Negative- and positive-ion chemical ionization mass spectra of aromatic amines: Surface-assisted reactions involving oxygen

The O₂–N₂ and O₂–Ar negative-ion chemical ionization mass spectra of aromatic amines show a series of unusual ions dominated by an addition appearing at [M + 14]^?˙. Other ions are observed at [M – 12]^?˙, [M + 5]^?˙, [M + 12]^?˙, [M + 28]^?˙ and [M + 30]^?˙. Ion formation was studied using a quadrupole instrument equipped with a conventional chemical ionization source and a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. These studies, which included the examination of ion chromatograms, measurement of positive-ion chemical ionization mass spectra, variation of ion source temperature and pressure and experiments with ¹⁸O₂, indicate that the [M + 14]^?˙ ion is formed by the electron-capture ionization of analytes altered by surfaceassisted reactions involving oxygen. This conversion is also observed under low-pressure conditions following source pretreatment with O₂. Experiments with [¹⁵N]aniline, [2,3,4,5,6-²H₅] aniline and [¹³C₆]aniline show that the [M + 14]^?˙ ion corresponds to [M + O ? 2H]^?˙, resulting from conversion of the amino group to a nitroso group. Additional ions in the spectra of aromatic amines also result from surface-assisted oxidation reactions, including oxidation of the amino group to a nitro group, oxidation and cleavage of the aromatic ring and, at higher analyte concentrations, intermolecular oxidation reactions.     

Extending the Row of Lanthanide Tetrafluorides: A Combined Matrix‐Isolation and Quantum‐Chemical Study

Only the neutral tetrafluorides of Ce, Pr, and Tb as well as the [LnF₇]^3? anions of Dy and Nd, with the metal in the +IV oxidation state, have been previously reported. We report our attempts to extend the row of neutral lanthanide tetrafluorides through the reaction of laser‐ablated metal atoms with fluorine and their stabilization and characterization by matrix‐isolation IR spectroscopy. In addition to the above three tetrafluorides, we found two new tetrafluorides, ³NdF₄ and ⁷DyF₄, both of which are in the +IV oxidation state, which extends this lanthanide oxidation state to two new metals. Our experimental results are supported by quantum‐chemical calculations and the role of the lanthanide oxidation state is discussed for both the LnF₄ and [LnF₄]^? species. Most of the LnF₄ species are predicted to be in the +IV oxidation state and all of the [LnF₄]^? anions are predicted to be in the +III oxidation state. The LnF₄ species are predicted to be strong oxidizing agents and the LnF₃ species are predicted to be moderate to strong Lewis acids.     

Einkristalle von La[AsO4] im Monazit‐ und Sm[AsO4] im Xenotim‐Typ

Single Crystals of La[AsO₄] with Monazite‐ and Sm[AsO₄] with Xenotime‐Type Structure Brick‐shaped, transparent single crystals of colourless monazite‐type La[AsO₄] (monoclinic, P2₁/n, a = 676.15(4), b = 721.03(4), c = 700.56(4) pm, β =104.507(4)°, Z = 4) and pale yellow xenotime‐type Sm[AsO₄] (tetragonal, I4₁/amd, a = 718.57(4), c = 639.06(4) pm, Z = 4) emerge as by‐products from alkali and rare‐earth metal chloride fluxes whenever the synthesis of lanthanide(III) oxoarsenate(III) derivatives from admixtures of the corresponding sesquioxides in sealed, evacuated silica ampoules is accompanied by air intrusion and subsequent oxidation. Nine oxygen atoms from seven discrete [AsO₄]^3? tetrahedra recruit the rather irregular coordination sphere of La³⁺ (d(La³⁺?O^2?) = 248 – 266 pm plus 291 pm) and even a tenth ligand could be considered at a distance of 332 pm. The trigonal dodecahedral figure of coordination consisting of eight oxygen atoms at distances of 236 and 248 pm (4× each) about Sm³⁺ is provided by only six isolated tetrahedral [AsO₄]^3? units. Alternating trans‐edge condensation of the latter with the [LaO₉₊₁] polyhedra of monazite‐type La[AsO₄] and the [SmO₈] polyhedra of xenotime‐type Sm[AsO₄] constitutes the main structural chain features along [100] or [001], respectively. The bond distances and angles of the complex [AsO₄]^3? anions range within common intervals (d(As⁵⁺?O^2?) = 167 – 169 pm, ?(O–As–O) = 100 – 116°) for both lanthanide(III) oxoarsenates(V) presented here.     

Metal‐catalyzed reversible conversion between chemical and electrical energy designed towards a sustainable society

Proton dissociation of an aqua‐Ru‐quinone complex, [Ru(trpy)(q)(OH₂)]²⁺ (trpy = 2,2′ : 6′,2″‐terpyridine, q = 3,5‐di‐t‐butylquinone) proceeded in two steps (pK_a = 5.5 and ca. 10.5). The first step simply produced [Ru(trpy)(q)(OH)]⁺, while the second one gave an unusual oxyl radical complex, [Ru(trpy)(sq)(O^?.)]⁰ (sq = 3,5‐di‐t‐butylsemiquinone), owing to an intramolecular electron transfer from the resultant O^2? to q. A dinuclear Ru complex bridged by an anthracene framework, [Ru₂(btpyan)(q)₂(OH)₂]²⁺ (btpyan = 1,8‐bis(2,2′‐terpyridyl)anthracene), was prepared to place two Ru(trpy)(q)(OH) groups at a close distance. Deprotonation of the two hydroxy protons of [Ru₂(btpyan)(q)₂(OH)₂]²⁺ generated two oxyl radical Ru‐O^?. groups, which worked as a precursor for O₂ evolution in the oxidation of water. The [Ru₂(btpyan)(q)₂(OH)₂](SbF₆)₂ modified ITO electrode effectively catalyzed four‐electron oxidation of water to evolve O₂ (TON = 33500) under electrolysis at +1.70 V in H₂O (pH 4.0). Various physical measurements and DFT calculations indicated that a radical coupling between two Ru(sq)(O^?.) groups forms a (cat)Ru‐O‐O‐Ru(sq) (cat = 3,5‐di‐t‐butylcathechol) framework with a μ‐superoxo bond. Successive removal of four electrons from the cat, sq, and superoxo groups of [Ru₂(btpyan)(cat)(sq)(μ‐O₂^?)]⁰ assisted with an attack of two water (or OH^?) to Ru centers, which causes smooth O₂ evolution with regeneration of [Ru₂(btpyan)(q)₂(OH)₂]²⁺. Deprotonation of an Ru‐quinone‐ammonia complex also gave the corresponding Ru‐semiquinone‐aminyl radical. The oxidized form of the latter showed a high catalytic activity towards the oxidation of methanol in the presence of base. Three complexes, [Ru(bpy)₂(CO)₂]²⁺, [Ru(bpy)₂(CO)(C(O)OH)]⁺, and [Ru(bpy)₂(CO)(CO₂)]⁰ exist as an equilibrium mixture in water. Treatment of [Ru(bpy)₂(CO)₂]²⁺ with BH₄^? gave [Ru(bpy)₂(CO)(C(O)H)]⁺, [Ru(bpy)₂(CO)(CH₂OH)]⁺, and [Ru(bpy)₂(CO)(OH₂)]²⁺ with generation of CH₃OH in aqueous conditions. Based on these results, a reasonable catalytic pathway from CO₂ to CH₃OH in electro‐ and photochemical CO₂ reduction is proposed. A new pbn (pbn = 2‐pyridylbenzo[b]‐1,5‐naphthyridine) ligand was designed as a renewable hydride donor for the six‐electron reduction of CO₂. A series of [Ru(bpy)_3‐n(pbn)_n]²⁺ (n = 1, 2, 3) complexes undergoes photochemical two‐ (n = 1), four‐ (n = 2), and six‐electron reductions (n = 3) under irradiation of visible light in the presence of N(CH₂CH₂OH)₃. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 169–186; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200800039     

Visible‐Light‐Driven Water Oxidation by a Molecular Manganese Vanadium Oxide Cluster

Photosynthetic water oxidation in plants occurs at an inorganic calcium manganese oxo cluster, which is known as the oxygen evolving complex (OEC), in photosystem II. Herein, we report a synthetic OEC model based on a molecular manganese vanadium oxide cluster, [Mn₄V₄O₁₇(OAc)₃]^3?. The compound is based on a [Mn₄O₄]⁶⁺ cubane core, which catalyzes the homogeneous, visible‐light‐driven oxidation of water to molecular oxygen and is stabilized by a tripodal [V₄O₁₃]^6? polyoxovanadate and three acetate ligands. When combined with the photosensitizer [Ru(bpy)₃]²⁺ and the oxidant persulfate, visible‐light‐driven water oxidation with turnover numbers of approximately 1150 and turnover frequencies of about 1.75 s^?1 is observed. Electrochemical, mass‐spectrometric, and spectroscopic studies provide insight into the cluster stability and reactivity. This compound could serve as a model for the molecular structure and reactivity of the OEC and for heterogeneous metal oxide water‐oxidation catalysts.     

Metal–Organic Frameworks (MOFs) of a Cubic Metal Cluster with Multicentered MnIMnI Bonds

MOFs with both multicentered metal–metal bonds and low‐oxidation‐state (LOS) metal ions have been underexplored hitherto. Here we report the first cubic [Mn^I₈] cluster‐based MOF ( 1 ) with multicentered Mn^I? Mn^I bonds and +1 oxidation state of manganese (Mn^I or Mn(I)), as is supported by single‐crystal structure determination, XPS analyses, and quantum chemical studies. Compound 1 possesses the shortest Mn^I? Mn^I bond of 2.372 Å. Theoretical studies with density functional theory (DFT) reveal extensive electron delocalization over the [Mn^I₈] cube. The 48 electrons in the [Mn^I₈] cube fully occupy half of the 3d‐based and the lowest 4s‐based bonding orbitals, with six electrons lying at the nonbonding 3d‐orbitals. This bonding feature renders so‐called cubic aromaticity. Magnetic properties measurements show that 1 is an antiferromagnet. This work is expected to inspire further investigation of cubic metal–metal bonding, MOF materials with LOS metals, and metalloaromatic theory.     

Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate

A mononuclear‐cobalt(II)‐substituted silicotungstate, K₁₀[Co(H₂O)₂(γ‐SiW₁₀O₃₅)₂] ? 23 H₂O (POM‐ 1 ), has been evaluated as a light‐driven water‐oxidation catalyst. With in situ photogenerated [Ru(bpy)₃]³⁺ (bpy=2,2′‐bipyridine) as the oxidant, quite high catalytic turnover number (TON; 313), turnover frequency (TOF; 3.2 s^?1), and quantum yield (Φ_QY; 27 %) for oxygen evolution at pH 9.0 were acquired. Comparison experiments with its structural analogues, namely [Ni(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 2 ) and [Mn(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 3 ), gave the conclusion that the cobalt center in POM‐ 1 is the active site. The hydrolytic stability of the title polyoxometalate (POM) was confirmed by extensive experiments, including UV/Vis spectroscopy, linear sweep voltammetry (LSV), and cathodic adsorption stripping analysis (CASA). As the [Ru(bpy)₃]²⁺/visible light/sodium persulfate system was introduced, a POM–photosensitizer complex formed within minutes before visible‐light irradiation. It was demonstrated that this complex functioned as the active species, which remained intact after the oxygen‐evolution reaction. Multiple experimental parameters were investigated and the catalytic activity was also compared with the well‐studied POM‐based water‐oxidation catalysts (i.e., [Co₄(H₂O)₂(α‐PW₉O₃₄)₂]^10? (Co₄‐POM) and [Co^IIICo^II(H₂O)W₁₁O₃₉]^7? (Co₂‐POM)) under optimum conditions.     

Comparison between various Keggin and Wells–Dawson sandwich‐type polyoxometalates in catalytic oxidation of cyclooctene and cyclohexene with hydrogen peroxide

The catalytic performance of tetra‐n‐butylammonium salts of Keggin and Wells–Dawson sandwich‐type polyoxotungstates, [M₄(PW₉O₃₄)₂]^m? and [M₄(P₂W₁₅O₅₆)₂]^n? (M = Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Zn²⁺), in the oxidation of cyclooctene and cyclohexene with 30% hydrogen peroxide under various conditions was investigated. In comparison, Wells–Dawson sandwich‐type polyoxometalates were found to be less active than Keggin ones. In both of them, those containing Zn and Fe gave higher conversions for different oxidation conditions. These catalysts showed very good reusability in the oxidation reaction. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of C8H10 alkylbenzenes by negative ion mass spectrometry

The O^?˙ chemical ionization mass spectrri of the C₈H₁₀ alkylbenzenes, o-, m-. andp -xylene and ethylbenzene, show formation of [M ? H + O]^?, [M ? H]^?, [M ? H₂]^?˙ and, for the xylenes, [M ? CH₃ + O]^? as primary reaction products; the relative importance of these products depends on the isomer. However, [OH]^? is a primary product from reaction of O^?˙ with both the C₈H₁₀ isomers and hydrogen-containing impurities; [OH]^? reacts further with the alkylbenzenes to produce [M ? H]^? with the result that the chemical ionization mass spectra depend on experimental conditions such as sample size and the presence of impurities. The collision-induced charge inversion mass spectra of the [M ? H + O]^? and [M ? H]^? products allow only distinction of ethylbenzene from the xylenes. However, the collision-induced charge inversion mass spectra of the [M ? H₂]^?˙ ions show differences which allow identification of each isomer.     

La3OCl[AsO3]2: Ein Lanthan‐Oxidchlorid‐Oxoarsenat(III) mit “lone‐pair”‐Kanalstruktur

La₃OCl[AsO₃]₂: A Lanthanum Oxide Chloride Oxoarsenate(III) with a “Lone‐Pair” Channel Structure La₃OCl[AsO₃]₂ was prepared by the solid‐state reaction between La₂O₃ and As₂O₃ using LaCl₃ and CsCl as fluxing agents in evacuated silica ampoules at 850 °C. The colourless crystals with pillar‐shaped habit crystallize tetragonally (a = 1299.96(9), c = 558.37(5) pm, c/a = 0.430) in the space group P4₂/mnm (no. 136) with four formula units per unit cell. The crystal structure contains two crystallographically different La³⁺ cations. (La1)³⁺ is coordinated by six oxygen atoms and two chloride anions in the shape of a bicapped trigonal prism (CN = 8), whereas (La2)³⁺ carries eight oxygen atoms and one Cl^? anion arranged in the shape of tricapped trigonal prism (CN = 9). The isolated pyramidal [AsO₃]^3? anions (d(As–O) = 175–179 pm) consist of three oxygen atoms (O2 and two O3), which surround the As³⁺ cations together with the free, non‐binding electron pair (lone pair) Ψ¹‐tetrahedrally (?(O–As–O) = 95°, 3×). One of the three crystallographically independent oxygen atoms (O1), however, is exclusively coordinated by four (La2)³⁺ cations in the shape of a real tetrahedron (d(O–La) = 236 pm, 4×). These [(O1)(La2)₄]¹⁰⁺ tetrahedra form endless chains in the direction of the c axis through trans‐edge condensation. Empty channels, constituted by the lone‐pair electrons of the Cl^? anions and the As³⁺ cations in the Ψ¹‐tetrahedral oxoarsenate(III) anions [AsO₃]^3?, run parallel to [001] as well.     

Photochemical,Electrochemical, and Photoelectrochemical Water Oxidation Catalyzed by Water‐Soluble Mononuclear Ruthenium Complexes

Two mononuclear ruthenium complexes [Ru(H₂tcbp)(isoq)₂] ( 1 ) and [Ru(H₂tcbp)(pic)₂] ( 2 ) (H₄tcbp=4,4′,6,6′‐tetracarboxy‐2,2′‐bipyridine, isoq=isoquinoline, pic=4‐picoline) are synthesized and fully characterized. Two spare carboxyl groups on the 4,4′‐positions are introduced to enhance the solubility of 1 and 2 in water and to simultaneously allow them to tether to the electrode surface by an ester linkage. The photochemical, electrochemical, and photoelectrochemical water oxidation performance of 1 in neutral aqueous solution is investigated. Under electrochemical conditions, water oxidation is conducted on the deposited indium‐tin‐oxide anode, and a turnover number higher than 15,000 per water oxidation catalyst (WOC) 1 is obtained during 10 h of electrolysis under 1.42 V vs. NHE, corresponding to a turnover frequency of 0.41 s^?1. The low overpotential (0.17 V) of electrochemical water oxidation for 1 in the homogeneous solution enables water oxidation under visible light by using [Ru(bpy)₃]²⁺ ( P1 ) (bpy=2,2′‐bipyridine) or [Ru(bpy)₂(4,4′‐(COOEt)₂‐bpy)]²⁺ ( P2 ) as a photosensitizer. In a three‐component system containing 1 or 2 as a light‐driven WOC, P1 or P2 as a photosensitizer, and Na₂S₂O₈ or [CoCl(NH₃)₅]Cl₂ as a sacrificial electron acceptor, a high turnover frequency of 0.81 s^?1 and a turnover number of up to 600 for 1 under different catalytic conditions are achieved. In a photoelectrochemical system, the WOC 1 and photosensitizer are immobilized together on the photoanode. The electrons efficiently transfer from the WOC to the photogenerated oxidizing photosensitizer, and a high photocurrent density of 85 μA cm^?2 is obtained by applying 0.3 V bias vs. NHE.     

Metal‐Free,Room‐Temperature Oxygen‐Atom Transfer in the N2O/CO Redox Couple as Catalyzed by [Si2Ox].+ (x=2–5)

The thermal reduction of N₂O by CO mediated by the metal‐free cluster cations [Si₂O_x]^.+ (x =2–5) has been examined in the gas phase using Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry in conjunction with quantum chemical calculations. Three successive oxidation/reduction steps occur starting from [Si₂O₂]^.+ and N₂O to form eventually [Si₂O₅]^.+; the latter as well as the intermediate oxide cluster ions react sequentially with CO molecules to regenerate [Si₂O₂]^.+. Thus, full catalytic cycles occur at ambient conditions in the gas phase. Mechanistic aspects of these sequential redox processes have been addressed to reveal the electronic origins of these unparalleled reactions.     

A Keggin Polyoxometalate Shows Water Oxidation Activity at Neutral pH: POM@ZIF‐8, an Efficient and Robust Electrocatalyst

Keggin‐type polyoxometalate anions [XM₁₂O₄₀]^n? are versatile, as their applications in interdisciplinary areas show. The Keggin anion [CoW₁₂O₄₀]^6? turns into an efficient and robust electrocatalyst upon its confinement in the well‐defined void space of ZIF‐8, a metal–organic framework (MOF). [H₆CoW₁₂O₄₀]@ZIF‐8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles. The catalyst has a turnover frequency (TOF) of 10.8 mol O₂(mol Co)^?1 s^?1, one of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoO_x in this electrocatalyic water oxidation.     

Dilead(II) trimercury(II) tetraoxide chromate(VI), Pb2(Hg3O4)(CrO4)

Pb₂(Hg₃O₄)(CrO₄) consists of [CrO₄]²⁻ tetra­hedra, linear O—Hg—O dumbbells and divalent Pb atoms in [3+5]‐coordination. The HgO₂ dumbbells are condensed into [Hg₃O₄]²⁻ units and can be regarded as a section of the HgO structure. The [Hg₃O₄]²⁻ complex anions are connected by inter­stitial Pb²⁺ ions, while the [CrO₄]²⁻ tetra­hedra are isolated.     

Co(en)3[B4O5(OH)4]Cl·3H2O和[Ni(en)3][B5O6(OH)4]2·2H2O的合成、结构以及热力学性质

利用水热法合成了两种过渡金属配合物为模板剂的含水硼酸盐晶体Co(en)3[B4O5(OH)4]Cl·3H2O(1) 和 [Ni(en)3][B5O6(OH)4]2·2H2O (2),并通过元素分析、X射线单晶衍射、红外光谱及热重分析对其进行了表征。化合物1晶体结构的主要特点是在所有组成Co(en)33+, [B4O5(OH)4]2–, Cl– 和 H2O之间通过O–H…O、O–H…Cl、N–H…Cl和N–H…O四种氢键连接形成网状超分子结构。化合物2晶体结构的特点是[B5O6(OH)4]–阴离子通过O–H…O氢键连接形成沿a方向有较大通道的三维超分子骨架,模板剂[Ni(en)3]2+阳离子和结晶水分子填充在通道中。     

Kinetics and mechanism of oxidation of the binary and ternary complexes of chromium(III) involving inosine and glycine by N -bromosuccinimide

The kinetics of oxidation of the chromium(III) complexes, [Cr(Ino)(H₂O)₅]³⁺ and [Cr(Ino)(Gly)(H₂O)₃]²⁺ (Ino?=?Inosine and Gly?=?Glycine) involving a ligands of biological significance by N-bromosuccinimide (NBS) in aqueous solution to chromium(VI) have been studied spectrophotometrically over the 25–45°C range. The reaction is first order with respect to both [NBS] and [Cr], and increases with pH over the 6.64–7.73 range in both cases. The experimental rate law is consistent with a mechanism in which the hydroxy complexes [Cr(Ino)(H₂O)₄(OH)]²⁺ and [Cr(Ino)(Gly)(H₂O)₂(OH)]⁺ are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant, k ₁, for the oxidation of the [Cr(Ino)(H₂O)₅]³⁺ (6.90?×?10^?4?s^?1) is lower than the value of k ₂ (9.66?×?10^?2?s^?1) for the oxidation of [Cr(Ino)(Gly)(H₂O)₂]²⁺ at 35°C and I?=?0.2?mol?dm^?3. The activation parameters have been calculated. Electron transfer apparently takes place via an inner-sphere mechanism.     

Über Reaktionen oxygenierter Kobalt(II)-Komplexe. IX. Oxydative Eigenschaften von Tetrakis(äthylendiamin)-μ-peroxo-μ-hydroxo-dikobalt(III)

Reactions of oxygenated cobalt(II) complexes. IX. Oxidative properties of tetrakis(ethylenediamine)-μ-peroxo-μ-hydroxo-dicobalt(III)

1 VIII s. [1].

[(en)₂Co(O₂, OH)Co(en)₂]³⁺ ( a ) reacts with I^? in acidic aqueous solution according to: Co^III(O₂, OH)Co^III + 21^? + 5H⁺ ? 2Co^III + 3H₂O + I₂. Using I^? in excess first order rate constants are obtained which, to a first approximation, are independent of [I^?]. Comparison with kinetic data of deoxygenation of [(en)₂Co(O₂, OH)Co(en)₂]³⁺ under analogous conditions suggests that both reactions have the same rate determining step. The singly bridged species [(en)₂(H₂O)CoO₂Co(H₂O) (en)₂]⁴⁺ is shown to be the reactive intermediate in the iodide oxidation (Schema 2).     

Mass spectrometric characterization of metal triflates and triflimides (Lewis superacid catalysts) by electrospray ionization and tandem mass spectrometry

Trifluoromethylsulfonate (triflate) and bis(trifluoromethylsulfonyl)imide (triflimide) salts, well‐known Lewis acid catalysts, present some difficulty in their characterization. By using nitromethane as the solvent, useful electrospray mass spectra in positive and negative ion mode were obtained for salts of metals in oxidation states +2 and +3. In positive mode, addition of a strong Lewis base (triphenylphosphine oxide, TPPO), capable of displacing a triflate (TfO^?) or a triflimide (Tf₂N^?) anion, is necessary for obtaining useful spectra. Under these conditions of solvent and added ligand, the most abundant ions were [M²⁺(A^?)(TPPO)₂]⁺ or [M³⁺(A^?)₂(TPPO)₂]⁺ with A^? = TfO^? or Tf₂N^?. The MS/MS spectra of these diagnostic ions provide additional analytical information. The breakdown curves, in the form of % dissociated as a function of the ion activation energy, offer a mean for investigating the bonding in these ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Predominantly sigma-bonded metal carbonyl cations (sigma-carbonyls): new synthetic,structural, and bonding concepts in metal carbonyl chemistry

Predominantly σ‐bonded metal carbonyl cations (σ‐carbonyls) are conveniently generated in the Lewis superacid SbF₅ or the conjugate Brønsted–Lewis superacid HF? SbF₅, primarily by solvolytic or reductive carbonylations. Thermally stable salts are formed with the fluoroantimonate(V ) ions [SbF₆]^? and [Sb₂F₁₁]^?. The salts are characterised by analytical, structural, spectroscopic and computational methods. Most homoleptic carbonyl cations have very regular geometries, comensurate with their d‐electron configurations: linear (d¹⁰), square planar (d⁸) or octahedral(d⁶). The cations with metals in oxidation states of +2 or +3 are termed “superelectrophilic”. Extended molecular structures form by significant interionic C? F contacts with electrophilic carbon as acceptor. To account for all experimental observations, a conceptually simple synergetic bonding model is proposed. An outlook at anticipated future developments based on very recent results is provided.     

Towards the Accurate Calculation of 183W NMR Chemical Shifts in Polyoxometalates: The Relevance of the Structure

DFT calculations were carried out to study ¹⁸³W NMR chemical shifts in the family of the Keggin anions with formula α‐[XW₁₂O₄₀]^q? (X=B, Al, Si, P, Ga, Ge, As, Zn), in the β‐ and γ‐[SiW₁₂O₄₀]^4? geometric isomers, in the derivative Dawson anion [P₂W₁₈O₆₂]^6?, and in the most symmetrical Lindqvist [W₆O₁₉]^2? anion and its derivative [W₁₀O₃₂]^4?. In this article, we show that the geometry employed in the calculation of NMR chemical shifts in polyoxotungstates is extremely important if we want to be quantitative. Using very large basis sets of QZ4P quality and taking into account the conductor‐like screening model (COSMO) to account for solvent effects (aqueous and organic solutions), good geometries were found for the polyoxoanions. From these optimal geometries the ¹⁸³W NMR chemical shifts were computed with the more standard basis sets of TZP quality and including spin–orbit corrections inside the zero‐order regular approximation (ZORA) to describe the relativistic effects of the internal electrons. With this strategy the mean absolute error between experimental and theoretical values was found to be less than 10 ppm, which is similar to the experimental error. We also discuss how the geometry of the polyoxoanion influences on the shielding.