David H. Templeton

X-ray study of solid ammonia

Ammonia and deutero-ammonia have been studied by single-crystal and powder x-ray methods. There are four molecules in the cubic unit cell, and the space group is confirmed to be P2/sub 1/3. The nitrogen parameter obtained by least-squares refinement is equal to 0.0401 for NH/sub 3/ at -102 deg C and the same for ND/sub 3/ at -160 deg C. Cell dimensions, determined by powder methods, are: a = 5.084 A for NH/sub 3/ at -196 deg C, 5.073 A for ND/sub 3/ at -196 deg C, 5.091 A for ND/sub 3/ at -160 deg C, and 5.138 A for NH/sub 3/ at -102 deg C. Each ammonia molecule is involved in six hydrogen bonds of approximate length 3.4 A. A possible assignmert of the hydrogen atoms to these bonds is given. Electron- density maps give evidence of hydrogen positions with coordinates (0.85, 0.14, 0.99), in agreement with this assignment, but with hydrogen off the bond axis, making the H-N-H angles more nearly tetrahedral. (auth)

CRYSTAL STRUCTURE OF CERIUM MAGNESIUM NITRATE HYDRATE

According to single‐crystal x‐ray diffraction data, crystals of Ce2Mg3(NO3)12·24H2O are rhombohedral, space group R3. The hexagonal cell with a = 11.004±0.006, c = 34.592±0.012 A contains three formula units. Atomic parameters were refined by least squares, and interatomic distances were corrected for thermal motion. The average N–O bond distance in nitrate is 1.26 A. The Ce atoms, on the threefold axis at z = ±0.2497, are each surrounded by 12 oxygen atoms at an average distance of 2.64 A. These oxygen atoms, belonging to six nitrate ions, are at the corners of a somewhat irregular icosahedron. The Mg atoms are of two kinds, located, respectively, at the origin and on the threefold axis at z = ±0.4279. Each Mg atom is surrounded by six water molecules with the oxygen atoms at the corners of an octahedron with an average Mg–O distance of 2.07 A. One‐fourth of the water molecules are not coordinated to cations. Evidence for the hydrogen atom positions from the diffraction data indicates that six of the ei...

Crystal Structure of Vanadyl Bisacetylacetonate. Geometry of Vanadium in Fivefold Coordination

The structure of vanadyl bisacetylacetonate has been determined from three‐dimensional x‐ray diffraction data. The crystals are triclinic, space group P1, with a=7.53±0.02 A, b=8.23±0.03 A, c=11.24±0.04 A, α=73.0°, β=71.3°, γ=66.6°, Z=2. The structure consists of discrete molecules of VO(C5H7O2)2. Each vanadium atom has five oxygen neighbors at the corners of a rectangular (nearly square) pyramid, with vanadium near its center of gravity. The vanadium‐oxygen distances are 1.56 A to the apex atom (vanadyl oxygen) and 1.96, 1.96, 1.97, and 1.98 A to the others. Other bond distances average 1.28 A for C–O, 1.40 A for C–C (ring), and 1.52 A for C–C (methyl). Standard deviations are 0.01 A for V–O bonds and 0.02 A for C–O and C–C bonds. Each acetylacetone skeleton is planar, and this plane makes an angle of 163° with the plane of the other acetylacetone skeleton of the same molecule.

A table of dispersion corrections for X‐ray scattering of atoms

Values are tabulated for the real and imaginary dispersion corrections for the x-ray scattering factors for elements 20 to 96 for K radiation of chromium, copper, and molybdenum. 0:

The crystal structure of ruthenocene

>Dicyclopentadienylruthenium, or ruthenocene, crystallizes in the orthorhombic space group Pnma with a = 7.13, b = 8.99, c = 12.81 A. There are four Ru(C/sub 5/H/sub 5/)/sub 2/ molecules per unit cell. The ruthenium atoms form approximately a face-centered lattice, and the cyclopentadienyl rings lie in an eclipsed configuration with respect to each other about each ruthenium atom. The structure was refined by Fourier and least-squares methods with 791 independent refiections. The ruthenium-carbon distance is 2.21 A, and the carboncarbon bond distance in the rings averages 1.43 A. (auth)

X‐Ray Diffraction Refinement of the Calcium Tungstate Structure

The crystal structure of CaWO4 (scheelite) has been refined with single‐crystal x‐ray diffraction data. For the tetragonal cell a=5.243±0.002, c=11.376±0.003 A. Oxygen coordinates 0.1504, 0.0085, and 0.2111 correspond to Ca–O distances 2.44 and 2.48 A and W–O distances 1.78 A.

Madelung Constants for Several Structures

Madelung constants are given for 38 structures, some of which are relatively complex. The Madelung constants for binary compounds are compared with an empirical rule previously formulated.

The crystal structure and hydrogen bonding of magnesium sulfate hexahydrate

The atomic parameters were refined by least squares, X-ray counter data being used for 2576 independent reflections. The positions of the hydrogen atoms found by least squares and by Fourier methods confirm the assignment of hydrogen bonds made previously for the isomorphous CoSO4.6H20. Average interatomic distances are: water coordinated to Mg, Mg-O = 2-06 A; hydrogen bonds, 0 -0=2 .82 A; sulfate ion, S-O=1.473 /~ (uncorrected), 1.486 ~ (corrected for thermal motion).

The crystal structures of CeB4 ThB4 and UB4

The compounds CeB4, ThB4, and UB4 have been shown to crystallize in a new structure, which has been worked out from x-ray diffraction patterns. This structure is designated as the ThB4-type structure, since that was the compound first observed. These borides were prepared by D. L. Sawyer and L. Brewer of this laboratory, who heated the metals and boron together in vacuum at about 1500 deg C. Powder diffraction patterns were obtained of the three compounds. Rotation and Weissenberg patterns were obtained for 110 and 001 axes of a small single crystal of ThB4. The patterns were indexed on tetragonal lattices whose dimensions are listed.

Polarized Octahedra in Barium Tetratitanate

Single‐crystal x‐ray diffraction studies show that BaTi4O9 is orthorhombic, space group Pmmn, with a = 14.53±0.02, b = 3.79±0.01, and c = 6.29±0.01 A, with two formula units per unit cell and calculated density 4.54 g cm—3. Each barium atom has four oxygen neighbors at 2.81 A, two at 2.96, and four at 3.09, at the corners of a pentagonal prism. Titanium atoms are in distorted octahedra of oxygen atoms. The Ti–O distances range from 1.77 to 2.32 A, with standard deviations of 0.03 A or less. Titanium atoms occur at points 0.30 and 0.21 A from the centers of gravity of the oxygen atoms of the two kinds of octahedra. This polarization of the two octahedra is similar to or greater in magnitude than that observed in the ferroelectric phases of BaTiO3 and PbTiO3.