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Single crystal neutron structures at several temperatures have been determined for β-phase urea inclusion compounds containing hexadecane, 1,6-dibromohexane, and 2,7-octanedione guests. The neutron structure of the "partial channel" cocrystal of urea and DMF is also reported. Here we present an in-depth discussion and analysis of the structure and bonding of this urea series, in particular, how the guest compound affects the symmetry and hydrogen bonding of the host urea network. Additionally, we address the challenge of obtaining crystals suitable for neutron diffraction and present a new heating/cooling device to aid crystallization. [ABSTRACT FROM AUTHOR]

Deuterium labeling is a powerful way to gain mechanistic information in biology and chemistry. However, selectivity is hard to control experimentally, and labeled sites can be difficult to assign both in solution and in the solid state. Here we show that very selective high-deuterium contents can be achieved for the polyhydride ruthenium phosphine complex [RuH2(H2)2 (PCyp3)2] (1) (PCyp3 = P(C3H9)3). The selectivity of the H/D exchange process is demonstrated by multinuclear NMR and neutron diifraction analyses. It has also been investigated through density functional theory (DFT) calculations. The reactions are performed under mild conditions at room temperature, and the extent of deuterium incorporation, involving selective C--H bond activation within the cyclopentyl rings of the phosphine ligands, can easily be tuned (solvent effects, D2 pressure). It is shown that D2 gas can inhibit the C--H/C--D exchange process. [ABSTRACT FROM AUTHOR]

Investigates the internal mean-square displacements of H atoms in xylitol using neutron diffraction study. Nuclear anisotropic displacement parameters; Rigid-body displacements; Molecular vibrations in xylitol.

Investigates the crystal structure of α-glycine during anomalous electrical behavior in the temperature range 288-427 K using neutron diffraction. Molecular structure; Expansion of the unit cell anisotropically with increasing temperature; Factors influencing the separation of antiferroelectric molecular layers with increasing temperature.

The crystal structures of ammonium tetraphenylborate, NH4+.BH4-, are determined by neutron diffraction at 20 and 293 K. At both temperatures, all four N - H vectors of the ammonium ion are time-average-oriented at the midpoints of the phenyl rings of neighboring anions. The N-H … Ph distances. H … M 2.067 and N … M 3.023 Å, are exceptionally short (M = aromatic midpoint). Even at 20 K the ammonium ion performs large amplitude motions which allow the N- H vectors to sample the entire face of the aromatic system. [ABSTRACT FROM AUTHOR]

Two isostructural complexes Ln(DOTAM)(H 2 O)(triflate) 3 ·3H 2 O (Ln = Eu, Nd) have been characterized by neutron diffraction analysis at different temperatures by means of two techniques, white-beam Laue at 65 K and monochromatic at 20 K, 65 K and 220 K. The high accuracy in the hydrogen-atom localization revealed the H-bonds network formed by the metal-coordinated water, the water molecules, the anions, and the macrocycle, as well as the non-symmetric orientation of the coordinated water with respect to the Ln-O w (w = water) axis. The accurate determination of Nd-H and Eu-H distances allows derivation of an averaged Gd-H value (2.974 Å at 220 K) that is in the range of the smaller values commonly used in relaxivity calculations for Gd-based contrast agents. [ABSTRACT FROM AUTHOR]

Neutron diffraction data have been collected at 12, 50, 150 and 295 K for the dipeptide glycyl-L-alanine, C5H10N2O3, in order to obtain accurate positional and anisotropic displacement parameters for the H atoms. The values of these parameters serve as a benchmark for assessing the equivalent parameters obtained from a so-called Hirshfeld-atom refinement of X-ray diffraction data described elsewhere [Capelli et al. (2014). IUCrJ, 1, 361-379]. The flexibility of the glycyl-L-alanine molecule in the solid and the hydrogen-bonding interactions as a function of temperature are also considered. [ABSTRACT FROM AUTHOR]

The monoclinic C2 crystal structure of an α-cyclodextrin/1-undecanol host-guest inclusion complex was solved using single-crystal neutron diffraction. Large high-quality crystals were specially produced by optimizing temperature-controlled growth conditions. The hydrate crystallizes in a channel-type structure formed by head-to-head dimer units of α-cyclodextrin molecules stacked like coins in a roll. The alkyl chain of the guest lipid is entirely embedded inside the tubular cavity delimited by the α-cyclodextrin dimer and adopts an all- trans planar zigzag conformation, while the alcohol polar head group is outside close to the α-cyclodextrin primary hydroxyl groups. The cyclodextrin dimer forms columns, which adopt a quasi-square arrangement much less compact than the quasi-hexagonal close packing already observed in the less hydrated α-cyclodextrin channel-type structures usually found with similar linear guests. The lack of compactness of this crystal form is related to the high number of interstitial water molecules. The replacement of 1-undecanol by 1-decanol does not modify the overall crystal structure of the hydrate as shown by additional X-ray diffraction investigations comparing the two host-guest assemblies. This is the first study that analyses the entire hydrogen-bonding network involved in the formation of a cyclodextrin dimer surrounded by its shell of water molecules. [ABSTRACT FROM AUTHOR]

d-Xylose isomerase (XI) converts the aldo-sugars xylose and glucose to their keto analogs xylulose and fructose, but is strongly inhibited by the polyols xylitol and sorbitol, especially at acidic pH. In order to understand the atomic details of polyol binding to the XI active site, a 2.0 Å resolution room-temperature joint X-ray/neutron structure of XI in complex with Ni2+ cofactors and sorbitol inhibitor at pH 5.9 and a room-temperature X-ray structure of XI containing Mg2+ ions and xylitol at the physiological pH of 7.7 were obtained. The protonation of oxygen O5 of the inhibitor, which was found to be deprotonated and negatively charged in previous structures of XI complexed with linear glucose and xylulose, was directly observed. The Ni2+ ions occupying the catalytic metal site (M2) were found at two locations, while Mg2+ in M2 is very mobile and has a high B factor. Under acidic conditions sorbitol gains a water-mediated interaction that connects its O1 hydroxyl to Asp257. This contact is not found in structures at basic pH. The new interaction that is formed may improve the binding of the inhibitor, providing an explanation for the increased affinity of the polyols for XI at low pH. [ABSTRACT FROM AUTHOR]

The article discusses a study on the structure of coenzyme cob (Cbl(2) determined from the monochromatic neutron data set gathered from the original D19 at the H11 thermal beam at the ILL to 0.92 A resolution. It reports preliminary studies of the feasibility of extending the structure's resolution further by gathering time-of-flight (TOF) neutron data during a short commissioning experiment on TOPAZ. It suggests that TOPAZ is an ideal instrument for developing new research based on ultra-high resolution neutron studies of biological macromolecules.

A neutron diffraction analysis was carried out at 20 K on a single crystal of FeH2(CO)2[P(OPh)3]2 in order to accurately locate the hydride ligands. The two hydrides are bonded terminally to the Fe atom, and their small size causes the title complex to assume a highly distorted octahedral geometry. Distances and angles involving the hydride ligands are as follows: Fe&z.sbnd;H(1)=1.521(2) A˚, Fe&z.sbnd;H(2)=1.529(2) A˚, H(1)⋯H(2)=2.011(3) A˚, and H(1)&z.sbnd;Fe&z.sbnd;H(2)=82.49(13)°. Final agreement factors: R(F)=2.8% and R(wF2)=5.4%. [Copyright &y& Elsevier]

Reaction of [RuCl(CNN)(dppb)] ( 1-Cl) (HCNN=2-aminomethyl-6-(4-methylphenyl)pyridine; dppb=Ph2P(CH2)4PPh2) with NaOCH2CF3 leads to the amine-alkoxide [Ru(CNN)(OCH2CF3)(dppb)] ( 1-OCH2CF3), whose neutron diffraction study reveals a short RuO ⋅⋅⋅HN bond length. Treatment of 1-Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)] ⋅(EtOH) n ( 1-OEt⋅ n EtOH), which equilibrates with the hydride [RuH(CNN)(dppb)] ( 1-H) and acetaldehyde. Compound 1-OEt⋅ n EtOH reacts reversibly with H2 leading to 1-H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1-OEt⋅ n EtOH and 1-H reveal hydrogen bond interactions and exchange processes. The chloride 1-Cl catalyzes the hydrogenation (5 atm of H2) of ketones to alcohols (turnover frequency (TOF) up to 6.5×104 h−1, 40 °C). DFT calculations were performed on the reaction of [RuH(CNN′)(dmpb)] ( 2-H) (HCNN′=2-aminomethyl-6-(phenyl)pyridine; dmpb=Me2P(CH2)4PMe2) with acetone and with one molecule of 2-propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru-hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH2 is mediated by the alcohol and leads to the key 'amide' intermediate. Regeneration of the hydride complex may occur by reaction with 2-propanol or with H2; both pathways have low barriers and are alcohol assisted. [ABSTRACT FROM AUTHOR]

Summary D-xylose isomerase (XI) is capable of sugar isomerization and slow conversion of some monosaccharides into their C2-epimers. We present X-ray and neutron crystallographic studies to locate H and D atoms during the respective isomerization and epimerization of L-arabinose to L-ribulose and L-ribose, respectively. Neutron structures in complex with cyclic and linear L-arabinose have demonstrated that the mechanism of ring-opening is the same as for the reaction with D-xylose. Structural evidence and QM/MM calculations show that in the reactive Michaelis complex L-arabinose is distorted to the high-energy 5 S 1 conformation; this may explain the apparent high K M for this sugar. MD-FEP simulations indicate that amino acid substitutions in a hydrophobic pocket near C5 of L-arabinose can enhance sugar binding. L-ribulose and L-ribose were found in furanose forms when bound to XI. We propose that these complexes containing Ni 2+ cofactors are Michaelis-like and the isomerization between these two sugars proceeds via a cis -ene-diol mechanism. [ABSTRACT FROM AUTHOR]

A novel vitreous carbon mount for macromolecular crystallography, suitable for neutron and X-ray crystallographic studies, has been developed. The technology described here is compatible both with X-ray and neutron cryo-crystallography. The mounts have low density and low background scattering for both neutrons and X-rays. They are prepared by laser cutting, allowing high standards of production quality, the ability to custom-design the mount to specific crystal sizes and large-scale production. [ABSTRACT FROM AUTHOR]

The title zwitterion (2 S)-2-azaniumyl-1-hydroxy-3-phenylpropan-1-olate, C9H11NO2, also known as L-phenylalanine, was characterized using synchrotron X-rays. It crystallized in the monoclinic space group P21 with four molecules in the asymmetric unit. The 0.62 Å resolution structure is assumed to be closely related to the fibrillar form of phenylalanine, as observed by electron microscopy and electron diffraction. The structure exists in a zwitterionic form in which π-π stacking and hydrogen-bonding interactions are believed to form the basis of the self-assembling properties. [ABSTRACT FROM AUTHOR]

Three new N-heterocyclic-silazane compounds, 1a--c, were prepared and employed as bidentate ligands to ruthenium, resulting in a series of [Ru(H){(κ-Si,N- (SiMe2-N-heterocycle)}3] complexes (3a--c) featuring the same RuSi3H motif. Detailed structural characterization of the RuSi3H complexes with X-ray diffraction, and in the case of triazabicyclo complex [Ru(H){κ-Si,N-(SiMe2)(C7-H12N3)}3] (3a), neutron diffraction, enabled a reliable description of the molecular geometry. The hydride ligand of (3a) is located closer to two of the silicon atoms than it is to the third. Such a geometry differs from that of the previously reported complex [Ru(H){(κ-Si,N-(SiMe2)N(SiMe2H)(CsH4N)}3] (3d), also characterized by neutron diffraction, where the hydride was found to be equidistant from all three silicon atoms. A DFT study revealed that the symmetric and less regular isomers are essentially degenerate. Information on the dynamics and on the Ru•••H•••Si interactions was gained from multinuclear solid-state (¹H wPMLG, 29Si CP MAS, and 2D ¹H-39Si dipolar HETCOR experiments) and solution NMR studies. The corresponding intermediate complexes, [Ru{κ-Si,N-(SiMe2-N-heterocycle)}(η4-C8H12)(η³-C8H11)] (2a--c), involving a single silazane ligand were isolated and characterized by multinuclear NMR and X-ray diffraction. Protonation of the RuSi3H complexes was also studied. Reaction of 3a with NH4PF6 gave rise to [Ru(H)(η²-H -- SiMe2)κ-N-(C7H12N3){κ-Si,N- (SiMe2)(C7H12N3)}2]+[PF6]-(4aPF6) which was isolated and characterized by NMR spectroscopy, X-ray crystallography, and DFT studies. The nature of the Si--H interactions in this silazane series was analyzed in detail. [ABSTRACT FROM AUTHOR]

The coordination of pyridine-2-amino(methyl)-dimethylsilane ligands to ruthenium has afforded access to a family of novel complexes that display multicenter Ru--H--Si interactions according to the number of incorporated ligands. The new complexes Ru[κ-Si,N-(SiMe2)N(Me)(C5H4N)](Β4- C8H12)(Β³-C8H11) (1), Ru2(μ-H)2(H)2[κ-Si,N-(SiMe2)N-(Me)(C5H4N)]4 (2), and Ru(H)[κ-Si,N-(SiMe2)N(Me)-(C5H4N)]3 (3) were isolated and fully characterized. The complexes exhibit different degrees of Si--H activation: complete Si--H cleavage, secondary interactions between the atoms (SISHA), and Β²-Si-H coordination. Reversible protonation of 3 leading to the cationic complex [RuH{(Β²-H-SiMe2)N(Me)κ-N-(C5H4N)}{κ-Si,N-(SiMe2)N(Me)(C5H4N)}2]+[BArF4]- (5) was also demonstrated. The coordination modes in these systems were carefully studied with a combination of X-ray and neutron diffraction analysis, DFT geometry optimization, and multinuclear NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH2(CH3)2]n[FeIIIFeII(HCOO)6]n. The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order-disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [FeIIIFeII(HCOO)6]n framework. In the low-temperature phase, a change in space group from P31c to R3c occurs, involving a tripling of the c-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different FeII and FeIII magnetic moments. [ABSTRACT FROM AUTHOR]

The unusual uranium reaction system in which uranium(4-4-) and uranium(3+) hydrides interconvert by formal bimetallic reductive elimination and oxidative addition reactions, [(C5Me5)2UH{2]2 (i) [(C5Me5)2UH]2 (2) + H2, was studied by employing multiconfigurational quantum chemical and density functional theory methods. 1 can act as a formal four-electron reductant, releasing H2 gas as the byproduct of four H2/H- redox couples. The calculated structures for both reactants and products are in good agreement with the X-ray diffraction data on 2 and 1 and the neutron diffraction data on 1 obtained under H2 as part of this study. The interconversion of the uranium(4+) and uranium(3+) hydride species was calculated to be near thermoneutral (∼2 kcal/mol). Comparison with the unlmown thorium analogue, [(C5Me5)2ThH]2 shows that the thorium(4-+-) to thorium(3+) hydride interconversion reaction is endothermic by 26 kcal/mol. [ABSTRACT FROM AUTHOR]

Preliminary studies of perdeuterated crystals of human transthyretin (TTR) have been carried out using the LADI-III and D19 diffractometers at the Institut Laue-Langevin in Grenoble. The results demonstrate the feasibility of a full crystallographic analysis to a resolution of 2.0 Å using Laue diffraction and also illustrate the potential of using monochromatic instruments such as D19 for higher resolution studies where larger crystals having smaller unit cells are available. This study will yield important information on hydrogen bonding, amino-acid protonation states and hydration in the protein. Such information will be of general interest for an understanding of the factors that stabilize/destabilize TTR and for the design of ligands that may be used to counter TTR amyloid fibrillogenesis. [ABSTRACT FROM AUTHOR]

Heteromultimetallic hydride clusters containing both rare-earth and d-transition metals are of interest in terms of both their structure and reactivity. However, such heterometallic complexes have not yet been investigated to a great extent because of difficulties in their synthesis and structural characterization. Here, we report the synthesis, X-ray and neutron diffraction studies, and hydrogen addition and release properties of a family of rare-earth/d-transition-metal heteromultimetallic polyhydride complexes of the core structure type 'Ln4MHn' (Ln = Y, Dy, Ho; M = Mo, W; n = 9, 11, 13). Monitoring of hydrogen addition to a hydride cluster such as [{(C5Me4SiMe3)Y}4(?-H)9Mo(C5Me5)] in a single-crystal to single-crystal process by X-ray diffraction has been achieved for the first time. Density functional theory studies reveal that the hydrogen addition process is cooperatively assisted by the Y/Mo heteromultimetallic sites, thus offering unprecedented insight into the hydrogen addition and release process of a metal hydride cluster. [ABSTRACT FROM AUTHOR]

The biological addition of oligosaccharide moieties to asparagine residues of N-glycoproteins influences the properties and bioactivities of these macromolecules. The low-temperature neutron crystal structures of three N-glycoprotein linkage models and analogues provide accurate characterization of the three-dimensional structure of the conserved GlcNAc-Asn linkage. These first crystal structures of N-acetylated carbohydrates obtained by neutron diffraction provide high-resolution geometrical parameters that can be used for force-field parametrization and subsequent molecular dynamics simulation of N-glycoproteins. The correct localization of hydrogen atoms demonstrates the occurrence of trifurcated hydrogen bonds and hydrophobic contacts. [ABSTRACT FROM AUTHOR]

The 1:1 and 2:1 cocrystals of benzene-1,2,4,5-tetra­carboxylic acid (BTA) and 4,4′-bipyridine (BPY) have been studied using neutron diffraction at 215 and 20 K, respectively. BTA and BPY crystallize in a 1:1 ratio with 1.8 mol­ecules of water, viz. 4,4′-bipyridinium 2,5-dicarboxy­benzene-1,4-dicarboxyl­ate 1.8-hydrate, C10H12N22+·C10H4O82−·1.8H2O, (I), in the space group P , with both BTA and BPY lying on inversion centres. BTA and BPY crystallize in a 2:1 ratio, viz. 4,4′-bipyridinium bis­(2,4,5-tricarboxy­benzoate), C10H12N22+·2C10H5O8−, (II), in the space group Cc. The crystal structure of the 1:1 cocrystal contains one short N—H⋯O hydrogen bond [N⋯O = 2.6047 (19) Å] and one intra­molecular O—H⋯O hydrogen bond [O⋯O = 2.423 (3) Å]. The crystal structure of the 2:1 cocrystal contains two N—H⋯O hydrogen bonds [N⋯O = 2.639 (3) and 2.674 (2) Å], and two intra­molecular [O⋯O = 2.404 (3) and 2.420 (3) Å] and four strong inter­molecular O—H⋯O hydrogen bonds [O⋯O = 2.613 (3), 2.718 (3), 2.628 (3) and 2.739 (3) Å]. [ABSTRACT FROM AUTHOR]

The article reports on the results of neutron diffraction studies that compare the structures of four metal-ion complexes of deuterated D-xylose isomerase, which represent the four stages in its biochemical catalytic reactions. An analysis of the structural changes provide insight on its biochemical mechanisms and the role of ionization. The variable charges in the substrate are important to the function of the metal ion in the isomerization.

Summary: Conversion of aldo to keto sugars by the metalloenzyme D-xylose isomerase (XI) is a multistep reaction that involves hydrogen transfer. We have determined the structure of this enzyme by neutron diffraction in order to locate H atoms (or their isotope D). Two studies are presented, one of XI containing cadmium and cyclic D-glucose (before sugar ring opening has occurred), and the other containing nickel and linear D-glucose (after ring opening has occurred but before isomerization). Previously we reported the neutron structures of ligand-free enzyme and enzyme with bound product. The data show that His54 is doubly protonated on the ring N in all four structures. Lys289 is neutral before ring opening and gains a proton after this; the catalytic metal-bound water is deprotonated to hydroxyl during isomerization and O5 is deprotonated. These results lead to new suggestions as to how changes might take place over the course of the reaction. [Copyright &y& Elsevier]

The novel disilazane compound 2-pyridinetetramethyldisilazane (1) has been synthesized. The competition between N-pyridine coordination and Si-H bond activation was studied through its reactivity with two ruthenium complexes. The reaction between. 1 and RuH2(H2)2(PCy3)2 led to the isolation of the new complex RuH2{(η²-HSiMe2)N(KN-C5H4N)(SiMe2H)}(PCy3)2 (2) resulting from the loss of two dihydrogen ligands and coordination of 1 to the ruthenium center via a K²N,(η²-Si-H) mode. Complex 2 has been characterized by multinuclear NMR experiments (¹H, 31P, 13C, 29Si), X-ray diffraction and DFT studies. In particular, the HMBC 29Si-¹H spectrum supports the presence of two different silicon environments: one Si-H bond is dangling, whereas the other one is η²-coordinated to the ruthenium with a JSIH value of 50 Hz. DFT calculations (B3PW91) were also carried out to evaluate the stability of the agostic species versus a formulation corresponding to a bis(σ-Si-H) isomer and confirmed that N-coordination overcomes any stabilization that could be gained by the establishment of SISHA interactions. There is no exchange between the two Si-H bonds present in 2, as demonstrated by deuterium-labeling experiments. Heating 2 at 70 °C under vacuum for 24 h, leads to the formal loss of one equivalent of H2 from 2 and formation of the 16- electron complex RuH{(SiMe2)N(κN-C5H4N)(SiMe2H)}(PCy3)2 (3) formulated as a hydrido(silyl) species on the basis of multinuclear NMR experiments. The dehydrogenation reaction is fully reversible under dihydrogen atmosphere. Reaction of Ru(COD)(COT) with 3 equiv of 1 under a H2 pressure led to the isolation of the new complex RuH{(SiMe2)N(κN-C5H4N)(SiMe2H)}3 (4) characterized as a hydridotrisilyl complex by multinuclear NMR techniques, X-ray and neutron diffractions, as well as DFT calculations. The 29Si HMBC experiments confirm the presence of two different silicon atoms in 4, with a signal at -14.64 ppm for three dangling Si-Me2H fragments and a signal at 64.94 ppm (correlating with the hydride signal) assigned to three Si-Me2N groups bound to Ru. Comparison of DFT and neutron parameters involving the hydride clearly indicates an excellent correlation. The Si-H distance of ∼2.15 Å is much shorter than the sum of the van der Waals radii and typically in the range of a significant interaction between a silicon and a hydrogen atom (SISHA interactions). In 4, three dangling Si-H groups remain accessible for further functionalization. [ABSTRACT FROM AUTHOR]

Abstract: The complete structure of {K(MeTHF)3}2{Yb{(μ-H)2BC8H14}4} including the positions of the H atoms has been determined by single-crystal neutron diffraction on the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin in Grenoble, France. Each [(μ-H)2BC8H14]− ligand is coordinated to the Yb atom via two Yb–H–B bridges, and two out of the four [(μ-H)2BC8H14]− units exhibit C–H···Yb agostic interactions. Crystallographic details: space group C2/c (Monoclinic); a =17.62 (4), b =19.92(4), c =21.05 (4)Å; β =95.62(9)Å; Z =4. Final agreement factor: R(F)=13.5% for 1668 unique reflections with I >2σ(I). [Copyright &y& Elsevier]

A four-coordinate hydrogen atom has been unambiguously located, by single-crystal neutron diffraction for the first time, in the center of the tetrahedral metal complex Y4H8(Cp′)4(THF) [Cp′=C5Me4-(SiMe3)]. The core of the molecule consists of a tetranuclear cluster with one interstitial, one face-bridging, and six edge-bridging hydride ligands. The compound was prepared via the reaction of YCp′(CH2SiMe3)2-(THF) with gaseous H2. Neutron data were collected on a 4 mm³ crystal at the Quasi-Laue diffractometer VIVALDI at ILL (GrenobIe)1a and on an 8 mm³ crystal at the SXD diffractometer at ISIS (Didcot). The final agreement factor is R = 8.9% for 4171 reflections. The existence of 4-coordinate hydrogen now completes the series of high-connectivity hydride ligands located in the interstitial cavities of molecular cluster complexes. We had previously reported the existence of 6-coordinate hydrogen in the octahedral cavity of [HCo6(CO)15]- in 1979, and 5-coordinate hydrogen in the square pyramidal cavities of [H2Rh13(CO)24]3- in 1997, also via single-crystal neutron analyses. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of Fe(CO)5 with CF3COOH/(CF3CO)2O, or with CF3COOH, in DMF at about 140°C produces the colourless compound 1, [Fe(DMF)6][Fe3(μ3-O) (CF3COO)6(DMF)3]2, constituted by the [Fe(DMF)6]2+ cation and by two [Fe3(μ3-O)(μ2-CF3COO)6(DMF)3]− anions, with a triangular disposition of the three iron atoms, the central substantially coplanar oxygen atom being formulated as a singly charged anion O(–I) stabilized by complexation to iron(II). [Copyright &y& Elsevier]

This paper deals with the preparation and structural investigation of asymmetric bis(silyl) niobocene hydrides, Cp2-Nb(SiHMe2)(H)(SiXMe2) (2; X = F (a), Cl (b), Br (c), I (d)) and Cp2Nb(SiXMe2)(H)(SiYMe2) (X,Y = F-I; X ≠ Y). Complexes 2a-d were prepared by selective electrophilic activation of the Si-H bond in Cp2Nb(SiHMe2)2(H). The Cp2Nb(SiXMe2)(H)(SiYMe2) complexes were prepared by electrophilic activation of the Si-H bond in 2a-d and, in some cases, by electrophilic exchange of the X halides in Cp2Nb(SiXMe2)2(H) (1) for other halides, V. The structures of complexes 2b and 2c have been studied by X-ray and neutron diffraction (ND). The ND results unequivocally established that the hydride ligand in 2c is shifted toward the SiBrMe2 ligand and that in 2b is positioned symmetrically between two nonequivalent silyl groups, with the H⋯SiClMe2 distance being shorter because of the shorter Nb-SiClMe2 bond length. Analysis of the X-ray structures of complexes 2a-d and complexes Cp2Nb(SiXMe2)(H)-(SiYMe2) shows that the largest structural distortions are observed for the silyl groups substituted by heavy halogen atoms. These trends are rationalized in terms of stronger interligand hypervalent interactions (IHI) Nb-H⋯Si-X for heavy atoms X from Group 7. [ABSTRACT FROM AUTHOR]

Four isomorphous complexes of formula [M(L)4(H2O)2]SO4·2H2O (M Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder-order transition on slow cooling that provides insight into the nature of communication between water squares. [ABSTRACT FROM AUTHOR]

A neutron diffraction study of the complex RuCl2[PPh2(2,6-Me2C6H3)]2 (1) defines the precise nature of the δ agostic interactions between the unsaturated metal center and two o-methyl groups of the xylyl substituents. The CH3 carbon atoms lie in the RuP2 equatorial plane with Ru…C distances of 2.637(7) and 2.668(6) Å, whereas four short Ru…H distances (from 2.113(11) to 2.507(11) Å) indicate that each methyl group interacts with two C-H bonds. A survey of the X-ray structures with β, γ, δ, and ϵ M…H3C-C moieties (no neutron data have been previously reported) shows a linear correlation between the angle M…C-C and the torsion of the methyl group about the C-C bond. Thus, the agostic interactions span the range between the classical (M…η²-HC) and the nonclassical (M…η³-H2C) types. A solution study of 1 shows intramolecular rearrangement of each xylyl substituent that equilibrates the environments of its two ortho CH3 groups. Activation parameters, evaluated from the analysis of ¹H NMR line shape as a function of temperature, are ΔH‡ = 9.6 ± 0.2 kcal mol-1 with ΔS‡ = -15.4 ± 0.7 eu (CDCl3). The related 14-electron complexes RuX2[PPh2(2,6-Me2C6H3)]2 (X = I, 2; NCO, 3), prepared from 1 and NaX, show a similar dynamic process in solution, with the iodo derivative displaying the most hindered rotation of the xylyl group. A DFT optimization of the complex RuCl2[PH2(2,6-Me2C6H3)]2 (1a) reproduces well the nonclassical Ru…η³-H2C agostic mode, whereas the classical Ru…η²-HC one corresponds to a transition state 1b, destabilized by 3.4 kcal mol-1. A similar barrier (ca. 3.8 kcal mol-1) is calculated for the xylyl rotation in the further simplified model RuCl2[PH2(2,6-Me2C6H3)][PH2CH=CHCH3] (1c), the absence of bulky phenyl substituents being largely responsible for the difference with respect to the experimental value. Finally, the MO analysis addresses the intrinsic stability of the 14-electron complex RuCl2(PH3)2 and, in agostic complexes, accounts for the different interactions between the methyl group and the metal atom in relation to the length of their interconnecting chain. [ABSTRACT FROM AUTHOR]

A single-crystal neutron diffraction analysis of the cluster complex [H4Co4(C5Me4Et)4] was carried out on the new quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin. The structure consists of four face-bridging hydrides attached to a tetrahedral cobalt metal core. Average distances and angles in the core of the molecule are as follows: Co-Co = 2.571(8), Co-C = 2.158(6), Co-H = 1.749(7), H…H = 2.366(9) Å; Co-H-Co = 94.6(3), H-Co-H -- 85.1 (3)°. The hydride ligands are located off the Co-Co-Co planes by an average distance of 0.923(8) Å. It is suggested that the dimensions of the HCo3 fragments found in this molecule provide reasonable estimates for analogous distances and angles associated with chemisorbed H atoms situated on the 3-fold hollows of a cobalt surface. Crystallographic details: space group P21/a (monoclinic); a = 21.979(2), b = 10.924(1), c = 34.406(2) Å; β = 90.81(1)°; Z= 8. Final agreement factor: R(F) = 0.099 for 3779 reflections [I > 2σ(I)] collected at 20 K. [ABSTRACT FROM AUTHOR]

Dimesitylborane dimer has been shown to exist in equilibrium with dimesitylborane monomer in solution. This equilibrium has been investigated by variable concentration and variable temperature multinuclear NMR spectroscopy and values for the dissociation constant, enthalpy and entropy of dissociation were found to be Kdiss=(3.2±0.4)×10−3 M, ΔH=70 kJ mol−1, and ΔS=212 J K−1mol−1, respectively. Ab initio methods have been used to investigate the gas-phase structures and energies of both monomer and dimer, and calculated 11B-NMR shifts are also presented. The solid-state structure of dimesitylborane dimer has been investigated by single crystal X-ray diffraction at 100 K and the position of the bridging hydrogen atoms (B&z.sbnd;H=1.340(2), 1.342(2) A˚, H&z.sbnd;B&z.sbnd;H=92.46(14)°) has been determined accurately, for the first time, by single crystal neutron diffraction at 20 K. [Copyright &y& Elsevier]

Studies the structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethyllan- thracene -9-ol using x-ray diffraction at room temperature and neutron diffraction at very low temperature. Presence of the two bifurcated hydrogen bonds; Evidence of very close pseudosymmetry in both molecules A and B.

Examines the reactivity a tantalum complex with a bridging nitrogen unit. Synthesis of dinitrogen complexes; Reduction of dinitrogen moiety via reductive hydrogen elimination; Application of density functional theory calculations; Interactions involved in the side-on end-on bonding dinitrogen complex.

Presents a study which determined the crystal structures of all five crystalline methyl D-pentofuranosides. Use of cryogenic X-ray and neutron crystallography; Role of hydrogen-bonding in of H-atom positions; Geometrical and conformational parameters of the structures of all five crystalline pentofuranosides.

Examines the syntheses of uranium complexes. Determination of hydrogen positions; Methods and materials used in the study; Examination of the coordination sphere around the uranium atom; Results of experimentation.

The article reports that dihydrogen complexes were a curiosity 20 years ago when the first paper by G.J. Kubas demonstrated that dihydrogen could coordinate to a metal center without H-H bond breaking. The dihydrogen bonding in W(η2-H2(CO)3(PiPr3)2 was established clearly by single-crystal neutron diffraction, showing a H-H bond distance of 0.82 Å. A number of polyhydride species were then reformulated, and the number of dihydrogen complexes grew swiftly. Most complexes contain only one dihydrogen ligand in the octahedral coordination sphere of a d6.

Reports on the synthesis and structural analysis by single-crystal neutron diffraction of a phenol...nitroxide hydrogen bonded complex. Hydrogen atom abstraction by peroxy radicals from vitamin E and related phenolic antioxidants; Interaction of radicals with phenolic antioxidants under steric and electronic environments.