Allan Zalkin

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.

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.

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).

Crystal Structure of CsMnF3

A single‐crystal x‐ray diffraction study shows that CsMnF3 has the hexagonal BaTiO3‐type structure. The space group is P63/mmc. The unit cell with a=6.213 A, c=15.074 A contains six formula units. Each cesium atom has 12 fluorine neighbors at an average distance of 3.13 A. One third of the manganese atoms occupy the centers of fluorine octahedra that share their corners with other octahedra as in the perovskite structure. The remaining two thirds of the manganese atoms are in distorted fluorine octahedra that each share one face and three corners with other octahedra; these manganese atoms are in pairs 3.00 A apart. The average Mn–F distance in the octahedra is 2.13 A.

Synthesis of bis(η-1,3,5-tri-t-butylbenzene) sandwich complexes of yttrium(0) and gadolinium(0); the X-ray crystal structure of the first authentic lanthanide(0) complex, [Gd(η-But3C6H3)2]

The vapours of yttrium and gadolinium react with 1,3,5-tri-t-butylbenzene to afford the metal(0) complexes [(M(η-But3C6H3)2], M = Y, Gd; the X-ray crystal structure of the gadolinium complex shows the molecule to possess the parallel ring sandwich structure.

The crystal structure of osmium tetroxide

ing line between neighbouring oxygen atoms then in accordance with the valency angle of oxygen the donoracceptor direction in the helices is likely to be as indicated in Fig. 2. As mentioned above, the three oxygen atoms of the molecule are all found on the same side of the plane of the benzene ring. This may be related to the situation that the six neighbouring oxygen atoms to which these three are linked by hydrogen bonding are also found on this same side of the plane. As there are no short intermolecular distances in the direction normal to the plane of the benzene ring, the non-planarity of the molecule as a whole (considering carbon and oxygen atoms only), may be due to internal conditions rather than to external ones. An analysis of the parameters describing the anisotropic thermal motion shows that the largest axes of the vibrational ellipsoids are roughly perpendicular to the plane of the molecule. On request, a list of structure amplitudes is available from the author.

Crystal and Molecular Structure of Ferrichrome A.

The crystal structure of ferrichrome A (C41H58N9O20Fe�4H2O) has been determined by x-ray diffraction. The amino acid sequence in the hexapeptide ring is confirmed to be -Orn-Orn-Orn-Ser-Ser-Gly-, and the conformation of this ring is trans at each peptide linkage. The absolute configuration of the three hydroxamate rings at the iron atom is that of a left-handed propeller. Disorder is found concerning the positions of some of the side chains and one of the four water molecules.

Preparation and properties of the actinide borohydrides: protactinium(IV), neptunium(IV), and plutonium(IV) borohydrides

All five actinide borohydrides are made by reaction of the anhydrous tetrafluoride with Al(BH/sub 4/)/sub 3/. Synthesis of Pa(BH/sub 4/)/sub 4/ is a modification of that of Th (BH/sub 4/)/sub 4/ by Hoekstra and Katz. The Np and Pu borohydrides were synthesized at O/sup 0/C, followed by cold trapping of the products at -78 and -196/sup 0/C. Physical properties of these borohydrides (color, stability, mp, vapor pressure, M/sup 4 +/ radius, structure, density, gas-phase infrared spectra) were compared with those of Th, U, and Hf borohydrides. (DLC)

Crystal and Molecular Structure of a Double Complex of Manganese with Phthalocyanato and Pyridine Ligands

A crystalline solid, formed by oxidation of phthalocyanatomanganese(II) in pyridine, has been identified as phthalocyanatopyridinemanganese(III)-�-oxo-phthalocyanatopyridinemanganese(III)dipyridinate(C74H42Mn2N18O2C5H5N) byx-ray diffraction methods. This novel molecule consists of two manganese complexes joined by an essentially linear Mn—O—Mn bridge. Its structure may have some relation to oxidation processes in biological systems.