John H. Burns

The molecular and crystal structure of tetracyclopentadienyluranium(IV)

Abstract The crystal structure of (C 5 H 5 ) 4 U was determined from single-crystal X-ray diffraction data. The body-centered tetragonal unit cell contains two molecules and has dimensions a 8.635(2) and c 10.542(3) A. A structural model based on a random mixture of a pair of enantiomorphic molecules in the crystal accounts for the space-group symmetry, I 4 2 m , while individual molecules have point symmetry S 4 . In each molecule, planar C 5 rings are in a regular tetrahedral array around a uranium atom and are pentahapto -bonded to it. The CC bond lengths are all equal within experimental error and have a mean value of 1.386(5) A; the same is true for the UC bonds whose mean is 2.807(11) A.

Molecular and crystal structure of the adduct of cyclohexylisonitrile and praseodymium tricyclopentadienide

The crystal structure of (C5H5)3Pr·CNC6H11 was determined from single-crystal X-ray diffraction data. The monoclinic unit cell of dimensions a = 8.298(3), b = 21.66(1), c = 11.943(4) A, and β = 104.98(3)° contains four molecules in general positions of space group P21/c. Each molecule is composed of three C5H5 rings in a nearly exact trigonal array, η5-bonded to the Pr atom at a distance of 2.53 A to the centroid of each ring, plus a single CNC6H11 adduct attached to the Pr atom along the trigonal axis at 2.65 A. The presence of a CN triple bond in the isonitrile moiety and the nearly linear CNC configuration add credence to the previous proposal that there is a pure donor bond from the isonitrile carbon to the metal atom.

Photochemistry of anthracene in water

Abstract Photolysis of anthracene (350 nm) in aerated water yields endoperoxide and 9,10-anthraquinone as the major primary photoproducts. Photolysis of anthracene in oxygen-deficient aqueous solutions yields the three isomers of 10,10′-dihydroxy-9,9′,10,10′-tetrahydro-9,9′-bianthryl as the primary photoproduct. Involvement of a cation radical mechanism is suggested.

Crystallographic studies of some transuranic trihalides: 239PuCl3, 244CmBr3, 249BkBr3 and 249CfBr3☆

Abstract Single-crystal X-ray diffraction methods were used to refine the structures of PuCl3, CmBr3, and CfBr3. In PuCl3 (UCl3-type) the Pu ion has nine Cl-ion neighbors, three at 2·919(1) A and six at 2·886(1) A. A radius of 0·995 A was derived for the six-coordinated Pu3+ ion. In CmBr3 (PuBr3-type) the eight-coordinated Cm ion has two Br ions at 2·865(6) A, four at 2·983(4) A, and two at 3·137(4) A. Californium tribromide was shown to crystallize in both the AlCl3- and FeCl3-type structures. In the former type, the Cf ion is six coordinated and the three independent CfBr bond lenghts are 2·795(9) A, 2·827(11) A and 2·828(8) A. Berkelium tribromide was prepared and shown by powder X-ray diffraction to exhibit the AlCl3-, PuBr3-, and possibly FeCl3-type structures. The new findings on CfBr3 and BkBr3 were used to produce a more complete description of the structural relationships among the lanthanide and actinide tribromides.

Hexagonal and orthorhombic crystal structures of californium trichloride

Abstract Californium trichloride has been prepared in two crystalline modifications and single-crystal specimens of each have been studied by X-ray diffraction. The hexagonal UCl3-type crystal has unit-cell dimensions of a = 7·379(1) A and c = 4·0900(5) A and the orthorhombic PuBr3-type, a = 3·869(2) A , b = 11·748(7) A and c = 8·561(4) A . Structural parameters including anisotropic thermal motion have been refined by the method of least squares. In the hexagonal form the Cf atom is 9-coordinated by six Cl atoms at 2·815(3) A and three at 2·924(4) A, while in the orthorhombic form the coordination is 8-fold with two Cf-Cl distances of 2·690(7) A; four of 2·806(4) A and two of 2·940(6) A. An ionic radius of 0·932(3) A was derived for the 6-coordinated Cf3+ ion.

Crystal Structure of Li6BeF4ZrF8

The crystal structure of Li6BeF4ZrF8 has been determined by x‐ray diffraction. The tetragonal unit cell, having a=6.57, c=18.62 A, contains four formula weights; the space group is D4h19—I41amd. Discrete BeF42— and ZrF84— ions are connected by shared Li+ ions. The BeF42— tetrahedron is quite regular with a Be–F distance of 1.57±0.01 A; the ZrF84— dodecahedron has two independent Zr–F bonds of 2.05±0.01 A and 2.16±0.01 A, and deviates considerably from the shape predicted by theory.

Single crystal and powder diffraction studies of curium-248 trichloride, 248CmCl3☆

Abstract A single crystal of 248 CmCl 3 has been grown from the melt and studied by X-ray diffraction. The UCl 3 -type hexagonal unit cell has (at 23°C) dimensions of a o = 7·3743(11) and c o = 4·1850(7) A, where the standard errors are given in parentheses. Structural parameters including anisotropic thermal motion have been refined by the method of least-squares. A radius of 0·971 (3) A was derived for the six-coordinated Cm 3+ ion. Powder diffraction studies on three 248 CmCl 3 samples have shown the apparent absence of radiation-induced expansion in the previous 244 CmCl 3 studies. The melting point of 248 CmCl 3 was determined to be 695 ± 10°C.

Structure of a hydrogen-bonded lattice compound between phosphoric acid and 18-Crown-6: H3PO4·0.5(C12H24O6)·3H2O

Abstract Phosphoric acid and 1,4,7,10,13,16-hexaoxa-cyclooctadecane (18-crown-6) have been shown to form a hydrated lattice compound held together by hydrogen bonds. Its crystal structure at 297 K was determined by X-ray diffraction methods. The crystals are monoclinic, space group P 2 1 / c , with a = 8.494(2), b = 10.701(3), c = 15.210(5) A, β = 104.41(2)° and Z = 4. The phosphoric acid molecules form hydrogen-bonded dimers, which are linked by intermediate water molecules to crown ether rings through a series of hydrogen bonds. Each crown ether molecule receives a hydrogen bond to each of its six oxygen atoms, and in this symmetrical arrangement adopts the pseudo- D 3 d conformation often found in crown ether—cation complexes instead of the elongated shape it has in the uncomplexed state.

Synthesis and structures of isomerically pure bis-(alkylbenzo) crown ethers

Abstract A convenient method for the synthesis of bis-(4-alkyl-2-hydroxyphenoxy) alkoxy ethers, precursors to highly lipophilic, alkylbenzo-substituted crown ethers, is described. Thirteen isomerically-pure, bis-t-alkylbenzo crown ethers were prepared. The solid-state structures of three representative, bis-t-octylbenzo crown ethers are reported, representing the first structures ever reported for t-octylbenzocrown ethers.

The determination of local structure in organofluorides using fluorine-19 carbon-13 dipolar coupling☆

Abstract 1H19F13C double cross polarization (DCP)/magic angle spinning (MAS) 13C n.m.r. and 13C19F rotational echo double resonance (REDOR) CP/MAS 13C n.m.r. experiments performed on two low-molecular-weight monofluorinated organic compounds are reported. DCP n.m.r. permits the selective identification of resonances of carbons one- and two-bonds removed from a fluorine atom in these substances. Under our experimental conditions the 19F T2 is on the order of 1 ms or less. This relaxation process is beneficial in the DCP experiment. It defeats proper echo formation in 13C19F REDOR CP/MAS 13C n.m.r. experiments in which MAS speed and 19F(T2)−1 are comparable. Potential remains for REDOR in coal structure analysis under experimental conditions that result in lengthened 19F T2.