Synthesis and characterization of ammonioundecafluoro-closo-dodecaborates(1-). New superweak anions

The ammonioborane monoanion H(3)NB(12)H(11)(-) was per-B-fluorinated with elemental fluorine in liquid hydrogen fluoride to yield the first member of a new class of weakly coordinating anions, H(3)NB(12)F(11)(-) (isolated as [N(n-Bu)(4)](2)[H(2)NB(12)F(11)] in 41% yield). The pK(a) of the H(3)NB(12)F(11)(-) anion is 9.6. Several salts of the tri-N-alkylated anions Me(3)NB(12)F(11)(-) and Dd(3)NB(12)F(11)(-) (Dd = n-C(12)H(25)) were also prepared. The structure of [CPh(3)][Me(3)NB(12)F(11)] was determined by single-crystal X-ray diffraction: monoclinic, space group P2(1)/c, a = 18.053(3) A, b = 33.139(5) A, c = 9.600(2) A, beta = 91.459(4) degrees, V = 5742(2) A(3), Z = 8, T = 173(2) K, R(1) = 0.045. It revealed that the only direct interactions between the undecafluoroammonioborate monoanions and the trityl cations in the two independent ion pairs were long and weak BF...CPh(3) interactions of 2.992(6) and 2.942(6) A. Salts of the new anions were chemically, electrochemically, and thermally stable. The conductivity of Li(Me(3)NB(12)F(11)) in dimethoxyethane was comparable to that of LiPF(6) but less than half the value of Li(1-Me-CB(11)F(11)).     

Spectral-luminescence properties and basicities of 2-(4-pyridyl)-5-(4-r-phenyl)oxazoles

The spectral-luminescence and acid-base properties of 2-(4-pyridyl)-5-(4-R-phenyl)oxazoles were studied. Significant -electron conjugation between the individual fragments exists in the molecules of these compounds in solutions at room temperature. Bathochromic and bathofluoric effects, which are particularly appreciable for electron-donor substituents, are observed when substituents R are introduced into the 5-phenyl ring. Ethanol solutions of the investigated compounds have high fluorescence quantum yields which, for some of them, are close to unity. Electron-donor substituents R increase the basicity of the pyridine nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 479–482, April, 1985.     

Molecular structures and energetics of the (TiO2)n (n = 1-4) clusters and their anions

The (TiO2)n clusters and their anions for n = 1-4 have been studied with coupled cluster theory [CCSD(T)] and density functional theory (DFT). For n > 1, numerous conformations are located for both the neutral and anionic clusters, and their relative energies are calculated at both the DFT and CCSD(T) levels. The CCSD(T) energies are extrapolated to the complete basis set limit for the monomer and dimer and calculated up to the triple-zeta level for the trimer and tetramer. The adiabatic and vertical electron detachment energies of the anionic clusters to the ground and first excited states of the neutral clusters are calculated at both levels and compared with the experimental results. The comparison allows for the definitive assignment of the ground-state structures of the anionic clusters. Anions of the dimer and tetramer are found to have very closely lying conformations within 2 kcal/mol at the CCSD(T) level, whereas that of the trimer does not. In addition, accurate clustering energies and heats of formation are calculated for the neutral clusters and compared with the available experimental data. Estimates of the titanium-oxygen bond energies show that they are stronger than the group VIB transition metal-oxygen bonds except for tungsten. The atomization energies of these clusters display much stronger basis set dependence than the clustering energies. This allows the calculation of more accurate heats of formation for larger clusters on the basis of calculated clustering energies.     

Infrared spectra and structures of the stable CuH(2)(-), AgH(2)(-), AuH(2)(-), and AuH(4)(-) anions and the AuH(2) molecule

Gold is noble, but excited gold is reactive. Reactions of laser-ablated copper, silver, and gold with H(2) in excess argon, neon, and pure hydrogen during condensation at 3.5 K give the MH molecules and the (H(2))MH complexes as major products and the MH(2)(-) and AuH(4)(-) anions as minor products. These new molecular anions are identified from matrix infrared spectra with isotopic substitution (HD, D(2), and H(2) + D(2)) and comparison to frequencies calculated by density functional theory. The stable linear MH(2)(-) anions are unique in that their corresponding neutral MH(2) molecules are higher in energy than M + H(2) and thus unstable to M + H(2) decomposition. Infrared spectra are observed for the bending modes of AuH(2), AuHD, and AuD(2) in solid H(2), HD, and D(2), respectively. The observation of square-planar AuH(4)(-) attests the stability of the higher Au(III) oxidation state for gold. The synthesis of CuH(2)(-) in solid compounds has potential for use in hydrogen storage.     

Relative stabilities of metal complexes of 4-(2-pyridylazo)resorcinol and 4-(2-thiazolylazo)resorcinol

The stability constants of 1:1 complexes of 4-(2-pyridylazo)resorcinol (PAR) and 4-(2-thiazolylazo)resorcinol (TAR) with Mn(II), Ni(II), Cu(II) and Zn(II) have been determined spectrophotometrically at μ = 0.1 and 25°C. The method is based on indirect estimation of the protonated and normal complexes by measuring the ligand absorption peak. Both protonated and normal complexes of these metals with PAR are more stable than those with TAR. The reverse order was previously observed for the pronated complexes of the lanthanides(III). The different behaviour of the 3d transition metals(II) compared to the lanthanides(III) is discussed. The proton dissociation constants of the protonated complexes of PAR or TAR with various metals are also discussed.     

LiSc(BH4)4: a novel salt of Li+ and discrete Sc(BH4)4(-) complex anions

LiSc(BH4)4 has been prepared by ball milling of LiBH4 and ScCl3. Vibrational spectroscopy indicates the presence of discrete Sc(BH4)4(-) ions. DFT calculations of this isolated complex ion confirm that it is a stable complex, and the calculated vibrational spectra agree well with the experimental ones. The four BH4(-) groups are oriented with a tilted plane of three hydrogen atoms directed to the central Sc ion, resulting in a global 8 + 4 coordination. The crystal structure obtained by high-resolution synchrotron powder diffraction reveals a tetragonal unit cell with a = 6.076 A and c = 12.034 A (space group P-42c). The local structure of the Sc(BH4)4(-) complex is refined as a distorted form of the theoretical structure. The Li ions are found to be disordered along the z axis.     

Nature of the chemical bond in polypnictides: the lone pair aromatic anions P4(2-) and As4(2-)

The nature of the chemical bond in inorganic 6pi aromatic systems such as P4(2-), S4(2+), or S2N2 is a matter of particular interest because the phenomenon of aromaticity is not as well established in these compounds as it is in the classic aromatic hydrocarbons. Here we present the synthesis, NMR spectra, and crystal structures of bis(potassium(18-crown-6))cyclotetraphosphide-ammonia(1/2) (K@18-crown-6)2P4 x 2 NH3, bis(rubidium(18-crown-6))cyclotetraphosphide-cyclotetraarsenide-ammonia(1/3) (Rb@18-crown-6)2(P4)0.85(As4)0.15 x 3 NH3, both containing the 6pi aromatic cyclotetraphosphide anion, P4(2-), and the synthesis and crystal structure of bis(potassium(18-crown-6))cyclotetraarsenide (K@18-crown-6)2As4. As a common motive, all three compounds feature neutral molecules with a tripledecker-like coordination of the cyclotetrapnictide anion between two crown ether-coordinated alkali metal cations. With ab initio calculations on the HF level and by employing the concept of the electron localization function ELF, we established that the cyclotetraarsenide anion, As4(2-), shows electron delocalization primarily through the lone pairs, as does P4(2-), and may consequently also be described as lone pair aromatic.     

Silicon monohydride clusters Si(n)H (n = 4-10) and their anions: structures, thermochemistry, and electron affinities

The molecular structures, electron affinities, and dissociation energies of the Si(n)H/Si(n)H- (n = 4-10) species have been examined via five hybrid and pure density functional theory (DFT) methods. The basis set used in this work is of double-zeta plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. The three different types of neutral-anion energy separations presented in this work are the adiabatic electron affinity (EA(ad)), the vertical electron affinity (EA(vert)), and the vertical detachment energy (VDE). The first Si-H dissociation energies, D(e)(Si(n)H --> Si(n) + H) for neutral Si(n)H and D(e)(Si(n)H- --> Si(n)- + H) for anionic Si(n)H- species, have also been reported. The structures of the ground states of these clusters are traditional H-Si single-bond forms. The ground-state geometries of Si5H, Si6H, Si8H, and Si9H predicted by the DFT methods are different from previous calculations, such as those obtained by Car-Parrinello molecular dynamics and nonorthogonal tight-binding molecular dynamics schemes. The most reliable EA(ad) values obtained at the B3LYP level of theory are 2.59 (Si4H), 2.84 (Si5H), 2.86 (Si6H), 3.19 (Si7H), 3.14 (Si8H), 3.36 (Si9H), and 3.56 (Si10H) eV. The first dissociation energies (Si(n)H --> Si(n) + H) predicted by all of these methods are 2.20-2.29 (Si4H), 2.30-2.83 (Si5H), 2.12-2.41 (Si6H), 1.75-2.03 (Si7H), 2.41-2.72 (Si8H), 1.86-2.11 (Si9H), and 1.92-2.27 (Si10H) eV. For the negatively charged ion clusters (Si(n)H- --> Si(n)- + H), the dissociation energies predicted are 2.56-2.69 (Si4H-), 2.80-3.01 (Si5H-), 2.86-3.06 (Si6H-), 2.80-3.03 (Si7H-), 2.69-2.92 (Si8H-), 2.92-3.18 (Si9H-), and 2.89-3.25 (Si10H-) eV.     

Photoelectron spectroscopy of higher bromine and iodine oxide anions: electron affinities and electronic structures of BrO(2,3) and IO(2-4) radicals

This report details a photoelectron spectroscopy (PES) and theoretical investigation of electron affinities (EAs) and electronic structures of several atmospherically relevant higher bromine and iodine oxide molecules in the gas phase. PES spectra of BrO(2)(-) and IO(2)(-) were recorded at 12 K and four photon energies--355 nm/3.496 eV, 266 nm/4.661 eV, 193 nm/6.424 eV, and 157 nm/7.867 eV--while BrO(3)(-), IO(3)(-), and IO(4)(-) were only studied at 193 and 157 nm due to their expected high electron binding energies. Spectral features corresponding to transitions from the anionic ground state to the ground and excited states of the neutral are unraveled and resolved for each species. The EAs of these bromine and iodine oxides are experimentally determined for the first time (except for IO(2)) to be 2.515 ± 0.010 (BrO(2)), 2.575 ± 0.010 (IO(2)), 4.60 ± 0.05 (BrO(3)), 4.70 ± 0.05 (IO(3)), and 6.05 ± 0.05 eV (IO(4)). Three low-lying excited states along with their respective excitation energies are obtained for BrO(2) [1.69 (A (2)B(2)), 1.79 (B (2)A(1)), 1.99 eV (C (2)A(2))], BrO(3) [0.7 (A (2)A(2)), 1.6 (B (2)E), 3.1 eV (C (2)E)], and IO(3) [0.60 (A (2)A(2)), 1.20 (B (2)E), ～3.0 eV (C (2)E)], whereas six excited states of IO(2) are determined along with their respective excitation energies of 1.63 (A (2)B(2)), 1.73 (B (2)A(1)), 1.83 (C (2)A(2)), 4.23 (D (2)A(1)), 4.63 (E (2)B(2)), and 5.23 eV (F (2)B(1)). Periodate (IO(4)(-)) possesses a very high electron binding energy. Only one excited state feature with 0.95 eV excitation energy is shown in the 157 nm spectrum. Accompanying theoretical calculations reveal structural changes from the anions to the neutrals, and the calculated EAs are in good agreement with experimentally determined values. Franck-Condon factors simulations nicely reproduce the observed vibrational progressions for BrO(2) and IO(2). The low-lying excited state information is compared with theoretical calculations and discussed with their atmospheric implications.     

Synthesis,Characterization, and Application of Two Al(ORF)3 Lewis Superacids

We report herein the synthesis and full characterization of the donor‐free Lewis superacids Al(OR^F)₃ with OR^F=OC(CF₃)₃ ( 1 ) and OC(C₅F₁₀)C₆F₅ ( 2 ), the stabilization of 1 as adducts with the very weak Lewis bases PhF, 1,2‐F₂C₆H₄, and SO₂, as well as the internal C? F activation pathway of 1 leading to Al₂(F)(OR^F)₅ ( 4 ) and trimeric [FAl(OR^F)₂]₃ ( 5 , OR^F=OC(CF₃)₃). Insights have been gained from NMR studies, single‐crystal structure determinations, and DFT calculations. The usefulness of these Lewis acids for halide abstractions has been demonstrated by reactions with trityl chloride (NMR; crystal structures). The trityl salts allow the introduction of new, heteroleptic weakly coordinating [Cl‐Al(OR^F)₃]^? anions, for example, by hydride or alkyl abstraction reactions.     

The crystal and molecular structures of the diastereomeric (4Z)- and (4E)-3-oxo-2,3-dihydrobilatrienes-abc

The molecular and crystal structures of two diastereomeric 3-oxo-2,3-dihydrobilatrienes-abc1 and2 are determined at low (1, 2) and room temperature (2). The configurations at the exocyclic double bond in position 4 are found to be (Z) for1 and (E) for2. Tautomerism, conformation and crystal packing of1 and2 can be understood on the basis of the pattern of intra- and intermolecular hydrogen bonds. Compared to1, a more open helix conformation is found for the (E) diastereomer2. An analysis of crystallographically observed temperature factors of2 yields the result that the highest flexibility is found for the saturated lactam ring.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.     

Relative stability of 1-(4-R-2,6-dinitrophenyl)-2,2-diphenylhydrazides

Substitution of the nitro group for methyl in the position 4 of the picrylic fragment of 1-(2,4,6-trinitrophenyl)-2,2-diphenylhydrazyl increases the relative stability of hydrazyl radical in reaction with CH-acids. The reaction rate of 1-(2,4,6-trinitrophenyl)-2,2-diphenylhydrazyl with acetylacetone and ethyl acetoacetate is described with equations of first order with respect to the radical and the СН-acid and is determined by the energy of electron transfer from HOMO of СН-acid on LUMO of the radical, which is its acceptor.     

Reaction of 2-Phenyl-4-(ethoxymethylene)-5(4H)-oxazolone with 3,4-Dithio-toluene in the Presence of Lewis Base

A convenient procedure for the synthesis of thiocoumarin by the condensation of 2-phenyl-4-(ethoxymethylene)-5-(4H)-oxazolone with 3,4-dithio-toluene in the presence of triethylamine is reported. Here, both thio groups are able to react with the carbonyl group to produce a mixture of isomeric products at ambient temperature. Only one of the isomers upon heating gives a new coumarin product.     

Molecular modeling of hydrotalcite structure intercalated with transition metal oxide anions: CrO4(2-) and VO4(3-)

Molecular dynamics (MD) simulations are used to study the interlayer structure, hydrogen bonding, and energetics of hydration of Mg/Al (2:1 and 4:1) layered double hydroxide (LDH) or hydrotalcite (HT) intercalated with oxymetal anions, CrO(4)(2-), and VO(4)(3-). The ab initio forcefield COMPASS is employed for the simulations. The charge on the oxymetal anions is determined by quantum mechanical density functional theory. The structural behavior of the oxymetal anions in LDH directly relates to the energetic relationships, with electrostatic and H-bonding interactions between the anions, hydroxide sites of the metal hydroxide layers, and the interlayer water molecules. Distinct minima in the hydration energy indicate the presence of energetically well-defined structural states with specific water content. The experimentally identified variability in the retention of the CrO(4)(2-) and VO(4)(3-) is well reflected in the calculations and self-diffusion coefficients obtained from the simulations give insight into the mobility of the intercalated species.     

Charged molecular alloys: synthesis and characterization of the binary anions Pd(7)As(16)(4-) and Pd(2)As(14)(4-)

Pd(PCy(3))(2) (Cy = cyclohexyl) reacts with As(7)(3-) in en/tol solvent mixtures to give Pd(2)As(14)(4-) (2) and Pd(7)As(16)(4-) (4) as the [K(2,2,2-crypt)](+) salts. The anions were characterized by EDX, ESI-MS, and single-crystal X-ray diffraction. Anion 2 formally contains two norbornadiene-like As(7)(5-) groups bound to square-planar Pd(III) centers linked by a Pd-Pd bond (d(Pd)(-)(Pd) = 2.7144(6) A). Anion 4 has a highly distorted capped trigonal prismatic Pd(7) core stabilized by 2 As(5)(1-), 2 As(2)(2-), and 2 As(3-) anions. The 6 Pd(I) ions are in distorted 5-coordinate environments whereas the lone Pd(II) ion is square planar. Complexes 2 and 4 are rare examples of organic-free, homoleptic transition metal anions containing group 15 elements, and they represent an emerging class of charged "molecular alloys".     

Oxygen cluster anions revisited: solvent-mediated dissociation of the core O4(-) anion

The electronic structure and photochemistry of the O(2n)(-)(H(2)O)(m), n = 1-6, m = 0-1 cluster anions is investigated at 532 nm using photoelectron imaging and photofragment mass-spectroscopy. The results indicate that both pure oxygen clusters and their hydrated counterparts with n ≥ 2 form an O(4)(-) core. Fragmentation of these clusters yields predominantly O(2)(-) and O(2)(-)·H(2)O anionic products, with the addition of O(4)(-) fragments for larger parent clusters. The fragment autodetachment patterns observed for O(6)(-) and larger O(2n)(-) species, as well as some of their hydrated counterparts, indicate that the corresponding O(2)(-) fragments are formed in excited vibrational states (v ≥ 4). Yet, surprisingly, the unsolvated O(4)(-) anion itself does not show fragment autodetachment at 532 nm. It is hypothesized that the vibrationally excited O(2)(-) is formed in the intra-cluster photodissociation of the O(4)(-) core anion via a charge-hopping electronic relaxation mechanism mediated by asymmetric solvation of the nascent photofragments: O(4)(-) → O(2)(-)(X(2)Π(g)) + O(2)(a(1)Δ(g)) → O(2)(X(3)Σ(g)(-)) + O(2)(-)(X(2)Π(g)). This process depends on the presence of solvent molecules and leads to vibrationally excited O(2)(-)(X(2)Π(g)) products.     

IR spectroscopy on isolated Co(n)(alcohol)m cluster anions (n=1-4, m=1-3): structures and spin states

Isolated cobalt-alcohol cluster anions containing n=1-4 cobalt and m=1-3 alcohol molecules (alcohol=methanol, ethanol, propanol) are produced in a supersonic beam by using a laser ablation source. By applying IR photodissociation spectroscopy vibrational spectra in the OH stretching region are obtained. Several structures in different spin states are discussed for the (n,m) clusters. In comparison with density functional theory calculations applied to both the Co/alcohol clusters and the naked Co cluster anions, an unambiguous structural assignment is achieved. It turns out that structures are preferred with a maximum number of hydrogen bonds between the OH groups and the Co···Co units. These hydrogen bonds are typical for anionic species leading to an activation of the OH groups which is indicated by large red-shifts of the OH stretching frequencies compared to the naked alcohols. For each (n,m) cluster, the frequency shifts systematically with respect to the different alcohols, but the type of structure is identical for all alcohol ligands. The application of IR spectroscopy turns out to be an ideal tool not only as a probe for structures but also for spin states which significantly influence the predicted OH stretching frequencies.     

The facile preparation of weakly coordinating anions: structure and characterisation of silverpolyfluoroalkoxyaluminates AgAl(ORF)4, calculation of the alkoxide ion affinity

Purified LiAlH4 reacts with fluorinated alcohols HORF to give LiAl(ORF)4 (RF=-CH(CF3)2, 2a; -C(CH3)(CF3)2, 2b; -C(CF3)3, 2c) in 77 to 90% yield. The crude lithium aluminates LiAl(ORF)4 react metathetically with AgF to give the silver aluminates AgAl(ORF)4 (RF=-CH(CF3)2, 3a; -C(CH3)(CF3)2, 3b; -C(CF3)3, 3c) in almost quantitative yield. The solid-state structures of solvated 3a-c showed that the silver cation is only weakly coordinated (CN(Ag)=6-10; CN = coordination number) by the solvent and/or weak cation - anion contacts Ag-X (X=O, F, Cl, C). The strength of the Ag-X contacts of 3a-c was analysed by Brown's bond-valence method and then compared with other silver salts of weakly coordinating anions (WCAs), for example [CB11H6Cl6]- and [M(OTeF5)n]- (M=B, Sb, n=4, 6). Based on this quantitative picture we showed that the Al[OC(CF3)3]4 anion is one of the most weakly coordinating anions known. Moreover, the AgAl(ORF)4 species are certainly the easiest WCAs to access preparatively (20 g in two days), additionally at low cost. The Al-O bond length of Al(ORF)4- is shortest in the sterically congested Al[OC(CF3)3]4- anion-which is stable in H2O and aqueous HNO3 (35 weight%)--and indicates a strong and highly polar Al-O bond that is resistant towards heterolytic alkoxide ion abstraction. This observation was supported by a series of HF-DFT calculations of OR-, Al(OR)3 and Al(OR)4- at the MPW1PW91 and B3LYP levels (R= CH3, CF3, C(CF3)3). The alkoxide ion affinity (AIA) is highest for R=CF3 (AlA=384 +/- 9 kJ x mol(-1)) and R= C(CF3)3 (AIA=390 +/- 3 kJ x mol(-1)), but lowest for R=CH3 (AIA=363 +/- 7 kJ X mol(-1)). The gaseous AL(ORF)4-anions are stable against the action of the strong Lewis acid ALF3(g) by 88.5 +/- 2.5 (RF=CF3) and 63 +/- 12 kJ X mol(-1) (RF=C(CF3)3), while AL(OCH3)4- decomposes with -91 +/- 2 kJ X mol(-1). Therefore the presented fluorinated aluminates AL(ORF)4- appear to be ideal candidates when large and resistant WCAs are needed, for example, in cationic homogenous catalysis, for highly electrophilic cations or for weak cationic Lewis acid/base complexes.     

OH(3) (-) and O(2)H(5) (-) double Rydberg anions: predictions and comparisons with NH(4) (-) and N(2)H(7) (-)

A low barrier in the reaction pathway between the double Rydberg isomer of OH(3) (-) and a hydride-water complex indicates that the former species is more difficult to isolate and characterize through anion photoelectron spectroscopy than the well known double Rydberg anion (DRA), tetrahedral NH(4) (-). Electron propagator calculations of vertical electron detachment energies (VEDEs) and isosurface plots of the electron localization function disclose that the transition state's electronic structure more closely resembles that of the DRA than that of the hydride-water complex. Possible stabilization of the OH(3) (-) DRA through hydrogen bonding or ion-dipole interactions is examined through calculations on O(2)H(5) (-) species. Three O(2)H(5) (-) minima with H(-)(H(2)O)(2), hydrogen-bridged, and DRA-molecule structures resemble previously discovered N(2)H(7) (-) species and have well separated VEDEs that may be observable in anion photoelectron spectra.