Hypervalence and the delocalizing versus localizing propensities of H 3– , Li 3– , CH 5– and SiH 5–

Lithium and silicon have the capability to form hypervalent structures, such as Li₃^– and SiH₅^–, which is contrasted by the absence of this capability in hydrogen and carbon, as exemplified by H₃^– and CH₅^– which, although isoelectronic to the former two species, have a distortive, bond-localizing propensity. This well-known fact is nicely confirmed in our DFT study at BP86/TZ2P. We furthermore show that the hypervalence of Li and Si neither originates from the availability of low-energy 2p and 3d AOs, respectively, nor from differences in the bonding pattern of the valence molecular orbitals; there is, in all cases, a 3-center-4-electron bond in the axial X–A–X unit. Instead, we find that the discriminating factor is the smaller effective size of C compared to the larger Si atom, and the resulting lack of space around the former. Interestingly, a similar steric mechanism is responsible for the difference in bonding capabilities between H and the effectively larger Li atom. This is so, despite the fact that the substituents in the corresponding symmetric and linear dicoordinate H₃^– and Li₃^– are on opposite sides of the central atom. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Isomerism of metal complexes with the boron cluster anions B10H 102? and B12H 122?

A new type of inner-sphere isomerism in coordination chemistry observed in metal complexes with boron cluster anions B _n H _n ²⁻ (n = 10, 12) is discussed. Specific structure of the closo-borohydride anions gives rise to edge and facial isomers, among which mirror isomers have been found. Examples of edge and facial isomers of metal complexes with the B₁₀H₁₀²⁻ and B₁₂H₁₂²⁻, anions obtained experimentally and studied by X-ray diffraction are considered. Analysis of their structure revealed a new type of isomerism, which was called “positional.”     

Kinetic study of the oxidation of L-threonine by MnO4? ions

A self-catalytic effect attributed to Mn²⁺ ions was observed when studying the oxidation of L-threonine by permanganate ions. The process obeys the rate equation:

Structure and thermal properties of [RhPy4Cl2]X complex salts (X = Cl?, ReO 4? , ClO 4? )

[RhPy₄Cl₂]Cl·4H₂O (I), [RhPy₄Cl₂]ReO₄ (II), [RhPy₄Cl₂]ClO₄ (III), and [RhPy₄Cl₂]ReO₄·2H₂O complex salts were synthesized. The crystal structure of compounds II (P4/ncc, a = 25.5655(3) ?, c = 14.3521(4) ?), III (P2₁/n, a = 13.5308(3) ?, b = 15.1044(5) ?, c = 23.3457(8) ?, β = 93.327°), and dyhydrate of II (Pbcm, a = 10.6199(9) ?, b = 10.4964(9) ?, c = 22.9834(16)?) was determined by X-ray diffraction analysis. The thermal transformations of the complexes were studied by differential thermal analysis. The substances were characterized by IR spectroscopy, XRPA, and element analysis Original Russian Text Copyright ? 2009 by D. B. Vasilchenko, I. A. Baidina, E. Yu. Filatov, and S. V. Korenev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 2, pp. 349–356, March–April, 2009.     

Is the FeC cluster linear? Theoretical study of the equilibrium structure and bonding of FeC

Ab initio electron correlation methods and density functional theory are used to investigate the structure, bonding, and stability of FeC. Theoretical calculations show that the ground state of the FeC anion strongly depends on the level of theory. The linear ⁴Σ^? state with an open configuration δ²σ¹ is predicted to be the ground state of FeC at the coupled‐cluster theory restricted to single, double, and noniterative triple excitations (CCSD[T])//CISD and multireference (MR) second‐order Moller–Plesset (MP2)//CAS self‐consistent field (SCF) levels. Next stable conformations are a C_2V ring structure II (⁴B₂) and a C_2V structure III (⁴A₂) in which Fe is bonded to one carbon atom of a triangular C₃. However, CISD and CCSD//CISD calculations show that the C_2V ring structure II and the C_2V structure III are more slightly stable than is the linear structure I of FeC. The harmonic vibrational frequencies and relevant vertical electron binding energies are reported. Possible detachment transitions in the photoelectron spectrum of FeC are discussed on the basis of current calculations. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 275–279, 2003     

Synthesis and structure of C17H22FN3O 32+ ?CuCl 42-

A new compound C₁₇H₂₂FN₃O₃ ²⁺ • CuCl₄ ^2- [pefloxacindium tetrachlorocuprate(II)], C₁₇H₂₀FN₃O₃ — 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(4-methyl-1-piperazinyl)-3-quinoline carboxylic acid (pefloxacin, PefH) is synthesized and characterized by single crystal X-ray diffraction technique. The crystal structure of the compound contains one PefH₃ ²⁺ cation and one CuCl₄ ^2- anion. The supramolecular architecture of the crystal is determined.     

Theoretical study of the structure and stability of cage-substituted icosahedral closo-boranes, alanes, and gallanes MiM′12 ? iH 122? (M, M′ = B, Al, and Ga; i = 0–12)

The equilibrium geometric parameters and energetic and spectroscopic characteristics of low-lying conformers for several series of model cage-substituted (mixed) borane, alane, and gallane closo-dianions M _i M′_{12 − i} H₁₂²⁻(M, M′ = B, Al, Ga), as well as of “bare” gallium-aluminum anions Ga _i Al_12−i ⁻ with i = 0–12, were calculated within the B3LYP approximation of the density functional theory using 6–31G* and 6–311+G** basis sets. Differences in structure and stability between alanoborane clusters of similar composition are revealed. In clusters where the M and M’ heteroatoms are close in size and electronegativity (in gallonoalanes and gallium-aluminum anions), successive substitutions of M′ for M are accompanied by small energy changes and occur quasi-stochastically in different positions of the cage. When the substituents are significantly different (in alanoboranes), mixed clusters are unstable against disproportionation into homonuclear “predecessors” M₁₂H₁₂²⁻ and M′₁₂H₁₂²⁻, and the most favorable M _i M′_{12 − i} H₁₂²⁻ structures among them are those in which M _i M′_{12 − i} the cages are subdivided into homonuclear “subclusters” M _i and M′t′_12−i with a maximal number of homonuclear bonds (M-M and M′-M′) and a minimal number of heteronuclear bonds (M-M′).     

Synthesis and structure of cobalt complexes [Ph3(n-Pr)P 2+ [CoI4]2? and [Ph3(n-Am)P 2+ [CoI4]2?

Complexes Ph₃(n-Pr)P₂⁺[CoI₄]²⁻ (I) and [Ph₃(n-Am)P]₂⁺ [CoI₄]²⁻ (II) were synthesized by reactions of triphenyl(alkyl)phosphonium iodide with cobalt(II) iodide in acetone. According to the X-ray diffraction data, complexes I and II consist of tetrahedral triphenyl(alkyl)phosphonium cations (for I, P-C is 1.787(4)–1.804(4) ? and CPC is 106.73(18)°–111.4(18)°; for II P-C is 1.786(6)–1.802(6) ? and CPC is 107.6(3)°–111.7(3)°) and [CoI₄]²⁻ anions (Co-I 2.5923(6)–2.6189(6) ?, ICoI 101.86(2)°–113.25(2)° for I; Co-I 2.5899(9)–2.6171(9) 107.01(3)°–110.47(3)° for II).     

On the catalytic mechanism of Pt 4+/? in the oxygen transport activation of N2O by CO

The two-state reaction mechanism of the Pt₄^+/− with N₂O (CO) on the quartet and doublet potential energy surfaces has been investigated at the B3LYP level. The effect of Pt₄ ⁻ anion assistance is analyzed using the activation strain model in which the activation energy (ΔΕ ^≠) is decomposed into the distortion energies (\Updelta E ¹ _\textdist ) (\Updelta E^{ \ne }_{\text{dist}} ) and the stabilizing transition state (TS) interaction energies (\Updelta E ¹ _\textint ) (\Updelta E^{ \ne }_{\text{int}} ) , namely \Updelta E ¹ = \Updelta E ¹ _\textdist + \Updelta E ¹ _\textint \Updelta E^{ \ne } = \Updelta E^{ \ne }_{\text{dist}} + \Updelta E^{ \ne }_{\text{int}} . The lowering of activation barriers through Pt₄ ⁻ anion assistance is caused by the TS interaction \Updelta E ¹ _\textint \Updelta E^{ \ne }_{\text{int}} (−90.7 to −95.6 kcal/mol) becoming more stabilizing. This is attributed to the N₂O π*-LUMO and Pt d HOMO back-donation interactions. However, the strength of the back-donation interactions has significantly impact on the reaction mechanism. For the Pt₄ ⁻ anion system, it has very significant back-bonding interaction (N₂O negative charge of 0.79e), HOMO has 81.5% π* LUMO(N₂O) character, with 3d orbital contributions of 10.7% from Pt₍₃₎ and 7.7% from Pt₍₇₎ near the ⁴TS4 transition state. This facilitates the bending of the N₂O molecule, the N–O bond weakening, and an O⁻(²P) dissociation without surface crossing. For the Pt₄ ⁺ cation system, the strength of the charge transfer is weaker, which leads to the diabatic (spin conserving) dissociation of N₂O: N₂O(¹∑⁺) → N₂(¹∑_g⁺) + O(¹D). The quartet to doublet state transition should occur efficiently near the ⁴TS1 due to the larger SOC value calculated of 677.9 cm⁻¹. Not only will the reaction overcome spin-change-induced barrier (ca. 7 kcal/mol) but also overcome adiabatic barrier (ca. 40.1 kcal/mol).Therefore, the lack of a thermodynamic driving force is an important factor contributing to the low efficiency of the reaction system.     

Measurement of mean ionic activity coefficients for tetra-n-butyl ammonium salts of PF 6? and [B(C6F5)4]? in tetrahydrofuran and acetonitrile

Osmotic coefficients were measured for tetra-n-butylammonium hexafluorophosphate (TBA PF₆) and tetra-n-butylammonium tetrakis(pentafluorophenyl)borate (TBABARF) in tetrahydrofuran and in acetonitrile. These osmotic coefficients were fit using equations first derived by Pitzer. Mean ionic activity coefficients were determined using the integrated form of the Pitzer equations. Densities were measured for each of the solutions and the results were used to convert mean ionic activity coefficients on the molal scale to the molar scale. Remarkably, over concentrations ranging from 0.1 to 1.0 m in acetonitrile, the behavior of TBABARF is consistent with the simple Debye-Hückel equation. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 1, pp. 66–73. The text was submitted by the authors in English.     

Molecular and crystal structures of [FeCl(HMPA)3(H2O)2]2+(FeCl4) 2? · 3HMPA

IR and single-crystal X-ray diffraction study are carried out for compound, C₃₆H₁₁₂Cl₉Fe₃N₁₈O₈P₆(I). It crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 14.2992(3), b = 21.4351(4), c = 25.5407(5) ?, V = 7828.3(3) ?³, ρ_calcd = 1.553 g/cm³, Z = 4. The FeCl fragment is coordinated with chlorine atom of two water molecules and three HMPA molecules to form a cation, with a distorted octahedral coordinate geometry. In the crystal I, the cation is linked with HMPA by the O-H…O hydrogen bond. The chiral crystal is formed through self-assembly even from achiral molecules.     

Structure of the C17H20FN3O 32+ ·2HSO 4? · H2O compound

A new compound of C₁₇H₂₀FN₃O₃²⁺ · 2HSO₄⁻·H₂O [ciprofloxacindi-um bis(hydrosulfate) monohydrate], C₁₇H₁₈FN₃O₃ 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid (CfH, ciprofloxacin) is obtained and its crystal structure is determined. The crystal contains CfH₃²⁺ and HSO₄⁻ ions and crystallization water molecules. Hydrogen (H3), which forms an intramolecular hydrogen bond with oxygen O2 of the carboxyl group, is attached to the carbonyl O1 atom. Hydrogen H4 of the carboxyl group is hydrogen bonded to the crystallization water molecule which links CfH₃²⁺ with two HSO₄⁻ groups by hydrogen bonds. Both H atoms at N3 of the piperazine ring form hydrogen bonds with two oxygen atoms of other HSO₄⁻ anions. Intramolecular hydrogen bonds of two types are present in the CfH₃²⁺ cation. One of them forms a six-membered ring, bonding O1 and O2 atoms, while the other, also enclosing a six-membered ring, links fluorine and carbon C14 atoms. Original Russian Text Copyright ? 2009 by A. D. Vasiliev, N. N. Golovnev, and I. A. Baidina __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 1, pp. 165–168, January–February, 2009.     

Unusual ion UO4? formed upon collision induced dissociation of [UO2(NO3)3]?, [UO2(ClO4)3]?, [UO2(CH3COO)3]? ions

The following ions [UO₂(NO₃)₃]⁻, [UO₂(ClO₄)₃]⁻, [UO₂(CH₃COO)₃]⁻ were generated from respective salts (UO₂(NO₃)₂, UO₂(ClO₄)₃, UO₂(CH3COO)2) by laser desorption/ionization (LDI). Collision induced dissociation of the ions has led, among others, to the formation of UO₄ ⁻ ion (m/z 302). The undertaken quantum mechanical calculations showed this ion is most likely to possess square planar geometry as suggested by MP2 results or strongly deformed geometry in between tetrahedral and square planar as indicated by DFT results. Interestingly, geometrical parameters and analysis of electron density suggest it is an U^VI compound, in which oxygen atoms bear unpaired electron and negative charge.     

Kinetics of the ?OH-radical initiated reactions of acetic acid and its deuterated isomers

Kinetics of the ^•OH-initiated reactions of acetic acid and its deuterated isomers have been investigated performing simulation chamber experiments at T = 300 ± 2 K. The following rate constant values have been obtained (± 1σ, in cm³ molecule⁻¹ s⁻¹): k ₁(CH₃C(O)OH + ^•OH) = (6.3 ± 0.9) × 10⁻¹³, k ₂(CH₃C(O)OD + ^•OH) = (1.5 ± 0.3) × 10⁻¹³, k ₃(CD₃C(O)OH + ^•OH) = (6.3 ± 0.9) × 10⁻¹³, and k ₄(CD₃C(O)OD + ^•OH) = (0.90 ± 0.1) × 10⁻¹³. This study presents the first data on k ₂(CH₃C(O)OD + ^•OH). Glyoxylic acid has been detected among the products confirming the fate of the ^•CH₂C(O)OH radical as suggested by recent theoretical studies.     

Crystal structure of pefloxancindium tetrabromidozinkate C17H22FN3O 32+ · ZnBr 42?

A new compound, namely pefloxancindium tetrabromidozincateC₁₇H₂₂FN₃O₃²⁺ · ZnBr₄²⁺ where C₁₇H₂₀FN₃O₃ is 1-ethyl-N-methyl-6-fluoro-1,4-dihydro-4-oxo-7-(4-methyl-1-piperazinyl)-3-quinoline carboxylic acid (PefH, pefloxacin), has been synthesized and its crystal and molecular structure has been solved. It contains PefH₃²⁺ and ZnBr₄²⁻ ions. The latter is a slightly distorted tetrahedron. The supramolecular architecture of a crystal has been analyzed.     

Die halbquantitative Bestimmung von Cl?, Br?, J?, SCN?, AsO43?, Cr2O72? und [Fe(CN)6]3?

Ohne Zusammenfassung     

Synthesis, characterization, and crystal structural study of the iron(II) 4,4′-bithiazole complex [Fe(C6H4N2S2)3]2+(NO3?)2

Abstract  

The complex [Fe(C₆H₄N₂S₂)₃]²⁺(NO₃⁻)₂ was prepared from the reaction of 4,4′-bithiazole with Fe(NO₃)₃·9H₂O in methanol. It was characterized by IR, UV-Vis, luminescence, ¹H NMR and ¹³C NMR spectroscopy, and X ray crystallography. The structure was solved in the orthorhombic space group P2₁2₁2₁ with a = 12.1500(5), b = 12.8434(6), c = 16.2222(7) ?, V = 2531.43(19) ?³, Z = 4, and with wR ₂  = 0.0897.     

Salt effects in the reaction between IrCl62? and MnEDTA2?

The oxidation of MnEDTA^2–. (EDTA=ethylenediaminetetra-acetate) by hexachloroiridate(IV) has been studied in concentrated electrolyte solutions at 298 K. The estimation of the activity coefficients of the species from the Stokes-Robinson hydration theory indicates that the observed salt effects have their origin in a greater destabilization of the initial state with respect to the transition state when increasing salt concentration. MnEDTA^2– (EDTA= ) (IV) . -, , .