C−H Bond Trifluoromethylation of Arenes Enabled by a Robust,High‐Valent Nickel(IV) Complex

The robust, high‐valent Ni^IV complex [(Py)₂Ni^IVF₂(CF₃)₂] (Py=pyridine) was synthesized and fully characterized by NMR spectroscopy, X‐ray diffraction, and elemental analysis. It reacts with aromatic compounds at 25 °C to form the corresponding benzotrifluorides in nearly quantitative yield. The monomeric and dimeric Ni^IIICF₃ complexes 2 ⋅Py and 2 were identified as key intermediates, and their structures were unambiguously determined by EPR spectroscopy and X‐ray diffraction. Preliminary kinetic studies in combination with the isolation of reaction intermediates confirmed that the C−H bond‐breaking/C−CF₃ bond‐forming sequence can occur both at Ni^IVCF₃ and Ni^IIICF₃ centers.     

C−H Bond Trifluoromethylation of Arenes Enabled by a Robust,High‐Valent Nickel(IV) Complex

The robust, high‐valent Ni^IV complex [(Py)₂Ni^IVF₂(CF₃)₂] (Py=pyridine) was synthesized and fully characterized by NMR spectroscopy, X‐ray diffraction, and elemental analysis. It reacts with aromatic compounds at 25 °C to form the corresponding benzotrifluorides in nearly quantitative yield. The monomeric and dimeric Ni^IIICF₃ complexes 2 ⋅Py and 2 were identified as key intermediates, and their structures were unambiguously determined by EPR spectroscopy and X‐ray diffraction. Preliminary kinetic studies in combination with the isolation of reaction intermediates confirmed that the C−H bond‐breaking/C−CF₃ bond‐forming sequence can occur both at Ni^IVCF₃ and Ni^IIICF₃ centers.     

Oxovanadium(IV), manganese(II) and manganese(III) carbodithioates exhibiting abnormal magnetic behaviour

Summary New carbodithioate complexes of the oxovanadium(IV), manganese(II) and manganese(III) ions have been prepared and studied by i.r. and electronic spectral and variable temperature magnetic susceptibility (77K to room temperature) measurements. The carbodithioate ligands, 4-methylpiperazine-1-carbodithioate (4-MPipzcdt) and 4-phenylpiperazine-1-carbodithioate (4-PPipzcdt), were derived from heterocyclic secondary amines. The VO(4-MPipzcdt)₂ and VO(4-PPipzcdt)₂ complexes possess C _4v symmetry; Mn(4-PPipzcdt)₂ is tetrahedral and Mn(4-PPipzcdt)₃ is octahedral. All exhibit abnormal room temperature magnetic moments and the variable temperature magnetic moments suggest antiferromagnetism for the oxovanadium(IV) and the manganese(II) complexes and the occurrence of low spin (³ T _1g ) high spin (⁵ E _g ) equilibrium in addition to antiferromagnetic interactions in the manganese(III) complex. The spin-spin exchange parameter (-2J) value for the VO(4-MPipzcdt)₂ complex has been calculated using variable temperature magnetic susceptibility data.     

Octacyanidotungstate(IV) Coordination Chains Demonstrate a Light‐Induced Excited Spin State Trapping Behavior and Magnetic Exchange Photoswitching

A huge increase in the magnetization of two coordination chains based on tetravalent octacyanidometalates (W^IV and Mo^IV) is observed on irradiation with 436 nm light, while no such behavior is observed for the Nb^IV analogue. A photomagnetic response based solely on [W^IV(CN)₈]⁴⁻ is demonstrated for the first time. The observed behavior is attributed to the light‐induced excited spin state trapping (LIESST) effect at the octacyanidometalate, and to the resulting magnetic exchange ON/OFF photoswitching between the Mn^II center and the photoinduced high‐spin (S =1) W^IV or Mo^IV centers.     

Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes

Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp³)?C and C(sp³)?O bond‐forming reactions at high‐valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral Ni^IV complex ligated by tris(pyrazolyl)borate and a cationic octahedral Ni^III complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp³)?C(sp²) bond‐forming reductive elimination occurs from both centers, but the Ni^III complex reacts up to 300‐fold faster than the Ni^IV, depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO^?), the Ni^IV complex exclusively undergoes C(sp³)?OAc bond formation, while the Ni^III analogue forms the C(sp³)?C(sp²) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M?C(sp³) bonds, and thus their relative reactivity towards outer‐sphere S_N2‐type bond‐forming reactions.     

A non‐oxo methanolate‐bridged divanadium(IV) complex with tris(2‐sulfanidylphenyl)phosphane ligands: synthesis,structural characterization and magnetic investigation

Vanadium chemistry is of interest due its biological relevance and medical applications. In particular, the interactions of high‐valent vanadium ions with sulfur‐containing biologically important molecules, such as cysteine and glutathione, might be related to the redox conversion of vanadium in ascidians, the function of amavadin (a vanadium‐containing anion) and the antidiabetic behaviour of vanadium compounds. A mechanistic understanding of these aspects is important. In an effort to investigate high‐valent vanadium–sulfur chemistry, we have synthesized and characterized the non‐oxo divanadium(IV) complex salt tetraphenylphosphonium tri‐μ‐<!?tlsb=‐0.11pt>methanolato‐κ⁶O:O‐bis({tris[2‐sulfanidyl‐3‐(trimethylsilyl)phenyl]phosphane‐κ⁴P,S,S′,S′′}vanadium(IV)) methanol disolvate, (C₂₄H₂₀P)[V^IV₂(μ‐OCH₃)₃(C₂₇H₃₆PS₃)₂]·2CH₃OH. Two V^IV metal centres are bridged by three methanolate ligands, giving a C2‐symmetric V₂(μ‐OMe)₃ core structure. Each V^IV centre adopts a monocapped trigonal antiprismatic geometry, with the P atom situated in the capping position and the three S atoms and three O atoms forming two triangular faces of the trigonal antiprism. The magnetic data indicate a paramagnetic nature of the salt, with an S = 1 spin state.     

Magnetische Eigenschaften der ternären Phase (Co x Ni1−x )11Se8

The composition range of the ternary body-centered tetragonal phase (Co _x Ni_1–x )₁₁Se₈ extends fromx=0.03 tox=0.37 at 580°C. The magnetic susceptibilities and their variation with temperature and composition were investigated within the temperature range from 100 to 300 K using a magnetic balance. The temperature dependence of the magnetic suceptibilities was found to be consistent with theCurie-Weiss law from which magnetic moments were derived. Assuming the magnetic moments as spin-only values each cobalt atom contributes two unpaired electrons. Change in composition did not affect the magnitude of the magnetic moments. Based on crystallographic and magnetic data a simple model for the mutual distribution of cobalt and nickel atoms could be constructed.

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The effect of coordinated water on the connectivity of uranium(IV) sulfate x‐hydrate: [U(SO4)2(H2O)5]·H2O and [U(SO4)2(H2O)6]·2H2O,and a comparison with other known structures

Two new solid‐state uranium(IV) sulfate x‐hydrate complexes (where x is the total number of coordinated plus solvent waters), namely catena‐poly[[pentaaquauranium(IV)]‐di‐μ‐sulfato‐κ⁴O:O′] monohydrate], {[U(SO₄)₂(H₂O)₅]·H₂O}_n, and hexaaquabis(sulfato‐κ²O,O′)uranium(IV) dihydrate, [U(SO₄)₂(H₂O)₆]·2H₂O, have been synthesized, structurally characterized by single‐crystal X‐ray diffraction and analyzed by vibrational (IR and Raman) spectroscopy. By comparing these structures with those of four other known uranium(IV) sulfate x‐hydrates, the effect of additional coordinated water molecules on their structures has been elucidated. As the number of coordinated water molecules increases, the sulfate bonds are displaced, thus changing the binding mode of the sulfate ligands to the uranium centre. As a result, uranium(IV) sulfate x‐hydrate changes from being fully crosslinked in three dimensions in the anhydrous compound, through sheet and chain linking in the tetra‐ and hexahydrates, to fully unlinked molecules in the octa‐ and nonahydrates. It can be concluded that coordinated waters play an important role in determining the structure and connectivity of U^IV sulfate complexes.     

Between MOFs and molecules: organolead(IV) compounds with chain structures

Organolead compounds are of interest mainly as catalysts and organolead halides have proved to be very efficient materials for solar cells. Two organolead(IV) dimethylarsinates, namely catena‐poly[[triphenyllead(IV)]‐μ‐chlorido‐[triphenyllead(IV)]‐μ‐dimethylarsinato‐κ²O:O′], [Pb₂(C₆H₅)₆(C₂H₆AsO₂)Cl]_n or [(Ph₃Pb)₂Cl(O₂AsMe₂)], ( 1 ), and poly[chlorido(μ₃‐dimethylarsinato‐κ³O:O,O′:O′)diphenyllead(IV)], [Pb(C₆H₅)₂(C₂H₆AsO₂)Cl]_n or [(Ph₂ClPb)(O₂AsMe₂)], ( 2 ), together with the triphenyllead(IV) diphenylphosphinate catena‐poly[[triphenyllead(IV)]‐μ‐diphenylphosphinato‐κ²O:O′], [Pb(C₆H₅)₃(C₁₂H₁₀O₂P)]_n or [(Ph₃Pb)(O₂PPh₂)], ( 3 ), have been synthesized and characterized by single‐crystal X‐ray diffraction, IR spectroscopy and mass spectrometry. In ( 1 ), a chain structure was found with alternating chloride and Pb—O—As—O—Pb arsinate bridges between five‐coordinate Pb^IV atoms. In ( 2 ), bidentate and chelate‐like bonded dimethylarsinate ligands form double chains with heptacoordinated Pb^IV atoms. In ( 3 ), a pentacoordinated Pb^IV atom is connected by Pb—O—P—O—Pb phosphinate bridges to form a linear chain. Obviously, the steric demand of the phenyl ligands at Pb^IV reduces the possibility of interconnections via polydentate ligands to one dimension only. Thus, no metal–organic frameworks (MOF) are formed but instead various chain structures are observed.     

Synthesis,Crystal Structure and Magnetic Properties of a Novel Heterobimetallic Rhenium(IV)–Dysprosium(III) Chain

The use of the mononuclear rhenium(IV) precursor [ReBr₅(H₂pydc)]^? (H₂pydc=3,5‐pyridinedicarboxylic acid) as a metalloligand towards dysprosium(III) afforded the first heterobimetallic Re^IV–Dy^III complex. Crystal structures and static and dynamic magnetic properties of both rhenium‐containing species are reported herein. The 5d–4f compound shows an extended 1D structure and the AC magnetic measurements reveal frequency dependence at low temperature suggesting slow relaxation of the magnetization.     

Structural Properties,Mössbauer Spectra,and Magnetism of Perovskite‐Type Oxides SrFe1–xTixO3–y

Perovskite‐type phases SrFe_1–xTi_xO_3–y with 0.1 ≤ x ≤ 0.7 have been prepared from the oxides, and, in order to reach high oxygen contents and Fe^IV fractions, annealed at oxygen pressures of 60 MPa. The materials were characterised by powder x‐ray and neutron diffraction, ⁵⁷Fe Mössbauer spectroscopy, and magnetic susceptibility measurements. All samples of the series crystallise in a cubic perovskite structure and reveal considerable oxygen deficiency. The Mössbauer parameters suggest that for x = 0.1, where the Fe^IV fraction is about 90%, the itinerant electronic state of SrFeO₃ is essentially retained. In materials with larger x increasing amounts of Ti^IV and Fe^III ions lead to a stronger localisation of the σ* (Fe 3 d – O 2 p) electrons. There is no evidence for a charge disproportionation of Fe^IV in any of the materials. Magnetic susceptibility measurements show a divergence of zero‐field cooled and field‐cooled data below a temperature T_m and deviations from Curie‐Weiss behaviour above T_m. The data are indicative of spin‐glass behaviour due to disorder and competing exchange interactions.     

Intramolecular Gas‐Phase Reactions of Synthetic Nonheme Oxoiron(IV) Ions: Proximity and Spin‐State Reactivity Rules

The intramolecular gas‐phase reactivity of four oxoiron(IV) complexes supported by tetradentate N₄ ligands ( L ) has been studied by means of tandem mass spectrometry measurements in which the gas‐phase ions [Fe^IV(O)( L )(OTf)]⁺ (OTf=trifluoromethanesulfonate) and [Fe^IV(O)( L )]²⁺ were isolated and then allowed to fragment by collision‐induced decay (CID). CID fragmentation of cations derived from oxoiron(IV) complexes of 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane (tmc) and N,N′‐bis(2‐pyridylmethyl)‐1,5‐diazacyclooctane ( L ⁸Py₂) afforded the same predominant products irrespective of whether they were hexacoordinate or pentacoordinate. These products resulted from the loss of water by dehydrogenation of ethylene or propylene linkers on the tetradentate ligand. In contrast, CID fragmentation of ions derived from oxoiron(IV) complexes of linear tetradentate ligands N,N′‐bis(2‐pyridylmethyl)‐1,2‐diaminoethane (bpmen) and N,N′‐bis(2‐pyridylmethyl)‐1,3‐diaminopropane (bpmpn) showed predominant oxidative N‐dealkylation for the hexacoordinate [Fe^IV(O)( L )(OTf)]⁺ cations and predominant dehydrogenation of the diaminoethane/propane backbone for the pentacoordinate [Fe^IV(O)( L )]²⁺ cations. DFT calculations on [Fe^IV(O)(bpmen)] ions showed that the experimentally observed preference for oxidative N‐dealkylation versus dehydrogenation of the diaminoethane linker for the hexa‐ and pentacoordinate ions, respectively, is dictated by the proximity of the target C? H bond to the oxoiron(IV) moiety and the reactive spin state. Therefore, there must be a difference in ligand topology between the two ions. More importantly, despite the constraints on the geometries of the TS that prohibit the usual upright σ trajectory and prevent optimal σ_CH–σ* overlap, all the reactions still proceed preferentially on the quintet (S=2) state surface, which increases the number of exchange interactions in the d block of iron and leads thereby to exchange enhanced reactivity (EER). As such, EER is responsible for the dominance of the S=2 reactions for both hexa‐ and pentacoordinate complexes.     

A mixed‐valence manganese(III)–manganese(IV) di‐μ‐oxo complex, [(cyclam)MnO]2(ClO4)2(NO3)

The title dinuclear di‐μ‐oxo‐bis­[(1,4,8,11‐tetra­aza­cyclo­tetra­decane‐κ⁴N)­manganese(III,IV)] diperchlorate nitrate complex, [Mn₂O₂(C₁₀H₂₄N₄)₂](ClO₄)₂(NO₃) or [(cyclam)Mn­O]₂(ClO₄)₂(NO₃), was self‐assembled by the reaction of Mn²⁺ with 1,4,8,11‐tetra­aza­cyclo­tetra­decane in aqueous media. The structure of this compound consists of a centrosymmetric binuclear [(cyclam)MnO]³⁺ unit, two perchlorate anions and one nitrate anion. While the low‐temperature electron paramagnetic resonance spectra show a typical 16‐line signal for a di‐μ‐oxo Mn^III/Mn^IV dimer, the magnetic susceptibility studies also confirm a characteristic antiferromagnetic coupling between the electronic spins of the Mn^IV and Mn^III ions.     

Trapping of a Highly Reactive Oxoiron(IV) Complex in the Catalytic Epoxidation of Olefins by Hydrogen Peroxide

The generation of a nonheme oxoiron(IV) intermediate, [(cyclam)Fe^IV(O)(CH₃CN)]²⁺ ( 2 ; cyclam=1,4,8,11‐tetraazacyclotetradecane), is reported in the reactions of [(cyclam)Fe^II]²⁺ with aqueous hydrogen peroxide (H₂O₂) or a soluble iodosylbenzene (sPhIO) as a rare example of an oxoiron(IV) species that shows a preference for epoxidation over allylic oxidation in the oxidation of cyclohexene. Complex 2 is kinetically and catalytically competent to perform the epoxidation of olefins with high stereo‐ and regioselectivity. More importantly, 2 is likely to be the reactive intermediate involved in the catalytic epoxidation of olefins by [(cyclam)Fe^II]²⁺ and H₂O₂. In spite of the predominance of the oxoiron(IV) cores in biology, the present study is a rare example of high‐yield isolation and spectroscopic characterization of a catalytically relevant oxoiron(IV) intermediate in chemical oxidation reactions.     

N-benzamidosalicylaldimine complexes of copper(II), nickel(II), cobalt(II), iron(II), manganese(II), oxyvanadium(IV) and oxytitanium(IV)

Summary N-benzamidosalicylaldimine (H₂L) complexes of Cu^II, Ni^II, Co^II, Fe^II, Mn^II. VO_IV and TiO_IV have been prepared. The ligand probably coordinates to the metal from the hydroxyl, carbonyl and imino groups.     

Dioxygen Activation by Siloxide Complexes of Chromium(II) and Chromium(IV)

The reaction of a tripodal trisilanol with n‐butyllithium and CrCl₂ results in a dinuclear Cr^II complex ( 1 ), which is capable of cleaving O₂ to yield in a unique complex ( 2 ) with an asymmetric diamond core composed of two Cr^IV?O units. Magnetic susceptibility data reveal significant exchange coupling of Cr^II (S=2) in 1 and large zero‐field splitting for Cr^IV (S=1) in 2 owing to strong spin–orbit coupling of the ground state. The Cr^IV?O compound can also be generated using PhIO, and evidence was gathered that although it is the stable product isolated after excessive O₂ treatment, it further activates O₂ to yield an intermediate species that oxidizes THF or Me‐THF. By extensive ¹⁸O labeling studies we were able to show, that in the course of this process ¹⁸O₂ exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands.     

Selective tetrahydropyranylation of alcohols and phenols using titanium(IV) salophen trifluoromethanesulfonate as an efficient catalyst

Titanium(IV) salophen trifluoromethanesulfonate, [Ti^IV(salophen)(OSO₂CF₃)₂], as a catalyst enables selective tetrahydropyranylation of alcohols and phenols with 3,4‐dihydro‐2H‐pyran. Using this catalytic system, primary, secondary and tertiary alcohols, as well as phenols, were converted to their corresponding tetrahydropyranyl ethers in high yields and short reaction times at room temperature. Investigation of the chemoselectivity of this method showed discrimination between the activity of primary alcohols in the presence of secondary and tertiary alcohols and phenols. This heterogenized catalyst could be reused several times without loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Combined Experimental and Computational Studies of a Na2Ni1−xCuxFe(CN)6 Cathode with Tunable Potential for Aqueous Rechargeable Sodium‐Ion Batteries

Herein, potential‐tunable Na₂Ni_1?xCu_xFe(CN)₆ nanoparticles with three‐dimensional frameworks and large interstitial spaces were synthesized as alternative cathode materials for aqueous sodium‐ion batteries by controlling the molar ratio of Ni^II to Cu^II at ambient temperature. The influence of the value of x on the crystalline structure, lattice parameters, electrochemical properties, and charge transfer of the resultant compound was explored by using powder X‐ray diffractometry, density functional theory, cyclic voltammetry, galvanostatic charge–discharge techniques, and Bader charge analysis. Of the various formulations investigated, that with x=0.25 delivered the highest reversible capacity, superior rate capability, and outstanding cycling performance. These attributes are ascribed to its unique face‐centered cubic structure for facile sodium‐ion insertion/extraction and the strong interactions between Cu and N atoms, which promote structural stability.     

[UF6]2−: A Molecular Hexafluorido Actinide(IV) Complex with Compensating Spin and Orbital Magnetic Moments

The first structurally characterized hexafluorido complex of a tetravalent actinide ion, the [UF₆]^2? anion, is reported in the (NEt₄)₂[UF₆]?2 H₂O salt ( 1 ). The weak magnetic response of 1 results from both U^IV spin and orbital contributions, as established by combining X‐ray magnetic circular dichroism (XMCD) spectroscopy and bulk magnetization measurements. The spin and orbital moments are virtually identical in magnitude, but opposite in sign, resulting in an almost perfect cancellation, which is corroborated by ab initio calculations. This work constitutes the first experimental demonstration of a seemingly non‐magnetic molecular actinide complex carrying sizable spin and orbital magnetic moments.     

Preparation,Crystallographic, Spectroscopic and Magnetic Characterization of Low‐Valency Nitridometalates Li2[(Li1‐xMx)N] with M = Cu,Ni

Thermogravimetric and difference thermal analyses show that the reactions of lithium nitride with the transition metals Cu and Ni under molecular nitrogen to form phases Li₂[(Li_1‐xM^I_x)N] take place above 673 K. The maximum weight gains are reached at 926 K and 968 K for M = Cu and Ni, respectively. At higher temperatures, the ternary phases Li₂[(Li_1‐xM^I_x)N] decompose, limiting the substitutional level x. In the temperature range of 773 K — 873 K, the successful synthesis of Li₂[(Li_1‐xNi^I_x)N] (0 < x ≤ 0.85(1)) single phase products is demonstrated. Maximum substitution obtained for the Cu phases is x_max= 0.43(1). The dependence of the lattice parameters of the hexagonal unit cell on x is almost linear. The magnetic moment of M strongly depends on x. At low x the magnetic moments in phases with M = Ni are presumably enhanced by orbital effects. A decrease of μ_eff with x to μ_eff(x = 1) → 0 is explained by delocalization of the magnetic moments and by the gradual formation of a metal for the hypothetical compound Li₂[NiN] (x = 1). XAS spectroscopy at the transition metal K‐edges shows that Cu and Ni principally correspond to d¹⁰‐ and d⁹‐configurations, respectively.