal X-ray diffraction methods were used to refine the structures of PuCl 3, CmBr 3, and CfBr 3. In PuCl 3 (UCl 3-type) the Pu ion has nine Cl-ion neighbors, three at 2·919(1) Å and six at 2·886(1) Å. A radius of 0·995 Å was derived for the six-coordinated Pu 3+ ion. In CmBr 3 (PuBr 3-type) the eight-coordinated Cm ion has two Br ions at 2·865(6) Å, four at 2·983(4) Å, and two at 3·137(4) Å. Californium tribromide was shown to crystallize in both the AlCl 3- and FeCl 3-type structures. In the former type, the Cf ion is six coordinated and the three independent CfBr bond lenghts are 2·795(9) Å, 2·827(11) Å and 2·828(8) Å. Berkelium tribromide was prepared and shown by powder X-ray diffraction to exhibit the AlCl 3-, PuBr 3-, and possibly FeCl 3-type structures. The new findings on CfBr 3 and BkBr 3 were used to produce a more complete description of the structural relationships among the lanthanide and actinide tribromides.

Crystal and molecular structure of the 2 : 3 complex of N-methylphenazinium with ααα′α′-tetracyanoquinodimethane, [(nmp)2]2+[(tcnq)3]2–

Crystals of the title compound (I) are triclinic with reduced cell dimensions a= 17.360(15), b= 7.695(6), c= 9.858 Å, α= 71.65(7), β= 76.08(8), γ= 86.92(8)°, Z= 1. The structure was solved from a three-dimensional Patterson function and refined in space group P to 0.105, by use of 2 346 diffractometer data. The tcnq units form triads with the central planar unit on a centre of symmetry. No distinction, based on bond lengths, can be made between charged and neutral molecules. The non-planar nmp+ ion retains an approximate mirror plane through the two nitrogen atoms and there are two different C–N bond lenghts (1.335 and 1.371 Å) in the central ring. The crystal structure is built up of tcnq triads which repeat along the c axis while the holes are filled with centrosymmetrically related pairs of nmp+ ions. Within the triads the separation between consecutive units is ca. 3.15 Å and two consecutive triads are separated by ca. 3.26 Å.

The crystal and molecular structure of bis-dimethylaminotitanium difluoride tetramer

Abstract The crystal structure of [(Me2N)2TiF24 has been determined by single-crystal X-ray diffraction. The crystals are tetragonal, I 4 , a = b = 11.313(5), c = 12.862(4) A, Z = 2. The titanium atoms display a distorted octahedral coordination and are linked by TiFTi and TiNMe2Ti bridges to form a tetramer, which possesses a crystallographic inverse tetrad axis at its centre. One fluorine and one dimethylamino group do not participate in the bridging. The principal bond lenghts are TiF(bridging) 2.00(2) and 2.06(2), TiF (terminal) 1.77(2), TiN(bridging) 2.14(3) and 2.19(3), TiN(terminal) 1.99(30) A. The structure has been refined to R = 0.077 for 231 visually estimated unique reflections.

Stereochemistry and bonding in nickel  olefin complexes. The structure of t etramethylethylenenickel 1,2-bis (dicyclohexylphosphino)ethane

The structure of tetramethylethylenenickel 1,2-bis(dicyclohexylphosphino) ethane, (CH3)2C2(CH3)2Ni[(C6H11)2PCH2CH2P(C6H11)2], has been determined from 4995 observed, absorption-corrected reflections collected by counter methods. The compound crystallizes in the monoclinic space group C52h  P21/n with cell dimensions a 17.1306(7), b 16.9016(7), c 11.4899(8)» and > 100.082(5)°. The calculated density is 1.147 g/cm3 for Z=4. Least-square refinement yielded a final conventional R value of 0.036. If one coordination site is assigned to the olefin, the nickel atom is three-coordinate. Although no crystallographic symmetry is required, the molecule posses idealized C2 symmetry. The average NiC and NiP bond lenghts are 1.981(2) and 2.156(6)», respectively. The central bond of the olefin has beenlengthened upon coordination to 1.421(3) ». The tetramethylethylene moiety is distorted from planarity with the C(CH3)2 planes bent away from the nickel atom 27.2(6)°. The nickel atom and four atoms bonded to it are not coplanar, the central bond of the tetramethylethylene species forming a 16.5° angle with the Ni,P(1),P(2) plane. A segmented rigid-body analysis of the thermal motion of the molecule indicates that the barrier to rotation of the olefin is 18 kcal/mole.

X-ray study of barenylmercury halides spontaneous symmetrization of phenylbarenylmercury iodide in the crystal

A crystallographic investigation of the structure of (methyl- and phenyl- barenyl)mercury bromide and (phenylbarenyl)mercury iodide has been undertaken. The bond lenghts of the HgBr and HgI bonds of these compounds are unchanged in comparison with those in compounds containing less electron-acceptor radicals. Only in the case of the (phenylbarenyl)mercury iodide does the intermolecular contact Hg…I decrease (3.29 Å instead of the usual 3.81−4.2 Å). In the crystal state (phenylbarenyl)mercury iodide was observed to undergo spontaneous symmetrization. This effect has been explained in terms of the strong intermolecular coordination between the mercury and iodine atoms of the two molecules in the crystallographic dimer.

The crystal and molecular structure of two carbonyl-stabilised ammonium ylides

The crystal structures of two carbonyl-stabilised, ammonium ylides are reported; bond lenghts and angles indicate that the stabilisation results principally from electron delocalisation towards the carbonyl oxygen atom.

Bond lengths in diphenyloctatetraene

AbstractThe crystal structure of all trans‐diphenyloctatetraene has been refined. The C‐C bond lenghts from previous work were confirmed. The experimental bond lenghts are compared with the values calculated by the Hückel method both with constant and variable β, and with those calculated by the approximate SCMO method for three sets of parameters. The discrepancies between the best theoretical bond lengths and the experimental values need not be significant.

Redetermination of oxygen parameters in xenotime, YPO4

Oxygen parameters in xenotime have been refined in order to compare bond lenghts in two isostructural minerals, zircon ard xenotime. The results have shown that the different behaviour toward metamictization of these minerals could not be explained on the basis of cation–anion distances alone.

Structure and properties of nitroso compounds

The electronic structure of organic compounds containing NO bonds has been considered in relation to their observed lengths and characteristic frequencies. The relation between these properties and “bond-order” has been examined for a number of molecules and ions for which the electronic structures are well defined. These relationships are then used for the discussion of other compounds for which the electronic structures are less certain. It has been shown that many of the molecules contain bonds of non-integral order; structures in which the NO bonds contain an odd number of electrons have been proposed in certain cases, the double-quartet hypothesis being used to describe the electron distribution. It has been shown that the pattern of bond lenghts and characteristic frequencies can then be understood, as well as such unexplained observations as the dimerization of alkyl nitroso-compounds and the non-existence of dimers of nitrosyl halides.

Emission spectrum of SiF 2: Part I. The band system in the region 2755-2179 A

The band system in the region 2755-2179 A obtained by exciting flowing SiF 4 vapor is analyzed as due to a non-linear SiF 2 molecule. The vibrational frequencies obtained for the lower electronic state are ν 1 = 778 cm −1, ν 2 = 427 cm −1, and ν 3 = 947 cm −1, while those for the upper electronic state are ν 1 = 597.5 cm −1 and ν 2 = 342 cm −1. From the rotational K-sub-heads observed for four bands, it is shown that the band system belongs to a perpendicular type. The rotational constants obtained from the analysis are C′ = 3.0 cm −1 and C″ = 1.9 cm −1. The following molecular parameters are obtained for the lower electronic state: angle FSiF = 124° ± 2°, and bond lenght SiF = 1.46 ± 0.07 A .

Bond lengths in the cyclo-octatetraene dianion C 8H 8

Simple molecular orbital calculations suggest that the C 8H 8 dianion is planar with equal bond lenghts 1·409 Å.