Atomic Cations Research Articles

81Br NQR and crystal structure of 4-bromopyridinium pentabromoantimonate(III); 3c–4e bonding and NQR trans influence

The crystal structure of (4-BrC5H4NH)2SbBr5 was determined by a single crystal X-ray diffraction at 193K. The crystals belong to the triclinic system (P1¯) with a=9.1861(19)Å, b=10.622(2)Å, c=10.703(2)Å, α=99.665(3)°, β=97.393(3)°, γ=108.539(3)°, and Z=2. There exists an anion dimer Sb2Br104− in the crystal structure which consists of an edge-sharing between two SbBr6 octahedra. The inversion center situated at the center of the shared-edge of the dimer relates two asymmetric units, which consist of a SbBr52− moiety and two nonequivalent cations. Each cation is bound to the apical Br atoms of Sb2Br104− through N–H…Br hydrogen bonds. Seven 81Br NQR resonance lines including those for two Br atoms in the nonequivalent cations have been observed in the temperature range of 77 to ca. 360K in accordance with the crystal structure. The frequencies of each of the respective pairs of NQR lines for the apical Br and for the equatorial Br atoms showed unusual positive temperature dependence with almost linear changes. For these curves, the other lines of pairs showed symmetrical temperature dependence, maintaining the center of mass almost constant in frequency. These observations may indicate the existence of NQR trans influence which were manifested through the occurrence of substantial electronic redistributions in the 3c–4e (Br–Sb–Br) bonds with temperature changes.

Gas-Phase Reactions of Atomic Lanthanide Cations with Ammonia: Room-Temperature Kinetics and Periodicity in Reactivity

Reactions of (14) atomic lanthanide cations (excluding Pm(+)) with ammonia have been surveyed in the gas phase by using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer to measure rate coefficients and product distributions in He at 0.35 +/- 0.01 Torr and 295 +/- 2 K. Primary reaction channels were observed corresponding to H(2) elimination with formation of the protonated lanthanum nitride and NH(3) addition. H(2) elimination was seen only in the reactions with La(+), Ce(+), Gd(+), and Tb(+) and occurs with these ions exclusively. NH(3) addition was seen with Pr(+), Nd(+), Sm(+), Eu(+), Dy(+), Ho(+), Er(+), Tm(+), Yb(+), and Lu(+). Higher-order sequential addition of up to five NH(3) molecules was observed with the Ln(+)(NH(3)) and LnNH(+) ions. The reaction efficiency of the primary reactions is seen to decrease as the energy required to promote an electron to make two non-f electrons available for bonding increases. The periodic trend in reaction efficiency along the lanthanide series matches quite closely the periodic trend in the electron-promotion energy required to achieve a d(1)s(1) or d(2) excited electronic configuration in the lanthanide cation. With La(+), Ce(+), Gd(+), and Tb(+), the electrostatic attraction between the atomic lanthanide cation and ammonia is sufficiently strong to provide enough energy to achieve electron promotion and to overcome any barriers to subsequent N-H bond insertion and H(2) loss, but this is not the case with the other lanthanide cations with which collisional stabilization of the intermediate adduct ion, with or without insertion of Ln(+), predominates.

Guided Ion Beam and Theoretical Studies of the Reactions of Pd+with CS2: Thermochemistry of PdS+and PdCS+

The gas-phase reactivity of the atomic palladium cation with CS(2) is investigated using guided-ion beam mass spectrometry. Endothermic reactions forming PdS(+) and PdCS(+) are observed. Analysis of the kinetic energy dependence of the cross sections for formation of the two products yields the 0 K bond energies of D(0)(Pd(+)-S) = 2.36 +/- 0.11 eV and D(0)(Pd(+)-CS) = 2.67 +/- 0.21 eV. Quantum chemical calculations are used to investigate the electronic structure of the two product ions. In addition, detailed calculations of the potential energy surfaces reveal that the mechanism involves oxidative addition of a CS bond to the metal cation followed by simple bond cleavages. Formation of the ground-state PdS(+) ((4)Sigma(-)) product is spin-forbidden from ground-state Pd(+) ((2)D) whereas PdCS(+) ((2)Sigma(+)) formation is spin-allowed. Crossing points between the doublet and quartet surfaces are located in the region of the SPd(+)(CS) intermediate, which suggests that coupling between the surfaces is efficient, consistent with experimental indications.

A DFT-Based Analysis of the Grossly Varying Reactivity Pattern in Room-Temperature Activation and Dehydrogenation of CH4by Main-Group Atomic M+(M=Ga, Ge, As, and Se)

Insight into the mechanism(s) of the recently reported thermal reactions of methane with the main-group atomic cations Ga+, Ge+, As+ and Se+ (A. Shayesteh et al. J. Phys. Chem. A 2009, 113, 5602) has been obtained from DFT-based calculations including relativistic effects. Excellent agreement with the experimental findings has been achieved, and a coherent description of the reactivity is provided. For example, the chemical inertness of the Ga+/CH4 couple is due to an endergonic formation of an encounter complex as well as a high endothermicity for the dehydrogenation of methane (DeltaG298=84.7 kcal mol(-1)). For Ge+/CH4, formation of an encounter complex is slightly exergonic (DeltaG298=-8.9 kcal mol(-1)) and thus is observed with low efficiency; the dehydrogenation path, however, is not accessible (DeltaG298=13.6 kcal mol(-1)). For the Se+/CH4 couple, the significantly enhanced rate of adduct formation is suggested to result from a spin-orbit-mediated quartet-doublet spin flip that generates the insertion product [(H)Se(CH3)]+, 2Se-3, in its doublet state rather than forming a simple encounter complex. For the dehydrogenation of 2Se-3 to generate 2[Se(CH2)]+, various mechanistic variants have been explored, all of which, however, involve transition structures that are located energetically above the entrance channel, thus preventing the reaction from occurring. In contrast, facile and efficient dehydrogenation of CH4 by ground-state As+ (3P0) takes place, and this reaction constitutes a textbook example of the operation of a two-state reactivity scenario. Here, a triplet-singlet conversion occurs along the oxidative insertion of As+ into the C-H bond of CH4 to generate [(H)As(CH3)]+ in its singlet state. From this intermediate, which constitutes the global minimum on the As+/CH4 potential energy surface, dehydrogenation is brought about by a sequence of alpha-hydrogen migration and reductive elimination of molecular hydrogen from the hydride carbene complex 1As-5. The potential energy surfaces for the As+/CH4 couple are remarkably similar irrespective of including or ignoring relativistic effects in the calculations.

Experimental and Theoretical Studies of the Reaction of Rh+ with CS2 in the Gas Phase: Thermochemistry of RhS+ and RhCS+

The gas-phase reactivity of the atomic transition-metal cation rhodium, Rh(+), with CS(2) is investigated using guided-ion-beam mass spectrometry (GIBMS). Endothermic reactions forming RhS(+) and RhCS(+) are observed. Analysis of the kinetic energy dependence of the cross sections for formation of these two products yields the 0 K bond energies of D(0)(Rh(+)-S) = 2.61 +/- 0.12 eV and D(0)(Rh(+)-CS) = 2.66 +/- 0.19 eV. These compare favorably with quantum chemical calculations at the CCSD(T)/Def2TZVPP//B3LYP/Def2TZVPP and CCSD(T)/Def2TZVPP levels of theory, where the former is also used to explore the complete potential energy surface of the reaction. It is found that the reaction initially involves insertion of the rhodium cation into one of the CS bonds of CS(2), followed by metal ligand cleavages to form the two product channels. The formation of ground state RhS(+) products is spin-forbidden, whereas RhCS(+) formation is spin-allowed. Crossing points between the triplet and quintet surfaces are located in the region of the SRh(+)(CS) intermediate, which suggests that coupling between the surfaces is reasonably efficient, consistent with experiment.

Aluminium triplets in dealuminated zeolites detected by 27Al NMR correlation spectroscopy

Arrangements associating three aluminium atoms in dealuminated Y zeolites are for the first time detected using a combination of multiple-quantum MAS (MQMAS) and 2D double-quantum homonuclear NMR correlation spectroscopy. From these results, we propose a model describing the enhanced Brønsted acid sites in dealuminated Y zeolite, consisting in a configuration where framework aluminium pairs are interacting with cationic extra-framework aluminium atoms.

Catalytic activity and long-term stability of palladium oxide catalysts for natural gas combustion: Pd supported on LaMnO3-ZrO2

The catalytic activity and long-term stability of 2% Pd/LaMnO3-ZrO2 catalysts for natural gas combustion were deeply investigated. The catalyst, prepared via solution combustion synthesis, was completely characterized (XRD, BET, FESEM/EDS, TPC/TPD/TPR and FT-IR analysis) in the fresh status, and in the aged one, after prolonged treatment under hydro-thermal ageing and S-compounds poisoning (up to 3 weeks of hydro-thermal treatment at 800°C under a flow of domestic boiler exhaust gases typical composition of 9% CO2, 18% H2O, 2% O2 in N2, including 200ppmv of SO2). An increased catalytic activity towards NG combustion with ageing was detected: the T50, in fact, got lowered from 570 (fresh sample) to 465°C (after 3 weeks ageing). Highly dispersed Pd centers were predominant on fresh catalyst. Upon ageing, oxygen covered Pd metal particles formed, at the expense of dispersed cationic and zerovalent Pd atoms. The increase in the catalytic activity was associated to the phase modification occurring in the bulk support, where Mn oxides, active towards CH4 combustion, segregated. Moreover, bands due to sulfate species were detected in aged samples: IR analysis showed that Pd atoms did not interact significantly with these species. The bands of sulfate species decreased in intensity after 3 weeks ageing, likely mostly due to sintering of the catalyst, with the corresponding decrease in the surface area.

Using electronic polarization from the internal continuum (EPIC) for intermolecular interactions

Recently, the vacuum-phase molecular polarizability tensor of various molecules has been accurately modeled (Truchon et al., J Chem Theory Comput 2008, 4, 1480) with an intramolecular continuum dielectric model. This preliminary study showed that electronic polarization can be accurately modeled when combined with appropriate dielectric constants and atomic radii. In this article, using the parameters developed to reproduce ab initio quantum mechanical (QM) molecular polarizability tensors, we extend the application of the "electronic polarization from internal continuu" (EPIC) approach to intermolecular interactions. We first derive a dielectric-adapted least-square-fit procedure similar to RESP, called DRESP, to generate atomic partial charges based on a fit to a QM abinitio electrostatic potential (ESP). We also outline a procedure to adapt any existing charge model to EPIC. The ability of this to reproduce local polarization, as opposed to uniform polarization, is also examined leading to an induced ESP relative root mean square deviation of 1%, relative to ab initio, when averaged over 37 molecules including aromatics and alkanes. The advantage of using a continuum model as opposed to an atom-centered polarizable potential is illustrated with a symmetrically perturbed atom and benzene. We apply EPIC to a cation-pi binding system formed by an atomic cation and benzene and show that the EPIC approach can accurately account for the induction energy. Finally, this article shows that the ab initio electrostatic component in the difficult case of the H-bonded 4-pyridone dimer, a highly polar and polarized interaction, is well reproduced without adjusting the vacuum-phase parameters.

Relative stability of onium states of nitrogen, oxygen, sulfur, and selenium atoms in cations formed in the elimination processes

Using the HF, B3LYP, and MP2 methods in the 6−31+G(d) basis with zero-point energy corrections, quantum chemical calculations of energy characteristics were carried out for the model molecules CH2=XH+ (X = NH, O, S, Se) formed from the molecules YCH2XH (Y = NH2, OH, SH, SeH, Cl) either through the elimination of Y-anions or as a result of the abstraction of neutral species YH from these molecules upon their interaction with a proton. Stabilities of the onium states of nitrogen atom were shown to be considerably higher than those of the onium states of chalcogen derivatives, with the lowest stability shown by the models with the Cl atom being in the onium state. The results have been formulated in the form of stability series of the onium compounds and allowed one to interpret certain features of the aminomethylation reaction (the Mannich reaction), hydroxy- and alkoxymethylation, thio- and selenomethylation, and chloromethylation (the Blanc reaction).

4-Aminopyridinium 4-aminobenzoate dihydrate and 4-aminopyridinium nicotinate

In the title compounds, 4-aminopyridinium 4-aminobenzoate dihydrate, C(7)H(6)NO(2)(-).C(5)H(7)N(2)(+).2H(2)O, (I), and 4-aminopyridinium nicotinate, C(5)H(7)N(2)(+).C(6)H(4)NO(2)(-), (II), the aromatic N atoms of the 4-aminopyridinium cations are protonated. In (I), the asymmetric unit is composed of two 4-aminopyridinium cations, two 4-aminobenzoate anions and four water molecules, and the compound crystallizes in a noncentrosymmetric space group. The two sets of independent molecules of (I) are related by a centre of symmetry which is not part of the space group. In (I), the protonated pyridinium ring H atoms are involved in bifurcated hydrogen bonding with carboxylate O atoms to form an R(1)(2)(4) ring motif. The water molecules link the ions to form a two-dimensional network along the (101) plane. In (II), an intramolecular bifurcated hydrogen bond generates an R(1)(2)(4) ring motif and inter-ion hydrogen bonding generates an R(4)(2)(16) ring motif. The packing of adduct (II) is consolidated via N-H...O and N-H...N hydrogen bonds to form a two-dimensional network along the (102) plane.

Charge Delocalization in a Heterobimetallic Ferrocene−(Vinyl)Ru(CO)Cl(PiPr3)2 System†Dedicated to Prof. Dr. Helmut Werner on the occasion of his 75th birthday

Ru(CH═CHFc)Cl(CO)(PiPr3)2 (Fc = ferrocenyl, (η5-C5H4)Fe(η5-C5H5)), 1, has been prepared by hydroruthenation of ethynylferrocene and characterized by NMR, IR, ESI-MS, and Moessbauer spectroscopy and by X-ray crystallography. Complex 1 features conjoined ferrocene and (vinyl)ruthenium redox sites and undergoes two consecutive reversible oxidations. Pure samples of crystalline, monooxidized 1•+ have been prepared by chemical oxidation of 1 with the ferrocenium ion. Structural comparison with 1 reveals an increase of Fe−C and Fe−Cpcentr. bond lengths and ring tilting of the Cp decks, as is typical of ferrocenium ions, but also a discernible lengthening of the Ru−C(CO) and Ru−P bonds and a shortening of the Ru−C(vinyl) bond upon oxidation. This supports the general idea of charge delocalization over both redox sites in 1•+. Band shifts of the charge-sensitive IR labels (ν(CO) for Ru, ν(C−H, Cp) for Fc), the rather small g-anisotropy in the ESR spectrum of 1•+, and the results of quantum chemical calculations indicate that in solution the positive charge partly resides on the vinyl ruthenium moiety. Comparison of IR shifts in the solid state and in solution and the quadrupole splitting in the Moessbauer spectrum of powdered 1•+ point to a larger extent of charge localization on the ferrocenyl site in solid samples. This is probably due to CH···F hydrogen bonding interactions between the cyclopentadienyl hydrogen atoms of the radical cations and the PF6− counterions. Monooxidized 1•+ displays low-energy electronic absorption bands at 1370 and 2150 nm. According to quantum chemical calculations, the underlying transitions are largely localized on the ferrocene part of the molecule with only little charge transfer into the vinyl ruthenium subunit. The second oxidation is more biased toward the (vinyl)ruthenium site.

Low-dimensional compounds containing cyano groups. XIX. Crystal structure, spectroscopic, thermal and magnetic properties of {[Cu( tn) 2] 3[Pt(CN) 4] 2}[Pt(CN) 4] ( tn = 1,3-diaminopropane) complex

Violet prismatic crystals of {[Cu( tn) 2] 3[Pt(CN) 4] 2}[Pt(CN) 4] ( tn = 1,3-diaminopropane) were crystallized from the water–methanol solution containing CuCl 2·2H 2O, tn and K 2[Pt(CN) 4]·3H 2O. Prepared complex was characterized using elemental analysis, infrared and UV–Vis spectroscopy, magnetic measurement and thermal analysis. X-ray analysis revealed an ionic character of the complex containing mononuclear square planar [Pt(CN) 4] 2− complex anions and penta-nuclear [Cu( tn) 2-Pt(CN) 4-Cu( tn) 2-Pt(CN) 4-Cu( tn) 2] 2+ complex cations. The inner Cu(II) atom of the complex cation is hexa-coordinated, whereas two crystallographically equivalent peripheral Cu(II) atoms are penta-coordinated in the shape of a deformed square pyramid. Four v(C N) absorption bands observed in the IR spectrum are in agreement with the higher number of crystallographically different cyano groups and a broad highly asymmetric band observed in the reflectance UV–Vis spectrum is consistent with the presence of both hexa- and penta-coordinated Cu(II) atoms in the structure. The temperature dependence of the inverse susceptibility suggests the presence of a weak antiferromagnetic exchange coupling between Cu(II) ions. The complex is stable up to 210 °C when its two-stage thermal decomposition starts.

Splendid Isolation for a Nonmetallic Dication

Confined, but happy: The triflate salt of a germanium(II) dication, an atomic cation of a nonmetal, was isolated by encapsulation in [2.2.2]cryptand (see formula and molecular structure in the crystal). The cryptand satisfies the electron demand of the cation and sterically protects it (see space-filling depiction, right).

Bis(3-nitroanilinium) sulfate

In the title salt, 2C6H7N2O2 +·SO4 2−, all the non-H atoms of both cations and the S atom and two O atoms of the anion lie on a crystallographic mirror plane. In the crystal structure, N—H⋯O and C—H⋯O hydrogen bonds help to establish the packing.

Synthesis of Bis(m-phenylene)-32-crown-10-Based Discrete Rhomboids Driven by Metal-Coordination and Complexation with Paraquat

Two bis(m-phenylene)-32-crown-10 derivatives containing two pyridyl or carboxyl groups were made. They were used to prepare three bis(m-phenylene)-32-crown-10-based discrete rhomboids by coordination-driven self-assembly with high yields. The formation of these crown ether-based rhomboids was confirmed by NMR, UV-vis, CSI-TOF-MS, and elemental analysis. The complexation of these crown ether-based assemblies with paraquat (N,N'-dimethyl-4,4'-bipyridinium) was studied. The complexation of neutral bis(crown ether) rhomboid 1 with paraquat was found to be statistical with a 1:2 stoichiometry. The average apparent association constant K(av) of the complexation of rhomboid 1 with paraquat was found to be about 8.8(+/-0.8) x 10(3) M(-1) in acetone, about 17 times higher than the reported association constant value for the complexation of the corresponding simple bis(m-phenylene)-32-crown-10 with paraquat. This is possibly because the carboxylate groups provide additional noncovalent interactions between the host and guest. No obvious complexation was observed between the cationic rhomboids and paraquat when studied by NMR, UV-vis, and CSI-TOF-MS analysis. This could be attributed to the combination of the charge repulsion between cationic pyridinium rings and cationic platinum atoms and the weak pi-pi stacking and charge transfer interactions between the phenyl rings and the pyridinium rings caused by the electron-withdrawing effect of the cationic platinum atoms.

Reactions of Atomic Cations with Methane: Gas Phase Room-Temperature Kinetics and Periodicities in Reactivity

Reactions of methane have been measured with 59 atomic metal cations at room temperature in helium bath gas at 0.35 Torr using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The atomic cations were produced at approximately 5500 K in an ICP source and allowed to decay radiatively and to thermalize by collisions with argon and helium atoms prior to reaction. Rate coefficients and product distributions are reported for the reactions of fourth-row atomic cations from K(+) to Se(+), of fifth-row atomic cations from Rb(+) to Te(+) (excluding Tc(+)), of sixth-row atomic cations from Cs(+) to Bi(+), and of the lanthanide cations from La(+) to Lu(+) (excluding Pm(+)). Two primary reaction channels were observed: C-H bond insertion with elimination of H(2), and CH(4) addition. The bimolecular H(2) elimination was observed in the reactions of CH(4) with As(+), Nb(+), and some sixth-row metal cations, i.e., Ta(+), W(+), Os(+), Ir(+), Pt(+); secondary and higher-order H(2) elimination was observed exclusively for Ta(+), W(+), and Ir(+) ions. All other transition-metal cations except Mn(+) and Re(+) were observed to react with CH(4) exclusively by addition, and up to two methane molecules were observed to add sequentially to most transition-metal ions. CH(4) addition was also observed for Ge(+), Se(+), La(+), Ce(+), and Gd(+) ions, while the other main-group and lanthanide cations did not react measurably with methane.

Pronounced Cluster-Size Effects: Gas-Phase Reactivity of Bare Vanadium Cluster Cations Vn+(n= 1−7) Toward Methanol

Mass spectrometric experiments are used to examine the size-dependent interactions of bare vanadium cluster cations V(n)(+) (n = 1-7) with methanol. The reactivity patterns exhibit enormous size effects throughout the range of clusters investigated. For example, dehydrogenation of methanol to produce V(n)OC(+) is only brought about by clusters with n > or = 3. Atomic vanadium cation V(+) also is reactive, but instead of dehydrogenation of the alcohol, expulsions of either methane or a methyl radical take place. In marked contrast, the reaction efficiency of the dinuclear cluster V(2)(+) is extremely low. For the cluster cations V(n)(+) (n = 3-7), complete and efficient dehydrogenation of methanol to produce V(n)OC(+) and two hydrogen molecules prevails. DFT calculations shed light on the mechanism of the dehydrogenation of methanol by the smallest reactive cluster cation V(3)(+) and propose the occurrence of chemisorption concomitant with C-O bond cleavage rather than adsorption of an intact carbon monoxide molecule by the cluster.

ChemInform Abstract: Gas‐Phase Reactions of Sulfur Hexafluoride with Transition Metal and Main Group Atomic Cations: Room‐Temperature Kinetics and Periodicities in Reactivity.

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Absence of the bowing character in the common-anion II–VI ternary alloys

The absence of bandgap bowing in the common-anion II–VI semiconductor ternary alloys is investigated. As examples, we consider the C d 1 − x Z n x T e and C d 1 − x Z n x S e alloys. The sp 3s * tight-binding method with the inclusion of spin–orbit interactions is employed to calculate the alloy’s band structure and its corresponding constituents’ charge states (ionicities) as a function of composition. The variation is found to be nearly linear. The vanishingly small valence-band offset ( VBO ≃ 0 ) in common-anion compounds would yield a linear scaling of bandgap energy with composition, especially as the conduction-band edge state being a singlet state with spherical symmetry. Furthermore, the two cation atoms ( Cd and Zn) are found not to compete in changing their charge states as the composition is varied. The absence of such competition is believed to be the main reason for the absence of bowing. The theoretical results are compared to the available experimental data and found to be in good agreement.

Synthesis and structure of bismuth complexes [Ph3(n-Pr)P] 2 + [Bi2I8 · 2Me2S=O]2−, [Ph3(iso-Bu)P] 2 + [Bi2I8 · 2Me2S=O]2−, [Ph3(n-Bu)P] 2 + [Bi2I8 · 2Me2S=O] 2−, and [Ph3(n-Am)P] 2 + [Bi2I8 · 2Me2S=O]2−

The complexes [Ph3(n-Pr)P]2+[Bi2I8 · 2Me2S=O]2− (I), [Ph3(iso-Bu)P]2+[Bi2I8 · 2Me2S=O]2− (II), [Ph3(n-Bu)P]2+[Bi2I8 · 2Me2S=O]2− (III), and [Ph3(n-Am)P]2+[Bi2I8 · 2Me2S=O] 2− (IV) are synthesized by reactions of triphenylalkylphosphonium iodide with bismuth iodide in dimethyl sulfoxide. In all complexes, the P atoms in cations have a distorted tetrahedral coordination (the CPC angles vary from 106.4(8)° to 114.8(2)°). In the dihedral centrosymmetric anions, the octahedral bismuth atoms are bound to each other by two bridging (br) iodine atoms (Bi-Ibr 3.167(1), 3.273(1) A (I); 3.1557(2), 3.2589(2) A (II); 3.1961(3), 3.3108(3) A (III); 3.1913(4), 3.3161(4) A (IV)), which are coplanar to four terminal (t) iodine atoms (Bi-It 2.956(1), 2.989(1) A (I); 2.9557(2), 2.9872(2) A (II); 2.9206(3), 2.9706(3) A ( III ); 2.9328(4), 2.9890(4) A (IV)). Two remaining positions at the bismuth atoms are occupied by the iodine atom (Bi-I 2.987(1) A (I); 3.0051(2) A (II); 2.8984(3) A (III); 2.9046(4) A (IV)) and the dimethyl sulfoxide molecule (Bi-O 2.458(12) A (I); 2.430(2) A (II); 2.507(3) A (III); 2.544(4) A (IV)).