Crystal and molecular structure of the sesquiterpene humulane alcohol juniferol

The spatial structure of the sesquiterpene humulane alcohol juniferol, which is represented in the crystal by two conformers, IA and IB, differing by the conformation of the C2...C9 section, has been established by the x-ray structural method. The strain energies of the conformers have been calculated by the method of molecular mechanics. The barrier to the interconversion of the conformers by rotation of the C2...C9 section has been calculated; it amounts to 7–8 kcal/mole. This value of the transformation barrier permits the assumption that the two conformers also exist in solution, their interconversion being hindered.Institute of Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Institute of Crystallography, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 757–762, November–December, 1990.     

Molecular and crystal structure of 1∶1 guest-host bis(hexafluoroacetylacetonato)calcium complex with 18-crown-6

We have carried out an X-ray structural study of the title complex (a CAD-4F diffractometer, MoK, graphite monochromator, /2 scan mode, _max, direct methods, 1465 reflections, R=0.036). Crystals are monoclinic with a=17.971(13), b=13.475(3), c=13.379(8) , =106.67(5)°, Z=4CaO₁₀C₂₂H₂₆F₁₂, space group C2/c, d _calc =1.537 g/cm³. The complex (C₂ symmetry) has a molecular structure and belongs to the guest-host type. The Ca atom is located in the center of the 18-crown-6 cavity; bidentate hexafluoroacetylacetonate guest ligands occupy the trans-positions relative to the plane of a maxidentate macrocycle. The Ca–O distances in a ten-vertex Ca polyhedron are 2.474–2.666 . The macrocycle conformation is characterized by six gauche C–C bonds and two gauche and ten trans C–O bonds. The dihedral COCC angle differs significantly (by 38.1°) from the angle of 60°, which is common to a gauche conformation. The six-membered cycle formed by oxygen atoms has a twist form with the annular O–O distances of 5.132–5.329 . Structural features explaining an easy sublimation of the compound are discussed.X-ray structural analysis and the interpretation of results.Synthesis of single crystals.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 56–65, November–December 1993.Translated by T. Yudanova     

Crystal structure of octapotassium octasulfatodiceriate pentahydrate

Single crystals without Co and Ni have been crystallized by the substitution method in the K₂Ni(SO₄)₂-Ce(SO₄)₂-H₂SO₄-H₂O system using K₂Co(SO₄)₂ · 6H₂O, K₂ (Co,Ni)(SO₄)₂ · 6H₂O, or K₂Ni(SO₄)₂ · 6H₂O as protocrystals. The structure of the single crystals obtained has been established by X-ray diffraction analysis. The crystal structure contains dimer complex anions [Ce₂(μ-SO₄)₂(SO₄)₆]⁸⁻, K⁺ cations, and crystallization water molecules.     

A product of the reaction of bis(methylcarboranyl)chlorophosphine with methylcarboranyllithium

Conclusions 1. An x-ray crystallographic structural study has shown that each phosphorus atom in penta(methyl-o-carboranyl)diphosphine is attached to two o-carboranyl rings directly through a carboranyl carbon atom, while the third ring is attached through a methylene group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2346–2348, October, 1979.The authors thank V. F. Sizyi and Yu. S. Nekrasov for taking and interpreting the mass spectra.     

Simulation of defects formed by cations of bivalent and trivalent metals in the structure of potassium dihydrogen phosphate: A computational technique

This paper reports on the results of crystal chemical analysis and computer simulation of the defect structure of potassium dihydrogen phosphate (KDP) containing impurities of bivalent and trivalent metals. It is shown that these impurities can form defect centers of different types: isolated centers formed by M ³⁺ and Ni²⁺ ions and, in part, by Co²⁺ ions at interstitial sites, chains composed of M ²⁺ impurity ions with radii from ≈0.65 to ≈1.1 Å, and centers created through the substitution of large-sized bivalent cations for potassium ions either with the formation of additional potassium vacancies or through the heterovalent isomorphism mechanism. The calculations are performed using different-type interatomic interaction potentials, and a comparative analysis of the results obtained is carried out.     

Refinement of the atomic structure of specimens cut out from different growth pyramids of a K(H0.052D0.948)2 PO4 single crystal

The structures of two crystalline specimens cut out from the pyramidal and prismatic growth sectors of a K(H_0.052D_0.948)₂PO₄ single crystal have been studied by diffuse neutron scattering and precision diffuse X-ray scattering. Diffuse scattering is concentrated in the vicinity of the Bragg reflections and is practically the same in specimens cut out from different growth sectors of a single crystal. X-ray diffraction analysis using the extinction parameters provided the establishment of a higher perfection of the specimen cut out from the prismatic growth sector. The precision X-ray studies revealed different configurations of hydrogen bonds in the specimens.     

Single-crystal structure of vanadium-doped Nd5Mo3O16

The single-crystal structures of the oxygen-ion-conducting fluorite-type compounds Nd₅Mo_2.90V_0.10O_15.3 and Nd₅Mo_2.76V_0.24O_15.5 were determined by X-ray diffraction. It was found that the displacements of atoms in the structure are retained after the doping of these compounds with vanadium. The dopant atoms occupy the molybdenum sites. The X-ray diffraction data were used to calculate the activation energies and analyze the possible pathways for the oxygen ion migration in the structures.