Luminescence and nonradiative relaxation of Pb2+, Sn2+, Sb3+, and Bi3+ in oxide glasses

Absorption and fluorescence spectra of Sn²⁺ and Sb³⁺ in borax, phosphate, and germanate glasses were measured in the temperature range 87–295°K. Fluorescence decay times of these ions in borax glass at 87°K was a single exponent with τ ≈ 6–11 μsec. At 293°K, two decay times were resolved in the range of 50–2000 nsec. The nonexponential behavior is interpreted by the repopulation of the ³P₁ level from the ³P₀ level. The temperature dependence of fluorescence and the low values of quantum efficiencies of fluorescence are explained by means of the configurational coordinate diagram model.     

Synthesis and multinuclear NMR data of the ferrocenes (Me3Ecp)2Fe (E = C,Si, Ge,Sn, Pb)

The substituted cyclopentadienyl anions Me₃Ecp⁻ with E = C, Si, Ge, Sn, Pb have been prepared from either the mono- or disubstituted cyclopentadienes, including the hitherto unknown (Me₃Pb)₂C₅H₄. Representative examples have been characterized by ¹³C NMR spectroscopy. Treatment with iron(II) chloride yielded the ferrocenes (Me₃Ecp)₂Fe, which have been investigated by ¹H, ¹³C, ²⁹Si, ¹¹⁹Sn, and ²⁰⁷Pb NMR spectroscopy. ¹³C¹³C coupling and selective proton decoupling were used for the assignment of the ¹³C and ¹H signals. The shifts δ(¹³C) reflect the electron-releasing or -withdrawing power of the substituents Me₃E, but the isotope shifts ¹Δ¹³C(i)(¹³C(j)) do not show a similar trend. There is evidence that δ(¹¹⁹Sn) and δ(²⁰⁷Pb) are influenced by the coordination. The analysis of the coupling constants reveals that ¹J(¹³C(1)¹³C(2/5)) varies with the electronegativity of E. Because of the small range (4.5–5.0 Hz) of ¹J(⁵⁷Fe¹³C) the effect of E is apparent only when E = C is replaced by E = Si. As for the coupling between E and ¹³C or ¹H, the square root of the reduced coupling constant K is related linearly to the atomic number of E; exceptions are ¹K(²⁰⁷Pb¹³C).     

Synthesis of cis-(Me3Sn)2Fe(CO)4 by reaction of (Me3Sn)3Sb with Fe2(CO)9. Formation of (Me3E)3SbFe(CO)4 (E = Si,Ge)

(Me₃Sn)₃Sb and Fe₂(CO)₉ reacted to form (Me₃Sn)₂Fe(CO)₄ in 79% yield. From (Me₃E)₃Sb(E = Si or Ge) and Fe₂(CO)₉ the complexes (Me₃E)₃SbFe(CO)₄ were obtained     

Structural and electronic properties of Al12X+ (X=C, Si, Ge, Sn, and Pb) clusters

Using the first-principles method with the generalized gradient approximation, the authors have studied the structural and electronic properties of Al(12)X(+) (X=C, Si, Ge, Sn, and Pb) clusters in detail. The ground state of Al(12)C(+) is a low symmetry C(s) structure instead of an icosahedron. However, the Si, Ge, Sn, and Pb atom doped cationic clusters favor icosahedral structures. The ground states for Al(12)Si(+) and Al(12)Ge(+) are icosahedra, while the C(5nu) structures optimized from an icosahedron with a vertex capped by a tetravalent atom have the highest binding energy for Al(12)Sn(+) and Al(12)Pb(+) clusters. The I(h) structure and the C(5nu) structure are almost degenerate for Al(12)Ge(+), whose binding energy difference is only 0.03 eV. The electronic properties are altered much by removing an electron from the neutral cluster. The binding strength of a valence electron is enhanced, while the binding energy of the cluster is reduced much. Due to the open electronic shell, the band gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital are approximately 0.3 eV for the studied cationic clusters.     

The sixteen CB(11)H(n)Me(12-n)(-) anions with fivefold substitution symmetry: anodic oxidation and electronic structure

The 15 symmetrically methylated derivatives of the CB11H12(-) anion (1a) have been synthesized and found to vary greatly in ease of oxidation. Cyclic voltammetry in liquid SO2 yielded fully reversible oxidation potentials for five of those that have no adjacent unsubstituted vertices in positions 7-12; three others showed some indication of reversibility. The anions 1a-16a and the Jahn-Teller distorted neutral radicals 1r-16r have been characterized by ab initio and density functional theory calculations. In the state average CASSCF(13,12)/6-31+G* approximation, the ground state potential energy surface of 1r contains five symmetry-related pairs of minima. The computational results account for the reversible redox potentials very well when the solvent is included explicitly (RI-DFT(BP)/TZVP, COSMO). For display and for a semiquantitative understanding of methyl substituent effects in terms of perturbation theory, the molecular orbitals of 1a have been expressed in the symmetry-adapted cluster basis. The results serve as an underpinning for a set of additive empirical increments for redox potential prediction. Relative to the usual hydrogen standard, a single methyl group facilitates oxidation by approximately 50, 70, 70, and 10 mV in positions 1, 2, 7, and 12, respectively. This electron donor effect on the redox potential is due to a contribution, whereas those of (inductive and direct field) type are negligible.     

Studies on Synthetic Inorganic Ion Exchangers-III Quantitative Separations of Mg2+ -Pb2+, Zn2+ - Pb2+ Cu2+ - Pb2+, Al3+ - Pb2+, Zn2+ - Cd2+, and Mg2+ - Cd2+ on Lead Antimonate Columns

Abstract

A new inorganic ion exchanger, lead antimonate has been synthesized having an Pb:Sb ratio of 1:5 and cation exchange capacity of 1.46 mequiv./g. It is fairly stable in water and dilute solutions of acids, bases and salts. Ion distribution studies on twenty metal ions have been determined on this gel at pH 1,2,3 and 5. The following mixtures have been separated: Mg²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Zn²⁺ - Pb²⁺, Cu²⁺ - Pb²⁺, Al³⁺ - Pb²⁺, Zn²⁺ - Cd²⁺ and Mg²⁺ - Cd²⁺. Mg²⁺ and Al³⁺ were removed with 0.4 M ammonium nitrate, Cu²⁺ and Zn²⁺ with 0.4 M ammonium nitrate + 0.1M nitric acid (1:1), Pb²⁺ with 0.5M nitric acid and Cd²⁺ with 0.25M nitric acid. A tentative structure of this material is proposed on the basis of chemical analysis, pH titrations, thermogravimetry and IR spectrophotometry.     

Synthesis and characterization of imidocubanes with exocube Ge(IV) and Sn(IV) substituents: [M(mu3-NGeMe3)]4 (M = Sn, Ge, Pb); [Sn(mu3-NSnMe3)]4

The heteroleptic lithium amide, [(Me3Sn)(Me3Ge)NLi.(Et2O)]2 (2), reacts with MCl(2) (M = Sn, Ge, Pb) to yield the corresponding cubane complexes [M(mu3-NGeMe3)]4 [M = Sn (3), Ge (4), Pb (5)]. In an analogous reaction with SnCl2, the lithium stannylamide, [(Me3Sn)2NLi.(Et2O)]2 (1), produces the mixed-valent Sn congener [Sn(mu3-NSnMe3)]4 (6). All imidocubanes contain both di- and tetravalent group 14 metals that are bridged by N. These structures are comprised of M4N4 (M = Sn, Pb, Ge) cores that possess varying distortion from perfect cube geometry. The Pb derivative (5) exhibits enhanced volatility and vapor-phase integrity.     

Molecular view of the anomalous acidities of Sn2+, Pb2+, and Hg2+

Experimental results taken from both the condensed and gaseous phase show that, when associated with water, the three dications Sn(2+), Pb(2+), and Hg(2+) exhibit a facile proton-transfer reaction. In the gas phase, no stable [M.(H(2)O)(n)](2+) ions are observed; but instead the cations appear to undergo rapid hydrolysis to give ions of the form M(+)OH(H(2)O)(n-1). A series of ab initio calculations have been undertaken on the structures and proton-transfer reaction profiles associated with the complexes [M.(H(2)O)(2,4)](2+), where M is one of Sn, Pb, Hg, and Ca. The latter has been used as a reference point both in terms of comparisons with previous calculations, and the fact that Ca(2+) is a very weak acid. The calculations show that for Sn(2+), Pb(2+), and Hg(2+), the only barriers to proton transfer are those associated with the movement of water molecules. In the gas phase, these barriers could be overcome through energy gained during ion formation, and in the condensed phase the thermal motion of water molecules would be sufficient. In contrast, the calculations show that for Ca(2+) it is the proton-transfer step that provides the most significant reaction barrier. Proton transfer in Sn(2+) and Pb(2+) is further assisted by distortions in the geometries of [M.(H(2)O)(2,4)](2+) complexes due to voids created by the 5s(2) (6s(2)) inert lone pair. For Hg(2+), ease of proton transfer is derived partly from the high degree of covalent bonding found in both the reactants and products.     

Unexpected photochemistry and charge-transfer complexes of [CB(11)H(12)](-) carborane

Although the [CB(11)H(12)](-) carborane does not exhibit an absorption band in UV, its triplet excited state can be generated upon 308 nm laser excitation; also unexpectedly carborane acts as electron donor forming a charge transfer complex with methylviologen that upon illumination gives rise to viologen radical cation.     

Search for lowest-energy structure of Zintl dianion Si(12)(2-), Ge(12)(2-), and Sn(12)(2-)

We perform an unbiased search for the lowest-energy structures of Zintl dianions (Si(12)(2-), Ge(12)(2-), and Sn(12)(2-)), by using the basin-hopping (BH) global optimization method combined with density functional theory geometric optimization. High-level ab initio calculation at the coupled-cluster level is used to determine relative stabilities and energy ranking among competitive low-lying isomers of the dianions obtained from the BH search. For Si(12)(2-), all BH searches (based on independent initial structures) lead to the same lowest-energy structure Si(12a)(2-), a tricapped trigonal prism (TTP) with C(s) group symmetry. Coupled-cluster calculation, however, suggests that another TTP isomer of Si(12c)(2-) is nearly isoenergetic with Si(12a)(2-). For Sn(12)(2-), all BH searches lead to the icosahedral structure I(h)-Sn(12a)(2-), i.e., the stannaspherene. For Ge(12)(2-), however, most BH searches lead to the TTP-containing Ge(12b)(2-), while a few BH searches lead to the empty-cage icosahedral structure I(h)-Ge(12a)(2-) (named as germaniaspherene). High-level ab initio calculation indicates that I(h)-Ge(12a)(2-) and TTP-containing Ge(12b)(2-) are almost isoenergetic and, thus, both may be considered as candidates for the lowest-energy structure at 0 K. Ge(12a)(2-) has a much larger energy gap (2.04 eV) between highest occupied molecular orbital and lowest unoccupied molecular orbital than Ge(12b)(2-) (1.29 eV), while Ge(12b)(2-) has a lower free energy than I(h)-Ge(12a)(2-) at elevated temperature (>980 K). The TTP-containing Si(12a)(2-) and Ge(12b)(2-) exhibit large negative nuclear independent chemical shift (NICS) value (approximately -44) at the center of TTP, indicating aromatic character. In contrast, germaniaspherene I(h)-Ge(12a)(2-) and stannaspherene I(h)-Sn(12a)(2-) exhibit modest positive NICS values, approximately 12 and 3, respectively, at the center of the empty cage, indicating weakly antiaromatic character.     

Dissociation of energy selected Sn(CH3)4(+), Sn(CH3)3Cl+, and Sn(CH3)3Br+ ions: evidence for isolated excited state dynamics

The dissociation dynamics of Sn(CH(3))(4)(+), Sn(CH(3))(3)Cl(+), and Sn(CH(3))(3)Br(+) were investigated by threshold photoelectron photoion spectrometry using an electron imaging apparatus (iPEPICO) at the Swiss Light Source. The tetramethyltin ion was found to dissociate via Sn(CH(3))(4)(+) → Sn(CH(3))(3)(+) + CH(3) → Sn(CH(3))(2)(+) + 2CH(3), while the trimethyltin halide ions dissociated via methyl loss at low energies, and a competitive halogen loss at somewhat higher energies. The 0 K methyl loss onset for the three ions was found to be 9.410 ± 0.020 eV, 10.058 ± 0.020 eV, and 9.961 ± 0.020 eV, respectively. Statistical theory could not reproduce the observed onsets for the halogen loss steps in the halotrimethyltin ions. The halide loss signal as a function energy mimicked the excited state threshold photoelectron spectrum, from which we conclude that the halide loss from these ions takes place on an isolated excited state potential energy surface, which we describe by time dependent density functional calculations. The sequential loss of a second methyl group in the Sn(CH(3))(4)(+) ion, observed at about 3 eV higher energies than the first one, is also partially non-statistical. The derived product energy distribution resulting from the loss of the first methyl group is two-component with about 50% being statistical and the remainder associated with high translational energy products that peak at 2 eV. Time dependent DFT calculations show that a dissociative ?B state lies in the vicinity of the experimental measurements. We thus propose that 50% of the Sn(CH(3))(4)(+) ions produced in this energy range internally convert to the ?X state, on which they dissociate statistically, while the remainder dissociate directly from the repulsive ?B state leading to high kinetic energy products.     

Preparation and Optical Properties of Gold-Dispersed BaTiO3, PGO (Pb5Ge3O11) and PLT (Pb1-1.5xLaxTiO3) Thin Films by Sol-Gel Process

Gold-dispersed BaTiO₃, PGO and PLT thin films, which will be used for third-order nonlinear optical devices, were prepared by sol-gel process with spin-coating using HAuCl₄4H₂O, Ba(CH₃COO)₂, Ti[O(CH₂)₃CH₃]₄, Pb(CH₃COO)₂3H₂O, Ge[O-n-C₄H₉]₄, La(CH₃COO)₃1.5 H₂O as starting materials. The thin films were heat-treated in air at temperatures ranging from 400 to 800 for 1 h. The nonlinear optical property of these thin films was measured by the degenerate four-wave mixing (DFWM) method using a frequency-doubled Nd: YAG laser with 20 ps pulse duration. Third-order nonlinear susceptibility χ⁽³⁾ of gold-dispersed BaTiO₃, PGO and PLT thin films with 5 vol% of gold were 1.410⁻⁶ esu, 3.510⁻⁷ esu respectively. The large χ⁽³⁾ may be ascribed to the high dielectric constant of the films.     

Der chemische Transport von Ni3Ge,Ni5Ge3, Ni(Ge)-Mischkristall,CoSn, Co3Sn2, Cu41Sn11 (δ-Phase), Cu10Sn3 (ζ-Phase) und Cu(Sn)-Mischkristall

Chemical Vapour Transport of Intermetallic Systems. 7. Chemical Transport of Ni₃Ge, Ni₅Ge₃, Ni(Ge)-mixed Crystal, CoSn, Co₃Sn₂, Cu₄₁Sn₁₁ (δ-phase), Cu₁₀Sn₃ (ζ-phase), and Cu(Sn)-mixed Crystals By means of GaI₃ as transport agent some intermetallics in the Ni/Ge- and Co/Sn-system can be prepared by CVT-methods. Using Iodine Cu–Sn-compounds can be deposited in a similiar way.     

Reactions between M+ (M = Si,Ge, Sn and Pb) and benzene in the gas phase

Using a laser ablation/inert buffer gas ion source coupled with a reflectron time-of-flight mass spectrometer, the gas-phase reactions between the IVA group element ions M(+) (M = Si, Ge, Sn and Pb) and benzene seeded in argon gas were studied. In addition to the association reaction pathway (forming [M(C(6)H(6))(x)](+), x = 1, 2, etc.), benzene was dissociated to form complex ions [M(C(5)H(5))](+), [M(C(7)H(5))](+) and [M(C(9)H(x))](+) (x = 5, 7 and 9), etc. DFT theoretical calculations indicated that, in the association products [M(C(6)H(6))](+), the M atom is close to one carbon atom of benzene, while in most of the dissociation complexes, pentagonal structures (M/cyclopentadienyl derivatives) were formed, with the M atom situated near the fivefold axis of the five-membered ring. The bond patterns in these complexes are discussed.     

Interaction between cobaltocenium and decamethylcobaltocenium salts and Ph3ELi (E = Si,Ge, Sn)

Reactions of cobaltocenium salts [(C₅R₅)₂Co]PF₆ (R = H, Me) with Ph3ELi (E = Si, Ge, Sn) and with Ph₂SbLi mainly follow two pathways (nucleophilic addition and one-electron reduction), yielding cobalt cyclopentadiene-cyclope ntadienyl complexes (⁴-Ph₃EC₅R₅)(⁵-C₅R₅)Co (R = H, E = Si, Ge, Sn; R = Me, E = Si) and cobaltocenes (C₅R₅)₂Co (R = H, Me), respectively. The contribution of nucleophilic addition of Ph₃ELi decreases in the order of elements Si > Ge > Sn and when hydrogen atoms are replaced by methyl groups in the initial cobaltocenium salt. Thermal decomposition of cobalt cyclopentadiene-cyclopentadienyl complexes results in substituted cobaltocenes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2557–2560, October, 1996.     

Peculiarities of interaction of H+, Me3C+, and Me3Si+ ions with multifunctional molecules in the gas phase

Peculiarities of interaction of H⁺, Me₃C⁺, and Me₃Si⁺ ions with functional groups of molecules in the gas phase have been studied. Proton tends to form chelates with virtually all of the functional groups studied, whereas Me₃Si⁺ ions exhibit no capacity for chelation. Using isomeric xylenes as examples it was shown that Me₃Si⁺ ions (unlike Me₃C⁺ ions) experience virtually no steric hindrance when they react with nucleophilic centers. Effects of functional groups present in molecules of nitriles on the generation of [M+Me₃C]⁺ adducts in the gas phase and the Ritter reaction in solution were estimated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1767–1773, September, 1995.This work was carried out with financial support from the International Science Foundation (Grant MA7 000) and the Russian Foundation for Basic Research (Project No. 93-03-18033).     

Pressure-temperature phase diagrams of smectogenic 4'-alkyl-4-cyanobiphenyls (9CB, 10CB, 11CB and 12CB)

The pressure-temperature ( p - T ) phase diagrams for four smectogenic members of the 4'-alkyl-4-cyanobiphenyl homologous series ( n CB, n =9, 10, 11 and 12) over the temperature range 320-410 K and pressure range 0.1-300 MPa (3 kbar) were constructed using DTA. At 1 atm 9CB exhibits nematic and smectic A d phases, while the other members show only the smectic A d phase. However, at elevated pressures the clearing line splits in the case of 10CB and 11CB which indicates the induction of a nematic phase. It was found that the triple point, where the isotropic, nematic and smectic phases coexist, is strongly shifted to higher pressures with increasing chain length. This was interpreted as being caused by a loss of the rod-like shape of the molecules containing longer alkyl tails which explore a range of conformations. The slope of the clearing line, d T /d p , depends strongly on the length of the alkyl chain for the n CB series, but does not show a step-wise change between the nematogenic and smectogenic members.     

Sn12(2-): stannaspherene

Stannaspherene. The Sn122- cluster is discovered to be a highly stable and highly symmetric icosahedral cage bonded by four delocalized radial pi bonds and nine delocalized on-sphere sigma bonds from the 5p orbitals of the Sn atoms. It has a diameter of 6.1 A, with a large empty interior volume, and can host most transition metal atoms inside, giving rise to a large class of endohedral chemical building blocks for cluster-assembled nanomaterials.