Wim T. Klooster

Single-crystal X-ray and neutron diffraction structure determination and inelastic neutron scattering study of the dihydrogen complex trans-[Ru(H2)(H)(dppe)2][BPh4]

Abstract The structure of the complex trans -[Ru( η 2 -H 2 )(H)(dppe) 2 ][BPh 4 ]( 1 ),dppe = PPh 2 CH 2 CH 2 PPh 2 , has been determined by single-crystal X-ray diffraction at 123 K and neutron diffraction at 12 K. The core of the complex has a distorted octahedral geometry about ruthenium with the dihydrogen ligand trans to hydride and eclipsing a trans -PRuP axis that is bent away front the hydrogens with a PRuP angle of 167.9(4)°. The crystallographically determined H-H distance is 0.83(8) (X-ray) or 0.82(3) (neutron) A. The latter value, where corrected for the shortening caused by the torsional libration of the H 2 ligand, increases to about 0.94 A. The long Ru(H 2 ) distance of 1.81(2) A (neutron), compared to the terminal hydride to ruthenium distance of 1.64(2) A (neutron), is consistent with the lability of the dihydrogen ligand, which is partially lost from the crystal by treatment with vacuum. The analogous iron complex trans-[Fe(η) 2 -H 2 )(H)(dppe) 2 [BPh 4 ]( 2 ) has similar features except that the FeH(H 2 ) distances are much shorter and the H 2 ligand is correspondingly less labile. An inelastic neutron scattering study of the powder of 1 at 5 K reveals two broad inelastic peaks flanking the elastic peak. With the assumption that the dihydrogen librates in a double-minimum potential, the barrier to dihydrogen reorientation is calculated to be 1.0 to 1.4 kcal mol − , depending upon which of the HH distances is used. This barrier is less than that for the iron analog, determined for its BF 4 salt, therefore suggesting that there may be less d π → σ ∗ backbonding in 1 than 2 .

Protonation of Fischer-type alkylidyne carbonyltungsten complexes. Structural comparison of alkylidyne and alkylidene metal complexes, including a neutron diffraction study of [W(CHCH3)Cl2(CO)(PMe3)2]

Abstract Protonation of alkylidyne tungsten complexes of the types [W(CR)Cl(CO)(PMe3)3] or [W(CR)Cl(CO)(py)(PMe3)2] with HCl affords the η2-alkylidene tungsten complexes [W(CHR)Cl2(CO)(PMe3)2] (7) (R = Me, Et, Ph, p-Tol). Protonation of the complexes [W(CR)X(CO)(CNR′)(PMe3)2] with HOSO2CF3 or HBF4 gives the alkylidene complexes [W(CHR)X(CO)(CNR′)(PMe3)2][Y] (8) (R = Me, R′ = CMe3, X = Cl, Y = CF3SO3, R = Ph, X = Cl; R′ = CMe3, Y = CF3SO3, BF4; R′ = C6H11, Y = BF4; R′ = C6H3Me2-2,6, Y = CF3SO3, R = Ph, R′ = CMe3, X = I, Y = CF3SO3, BF4). The CH bonds of the alkylidene ligands are easily deprotonated with bases such as pyrrolidinocyclopentene or triethylamine. The solid state structures of [W(CPh)Cl(CO)(CNCMe3)(PMe3)2] (5b), [W(CHMe)Cl2(CO)(PMe3)2] (7a). [W(CHPh)Cl2(CO)(PMe3)2] (7c), and [W(CHPh)Cl(CO)(CNCMe3)(PMe3)2][BF4] (8c) were determined by X-ray crystallography. The structure of 7a was also determined by neutron diffraction. Based on the neutron diffraction data of 7a, and closely matching results from the X-ray diffraction studies, it is found that the η2-coordination mode of the alkylidene ligands gives rise to almost equal WC(R) and WH bond distances, 1.857(4) and 1.922(6) A, respectively, in the case of 7a. The length of the alkylidene CH bond in 7a is 1.185(7) A. The structural comparison of 5b and 8c reveals that the protonation of the alkylidyne ligand causes the WCPh bond to lengthen by less than 0.1 A and the WCPh angle to bend by about 15°. The major induced structural change, however, may be described as a lateral shift of the CPh group by about 0.6 A away from the coordination axis defined by the extension of the ClW vector.

Synthetic and reactivity studies of some asymmetric dinuclear platinum(II) monohydrido-bridged cations. The neutron diffraction structure of [(Pet3)2(Ph)Pt(μ-H)PtH(PEt3)2][BPh4]

Abstract The complexes [(PEt 3 ) 2 (Ar)Pt(μ-H)PtH(PEt 3 ) 2 ][BPh 4 ] (Ar=Ph,2,4-Me 2 C 6 H 3 , 2,4,6-Me 3 C 6 H 22 ) were prepared and characterized. Multinuclear, multidimensional NMR studies of these complexes show that, in solution, (i) they exist in rapidly intercoverting conformers which retainn the bent Pt(μ-H)PtH moieties found in the solid state, (ii) the coordination at each platinum atom is square planar, (iii) the two coordination planes are perpendicular to each other and (iv) the aryl group is perpendicular to the coordination plane of the platinum atom to which it is bonded. The complex [PEt 3 ) 2 Pt(μ-H)PtH(PEt 3 ) 2 ][BPh 4 ] does not react with C 2 H 4 and CH 2 :CH·CO 2 Me. At −60°C or above, [(PEt 3 ) 2 (Ph)Pt(μ-H)PtH(PEt 3 ) 2 )][BPh 4 ] reacts with CO giving the platinum(II) cations trans-[ PtX(CO)(PEt 3 ) 2 ]( Ph ) ∗ ( X = H and Ph ), and [PtH(PEt 3 ) 3 ] + and the platinum(0) carbonyl cluster [Pt 4 (μ-CO) 3 ) 4 ]. The cluster structure of I(PEt 3 ) 2 (Ph)·Pt(μ-H)PtH(PEt 3 ) 2 ][BPh 4 , obtained by neutron diffraction, shows that the Pt-H-Pt bond angle in this cation is 125(1)° indicating that the interaction between these three atoms is weak.

Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal ­structures of five crystalline methyl ­pentofuranosides

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl alpha-D-arabinofuranoside (1), methyl beta-D-arabinofuranoside (2), methyl alpha-D-lyxofuranoside (3), methyl beta-D-ribofuranoside (4) and methyl alpha-D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C(1) chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations.

Neutron structures of ammonium tetrafluoroberyllate

It is thought that hydrogen bonding is responsible for the ferroelectricity in ammonium tetrafluoroberyllate, (NH(4))(2)BeF(4). In the past X-ray data have been collected, but these did not permit accurate determination of the H-atom positions. In order to obtain more accurate information the neutron structures have now been determined for the paraelectric and ferroelectric phases. Going from the paraelectric to the ferroelectric phase, both the BeF(4)(2-) and the NH(4)(+) ions rotate and shift from the mirror planes of the paraelectric phase. This results in removal of the mirror-plane symmetry and formation of a superlattice with the a axis doubled. Along the polar c axis, the NH(4)(+) ions move towards the BeF(4)(2-) ions within chains of molecules and the chains move slightly relative to one another. The rotations and translations give rise to stronger hydrogen-bonding interactions.

Structure of strontium hydroxide octahydrate, Sr(OH)2·8H2O, at 20, 100 and 200 K from neutron diffraction

The crystal structure of Sr(OH)2*8H2O has been determined at 20, 100 and 200 K from neutron diffraction data. The structure consists of double layers of H2O and OH- ions separated by Sr2+ along the c axis. The Sr2+ ions are eight-coordinated by water O atoms in a square antiprism configuration. Each H2O molecule is engaged in three hydrogen bonds. The OH- ions form chains of acceptor and donor bonds along the fourfold axis with O atoms engaged in four bonds with H2O molecules, such that both non-equivalent O atoms have square-pyramidal environments of five H atoms and the overall bonding configurations of distorted octahedra.

Structural studies of the hydrido-bridged iridium gold complexes ‘IrHm{CH3C(CH2PPh2)3}{Au(PR3)}n’

Abstract The X-ray crystal structure of [{(triphos)H (3− x ) Ir}(μ-H) x {Au(PR 3 )}][PF 6 ] (triphos=CH 3 C(CH 2 PPh 2 ) 3 , x =2) shows that the gold atom builds two almost equal IrHAu bridges with the he ‘IrH 3 (triphos)’ building block. The IrHAu bridging parameters are typical of three-center-two-electron interactions. The X-ray crystal structure of [{(triphos)H (3− y ) Ir}(μ-H) y {Au(PR 3 )} 2 ][PF 6 ] 2 shows that each gold atom builds two Ir(μ 2 -H)Au bridges with the three hydrides of the ‘IrH 3 (triphos)’ building block; one Ir(μ 3 -H)Au 2 bridge is also present ( y =3). The relative positions of the Ir, H, Au and P atoms show that typical three-center-two-electron interactions predominate in this compound, in which there is no direct AuAu bonding. The neutron diffraction structure of [{(triphos)Ir}(μ-H) 2 {Au(PPh 3 )} 3 ][PF 6 ] 2 confirms the earlier hypothesis that only two of the three IrAu edges are associated with a hydride with formation of Ir(μ 2 -H)Au bridges. The presence or absence of the latter ligand changes the IrAu distance only marginally, in contrast to the general trend in hydride clusters. It is shown that the formation of a ‘classical’ cluster in this set of compounds requires a quadrimetallic unit and the two additional electrons generated by loss of a proton from an IrH bond in the trication [{(triphos)Ir (μ 2 -H) 3 {Au(PR 3 )} 3 } 3+ .

Single-crystal neutron diffraction study of β-Cs3(HSO4)2[H2−x(SxP1−x)O4] (x ≃ 0.5) at 15 K

The structure of β-Cs3(HSO4)2[H2−x(SxP1−x)O4] has been examined by single-crystal neutron diffraction at 15 K. The compound crystallizes in space group C2/c and contains four formula units in the unit cell, with lattice parameters a = 19.769 (9), b = 7.685 (2), c = 8.858 (3) A and β = 100.60 (4)°. Refinement of P, S and H site occupancies indicated that the value of x (in the stoichiometry) is 0.500 (6). This, together with the unit-cell volume of 1322.8 (14) A3, implies a density of 3.463 Mg m−3. The structure contains zigzag rows of XO4 anions, where X = P or S, that alternate, in a checkerboard fashion, with zigzag rows of Cs cations. Moreover, there is one proton site, H(3), with an occupancy of 0.25 and one X-atom site, X(1), that is occupied by 0.5 P and 0.5 S. These features are in general agreement with a previous X-ray structure determination carried out at 298 K. In contrast to the X-ray study, however, it was found that two different structural models adequately fit the diffraction data. In the first model, the proton vacancies and the P atoms were assumed to be randomly distributed over the H(3) and X(1) sites, respectively, and to have no impact on the local structure. In the second model, several atoms were assigned split occupancies over two neighboring sites, to reflect the presence or absence of a proton vacancy, and the presence of P or S on the X(1) site. Refinement assuming the first model, in which anisotropic displacement parameters for 12 of 14 atom sites in the asymmetric unit were employed, yielded residuals wR(F2) = 0.084 and wR(F) = 0.038. For the second model, in which anisotropic displacement parameters were utilized for only the five atoms that were not split relative to the first model, the residuals were wR(F2) = 0.081 and wR(F) = 0.036.

Crystal Growth, Structure Characterization, and Schemes for Economic Transport: An Integrated Approach to the Study of Natural Gas Hydrates

Abstract: In this paper, two themes are specifically targeted for developing a cost‐effective option to transport methane hydrates from distant locations. Under the first theme, data are presented on crystal growth techniques, sample preparation and neutron diffraction studies of 3.5Xe · 8CCl4· 136D2O, xCH4· 8CCl4· 136D2O, xH2S · 8CS2· 136 H2O, and 20Br2· 172D2O. Under the second theme, the GTL option is selected wherein methanol is the product of choice for transport. For GTL, the processing of aqueous CH4 by steam reforming is the preferred route to synthesis gas. Subsequent conversion of synthesis gas into methanol will require the formulation of advanced catalysts.

STRUCTURES OF 1,3-BIS(DIPHENYLPHOSPHINO)PROPANE PLATINUM(II) ALDITOLATE COMPLEXES

Abstract Single-crystal X-ray diffraction studies have been carried out on three crystalline (dppp)Pt(II)(alditolate) complexes derived from reactions of the sugar alcohols glycerol, erythritol, and galactitol with (dppp)Pt(CO3). The alditols bind to the platinum via adjacent, deprotonated hydroxyl groups to form a 2,5-dioxaplatinacyclopentane ring system having hydroxyalkyl substituent side-chains. The hydroxyl groups in these side-chains all engage in either intra- or intermolecular hydrogen bonds, the former preferentially involving hydrogen bond donation from a hydroxyl group on the β-carbon of the metallacycle dihydroxyethyl or trihydroxypropyl substituent to either the near or far metallacycle oxygen atoms to give a six- or seven-membered hydrogen-bonded ring system, respectively. Five-membered hydrogen-bonded ring systems to the adjacent metallacycle oxygen are observed for hydroxymethyl side-chains. These hydrogen-bonded interactions are believed to play a significant role in the complexation regioselectivity observed in these alditolate complexes. Conformations of the 2,5-dioxaplatinacyclopentane ring and dppp chelate ring are also discussed, as are comparisons with other alditolate and diolate structural determinations.