A dichromium(II) compound with an elongated metal-metal bond: Cr2(oxindolate)4(oxindole)2

The title compound has been prepared by reaction of (C₅H₅)₂Cr with oxindole (indole with CO in place of CH₂ at the 2-position). Red single crystals belong to space group P2₁/c with a = 10.107(4) Å, b = 22.496(7) Å, c = 9.210(3) Å, β = 93.26(3)°, V = 2091(2), and Z = 2. The centrosymmetric molecule has a CrCr distance of 2.495(4) Å. The mean CrO and CrN distances for the bonds to bridging oxindolate anions are 2.024(7) and 2.065(8) Å, respectively. There is an oxindole molecule bound at each end with a CrO axial bond of length 2.341(8) Å and a hydrogen bond from the oxindole NH group to an equatorial oxygen atom of length 2.83(1) Å. The significance of this compound with respect to CrCr bonding is discussed.     

The crystal structure of Mn(NO)3P(C6H5)3: The first x-ray analysis of a mononuclear metal trinitrosyl complex

The structure of Mn(NO)₃PPh₃ has been analyzed by single-crystal X-ray diffraction. It shows a tetrahedral geometry with essentially linear nitrosyl groups, and an eclipsed configuration around the MnP bond. Average distances and angles are: MnN 1.686(7) Å, MnP 2.315(2) Å, NO 1.165(10) Å, PC 1.815(4) Å, MnNO 177.2(7)°, PMnN 103.6(2)°, NMnN 114.7(4)°. Final R factor 7.3% for 2064 non-zero reflections. The structure of the five-coordinate nitrito complex Mn(NO)₂(ONO)(PEt₃)₂ is also mentioned briefly.     

Die kristall- und molekúlstruktur der dimeren dimethylaluminium- und dimethylgallium-N,N′-dimethylacetamidine [(CH3)2M(NCH3)2CCH3]2 (M = Al,Ga)

Dimethylaluminium- and dimethylgallium-N,N′-dimethylacetamidine (I and II) are doubly associated forming a puckered eight-membered ring. They crystallize isostructurally in the monoclinic space group P2₁/c with two dimers per unit cell. The lattice constants of I are a 8.187, b 7.266, c 14.778 Å, β 103.58° and those of II a 8.163, b 7.277, c 14.835 Å, β 103.46°. The MN and the NC bond lengths within the rings are nearly equal, their mean values are for I: AlN 1.925 Å, CN 1.330 Å and for II: GaN 1.979 Å, CN 1.335 Å. This is also true for the exocyclic bond lengths with average values AlC 1.975 Å, NC 1.474 Å, CC 1.509 Å (for I) and GaC 1.998 Å, NC 1.484 Å and CC 1.507 Å (for II). The metal atoms are tetrahedrally coordinated, and the distortion is only slight. The final R-values are 0.034 and 0.056, respectively.     

Crystal and molecular structure of 9-methyl-9-phenyl-9,10-dihydro-9-sila-3-azaanthrone

The crystal and molecular structure of 9-methyl-9-phenyl-9,10-dihydro-9-sila-3-azaanthrone has been determined from three-dimensional X-ray diffraction data. The title compound crystals are monoclinic, space group P2₁/b, a = 12.818(2), b = 16.508(2), c = 7.694(1) Å,γ = 105°, 34′(2), Z = 4 and D_cal = 1.278 g cm^?3. The structure was determined by direct methods and refined by full-matrix least-squares calculations in the block-diagonal anisotropic approximation for non-hydrogen atoms to R = 0.043 for 2190 independent reflections, registered at room temperature. This is the first crystal structure determination of a Si-dihydroanthracene derivative with two heterocycles and a planar carbon atom in the C10-position. The tricyclic fragment takes up a planar configuration, the silicon atom having a tetrahedral surrounding, with an endocyclic angle of 103.7(1)° and average bond length SiC, 1.862(1) Å. The CO, 1.220(2) Å, bond length in the carbonylic group exactly corresponds with the double bond length. Average distance NC is 1.335(3) Å, angle CNC, 116.5(2)°.     

The crystal structures of m-trifluoromethylphenylsilatranone and p-fluorophenylsilatranone

The crystal structures of two silatranone derivatives are reported. The close N → Si approach (2.106(3) Å in m-trifluoromethylphenyl-, and 2.129(3) Å in p-fluorophenyl-silatranone) indicates strong dative acceptor bonds. For various silatrane derivatives and inverse relation has been revealed between the mean group electronegativity of the substituent R attached to silicon and the N → Si dative bond distance. In both structures there are long (1.72 Å) SiO bonds in the SiOCO moiety. The m-trifluoromethylphenyl derivative contains a disordered CF₃ group.     

Two-dimensional vibrational analysis of the Lippincott-Schröder potential for OHO,NHO and NHN hydrogen bonds and the deuterium isotope effect

Two-dimensional vibrational analyses [i.e. crude adiabatic approximation, SCF approximation and variational method (crude adiabatic basis function)] are performed on the hydrogen bond systems consisting of the Lippincott-Schröder potentials for the OHO, NHO and NHN bonds. The OHO and NHN systems are supposed to be linear and the bent structure is considered for the NHO system. The frequency shift for the hydrogen bond length variation and its deuterium substitution effects are in good agreement with experiment. The anomalies in the frequency ratio ν_OH/ν_OD at an O—O distance of 2.5 Å, and in the interminimum distance shift on deuteration at 2.5 Å are well explained as the difference of double minimum behavior between the vibrational states of proton and deuterium. It is also shown that the Lippincott-Schröder model for the OHO system supplies the general features for proton tunneling, proton delocalization beyond the barrier and other type processes in hydrogen bonds.     

Ab initio studies of structural features not easily amenable to experiment: Part 6. Quantitative estimate of the effect of bond delocalization on structure and hyperconjugative interaction of the amide group

The structural changes, which occur in the amide unit when the NH₂-group is twisted out of plane by rotation about the NC bond, have been determined by comparing the completely relaxed ab initio geometries of planar and perpendicular formamide and acetamide. In the perpendicular conformation, in which the π-electron amide resonance is uncoupled, the NC bond distance is 0.080.09 Å longer than in the planar form; the CO bond distance is about 0.01 Å shorter; NH distances are about 0.01 Å longer; and HNC angles are 510° smaller, whereas the CNO angle is relatively constant. Because of the apparent invariance of CH₃-hyperconjugation effects in planar and perpendicular acetamide, it is tentatively postulated that anomeric orbital interactive effects (involving the lone pair on NH, the CO π-electron pair and antibonding π*-group-orbitals on C(α) in NHC(HR)C(O)), which should be an important factor in determining peptide chain conformation, do not vary significantly with small deviations from amide group planarity.     

Transition-metal complexes of two valence tautomers of a bulky phenoxide, 2,6-Bu-t2-4-MeC6H2O− (ArO−); preparation and crystal and molecular structure of a phenoxytitanium(III) and a cyclohexadienonylrhodium(I) complex, [Ti(η-C5H5)2 OAr] and [Rh(ArO-η5)(PPh3)2]

The 2,6-di-t-butyl-4-methylphenoxo ligand (ArO^?) is ambidentate, giving rise to the O-bonded 15-electron d¹ [Ti(η-C₅H₅)₂OAr] and the η⁵ -[C(2)-C(6)]-bonded 18-electron d⁸ complex [Rh(ArO-η⁵)(PPh₃)₂], obtained from [{Ti(η-C₅H₅)₂Cl}₂]-LiO Ar and [Rh{N(SiMe₃)₂}(PPh₃)₂]-ArOH, respectively; the average TiC(η) distance is 2.362(10) Å, TiO 1.892(2) Å, and O:C(of Ar) 1.352(3) Å, and TiOC 142.3(2)°; in the Rh^I complex, C(2)C(6) are coplanar (with CC(av.) 1.38(2) Å). C(1)O 1.28 Å, and Rh to C(2) C(6) bond lengthsare in the range 2.19–2.65 Å.     

Estimates for systematic empirical corrections of consistent 4–21G ab initio geometries and their correlations to total energy group increments

The structural parameters of the completely relaxed 4–21G ab initio geometries of more than 30 basic organic compounds are compared to experimental results. Some ranges for systematic empirical corrections, which relate 4–21G bond distances to experimental parameters, are associated with total energy increments. In general, for the currently feasible comparisons, the following corrections can be given which relate calculated distances to experimental r_g parameters and calculated angles to r_s-structures For CC single bond distances, deviations between calculated and observed parameters (r_g) are in the ranges of ?0.006(2) to ?0.010(2) Å for normal or unstrained hydrocarbons; ?0.011(3) to ?0.016(3) Å for cyclobutane type compounds; and +0.001(5) to +0.004(4) Å for CH₃ conjugated with CO. For CO single bonds the ranges are ?0.006(9) to +0.002(3) Å for CO conjugated with CO; and ?0.019(3) to ?0.027(9) Å for aliphatic and ether compounds. A very large and exceptional discrepancy exists for the highly strained ethylene oxide, r_s — r_e = ?0.049(5) Å and in CH₃OCH₃ and C₂H₅OCH₃ the r_s — r_e differences are ?0.029(5), ?0.040(10) and ?0.025(10) Å. Some of these discrepancies may also be due to deficiencies of the microwave substitution method caused by atomic coordinates close to inertial planes. For CN bonds, two types of NCH₃ corrections are from +0.005(6) to ?0.006(6) and from ?0.009(2) to ?0.014(6) Å; and the range for NCO is +0.012(3) to +0.028(4) Å. For isolated CC double bonds the range is + 0.025(2) to +0.028(2) Å. For conjugated CC double bonds the correction is less positive (+0.014(1) Å for benzene). For CO double bonds the corrections are ?0.004(3) to +0.003(3) Å. For bond angles of type HCH, CCH, CCC, CCO, CCO, OCO, NCO and CCC the corrections are of the order of magnitude about 1–2° (or better). Angles centered at heteroatoms are less accurate than that, when hydrogen atoms are involved. Differences in HOC and NHC angles were found in a range of ?2.3(5)° to ?6.2(4)°.     

Structural isomerism of propionato copper(II) complex: crystal and molecular structure of tetrakis(μ-o-propionato)bis(methyl 3-pyridyl-N-carbamate)dicopper(II) at 190 K

The crystal and molecular structure of tetrakis(μ-o-propionato)bis(methyl 3-pyridyl-N-carbamate)dicopper(II) at 190 K was determined by X-ray analysis. The internuclear Cu⋯Cu distance is 2.6395(3) Å. CuO bond lengths are 1.961(1), 1.9678(9), 1.9828(9) and 1.9979(9) Å and CuN bond length is 2.165(1) Å. The non-bonding Cu(II)⋯Cu(II) contacts for nine binuclear Cu(II) propionates and hexacoordination of Cu(II) ion in the structure of [Cu(CH₃CH₂COO)₂(mpc)₂]0.25H₂O (mpc=methyl 3-pyridyl-N-carbamate) is consistent with the bond–valence sum model.     

Spectroscopic and magnetic properties of a new class of two-dimensional bitriazole compounds: The X-ray structure of poly-bis(thiocyanato-N)-bis-μ-(4,4′-bis-1,2,4-triazole-N1,N1′)-cobalt(II) monohydrate

The synthesis of a new class of two-dimensional triazole compounds is described, including the crystal structure of [Co(NCS)₂(btr)₂]H₂O [btr stands for 4,4′-bis-1,2,4-triazole (C₄H₄N₆)]. Crystals are monoclinic, space group C2/c, a = 11.159(1) Å, b = 13.047(4) Å, c = 12.993(3) Å, β = 91.81(2)°, Z = 4. The structure has been solved by Fourier and direct methods and refined by full-matrix least squares to R = 0.0229, R_w = 0.0283. The structure consists of layers of six-coordinated cobalt atoms, each having two trans-oriented N-bonded thiocyanate groups [CoNCS 2.098(2) Å] and linked together in the equatorial plane by single bridges of btr to a two-dimensional network. The btr ligand coordinates through its N(1) and N(1′) atoms [CoN 2.128(1) and 2.142(1) Å]. The intralayer CoCo distance is 9.207(2) Å, and the inter-layer CoCo distance is 8.584(1) Å. The magnetic susceptibilities of the compound and of the isostructural nickel and iron compounds are discussed. The iron compound exhibits a high-spin-low-spin crossover at liquid-nitrogen temperatures, as shown by magnetic susceptibility.     

Crystal and molecular structure of [η5-C5(CH3)5]Co(O2C6H4), a cobalt(o-catecholate) complex

[η⁵-C₅(CH₃)₅]Co(O₂C₆H₄) crystallizes in the orthorhombic space group Pnma with a 12.942(4), b 12.902(4), c 8.543(3) Å, V 1426(1) ų, and Z = 4. Least-squares refinement of 1688 independent observed reflections, F(_obs) ? 2.5σ(F_obs), gives R_F 3.79 and R_wF 3.72%. The cyclopentadienyl ring contains two short (1.412(3) Å) and three longer (〈av〉 1.430(4) Å) CC bond lenghts, consistent with a slight preference for diolefin bonding. The O₂C₆H₄ fragment is best described as a catecholate with a CO bond distance of 1.338(3), and a CoO distance of 1.837(2) Å.     

The chemistry and the stereochemistry of poly(n-alkyliminoalanes) : III. The crystal and molecular structure of the adduct (HalN-i-Pr)6AlH3

The crystal and molecular structure of the adduct (HAlN-i-Pr)₆AlH₃ has been determined from single-crystal and three dimensional X-ray diffraction data collected by counter methods. The cage-type molecular structure consists of two six-membered rings, (AlN)₃, joined together by four adjacent transverse AlN bonds; the loss of two of these bonds allows the complexation of one alane molecule, with five-coordination of the aluminum (trigonal bipyramidal geometry), through two AlN bonds and two AlHAl bridge bonds. The AlN bond lengths range from 1.873 to 1.959 Å; the average AlH bond length is 1.50(1) Å for the four-coordinated aluminum atoms; the average distance of the two apical hydrogens from the five-coordinated aluminum atom is 1.92(5) Å. Colourless prismatic crystals of the compound have the following crystal data: triclinic space group P$\text{1}$; a = 17.13(2); b = 10.78(2); c = 10.20(2) Å; α = 124.3(4), β = 92.0(4), γ = 92.1(5); Z = 2; calculated density 1.157 g/cm³. The structure has been refined by block-matrix, least-squares methods using 4358 independent reflections to a standard unweighted R factor of 4.9%.     

The crystal and molecular structure of oxo-bis[tribenzylgermanium(IV)]

Crystals of oxo-bis[tribenzylgermanium(IV)], O[(PhCH₂)₃Ge]₂, are rhombohedral, space group R$\text{3}$, having a = 9.621(2) Å, α = 85.48(3)°. The structure was solved by Patterson methods using diffractometer data and refined by full-matrix least squares to R = 0.0876. The structure consists of molecules lying along the 3-fold axis of the unit cell, in which the GeOGe fragments are strictly linear and centrosymmetric. The GeO distance is 1.730(1) Å and the GeC distance is 1.980(5) Å.     

Small ring metallocycles : V. Crystal and molecular structure of hydrido-1,3-(1,1,3,3-tetramethyldisiloxanediyl)carbonylbis(triphenylphosphine)iridium(III), Me2SiOSiMe2Ir(H)(CO)(PPh3)2 · EtOH

The structure of the cyclo-metalladisiloxane, Me₂SiOSiMe₂Ir(H)(CO)(PPh₃)₂, has been determined by single crystal X-ray diffraction using Mo-K_α radiation. Data were collected to 20 = 45 ° giving 6060 unique reflections,of which 4582 had I ?3σ(I). The latter were used in the full-matrix refinement. Crystallographic data: space group, P$\text{1}$; cell constants: 12.604(7),12.470(4), 15.821(6) Å, 66.93(6)°, 105.34(7)°, 112.41(8)°;V 2095(3) ų; p(obs) 1.45 g/cm³; p(calc) 1.46g/cm³ (Z=2). The asymmetric unit consists of one iridium complex and one molecule of ethanol of salvation. The structure was solved by standard heavy atom methods and refined with all non-hydrogen atoms anisotrophic to final R factors, R₁ 0.034 and R₂ 0.042. The iridium metallocycle has approximate C_s symmetry with the mirror plane passing through the four-membered IrSiOSi ring. The average IrP, IrSi and SiO bond lengths are 2.38, 2.41, and 1.68 Å, respectively. The IrCO and CO bond lengths are 1.903(8) and 1.133(8). The H atom bonded to Ir was not located.The Ir atom is raised out of the basal, P₂Si₂ plane toward the carbonyl by about 0.26 Å. The most striking feature of the structure is the strain apparent in the four-membered ring. The internal angels are: 64.7 (SiIrSi), 96.8 (IrSiO), 97.8 (IrSiO), and 99.8 (SiOSi). In an unstrained molecule, the SiOSi angle is normally in the 130–150° range. It is proposed that the strain in the ring is consistent with the catalytic activity of the metallocycle.     

Vibro-conformational behaviour and normal coordinate analysis of fluorocarbonyl isocyanate,FC(O)NCO

Vibrational data of vapour, liquid and matrix-isolated fluorocarbonyl isocyanate, FC(O)NCO, were investigated. A subsequent normal coordinate analysis was performed for the A′ species of the predominant planar cis conformer (CO double bond cis with respect to the vicinal NC double bond). The following internal force constants were derived: f_CO= 12.88 mdyn Å⁻¹, f_CF=6.20 mdyn Å⁻¹ and F_CN= 4.42 mdyn Å⁻¹.     

An electron diffraction study of the molecular structure of hexamethyldisiloxane

An electron diffraction determination of the molecular geometry of hexamethyldisiloxane has removed much of the uncertainty concerning this structure. The length of the SiO bond and the SiOSi bond angle were determined to be 1.631 ± 0.003 Å and 148 ± 3°, respectively. The experimental data are consistent with a staggered conformation (C_2v symmetry) while a model with twist angles around the SiO bonds of about 30° cannot be excluded. The molecule is probably performing large amplitude intramolecular motion.     

The crystal structure of triphenyltin isothiocyanate

The crystal structure of Ph₃SnNCS has been determined by single crystal X-ray diffraction. The crystals are monoclinic, P2₁, a = 19.02(3), b = 11.67(2), c = 15.49(2)Å;, β = 95.64(10)°, Z = 8. The molecules are arranged in infinite zig-zag S…SnNCS…Sn&.sbnd; chains similar to those in Me₃SnNCS, but with slightly longer SnN, shorter SnS bonds, and almost planar SnC₃ units. Principal mean bond lengths and angles are: SnN, 2.22(5); NC, 1.17(8); CS, 1.58(7); SSn, 2.92(1); SnC, 2.09(3); CC, 1.38(2)Å; SnNCm 161(4); CSSn, 97(3); SSnN, 175(3) and CSnC, 119.8(1.5)°.     

Molecular structure and conformation of gaseous vinyldimethylchlorosilane as determined by electron diffraction

The molecular structure of vinyldimethylchlorosilane has been determined by gas phase electron diffraction at room temperature. The least squares values of the bond lengths (r_g) and bond angles (∠_α) are : r(CH) = 1.086(6) Å, r(CC) = 1.347(5) Å, r(SiC=) = 1.838(6) Å, r(SiC) = 1.876(3) Å, r(SiCl) = 2.078(2) Å, ∠CCSi = 127.8° (1.2) and ∠=CSiCl = 107° (1). Models with pure syn form and a mixture of syn and gauche gave equally good agreement with the diffraction data.     

The crystal structure of Ba2V2O7

Ba₂V₂O₇ is triclinic with a = 13.571(3), b = 7.320(2), c = 7.306(2) Å, α = 90.09(1), β = 99.48(1), β = 99.48(1), γ = 87.32(1)°, V = 7.15.1 ų, Z = 4, and space group $\text{P}\text{1}$. The crystal structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares analysis to a R_w of 0.034 (R = 0.034) using 2484 reflections measured on a Syntex $\text{P}\text{1}$ automatic four-circle diffractometer. The structure has two unique divanadate groups that are repeated by the b and c lattice translations to form sheets of divanadate groups parallel to (100). These sheets are linked by four unique Ba atoms that lie between these sheets. Ba(1) and Ba(3) are coordinated by eight oxygens arranged in a distorted biaugmented triangular prism and a distorted cubic antiprism, respectively. Ba(2) is coordinated by 10 oxygens arranged in a distorted gyroelongated square dipyramid and Ba(4) is coordinated by nine oxygens arranged in a distorted triaugmented triangular prism. These coordination numbers are substantiated by a bond strength analysis of the structure, and the variation in 〈BaO〉 distances is compatible with the assigned cation and anion coordination numbers. Both divanadate groups are in the eclipsed configuraton with 〈VO(br)〉 bond lengths of 1.821(4) and 1.824(4) Å and VO(br)V angles of 125.6(3) and 123.7(3)°, respectively. Examination of the divanadate groups in a series of structures allows certain generalizations to be made. Longer 〈VO(br)〉 bond lengths are generally associated with smaller VO(br)V angles. When VO(br)V < 140°, the divanadate group is generally in an eclipsed configuration; when VO(br)V > 140°, the divanadate group is generally in a staggered configuration. Nontetrahedral cations with large coordination numbers require more oxygens with which to bond, and hence O(br) is more likely to be three coordinate, with the divanadate group in the eclipsed configuration. In the eclipsed configuration, decrease in VO(br)V promotes bonding between O(br) and nontetrahedral cations, and hence smaller nontetrahedral cations are generally associated with smaller VO(br)V angles.