New rubidium pentaborate Rb[B5O7(OH)2] · 0.5H2O with a 5: [4Δ + 1T] anionic block and its relation to larderellite (NH4)[B5O7(OH)2] · H2O on the basis of the OD theory

A new rubidium pentaborate is synthesized under hydrothermal conditions. Its crystal structure is studied by the heavy-atom method without any a priori knowledge of chemical formula. The chemical formula is Rb[B₅O₆(OH)₄] · 0.5H₂O, sp. gr. $\bar P1$ , lattice parameters a = 7.679(4) Å, b = 9.253(6) Å, c = 12.053(9) Å, α = 98.55(5)°, β = 106.80(5)°, γ = 91.71°, R = 0.0573, R _w = 0.0638, S = 1.07. The anionic part of the structure consists of a chain of fundamental building blocks 5:[4Δ + 1T] built by four B triangles bound to one B tetrahedron, which are common to Na, K, Rb, and Cs pentaborates. This new pentaborate is closely related to the mineral larderellite (NH₄)[B₅O₆(OH)₄] · H₂O but possesses an original structure, which manifests itself in the different morphology of the new pentaborate and the absence of perfect cleavage. The Dornberger-Schiff OD theory allows one to describe in detail the structural relationships, predict possible hypothetical structures, and write the OD groupoid.     

Crystal structure of new decaborate Na<Subscript>2</Subscript>Ba<Subscript>2</Subscript>[B<Subscript>10</Subscript>O<Subscript>17</Subscript>(OH)<Subscript>2</Subscript>]

The crystal structure of a newly synthesized compound Na₂Ba₂[B₁₀O₁₇(OH)₂] has been determined (Syntex \(P\bar 1\) diffractometer, MoK_α radiation, 1784 crystallographically nonequivalent reflections, anisotropic approximation, R = 1.7%). The parameters of the monoclinic unit cell are a = 11.455(7), b = 6.675(4), c = 9.360(7) Å, β = 93.68(5)°, Z = 2, sp. gr. C2. The structure consists of double pseudohexagonal layers built by BO₄-tetrahedra and BO₃-triangles forming three-membered rings of two mutually orthogonal orientations. The neighboring layers along the [001] direction are bound by Na-polyhedra and hydrogen bonds with participation of OH groups. The interlayer tunnels along the [100] direction are filled with columns of Ba-polyhedra. The crystallochemical characteristics of a number of synthetic Ba-borates (to which the structure of new decaborate is related) are considered in terms of borate building blocks singled out in the structure.     

Solvent Effect on the Ligand Exchange between Bis(diethyldithiocarbamato)copper(II) and Bis(diethyldiselenocarbamato)copper(II)

EPR and spectrophotometric study on the products of ligand‐exchange taking place on mixing bis(diethyldiselenocarbamato)copper(II), [Cu(Et₂dsc)₂], and bis(diethyldithiocarbamato)copper(II), [Cu(Et₂dtc)₂], solutions is reported. EPR spectra monitored at room temperature for one month period reveal a stable equilibrium among the parents (chromophores CuS₄ and CuSe₄) and the obtained mixed‐chelate [Cu(Et₂dtc)(Et₂dsc)] complex (chromophore CuS₂Se₂) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl₄ and CHCl₃ two new additional EPR spectra appear attributed to the mixed‐chelate complexes with the chromophores CuSSe₃ and CuS₃Se which are not observed with electronic spectroscopy. The intensities of all five EPR spectra decrease with the time. It is assumed that the new mixed‐chelates observed in CCl₄ and CHCl₃ are obtained in a reaction of [Cu(Et₂dtc)(Et₂dsc)] or [Cu(Et₂dtc)₂] with the ester of diselenocarbamic acid which is formed in a parallel reaction of [Cu(dsc)₂]with CCl₄ or CHCl₃.     

The electrostatic potential at atomic sites as a reactivity index in the hydrogen bond formation

The paper reviews results from computational studies by molecular orbital and density functional theories on several series of hydrogen bonded complexes. These studies aim at quantifying the reactivity of molecules for the complexation process. Excellent linear relationships are found between the electrostatic potential values at the sites of the electron donor and electron accepting atoms and the energy of hydrogen bond formation (ΔE). The series studied are: (a) complexes of R–CHO and R–CN molecules with hydrogen fluoride; (b) complexes of mono-substituted acetylene derivatives with ammonia; (c) (HCN)_n hydrogen bonded cluster for n=2–7. All 22 studied complexes of carbonyl and nitrile compounds with hydrogen fluoride fall in the same dependence between the energy of hydrogen bond formation and the electrostatic potential at the atomic site of the carbonyl oxygen and nitrile nitrogen atoms, with linear regression correlation coefficient r=0.979. In the case of complexes of mono-substituted acetylene and diacetylene derivatives with NH₃, the correlation coefficient for the dependence between the electrostatic potential at the acidic hydrogen atom and ΔE equals 0.996. For the series of hydrogen bonded (HCN)_n clusters, the correlation coefficient for the relationship between the electrostatic potential at the end nitrogen atom and ΔE is r=0.9996. Similarly, the analogous relationship with the electrostatic potential at the end hydrogen atom has a regression coefficient equal to 0.9994. The dependencies found are theoretically substantiated by applying the Morokuma energy decomposition scheme. The results show that the molecular electrostatic potential at atomic sites can be successfully used to predict the ability of molecules to form hydrogen bonds.     

Selective dehydrogenation of tetralin on zeolites

The dehydrogenation of tetralin on two zeolite catalysts has been studied, the experiments were planned statistically according to the Orthogonal Central Composite Design. In order to determine the influence of coke deposits, the time-on-stream theory of catalyst decay is applied too.

---

. . .

     

Synthesis and crystal structure of new phosphate NaFe 4 2+ Fe 3 3+ [PO4]6

New sodium iron orthophosphate NaFe ₄ ²⁺ Fe ₃ ³⁺ [PO₄]₆ was synthesized by the hydrothermal method. The crystal structure (sp. gr. $P\bar 1$ ) was established by the heavy-atom method, with the exact chemical formula of the compound being unknown; R _hkl = 0.0492, R _whkl = 0.0544, S = 0.52. The new compound is analogous to iron phosphate Fe ₃ ²⁺ Fe ₄ ³⁺ [PO₄]₆ studied earlier. However, these two compounds differ in the Fe²⁺ and Fe³⁺ contents, because Na⁺ ions in the new compound are located at the centers of symmetry not occupied earlier.     

Refined crystal structure of Ca[B<Subscript>8</Subscript>O<Subscript>11</Subscript>(OH)<Subscript>4</Subscript>]—A synthetic calcium analog of strontioborite

A calcium analog of strontioborite, namely, Ca[B₈O₁₁(OH)₄], is synthesized under hydrothermal conditions (T = 270°C, P = 20 atm) within the framework of the study of the phase formation in the CaCl₂ · Rb₂CO₃ · B₂O₃ system. The crystal structure of the synthetic calcium borate [a = 7.4480(5) Å, b = 8.2627(5) Å, c = 9.8102(6) Å, β = 108.331(1)°, V = 573.09(6) ų, space group P2₁, Z = 2, ρ_calcd = 2.15 g/cm³; Brucker SMART CCD automated diffractometer, 5506 reflections, λMoK_α] is refined by the least-squares procedure in the anisotropic approximation of thermal atomic vibrations to R₁ = 0.050. The calcium borate studied has a crystal structure identical to the structure of the natural strontium borate (strontioborite) Sr[B₈O₁₁(OH)₄] and its calcium analog synthesized earlier. The crystal structure is built up of stacks consisting of skeleton layers (formed by boron-oxygen polyanions) and isolated strontium (calcium) polyhedra located in trigonal holes of the skeleton layers. Through channels that can contain H₂O molecules are formed between the stacks. The structure refinement and analysis of the IR spectrum of the synthetic calcium analog of strontioborite do not confirm the previously proposed hypothesis that water molecules are involved in the channels of the structure. A comparative crystal chemical analysis of the calcium borate under investigation and its formula analog, namely, the lead borate Pb[B₈O₁₁(OH)₄], is performed.     

Crystal structure of a new synthetic Ca,Li pentaborate: CaLi<Subscript>4</Subscript>[B<Subscript>5</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>2</Subscript>]<Subscript>2</Subscript>

When studying the phase formation in the CaO-Li₂O-B₂O₃-H₂O system, a new Ca,Li pentaborate was synthesized under hydrothermal conditions. The structure of a new compound with the crystallochemical formula CaLi₄[B₅O₈(OH)₂]₂ (sp. gr. Pb2n, a = 8.807(7), b = 9.372(7), c = 8.265(6) Å, V = 682.2(9) ų, Z = 2, d_calcd = 2.43 g/cm³, automated SYNTEX-\(P\bar 1\) diffractometer, 2690 reflections, 2θ/θ scan, λMo) is refined up to R_hkl = 0.0557 in the anisotropic approximation of atomic thermal vibrations with allowance for the localized H atoms. The structure of the Ca,Li pentaborate is formed by (010) open boron—oxygen layers formed by two independent [B₅O₈(OH)₂]^3? pentagroups, with each of them being formed by three B tetrahedra and two B triangles. The structure framework consists of the above boron—oxygen layers bound by isolated Li tetrahedra. The Ca cations are localized in the centers of eight-vertex polyhedra located in the [001] channels of the Li,B,O framework. Comparative crystallochemical analysis of the new Ca,Li pentaborate and Li pentaborate of the composition Li₃[B₅O₈(OH)₂]-II showed that the anionic matrices of both compounds are completely identical, whereas some of the cationic positions are different.     

Crystal structure of new synthetic calcium pentaborate Ca[B5O8(OH)] · H2O and its relation to pentaborates with similar boron-oxygen radicals

A new representative of pentaborates with the composition Ca[B₅O₈(OH)] · H₂O was synthesized under hydrothermal conditions within the framework of the study of phase formation in the CaCl₂-Na₂CO₃-B₂O₃ system. The crystal structure of the new pentaborate was established (a = 6.5303(9) Å, b = 19.613(3) Å, c = 6.5303(9) Å, β = 119.207(2)°, V = 2513(2) ų, sp. gr. P2₁/c, Z = 4, d _calcd = 2.74 g/cm³, automated Brucker SMART CCD diffractometer, 6871 reflections, λMo radiation, anisotropic refinement by least-squares, R _hkl = 0.076). The structure of calcium pentaborate is built by isolated B-Ca-B stacks parallel to the (010) plane. The central fragments of these stacks consists of nine-vertex Ca polyhedra. The Ca layers are located between loose B-O networks composed of [B ₂ ^t B ₃ ^Δ O₈(OH)]^2? pentaborate groups. The arrangement of the polyhedra around large cations in pentaborates with groups of two B tetrahedra and three B triangles was analyzed in terms of crystal chemistry. It is established that the structures of these compounds consist of large isolated polyhedra, columns, layers, and three-dimensional frameworks.     

Crystal structure of new synthetic Ca,Na,Li-carbonate-borate

In the process of studying the phase formation in the Li₂CO₃-CaO-B₂O₃-NaCl system, new Ca,Na, Li-carbonate-borate has been synthesized under hydrothermal conditions. The crystal structure of carbonate-borate with the crystallochemical formula Ca₄(Ca_0.7Na_0.3)₃(Na_0.7□ _0.3)Li₅[B ₁₂ ^t B ₁₀ ^Δ O₃₆(O,OH)₆](CO₃)(OH) · (OH,H₂O) was refined to R _hkl = 0.0716 by the least squares method in the isotropic approximation of atomic thermal vibrations without the preliminary knowledge of the chemical composition and the formula (sp. gr. R3, a _rh = 13.05(2) Å, α = 40.32(7)]°, V = 838(2) ų, a _h = 8.99(2), c _h = 35.91(2) Å, V = 2513(2) ų, Z = 3, d _calcd = 2.62 g/cm³, Syntex P $\bar 1$ diffractometer, 3459 reflections, 2θ-θ method, λMo). The structure has a new boron-oxygen radical [B ₁₂ ^t B ₁₀ ^Δ O₃₆(O,OH)₆] _∞∞ ^15? , a double layer of nine-membered [B ₆ ^t B ₃ ^Δ O₁₅(O,OH)₃]^7.5?-rings bound by BO₃-triangles, and twelve-membered [B ₆ ^t B ₆ ^Δ O_19.5(O,OH)₃]^7.5? rings. This allows one to relate this compound to megaborates with complex boron-oxygen radicals. The structure is built from two types of blocks consisting of Ca,Na,B-and Li,B-polyhedra alternating along the c-axis, which explains the perfect cleavage of the crystals along the (0001) plane.