N. G. Furmanova

Crystal structure of the new barium borate Ba5(BO3)2(B2O5)

The crystal structure of the new barium borate Ba5(BO3)2(B2O5) is established (R = 0.0436). Single crystals were grown by spontaneous crystallization in the BaO-B2O3-Na2O system using the flux method. This compound crystallizes in the orthorhombic system, sp. gr. P212121; the unit-cell parameters are a = 9.590(2) Å, b = 16.659(3) Å, c = 22.919(6) Å, and Z = 12. The structure consists of coordination polyhedra of barium cations and the anionic groups [BO3] (planar triangles) and [B2O5] (vertex-sharing double [BO3] triangles), which form a pseudohexagonal framework. Melting of barium borate occurs by a peritectic reaction at 1170 ± 10°C.

ORGANIC DITHIOCYANATES—REACTIVITY OF PRODUCTS OF ELECTRONIC TRANSFER AND MATRIX EFFECT

Abstract Reaction of 2,5-dithiocyanatothiophene with equimolecular amounts of the dipotassium salt of cyclooctatetraene dianion in THF yields potassium 2-thiocyanato-5-thienylmercaptide. The latter converts to a cyclic tetramer with disulfide bonds—tetra [(thienylen-2,5)disulfide], whose structure was determined by x-ray analysis. In the presence of 1,4,7,10,13,16-hexaoxacyclooctadecane (“18-crown-6-ether”), the cyclic tetramer formation becomes very difficult and the main product becomes poly [(thienylen-2,5)disulfide] with linear structure. It is suggested that the potassium cation takes part in forming a transition state as a coordinating center for thienylsulfidic fragments and thus produces the matrix effect.

Synthesis and crystal structures of coordination compounds of pyridoxine with zinc and cadmium sulfates

The pyridoxine complexes with zinc and cadmium sulfates are synthesized. The IR absorption spectra and thermal behavior of the synthesized compounds are described. Crystals of the [M(C8H11O3N)2(H2O)2]SO4 · 3H2O (M = Zn, Cd) compounds are investigated using X-ray diffraction. In the structures of both compounds, the M atoms are coordinated by the oxygen atoms of the deprotonated OH group and the CH2OH group retaining its own hydrogen atom, as well as by two H2O molecules, and have an octahedral coordination. The nitrogen atom of the heterocycle is protonated, so that the heterocycle acquires a pyridinium character. The cationic complexes form layers separated by the anions and crystallization water molecules located in between. The structural units of the crystals are joined together by a complex system of hydrogen bonds.

Crystal growth and properties of Rb2Ni(SO4)2 · 6H2O (RNSH)

Large single crystals of rubidium nickel hexahydrate Rb2Ni(SO4)2 · 6H2O (RNSH) of optical quality were grown for the first time. The atomic structure of RNSH crystals was refined. A comparative analysis of the crystal structures of (M1+)2Ni(SO4)2 · 6H2O, where M1+ is K, Rb, or Cs, was performed. The solubility curve of RNSH in water was measured. The optical and thermogravimetric properties of RNSH were investigated. The internal defect structure of RNSH crystals was studied by X-ray topography.

Growth and structure of barium sodium orthoborate NaBaBO3 crystals

Crystals of NaBaBO3 were grown by spontaneous crystallization on a platinum loop from the BaO-B2O3-Na2O system using the flux technique. The crystals have a highly disordered block structure. X-ray diffraction study λMoKα, 518 independent reflections, R = 0.0272) demonstrated that the structure of these crystals is identical with that established previously by other researchers for a sample prepared by cooling a stoichiometric melt.

Simulation of a defect region in KDP crystals doped with divalent iron ions. Comparison of defects induced by di-and trivalent metals

The crystal structure of FeII-doped KDP crystals was simulated with the use of specially developed partly covalent potentials. Different variants of introduction of impurity into the structure were analyzed. The M1 position was found to be more favorable for both isolated divalent and trivalent metal ions. Upon optimization, the coordinates of the FeII ion are (0.25, 0.44, 0.125). The FeII ions can aggregate to form “clusters” energetically more favorable than isolated defects. It seems that FeIII ions cannot form aggregates.

Crystal structures of dioxonium hexafluorotantalate and dioxonium hexafluoroniobate complexes with tetrabenzo-30-crown-10

Two isostructural complexes of dioxonium [H5O2]+ with tetrabenzo-30-crown-10 of the compositions [(tetrabenzo-30-crown-10 · H5O2)][TaF6] (I) and [(tetrabenzo-30-crown-10 · H5O2)][NbF6] (II) are studied using X-ray diffraction. The complexes crystallize in the monoclinic crystal system (space group C2/c, Z = 4). The unit cell parameters of these compounds are as follows: a = 15.6583(12) Å, b = 15.2259(13) Å, c = 16.4473(13) Å, and β = 99.398(6)° for complex I and a = 15.7117(12) Å, b = 15.2785(15) Å, c = 16.5247(15) Å, and β = 99.398(7)° for complex II. These complexes belong to the ionic type. The dioxonium cation [H5O2]+ in the form of the two-unit cluster [H3O · H2O]+ is stabilized by the strong hydrogen bond OH⋯O [O⋯O, 2.353(4) Å] and encapsulated by the crown ether. Each oxygen atom of the dioxonium cation also forms two oxygen bonds O⋯O(crown). The crown ether adopts an unusual two-level (pocket-like) conformation, which provides a complete encapsulation of the oxonium associate. The interaction of the cationic complex with the anion in the crystal occurs through contacts of the C-H⋯F type.

Crystal structure of zinc iodide complex with carbamide, ZnI2 · 2CO(NH2)2

The structure of ZnI2 · 2CO(NH2)2 is determined by single-crystal X-ray diffraction. The crystals are monoclinic, a = 12.694(3) Å, b = 6.886(2) Å, c = 13.161(3) Å, β = 110.58(2)°, Z = 4, space group P21/a, and R = 0.0337 for 2481 reflections. Similar to the chloride analogue, the structure consists of discrete molecules with tetrahedrally coordinated Zn atoms. The bond lengths and angles are as follows: Zn-I, 2.5749(8) and 2.5473(8) Å; Zn-O, 1.954(3) and 1.985(4) Å; IZnI, 113.74(3)°; OZnO, 100.5(2)°; and IZnO, 108.5°–113.1(1)°. The crystal structure agrees with the IR and electronic absorption spectra of the crystals.

Structural features of the KH2PO4: Cr single crystal

The precision X-ray structural investigation of KH2PO4 (KDP) crystal samples from different growth sectors of a single crystal containing chromium impurities is performed. It is demonstrated that the structure of the sample from the prismatic growth sector is more perfect than the structure of the sample from the pyramidal growth sector. The impurity trapping can lead to the formation of at least four different types of structural defects on the face of the pyramid, whereas only two of them can be formed on the face of the prism. A comparison with the relevant data for the “pure” KDP crystal shows that the number of defects and their character are approximately identical for all samples. The analysis of the IR spectra indicates that nitrate ions are contained in the samples from both growth sectors. Moreover, structurally bound water molecules and OH groups are revealed in the sample from the prismatic sector.

Crystal structures of complexes of the cys-syn-cys isomer of dicyclohexano-18-crown-6 with oxonium hexafluorotantalate and oxonium hexafluoroniobate

The crystal structures of [(cys-syn-cys-dicyclohexano-18-crown-6 · H3O)][TaF6] and [(cys-syn-cys-dicyclohexano-18-crown-6 · H3O)][NbF6] complex compounds are determined using X-ray diffraction analysis. The tantalum complex has two polymorphic modifications, namely, the monoclinic (I) and triclinic (II) modifications. The unit cell parameters of these compounds are as follows: a = 8.507(4) Å, b = 11.947(5) Å, c = 27.392(12) Å, β = 93.11(1)°, Z = 4, and space group P21/n for modification I; and a = 10.828(1) Å, b = 11.204(1) Å, c = 12.378(1) Å, α = 72.12(1)°, β = 79.40(1)°, γ = 73.70(1)°, Z = 2, and space group P-1 for modification II. The triclinic niobium complex [(cys-syn-cys-dicyclohexano-18-crown-6 · H3O)][NbF6] (III) with the unit cell parameters a = 10.796(3) Å, b = 11.183(3) Å, c = 12.352(3) Å, α = 72.364(5)°, β = 79.577(5)°, γ = 73.773(4)°, Z = 2, and space group P-1 is isostructural with tantalum complex II. The structures of all three complexes are ionic in character. The oxonium cation in complexes I–III is encapsulated by the crown ether and thus forms one ordinary and two bifurcated hydrogen bonds with the oxygen atoms of the crown ether. This macrocyclic cation is bound to the anions through the C-H...F contacts (H...F, 2.48–2.58 Å). The conformation of the macrocycle in complex I differs substantially from that in complex II (III).