Crystal structure of bis(3-carboxypyridinium) hexafluorosilicate

Complex [3-HO(O)CC₅H₄NH]₂SiF₆ is synthesized, and its structure is determined by single-crystal X-ray diffraction. In its ionic structure, the centrosymmetric SiF ₆ ^2? anions (the Si-F bond lengths are 1.6658(15)–1.7033(17) Å) and [3-HO(O)CC₅H₄NH]⁺ cations are linked through interionic H-bonds NH…F, NH…O, and OH…F (the N…F, N…O, and O…F distances are 2.752(3), 2.935(3), and 2.596(2) Å, respectively).     

Crystal structure of p-nitroanilinium hexafluorosilicate

Complex (p-O₂NC₆H₄NH₃)₂SiF₆ (I) is prepared by reacting fluorostlicic acid with p-nitroaniline in methanol and structurally studied using single-crystal X-ray diffraction. In the ionic structure of this complex, SiF ₆ ^2? centrosymmetrical anions (avg. Si-F, 1.671(3) Å) and O₂NC₆H₄NH ₃ ⁺ cations are linked through NH…F interionic H-bonds (N…F 2.823(5)-3.205(7) Å). The thermochemical features of complex I are discussed in light of the structure data.     

Phase equilibria in the fluorosilicic acid-o-phenylenediamine-water system at 25°C: The crystal structure of o-phenylenediammonium hexafluorosilicate

The interactions in the H₂SiF₆-o-phenylenediamine-H₂O (FSA-PDA-H₂O) system at 25°C is studied using the isothermal solubility method. The solid phases existing in the system are o-PDA (0-23.70 wt % H₂SiF₆) and hexafluorosilicate formulated as (o-PDAH₂)SiF₆ (23.70–44.60 wt % H₂SiF₆). The structure for the latter is solved in single-crystal X-ray diffraction experiments. In the ionic structure of the complex, o-PDAH ₂ ²⁺ cations and SiF ₆ ² anions are linked through H-bonds NH-F((N-F 2.865(2)-2.967(2) Å) into a two-dimensional net. The Si-F bond lengths are 1.6709(12)-1.6958(12) Å.     

Synthesis and crystal structure of <Emphasis Type="Italic">N,N</Emphasis>-dimethylbiguanidinium hexafluorosilicate

The complex [(CH₃)₂NC(NH₂)NHC(NH₂)NH₂]SiF₆ (I) was synthesized and its structure was determined by X-ray crystallography. The crystals are monoclinic: a = 7.4346(10) Å, b = 12.7628(10) Å, c = 11.0828(10) Å, β 104.080(10)°, V = 1020.01(18) ų, ρ_calc = 1.780 g/cm³, μ(MoK _α) = 0.302 mm^?1, Z = 4, space group P2₁/c. The crystals of I are composed of SiF ₆ ^2? anions (Si-F, 1.657(2)–1.699(2) Å) and N,N-dimethylbiguanidinium (H₂L²⁺) cations combined in a framework by interionic H-bonds NH···F. In the cations, protonation sites are the terminal imide groups.     

Intramolecular O → Si donor-acceptor interaction in R2P(=O)CH2CH2SiF3 molecules: Synthesis of dialkyl [2-(trifluorosilyl)ethyl]phosphonate and bis[(chloromethyl)dimethylsilyl] styrylphosphonate

The reaction of diethyl [2-(triethoxysilyl)ethyl]phosphonate with boron trifluoride etherate was used to synthesize diethyl [2-(trifluorosilyl)ethyl]phosphonate. The reaction of bis(trimethylsilyl) styrylphosphonate with chloro(chloromethyl)dimethylsilane gave bis[(chloromethyl)dimethylsilyl] styrylphosphonate. Multinuclear ¹H, ¹³C, ¹⁹F, ²⁹Si, and ³¹P NMR spectroscopy established the absence of a P=O → Si coordination bond in these compounds and the four-coordinate state of the silicon atom. Evidence for this finding was obtained by B3LYP/6-31G(d) quantum-chemical calculations. However, the same calculations for R₂P(=O)· CH₂CH₂SiF₃ (R = Me, Me₂N) showed the presence in such molecules of an O → Si coordination bond both in the gas phase and in CHCl₃ solution. The distance between the O and Si atoms in this series molecules decreases with R in the order: MeO > Me > Me₂N. The axial Si-F bond length increases in the same order and parallels the order of the Hammet σ ₀ ^m constants of these substituents, relating to their interaction with π-electron systems.     

Formation of five-connected three-dimensional coordination polymers through the bridging function of the anions

New coordination polymers based on 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (L) with the composition [M₂(L)₄A(NCS)₂] (M²⁺ = Co²⁺, Zn²⁺, Cd²⁺; A^2? = SiF ₆ ^2? , SeO ₄ ^2? ) have been synthesized and characterized by IR spectroscopy and X-ray diffraction. According to X-ray diffraction data, cobalt compounds crystallize in the orthorhombic system with the following unit cell parameters, [Co₂(L)₄SiF₆(NCS)₂] · 3CHCl₃ · CH₃OH: a = 20.568(4), b = 14.568(3), c = 22.929(5) Å, α = β = γ = 90°, V = 6870(2) ų, space group Pbca (no. 61), R(I > 2σ(I)) = 0.0514; [Co₂(L)₄SeO₄(NCS)₂] · 2CHCl₃ · 2CH₃OH · H₂O: a = 13.721(2), b = 21.539(3), c = 22.417(3) Å, α = β = γ = 90°, V = 6625(2) ų, space group P2₁2₁2₁ (no. 19), R(I > 2σ(I)) = 0.0452. The 3D structure of the coordination polymers is composed of wavelike two-dimensional coordination layers [ML₂]_n connected by bridging anions SiF ₆ ^2? , or Se O ₄ ^2? . The complexes have the same five-bonded topology but different symmetry.     

Crystal structure and Raman spectra of [Fe(H2O)6]3+(ClO 4 ? )3·3H2O

Single crystal X-ray diffraction is used to study the structure of colorless crystals isolated from the saturated aqueous solution of trivalent iron perchlorate (TIP) in 67.5% perchloric acid. It is found that the compound crystallizes in the trigonal crystal symmetry; parameters of the hexagonal unit cell: a = b = 16.079(2) ?, c = 11.369(2) ?, ?? = ?? = 90°, ?? = 120°, space group R{ie907-1}(S ₆), Z = 6, ??_calc = 2.021 g/cm³. The structural form of the crystal hydrate is [Fe(H₂O)₆]³⁺(ClO ₄ ^? )₃·3H₂O. The structure contains two independent complex iron cations. Each of them is in the special position {ie907-2}, but retains the regular octahedral structure: average bond lengths are r(Fe-O) = 1.997(1) ?, {ie907-3}O-Fe-O bond angles differ from 90° by only 0.93°. Independent [Fe(H₂O)₆]³⁺ cations form short H-bonds (O??O 2.64 ?) with three crystallization water molecules and somewhat longer H-bonds (O??O 2.73 ?) with three ClO ₄ ^? anions. The ClO ₄ ^? anion is disordered over two positions with occupancies of 0.62(2) and 0.37(2). Both positions correspond to the general position. The outer-sphere crystallization water molecule is characterized by the tetrahedral direction of H-bonds, which it forms with two anions and two independent [Fe(H₂O)₆]³⁺ cations. All water molecules are in the general position. The Raman spectroscopic study of polycrystalline samples reveals weak bands belonging to the internal vibrations of two types of water molecules. The least broad bands are assigned to the transitions of crystallization water molecules whose symmetry is insignificantly lowered by two anion-molecular Hbonds. Anomalously broad bands are assigned to the transitions of a coordinated water molecule whose symmetry is more lowered by intermolecular and anion-molecular H-bonds.     

Synthesis of bismuth complexes from bismuth iodide and ammonium and phosphonium salts

The complexes [Et₂NH₂] ₃ ⁺ [BiCl₆]^3? (I), [NH₄]⁺[BiI₄(C₅H₅N)₂]^?·2C₅H₅N (II), [Ph₃MeP] ₂ ⁺ [BiI₅]^2? (III), [Ph₃MeP] ₂ ⁺ [BiI₅(C₅H₅N)]^2?·C₅H₅N (IV), [Ph₃MeP] ₃ ⁺ [Bi₃I₁₂]^3? (V), [Ph₃(i-Pr)P] ₃ ⁺ [Bi₃I₁₂]^3?·2Me₂C=O (VI), [Ph₃BuP] ₂ ⁺ [Bi₂I₈·₂Me₂C=O]^2? (VII), and [Ph₃BuP] ₂ ⁺ [Bi₂I₈·2Me₂S=O]^2? (VIII) were obtained by reactions of bismuth iodide with ammonium and phosphonium iodides in acetone, pyridine, or dimethyl sulfoxide.     

Fluorkomplexe des Siliciums in wäßriger Lösung

The solubility of SiO₂ in aqueous solutions of hexafluorosilicates at various acid concentrations has been measured. The results are interpreted in terms of a series of mononuclear siliconfluorine complexes (SiF₆, SiF₅, SiF₄). The equilibrium constants β _x6 ^′ (x=4 and 5) of the reactionxSiF₆+(6?x)SiO₂+4(6?x)H=6SiF _x +2(6?x)H₂O in 4M-LiClO₄ have been determined (β ₄₆ ^′ =7·10^?8, β ₅₆ ^′ =9·10^?2). The influence of the ionic medium and the likely structures of the complexes are discussed. No conclusion can be drawn as to number and kind of other ligands than F (OH, OH₂).     

Structure of [NH3(CH2)4NH3]2P4O12·2H2O

After a short survey of what is the present state of the cyclophosphates associated with the organic molecule NH₂(CH₂)₄NH₂, we report chemical preparation and crystal structure for a new example of such compounds. [NH₃(CH₂)₄NH₃]₂P₄O₁₂.2H₂O is monoclinic (S.G. : P2₁/n), with Z = 2 and the following unit-cell parameters : a = 7.6728(8) Å, b = 18.962(3) Å, c = 7.9789(9) Å β = 111.751(9)°. Bidimensional layer arrangement of P₄O₁₂ rings connected to the water molecules thanks to weak H-bonds run parallel to the ab plane. The organic groupements located between these inorganic planes perform the three-dimensional cohesion by NH····O hydrogen bonds.     

The structure and mechanism of formation of C5H9O+ from ionized phytyl methyl ether

The recent proposal that ionized phytyl methyl ether [C₁₆H₃₃(CH₃)C=CHCH₂OCH ₃ ^+· ] undergoes an allylic rearrangement to ionized isophytyl methyl ether [CH₂=CHC(C₁₆H₃₃)(CH₃)OCH ₃ ^+· ] before elimination of an alkyl radical is discussed. Both literature precedent and new results in which the structure of the [M-C₁₆H ₃₃ ^· ]⁺ fragment ion is established by comparison of its collision-induced dissociation mass spectrum with the spectra of isomeric C₅H₉O⁺ ions of known structure are inconsistent with this proposal. The forma Hon of CH₃CH=CHCH=O⁺CH₃ by loss of a γ-alkyl substituent without skeletal isomerization rather than CH₂=CHC(CH₃)=O⁺CH₃ after allylic rearrangement is explained in terms of a mechanism that involves two 1,2-H shifts, followed by σ-cleavage of the resultant ionized enol ether, C₁₆H₃₃(CH₃)CH-CH=CHOCH ₃ ^+· .     

Preparation and disordered crystal structure of (18-crown-6)ammonium isothiocyanate hemihydrate

A crystalline complex salt, (18-crown-6)ammonium isothiocyanate hemihydrate [NH ₄ ⁺ (18C6)]·SCN^?·0.5H₂O, was prepared and studied by single-crystal X-ray diffraction. The crystal structure of this salt is highly disordered: Almost all the constituents (except the water molecule) are disordered over two different orientations: major and less occupied or weakly occupied. The geometric parameters (bond lengths, bond angles, etc.) of the molecular and ionic constituents of the salt were determined with reasonable accuracy, and the crystal packing was elucidated. The sale forms in the crystal a complex tetrahedral supramolecular hydrogen-bonded structure consisting of one water molecule, two complex cations [NH ₄ ⁺ (18C6)], and two SCN^? anions.     

Characterization of the C3H6O+· ion from 2-methoxyethanol. Mixture analysis by dissociation and neutralization—reionization

The C₃H₆O^+· ion formed upon the dissociative ionization of 2-methoxyethanol is identified by a combination of several tandem mass spectrometry methods, including metastable ion (MI) characteristics, collisionally activated dissociation (CAD), and neutralization—reionization mass spectrometry (NRMS). The experimental data conclusively show that 2-methoxyethanol molecular ion, namely, HOCH₂CH₂OCH ₃ ^+· , loses H₂O to yield mainly the distonic radical ion ·CH₂CH₂OCH ₂ ⁺ along with a smaller amount of ionized methyl vinyl ether, namely, CH₂=CHOCH ₃ ^+· . Ring-closed products, such as the oxetane or the propylene oxide ion are not observed. The proportion of ·CH₂CH₂OCH ₂ ⁺ increases with decreasing internal energy of the 2-methoxyethanol ion, which indicates a lower critical energy for the pathway leading to this product than for the competitive generation of CH₂=CHOCH ₃ ^+· . The present study also uses MI, CAD, and NRMS data to assess the structure of the distonic ion⁺ (CH₃)CHOCH₂· (ring-opened ionized propylene oxide) and evaluate its isomerization proclivity toward the methyl vinyl ether ion.     

Synthesis and crystal structures of 2,4,6-pyridine-tricarboxylic anions/guanidinium and tetraalkylammonium inclusion compounds

Two different hydrogen-bonded inclusion compounds, [2,4,6-C₅H₂N(COO^?)₃]_0.5·[C(NH₂) ₃ ⁺ ]_0.5·[(C₂H₅)₄N⁺]·2H₂O (1) and [2,4,6-C₅H₂N(COO^?)₃]·[C(NH₂) ₃ ⁺ ]·[(C₂H₅)₄N⁺]·[(C₃H₇)₄N⁺]·6H₂O (2) are reported in this paper, in which 2,4,6-pyridine-tricarboxylic anions, guanidiniums and water molecules jointly construct host lattices while tetraalkylammonium cations are accommodated as guest species. Both two compounds formed sandwich-like hydrogen-bond inclusion compounds. In compound 1, the dimers composed of 2,4,6-pyridine-tricarboxylic anions and guanidiniums form 2D hydrogen-bonded layers by connecting with water molecules. In compound 2, 2,4,6-pyridine-tricarboxylic anions, guanidiniums and water molecules contribute to generate an undulate rosette hydrogen-bonded architecture. Interestingly, in compound 2, there are two species of guest molecules, tetraethylammonium and tetrapropylammonium, which are alternately arranged between the neighboring layers. Mixed guest cations accommodated in hydrogen-bonded inclusion compounds are seldom seen.     

Hydrogen-bonding interaction in a complex of amino acid with urea studied by DFT calculations

Theoretical studies on hydrogen-bonded complexes between amino acids (glycine, alanine, and leucine) and urea in gas phase have been carried out using density functional theory (DFT) and ab initio methods at the B3LYP/6-311++g** and MP2/6-311++g** theory levels. The structures, binding energy, Chelpg (charges from electrostatic potentials using a grid-based method) charge distribution, and bond characteristics of the mentioned complexes were calculated. Urea is a good H-bond donor and an excellent receptor for highly electronegative atoms like O and N, through the formation of two or more hydrogen bonds. The NH₂ and COOH groups of amino acids can form several different types of H-bonds with urea molecular, as well as C^αH and alkyl side chains. The calculated high binding energy also suggests multiple H-bonds formed in one complex. The OH···O contact is the strongest hydrogen bond interaction with H···O separation around 1.65 Å and its relevant angle close to 176°. The closely linear amide H-bonds NH···O and OH···N strongly stabilize the amino acid–urea complex with H···O separation between 1.89 and 2.38 Å. The weaker CH···O/N H-bonds are also discussed as significant interaction in biological systems involving amino acids.     

Methyl propionate radical cation

Examination of the reactions of the long-lived (>0.5-s) radical cations of CD₃CH₂COOCH₃ and CH₃CH₂COOCD₃ indicates that the long-lived, nondecomposing methyl propionate radical cation CH₃CH₂C(O)OCH ₃ ^+· isomerizes to its enol form CH₃CH=C(OH)OCH ₃ ^+· (ΔH _{isomerization} ? ?32 kcal/mol) via two different pathways in the gas phase in a Fourier-transform ion cyclotron resonance mass spectrometer. A 1,4-shift of a β-hydrogen of the acid moiety to the carbonyl oxygen yields the distonic ion ^·CH₂CH₂C⁺ (OH)OCH₃ that then rearranges to CH₃CH=C(OH)OCH ₃ ^+· probably by consecutive 1,5- and 1,4-hydrogen shifts. This process is in competition with a 1,4-hydrogen transfer from the alcohol moiety to form another distonic ion, CH₃CH₂C⁺(OH)OCH ₂ ^· , that can undergo a 1,4-hydrogen shift to form CH₃CH=C(OH)OCH ₃ ^+· . Ab initio molecular orbital calculations carried out at the UMP2/6-31G** + ZPVE level of theory show that the two distonic ions lie more than 16 kcal/mol lower in energy than CH₃CH₂C(O)OCH ₃ ^+· . Hence, the first step of both rearrangement processes has a great driving force. The 1,4-hydrogen shift that involves the acid moiety is 3 kcal/mol more exothermic (ΔH _{isomerization}=?16 kcal/mol) and is associated with a 4-kcal/mol lower barrier (10 kcal/mol) than the shift that involves the alcohol moiety. Indeed, experimental findings suggest that the hydrogen shift from the acid moiety is likely to be the favored channel.     

Sampling of aryldiazonium, anilino, and aryl radicals by membrane introduction mass spectrometry: Thermolysis of aromatic diazoamino compounds

Membrane introduction mass spectrometry (MIMS) is used to sample free radicals generated by thermolysis at atmospheric pressure. This is done by heating the solid sample in a custom-made probe that is fitted with a silicone membrane to allow selective and rapid introduction of the pyrolysates into the ion source of a triple quadrupole mass spectrometer. Phenyldiazonium radical (C₆H₅N ₂ ^· ) and some of its ring-substituted analogs, the methoxy anilino radical CH₃OC₆H₄NH^·, and aryl radicals are generated by gas phase thermolysis of symmetrical aryl diazoamino compounds (ArNH-N₂Ar). The radicals are identified by measurement of their ionization energies (IE) using threshold ionization efficiency data. A linear correlation between the ionization energy of the phenyldiazonium radicals and their Brown σ⁺ values is observed, and this confirms the formation of these species and validates the applicability of MIMS in sampling these radicals. The ionization energies of the aryldiazonium radicals are estimated as IE (p-CH₃O-C₆H₄N ₂ ^· ), 6.74 ± 0.2 eV; IE (p-CH₃-C₆H₄N ₂ ^· ), 7.72 ± 0.2 eV; IE (C₆H₅N ₂ ^· ), 7.89 ± 0.2 eV; IE (m-Cl-C₆H₄N ₂ ^· ), 7.91 ± 0.2 eV; IE (p-F-C₆H ₄ ^· N ₂ ^· ), 8.03 ± 0.2 eV; and IE (m-NO₂-C₆H₄N ₂ ^· ), 8.90 = 0.2 eV. The ionization energies of the aryl radicals are estimated as IE (p-CH₃O-C₆H ₄ ^· ), 7.33 ± 0.2 eV; IE (p-CH₃-C₆H ₄ ^· ), 8.31 ± 0.2 eV; IE (C₆H ₅ ^· ), 8.44 ± 0.2 eV; IE (m-Cl-C₆H ₄ ^· ), 8.50 ± 0.2 eV and IE (p-F-C₆H ₄ ^· ), 8.54 ± 0.2 eV. Also, the ionization energy of the p-methoxyanilino radical (p-CH₃O-C₆H₄NH^·) is estimated as 7.63 ± 0.2 eV.     

Electrotransport, sorption, and photochemical properties of nanocluster polyoxomolybdates with a toroidal structure

The electrotransport, sorption, and photochemical properties of polyoxometalate NH₄)₃₂[MO ₁₁₀ ^VI MO ₂₈ ^V O₄₁₆H₆(H₂O)₅₈(CH₃CO₂)₆] · xH₂O (x ?? 250) with a toroidal structure are studied. Conditions for studying these characteristics are selected on the basis of data on the stability of POM, in dependence on the concentration and acidity of the medium and the processes of thermal decomposition. A set of independent physical and chemical methods of analysis is used. The possibility of the complexation of toroidal POM with polymer molecules is established. The photostabilizing effect of this POM on polymer molecules is revealed.     

Synthesis and structure of [Cr3O(CH3COO)6(H2O)3][UO2 (CH3COO)3] · 3H2O

Crystals of [Cr₃O(CH₃COO)₆(H₂O)₃][UO₂(CH₃COO)₃]·3H₂O (I) were synthesized for the first time and studied by X-ray crystallography. The crystals of I are orthorhombic: a = 8.3561(3) ?, b = 16.8421(5) ?, c = 25.7448(9) ?, V = 3623.2(2) ?³, space group P2₁2₁2₁, Z = 4, R = 0.0409. The structure is composed of trinuclear [Cr₃O(CH₃COO)₆(H₂O)₃]⁺ complexes and mononuclear [UO₂(CH₃COO)₃]^? complexes classified with crystal-chemical groups A₃M³B ₆ ² M ₃ ¹ (A = Cr³⁺, M³ = O^2?, B² = CH₃COO^?, M¹ = H₂O) and AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?), respectively. The complexes are bound to each other by electrostatic interactions and hydrogen bonds involving outer-sphere water molecules. The results of IR spectroscopic study of I are in good agreement with the structural data for the crystal.     

Phototransformations of azetidine radical cations stabilized in freonic matrices

It has been established that transformations of azetidine radical cations observed in freonic matrices under the action of light with λ = 436 nm (T = 77 K) are associated with C-N bond cleavage which corresponds to the cyclic form yielding a mixture of open distonic C-centered radical cations of the following structure: ·CH₂CH₂CH=NH ₂ ⁺