Studies of alkylmetal alkoxides of aluminium,gallium and indium : IV. The molecular structure of dimethylaluminium t-butoxide dimer by gas phase electron diffraction

The electron diffraction data for gaseous dimethylaluminium t-butoxide dimer are consistent with a molecular model of effective D_2h symmetry. The Al₂O₂ ring is planar and the three valencies of the O atoms are lying in a plane. The t-butyl groups undergo nonhindered or slightly hindered internal rotation. The most important bond distances and valence angles are: AlO = 1.864(6), AlC = 1.962(15), OC = 1.419(12), CC = 1.533(5) Å, ∠AlOAl = 98.1(0.7), ∠CAlC = 121.7(1.7) and ∠OCC = 110.4(0.5)°.     

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.     

The crystal structure of t-Bu2Si(OH)F. A cyclic hydrogen-bonded tetramer

An X-ray diffraction study has shown that t-Bu₂Si(OH)F crystallizes as hydrogen-bonded tetramers. The fluoride ligand does not take part in the hydrogen bonding, which involves OH--O linkages with an OH--O angle of 160°; the O---O---O angles are 89.7(3)°, but the four oxygen atoms are not quite coplanar (space group I$\text{4}$). The t-BuSiBu-t angle is 120.5(6)°.     

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.     

Electron diffraction study on the molecular structure of methyltrimethoxysilane

The electron diffraction data for methyltrimethoxysilane are consistent with a C₃ symmetry model, the predominant forms of which have rotational angle(s) between 100 and 155° around the SiO bond (the anti conformation of the CSiOC chain would respond to 0°). There is probably large amplitude motion around the SiO bonds. The following bond lengths and bond angles were determined: r_a(CH) 1.093 ± 0.005, r_a(SiC) 1.842 ± 0.013, r_a(SiO) 1.632 ± 0.004, r_a(OC) 1.425 ± 0.004 », ∠CSiO 109.6 ± 0.5°. and ∠SiOC 123.6 ± 0.5°.     

Structural chemistry of Magnéli phases TinO2n−1 (4 ≤ n ≤ 9). III. Valence ordering of titanium in Ti6O11 at 130 K

The phase transition at 147 K in Ti₆O₁₁ corresponds to the occurrence of a superstructure with tripling of the cell volume on cooling. Its reduced cell parameters at 130 ± 5 K are a = 7.517(1), b = 11.986(2), c = 13.397(2) Å, α = 98.29(1), β = 105.52(1), and γ = 107.79(1) degrees in space Group $\text{P}\text{1}$ with Z = 6. A systematic nomenclature adding one index to the substructure atom names permits calculation of the model's atomic coordinates in the asymmetric unit in terms of the rutile sub-substructure and keeps track of the structural changes. The superstructure was solved by direct methods and refined to R_F = 5.2% on 3062 observed reflections assuming isotropic thermal motion. A complex pattern of TiO and TiTi distance changes is observed. It is interpreted to correspond to valence ordering of the Ti atoms, probably complete in the shear-plane slab and partial in the rutile-like slab. The TiTi distances, with one very short approach of 2.65 Å at a shared face, seem to be consistent with “bipolarons” but can also be analyzed in terms of electrostatic repulsion which allows for the considerable lengthening of some distances as well.     

X-ray microanalysis and high-resolution transmission electron microscopy of the reduced titanium-niobium oxides

Phase relationships in TiNb₂O₇ and Ti₂Nb₁₀O₂₉ reductions at 1400°C were investigated by means of X-ray microanalytical electron microscopy and high-resolution transmission electron microscopy (TEM). Compositions of phases present in equilibrium were obtained by applying thin-crystal approximation by which $\text{Nb}\text{Ti}$ ratios in different phases were determined; their oxygen content was inferred from structural considerations. In this manner, phase relationships in that portion of the TiO₂NbO₂NbO_2.5 equilibrium diagram with 2.417 ≥ x (in MeO_x) ≥ 2 were defined. Data obtained, in combination with high-resolution electron microscopy observations, confirmed that the reduction reaction, in part, is a heterogeneous process controlled by outward diffusion of both metal and oxygen atoms. Recombination of the diffused particles leads to the formation of separate crystals. The original block structure phase undergoes transformation in a quasihomogeneous manner either to an isomorphous phase in the binary NbO system or to a structurally related lower composition oxide. A new superstructure Me₂₅O₆₀(Ti_7.16Nb_42.84O₁₂₀) has been detected as an intermediate metastable phase, generated in the reduction of TiNb₂O₇ to stable Me₁₂O₂₉(Ti_1.53Nb_10.47O₂₉) and MeO₂(Ti_0.52Nb_0.48O₂) phases. Consideration of phase relationships among Me₂₅O₆₀, Me₁₂O₂₉, and MeO₂ suggests a chemical mechanism for the reaction concerned. The Me₂₅O₆₀ superstructure has a monoclinic symmetry with cell parameters a = 19.0 Å, b = 3.8 Å, c = 26.6 Å, α = 90°, β = 90°, γ = 78.5°, as determined from the structure image calculations.     

Crystal structure and MAS-NMR study of rehydrated UiO-7

The framework of rehydrated UiO-7 has the ZON type of topology. The crystal structure is described on the basis of high resolution, synchrotron powder X-ray diffraction data. The chemical composition of the unit cell is Al₃₂P₃₂O₁₂₈·62H₂O. Its dimensions are a=14.4930(2), b=14.8731(2) and c=17.5738(3) Å; space group Pbca. Of the four non-equivalent Al atoms, two have normal tetrahedral coordination, whereas one obtains five-coordination and one achieves octahedral coordination on additional bonding to three non-equivalent water molecules. Six more water molecules are located in the channels and are interconnected via hydrogen bonds. These features were confirmed by solid-state ²⁷Al MAS NMR data. Site assignment of ³¹P signals is discussed on the basis of POAl angles and Al-coordination.     

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)°.     

Skew-trapezoidal bipyramidal diorganotin(IV) bischelates. Crystal structure of dimethylbis(2-pyridinethiolato-N-oxide)tin(IV)

Dimethylbis(2-pyridinethiolato-N-oxide)tin(IV), Me₂Sn(2-SPyO)₂, crystallizes in space group P2₁/c with a 9.877(3), b 11.980(4), c 13.577(3) Å, β 109.1(2)° and Z = 4. The structure was refined to R_F = 0.036 for 2263 Mo-K_α observed reflections. The coordination geometry at tin is a skew-trapezoidal bipyramid, with the oxygen [SnO 2.356(3), 2.410(4) Å] and sulfur [SnS 2.536(1), 2.566(1) Å] atoms of the chelating groups occupying the trapezoidal plane and the methyl groups [SnC 2.106(6), 2.128(7) Å] occupying the apical positions. The methyl-tin-methyl skeleton is bent [CSnC 138.9(2)°]. The SSnS angle is 77.8(1)°, but the OSnO angle is opened to 136.7(1)° to accommodate the intruding methyl groups. The carbontincarbon angles predicted from quadrupole splitting (^119mSn Mössbauer) and one-bond ¹¹⁹Sn¹³C coupling constant (solution ¹³C NMR) data agree closely with the experimental value.     

The structure of (dichloro) (DI-μ-acetato)(bis-triphenyl phosphine) dimolybdenum(II)

The title compound was obtained in crystalline form suitable for X-ray structure determination. It forms crystals in the monoclinic space group P2₁/c with two centrosymmetric molecules in a unit cell of dimensions, a = 10.888(1) Å, b = 10.182(2) Å, c = 17.929(4) Å, β = 104.33(1)°. The central Mo₂Cl₂(O₂C)₂P₂ core has effectively C_2h-symmetry with the following principal dimensions: MoMo = 2.091(1) Å, MoCl = 2.405 Å, MoP = 2.566(2) Å, MoO(av.) = 2.103[4] Å, MoMoP = 104.38(7)°, and MoMoCl = 116.23(8)°.     

Synthesis and crystal chemistry of NH3(MoO3)3

NH₃(MoO₃)₃ crystallizes with hexagonal symmetry, space group $\text{P6}{}_3\text{m}$, lattice constants a = 10.568 Å, c = 3.726 Å, and Z = 2. The crystal structure has been determined by Patterson synthesis and refined assuming isotropic temperature factors to a final conventional R value of 0.085. The structure shows a three-dimensional arrangement built up of double chains of distorted MoO₆ octahedra, parallel to the [001] direction. The octahedral double chains are linked among each other through common oxygen atoms. In addition to the shared oxygen atoms, each molybdenum is coordinated to one terminal oxygen. MoO distances range from 1.645 to 2.378 Å and OMoO angles from 74.3 to 114.3°. These results are consistent with the fact that molybdenum in high-valence states shows octahedral coordination with terminal oxygens.     

Structures of two polymorphic modifications of tris(p-chlorophenyl)arsinoxide and comparison with the structure of tris(p-chlorophenyl)arsinsulfide

A full X-ray structure analysis of two polymorphic modifications of tris(p-chlorophenyl)arsinoxide, C₁₈H₁₂AsOCl₃, has been performed. Modification I is triclinic, space group P$\text{1}$, Z = 4; modification II is hexagonal, space group P6₃, Z = 2. The geometrical parameters of the molecules in the two polymorphs are similar; the mean values for the bond distances and angles are: AsO 1.641, AsC 1.928, CCl 1.736 Å; CAsC 107.3, CAsO 111.6°. The packing modes in I and II are significantly different: in I supersymmetrical relationships between the molecules independent of space-group symmetry are found: in II cylindrical cavities of diameter ca. 5 Å are present along the 6₃ axes. The structures of the molecules in I and II are compared with that of tris(p-chlorophenyl)arsinsulfide, C₁₈H₁₂AsSCl₃ (III, space group P2₁/b, Z = 4).     

Strukturchemie dreigliedriger brückenliganden : II. Molekülstruktur eines zweikernigen titan-komplexes mit phosphonium-bismethylid-brücken

Ti₂(OMe)₆[(CH₂)₂PMe₂]₂ crystallizes in the triclinic space group P$\text{1}$ with a 860(1), b 968(1), c 1448(3) pm, α 103.22(14), β 92.02(13) and γ 93.77(14)° Two halves, each of an independent molecule are within the asymmetric unit. The titanium atoms (TiTi 325.4 and 326.5 pm) are bridged by two methoxy groups and two dimethylphosphonium-bismethylide ligands, the latter being trans to each other. By two additional methoxy groups each titanium atom reaches approximate octahedral coordination. TiO (bridge) 205 pm, TiO (termial) 180 pm, TiC 225 pm (mean values). Adaptation of the bite width of the ylide ligands to the metal—metal distance essentially results from C_s configuration of the five membered Ti₂C₂P rings and from opening of the TiCP angles to 119.5°. General aspects of the geometry of phosphonium-bismethylide ligands are discussed.     

The crystal structure of Na7Mg4.5(P2O7)4

The crystal structure of Na₇Mg_4.5(P₂O₇)₄ has been solved by direct methods from the three-dimensional X-ray data. The space group is $\text{P}\text{1}$. The crystal structure consists of Mg²⁺, Na⁺, and P₂O^4?₇ ions. One magnesium atom at symmetry center (0,0,0) and two sodium atoms at ±(?0.0421, ?0.0596, 0.2230) display occupation factors 0.5 each. A short interatomic distance between these Na⁺ and Mg²⁺ ions (1.80 ± 0.01 Å) excludes the occupation of both sites in the same unit cell. The crystal structure of Na₇Mg_4.5(P₂O₇)₄ consists of unit cells containing Na₈Mg₄(P₂O₇)₄ or Na₆Mg₅(P₂O₇)₄ with a statistical occurrence 1:1.Each Mg²⁺ ion is octahedrally coordinated by six O^2? ions at distances 1.979 – 2.270 Å. The coordination polyhedra around the Na⁺ ions are ill-defined. The bond angles POP in the P₂O^4?₇ groups are 126.6 and 133.6° (±0.3°). The final reliability factor R is 7.1%.     

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.     

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 and molecular structure of hexadecaphenyloctasiloxyspiro(9,9)titanate(IV)

The crystal and molecular structures of the title compound have been determined by single crystal X-ray diffraction methods. In the spiro molecule, the metal atom has a geometry very close to tetrahedral, with OTiO angles of 107.9–111.0(2)° and very short TiO bonds of length 1.777–1.791(5)Å. The two TiO₅Si₄ rings have different, ill-defined conformations; the SiO bond lengths and SiOSi angles are similar to those in (SiO)_n rings.     

Kristall- und molekülstruktur von hexaphenyldistannylselenid (C6H5)3SnSeSn(C6H5)3

The crystal and molecular structure of hexaphenylditin selenide (C₆H₅)₃SnSeSn(G₆H₅)₃ was determined by X-ray diffraction data and was refined to R  0.055. The compound is monoclinic, space group P2₁, with a  9.950(4), b  18.650(7), c  18.066(6) Å, β  106.81(4)°, Z  4. The two molecules in the asymmetric unit differ slightly in their conformations, both having approximate C₂ symmetry. Bond lengths and angles are: SnSe 2.526 (2.521(3) ? 2.538(3)) Å; SnC 2.138 (2.107(16)?2.168(19)) Å; SnSeSn 103.4(1)°, 105.2(1)°. There are only slight angular distortions at the SnSeC₃ tetrahedra (SeSnC angles: 104.3(5)?114.8(4)°). The bond data indicate essentially single bonds around the Sn atoms.     

Cyclometallation reactions in complexes of the type Rh(oq)(CO)(P(o-BrC6F4)Ph2): II. The molecular structure of [Rh(oq)Br(P(o-C6F4)Ph2)(H2O)]2 (oq = 8-oxyquinolinate)

The complex [uRh(oq)Br(P(o-Cu₆F₄)Ph₂)(H₂O)]₂ is obtained by refluxing a solution of Rh(oq)(CO)(P(o-BrC₆F₄)Ph₂) (oq = 8-oxyquinolinate) in toluene. The structure of this compound has been determined by X-ray diffraction and refined to R = 0.061 and R_w = 0.065 factors. The cell has monoclinic symmetry, space group P2₁/n; a 19.513(2), b 17.049(1), c 16.898(1) Å and β 99.69(1)°. The structure consists of two independent Rh(oq)Br(P(o-C₆F₄)Ph₂)H₂O) units linked by hydrogen bonds between the coordinated water molecules and oq ligands to form a distorted boat (six atom ring of junction between the two units). In each unit the metal atom has a distorted octahedral coordination, with a four-atom metallocyclic ring (uRhPCCu) with CRhP and RhPC angles 69.3(2) and 85.3(3)°, respectively, in one unit, and 70.0(2) and 81.1(2)° in the other. The water molecule is readily displaced by a variety of phosphorus donor ligands to form the complexes uRh(oq)Br(P(o-Cu₆F₄)Ph₂)P′, P′ = PPh₃, P(p-CH₃C₆H₄)₃ and P(OCH₃)₃, in which the P atoms are in trans-dispositions.