Richard K. McMullan

Urea-water-anion Lattices Part 1. Crystal structures of (C2H5)4N+X?(NH2)2CO2 H2O (X=Cl, Br, CN), an isomorphous series of layer-type inclusion complexes

The title ternary complexes (1, X=Cl;2, X=Br;3, X=CN) have been prepared and characterized by X-ray crystallography. Crystal data: space groupP21/n,Z=4;1,a=7.505(2),b=14.556(4),c=14.453(3) Å, β=98.13(2)o, andRF=0.088 for 1831 observed MoKα data;2,a=7.483(1),b=14.643(6),c=14.443 Å, β=98.25(2)o, andRF=0.113 for 923 data;3,a=7.490(2),b=14.646(5),c=14.594(5) Å, β=98.85(5)o, andRF=0.082 for 915 data. In the isomorphous crystal structure of1 and2, ordered (C2H5)4N+ cations are sandwiched between puckered layers matching the (020) family of planes, each being constructed from the cross-linking of planar zigzag chains of hydrogen-bonded urea molecules by the water molecules and halide ions. Compound3 has the same structure except that its cyanide group is disordered.

X-Ray and neutron diffraction studies on [Ru4(CO)8(µ-H)4{P(OCH3)3}4] at 293 and 20 K : characterisation of the vibrational behaviour of two-co-ordinate hydrogen atoms

X-Ray and neutron diffraction studies on the complex [Ru4(CO)8H4{P(OCH3)3}4] have been carried out at 293 and 20 K respectively. At room temperature the structure is monoclinic, space group P21/c with cell parameters a= 15.700(4), b= 11.775(3), c= 21.331(5)A, β= 100.49(4)°, and Z= 4. At 20 K the structure is triclinic, space group P with a= 15.371(3), b= 11.508(2), c= 21.079(3)A, α= 90.07(1), β= 100.09(1), γ= 92.09(2)°, and Z= 4. The X-ray determination shows the molecular structure to consist of distorted tetrahedral Ru4 units substituted so that each ruthenium atom is bound to two terminal carbonyl ligands, one trimethyl phosphite ligand, and two hydride ligands. Despite positional disorder affecting four methoxy groups, the µ-hydride ligands spanning four edges of the Ru4 tetrahedron were located and refined. At low temperature the structure is ordered with two molecules per asymmetric unit, and the neutron analysis provides precise characterization of the molecular structure. All the Ru–H–Ru bridges are symmetrical with mean Ru–H = 1.773(2)A and show closed three-centre two-electron bonding. Final agreement indices are R(F)= 0.043, R′(F)= 0.038 for 6 647 unique X-ray data, and R(F)= 0.048, R′(F)= 0.038 for 8 601 unique neutron data. Analysis of the vibrational behaviour of the hydride hydrogen atoms as determined in the neutron analysis indicates that this motion is consistent with these hydrogens residing in a single-minimum potential well provided by symmetric three-centre, two-electron Ru–H–Ru interactions.

Joint x-ray and neutron diffraction structure analysis of [(μ-H)3Re3(CO)8{(EtO)2POP(OEt)2}2]

Abstract The compound [(μ-H)3Re3(CO)8{(EtO)2POP(OEt)2}2] crystallises in the monoclinic space group P21/c with a 18.053(6), b 16.211(5), c 14.800(3) A, β = 102.41(2)°, and Z = 4. Simultaneous refinement of a single parameter set to fit 3212 X-Ray (sin θ/λ) > 0.352 A−1 and 1480 neutron data has led to final weighted residuals Rw(F) of 0.096 (X-Ray) and 0.095 (neutron). The molecule exhibits noncrystallographic C2 symmetry, with two edges of the Re3 triangle bridged by (OEt)2POP(OEt)2 ligands. The hydride ligands lie close to the trimetal plane with each hydride bridging an ReRe vector. Average molecular parameters involving the hydride ligands are ReH 1.812(17), ReRe 3.282(17) A, ReHRe 130(3) and HReH 107.6(27)/dg. All eight carbonyl ligands are terminal, the ligand polyhedron being derived from that in H3Re3(CO)12 by substitution of four axial carbonyls by two bidentate phosphite ligands.

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.

Crystal structure of 1-methyl-1,3,5,7-tetraazaadamantan-1-ium ammonium sulfate hydrate, a double salt containing puckered layers of hydrogen-bonded NH 4 + and SO 4 2− groups

The double salt [(CH2)6N4CH3](NH4)SO4·H2O crystallizes in space groupP21/a, witha=12.994(2),b=6.319(1),c=15.082(2) Å, β=93.78(2)o, andZ=4. The structure was solved by the heavy-atom method and refined toRF2=0.051 for 2478 MoKα data. The ammonium and sulfate ions are cross-linked by hydrogen bonds to form puckered layers disposed about the (001) family of planes. Each water molecule bridges a [(CH2)6N4CH3]+ ion and a sulfate group, so that the organic cations lying on both sides of a puckered layer have their methyl groups pointing inward and fitting into depressions.

Chains of Hydrogen-Bonded Molecules: Structural Data and Localized Modes

The acetanilide crystal (C6H5NHCOCH3 or ACN) contains parallel one-dimensional networks of hydrogen-bonded....H -N-C-O.... amide groups, like polypeptides(1). ACN displays some anomalous infrared and Raman modes, the origin of which is still a subject of controversy.

Self-trapped States in Chains of Hydrogen-Bonded Molecules: Optical Measurements, Neutron Scattering and Diffraction

Acetanilide (C6H5NHCOCH3 or ACN) is a quasi-one-dimensional crystal, containing parallel chains of hydrogen-bonded...H-N-C-O... amide groups (fig.1),like polypeptides and alpha-helix proteins.ACN displays some anomalous infrared and Raman modes(1), whose origin is subject of controversy.

Structures of the paraelectric and ferroelectric phases of NaD3(SeO3)2 by neutron diffraction

Abstract The crystal and molecular structure of the paraelectric and the ferroelectric phase of NaD3(SeO3)3 has been determined and refined using neutron diffraction data. Above Tc = 270°K the paraelectric phase is monoclinic, belonging to space group P21/n with Z=2, a=10.365(2), b=4.850(1), c=5.792(1) and β=91.16(3) at 298°K. The paraelectric phase is characterized by deuterium atoms in positions of two-fold disorder. The ferroelectric phase below Tc belongs to space group Pn with Z=4, a=10.314(3), b=9.663(2), c=5.768(2) and β=91.23(3) at 173°K. To collect proper neutron diffraction data on the ferroelectric phase, it was necessary to prevent small domain formation by poling the crystal in an external field of 15 Kv/cm during cooling-warming cycles through Tc. The deuterium atoms are ordered in the ferroelectric phase and the present determination of the particular way in which they are ordered resolves a disagreement between two previous resonance1,2 studies. Our results are in agreement with the model ...