D. L. Rogachev

Classification of fluorides and oxyfluorides of niobium(V) and tantalum(V) with alkali metals

On the basis of an analysis of the structures and chemical compositions of fluorides and oxyfluorides of niobium(V) and tantalum(V) the authors suggest a classification based on the dependence of the character of the crystal structure on the ratio of the number of nonmetal (O, F) ions to the number of Nb or Ta ions. If lithium ions are present in the structure, they are summed with Nb or Ta in view of their steric similarity.

Structure of binary hafnium and cesium sulfate

The authors determine the structure of a compound whose formula is Cs/sub 2//sup +/ /SUB x/ Hf(SO/sub 4/) /SUB 2+x/ (HSO/sub 4/) /SUB 2-x/ .3H/sub 2/O, was determined from diffractometric data. Eight atoms surrounding the Hf atom belong to four sulfate groups and a molecule of water. Three sulfate groups are bidentate-cyclic and one is monodentate with respect to Hf. The structure has deficiency of cesium in certain positions.

Structure of double sulfate of hafnium and rubidium

Compound Hf(SO4)2 x 2Rb2 (SO4) x H2O was obtained in a study of the system HfO2-H2SO4-Rb2SO4-H2O. The crystals are orthorhombic, = 9.728(2) A, b = 12.493(2) A, c = 15.025(3) A, Z = 4, space group P212121, V = 1826(1) AT, d/sub calc/ = 3.37 g/cmT. The unit-cell parameters and the intensities of 1927 observed independent reflections were measured on a four-circle automatic diffractometer (the Syntex P21) in Mo K/sub / radiation with a graphite monochromator, theta/2 theta scanning (sin theta/lambdamax = 0.651). The calculations were made in an ES 1022 computer by means of the Struktura Programs. The coordinates of the Hf atoms and some of the Rb atoms were determined by the Patterson method; the coordinate of the remaining atoms were found from the three-dimensional electron density distribution. The structure was refined by the method of least squares in the anisotropic approximation to R = 0.097; in the final refinement they used 1690 reflections. It is not altogether clear why the coordination number seven, less characteristic for Hf than eight, is realized here.

Refinement of the structure and composition of the tetrahydrate of hafnium hexasodium sulfate

The authors earlier described the structure of a compound whose formula was represented as Hf(SO/sub 4/)/sub 2/ x 3Na/sub 2/SO/sub 4/ x H/sub 2/O. A later investigation of the thermal properties of this compound, and also a study of the composition of the analogous zirconium sulfate, has shown that it contains a greater amount of water and corresponds to the formula Na/sub 6/Hf(SO/sub 4/)/sub 5/ x 4H/sub 2/O. We have continued study of the structure using the experimental data obtained previously and have located the oxygen atoms of the three H/sub 2/P molecules which were not revealed before, and also the coordinates of the H atoms of the water molecules. The electron density function does not contain other maxima which from the intensity and values of the distances from other atoms might be interpreted as oxygen atoms.

Crystal structure of cerium (IV)-di-potassium trisulfate monohydrate

The compound K2Ce(SO4)3 x H2O (I) was obtained in a study of the system Ce(SO4)2-K2SO4-H2O4-HO2 at 50-150C (1). The refined unit-cell parameters are: a = 20.600(3), b = 7.0744 (6), c = 18.583(3) A, US = 126.083(8), V = 2189(1) AT, Z = 8, rho/sub calc/ = 3.202(2) g/cmT, space group C2. The previously given unit-cell parameters are related to those given here by the matrices 100/010/0.5 0 1 and 100/010/-1 0-1. The intensities of 3416 independent reflections (3363 with I greater than or equal to 2sigma) and the unit cell parameters were measured on a Syntex P21 four-circle automatic diffractometer (lambdaMoK , theta/2 theta scanning at variable rate from 4 to 29.3 deg/min to theta = 60). The structural calculations were done on a Nova 1200 minicomputer by means of the Syntex XTL programs and on an ES 1022 computer by means of the Struktura programs. They used the heavy atom method; the final refinement over 3240 reflections (R = 0.071) was made allowing for the anisotropy of the thermal vibrations of the atoms.

The crystal structure of rubidium oxodisulfatoniobate

1. The structure of RbNbO(SO4)2 – a member of the isomorphous series of compounds of the type of ANbO(SO4)2, where A = NH4, Rb, Cs, was determined. The crystals were rhombic. 2. The compound was constructed from polymeric anionic layers with the composition NbO(SO4) 2 − and rubidium cations. The coordination of niobium is a distorted octahedron, the distances Nb-OSO4 lie within the range 1.96–2.26 a, and in the niobyl group this distance is equal to 1.73 a.