Wechselwirkungen in Kristallen, 176. Mitteilung,Redox‐Reaktionen von Hexahydropyren: Kristallstrukturen seiner Radikalanion‐Salze sowie von Trihydropyrenylium‐tetrachloroaluminat und Dichtefunktionaltheorie‐Berechnungen

Redox Reactions of Hexahydropyrene: Crystal Structures of Its Radical‐Anion Salts as well as of Trihydropyrenylium Tetrachloroaluminate and Density‐Functional‐Theory Calculations Hexahydropyrene 1 , a doubly propane‐1,3‐diyl‐bridged peri‐naphthalene derivative wtih 10 π‐electrons allows both oxidation to its cation as well as reduction to its radical‐anion salts, which could be crystallized and structurally characterized – a rather rare case for small unsaturated hydrocarbons. The unexpected formally threefold dehydrogenation by the oxidizing system AlCl₃/H₂CCl₂ (Bock's reagent) generated the hitherto unknown 1,2,3‐trihydropyrene cation in two polymorphic crystals, which contain 12 π‐electrons delocalized over three anellated six‐membered rings comprising 13 π‐centers. Structural comparison of the altogether four crystallized redox products [K⁺_solv][M^.−] 2a , [K⁺_solv][M^.−]_∞ 2b , [Na⁺_solv][M^.−] 2c , and [(M−3 H)⁺][AlCl⁻₄] 3 with the neutral hydrocarbon 1 reveals only small differences in bond lengths and angles, but establishes solvation contacts, π(η⁶)⋅⋅⋅K⁺ coordination in the polymer 2b , the flattening of one molecular half in the trihydropyren cation of 3 and ten H‐bonds CH⋅⋅⋅Cl to the AlCl₄⁻ counter anion of 3 . DFT/NBO Charge distributions, calculated based on the experimental structural parameters, show charge accumulation in the propanediyl bridges as well as in the peripheral naphthalene C−C bonds of the radical anions. The largest changes result expectedly for the formally triply dehydrogenated 1 , i.e. the trihydropyren cation of 3 , with two slightly positive and partly considerably less negative π‐centers.     

Tetrabutylammonium Salts of Aluminum(III) and Gallium(III) Phthalocyanine Radical Anions Bonded with Fluoren‐9‐olato− Anions and Indium(III) Phthalocyanine Bromide Radical Anions

Reduction of aluminum(III), gallium(III), and indium(III) phthalocyanine chlorides by sodium fluorenone ketyl in the presence of tetrabutylammonium cations yielded crystalline salts of the type (Bu₄N⁺)₂[M^III(HFl−O⁻)(Pc^.3−)]^.−(Br⁻) ⋅ 1.5 C₆H₄Cl₂ [M=Al ( 1 ), Ga ( 2 ); HFl−O⁻=fluoren‐9‐olato⁻ anion; Pc=phthalocyanine] and (Bu₄N⁺) [In^IIIBr(Pc^.3−)]^.− ⋅ 0.875 C₆H₄Cl₂ ⋅ 0.125 C₆H₁₄ ( 3 ). The salts were found to contain Pc^.3− radical anions with negatively charged phthalocyanine macrocycles, as evidenced by the presence of intense bands of Pc^.3− in the near‐IR region and a noticeable blueshift in both the Q and Soret bands of phthalocyanine. The metal(III) atoms coordinate HFl−O⁻ anions in 1 and 2 with short Al−O and Ga−O bond lengths of 1.749(2) and 1.836(6) Å, respectively. The C−O bonds [1.402(3) and 1.391(11) Å in 1 and 2 , respectively] in the HFl−O⁻ anions are longer than the same bond in the fluorenone ketyl (1.27–1.31 Å). Salts 1 – 3 show effective magnetic moments of 1.72, 1.66, and 1.79 μ_B at 300 K, respectively, owing to the presence of unpaired S= 1/2 spins on Pc^.3−. These spins are coupled antiferromagnetically with Weiss temperatures of −22, −14, and −30 K for 1 – 3 , respectively. Coupling can occur in the corrugated two‐dimensional phthalocyanine layers of 1 and 2 with an exchange interaction of J /k _B=−0.9 and −1.1 K, respectively, and in the π‐stacking {[In^IIIBr(Pc^.3−)]^.−}₂ dimers of 3 with an exchange interaction of J /k _B=−10.8 K. The salts show intense electron paramagnetic resonance (EPR) signals attributed to Pc^.3−. It was found that increasing the size of the central metal atom strongly broadened these EPR signals.     

Solid-State Properties of Hexaazatriphenylenehexacarbonitrile HAT(CN)6.− Radical Anions in Crystalline Salts Containing Cryptand(M+) and Crystal Violet Cations

Crystalline {Cryptand[2.2.2](Na⁺)}{HAT(CN)₆^.−}⋅0.5C₆H₄Cl₂ ( 1 ), {Cryptand[2.2.2](K⁺)}{HAT(CN)₆^.−} ( 2 ), (CV⁺){HAT(CN)₆^.−} ( 3 ), and (CV⁺){HAT(CN)₆^.−}⋅2C₆H₄Cl₂ ( 4 ) salts (where CV⁺ is the crystal violet cation) containing hexaazatriphenylenehexacarbonitrile radical anions have been obtained. The solid-state molecular structure as well as the optical and magnetic properties of HAT(CN)₆^.− are studied. The formation of HAT(CN)₆^.− in 1 – 4 leads to the appearance of new bands in the visible range, at 694 and 740 nm. The HAT(CN)₆^.− radical anions have spin state S=1/2 and are packed in one-dimensional stacks containing the {HAT(CN)₆^.−}₂ dimers alternated with weaker interacting pairs of HAT(CN)₆^.− in 1 and nearly isolated {HAT(CN)₆^.−}₂ dimers in 2 . The {HAT(CN)₆^.−}₂ dimers are diamagnetic in 1 but they effectively mediate one-dimensional antiferromagnetic coupling of spins within the stacks with moderate exchange interaction of J/k_B = −80 K. The behaviour of salt 2 is described by a singlet–triplet model for the {HAT(CN)₆^.−}₂ dimers with an energy gap of 434(±7) K. Magnetic behaviour of both salts agree well with the data of extended Hückel calculations. Salts 3 and 4 contain isolated stacks of alternated HAT(CN)₆^.− and CV⁺ ions, and in this case, nearly paramagnetic behaviour is observed with Weiss temperatures of −1 and −7 K, respectively. Narrow Lorentzian EPR signals with g = 2.0033–2.0039 were found for the HAT(CN)₆^.− radical anions in 1 and 4 but in solution g-factor shifts to 1.9964. The electronic structure of HAT(CN)₆^.− is analysed based on X-ray diffraction data for 2 , showing a Jahn–Teller distortion of the radical anion that reduces the symmetry from D_3h to C_s and splits the initially degenerated LUMOs.     

Radical Anions,Radical-Anion Salts,and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1 – 3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [ 1 ]^.− and [ 2 ]^.−, RA [ 3 ]^.− was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1 – 3 was performed and new thermally stable RA salts [K(THF)]⁺[ 2 ]^.− ( 8 ) and [K(18-crown-6)]⁺[ 2 ]^.− ( 9 ) were isolated in addition to known salt [K(THF)]⁺[ 1 ]^.− ( 7 ). On contact with air, RAs [ 1 ]^.− and [ 2 ]^.− underwent fast decomposition in solution with the formation of anions [ECN]⁻, which were isolated in the form of salts [K(18-crown-6)]⁺[ECN]⁻ ( 10 , E=S; 11 , E=Se). In the case of 3 , RA [ 3 ]^.− was detected by EPR spectroscopy as the first representative of tellurium–nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]⁺₂[ 3 -Te₂]²⁻ ( 12 ) featuring a new anionic complex with coordinate Te−Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]⁺₂[ 3 -Te₄- 3 ]²⁻ ( 13 ) containing an anionic complex with two coordinate Te−Te bonds. The structures of 8 – 13 were confirmed by XRD, and the nature of the Te−Te coordinate bond in [ 3 -Te₂]²⁻ and [ 3 -Te₄- 3 ]²⁻ was studied by DFT calculations and QTAIM analysis.     

Potassium Carboxylates by Direct Carbonylation of Potassium Alkoxides

Reaction of the K⁺ alkoxide of linalool ( 1 ) in benzene with CO at 425–440 bar and 120–130° for 12–30 h gave the K⁺ salt of 2,6-dimethyl-2-vinyl-5-heptenoic acid ( 4a ) in a ca. 25% yield based on ca. 65% converted alkoxide. Reaction of the [K⁺ ? 18-crown-6] alkoxide of 1 with CO at 50–55 bar and 40° for 90–140 h gave a mixture containing mainly the [K⁺ ? 18-c-6] salts of 4a (ca. 62%) and of the homogeranic acids 3a and 6a (together ca. 27% of the mixture) in a ca. 35% combined yield based on 50–60% converted alkoxide. The uncomplexed or complexed K⁺ alkoxide of (S)? 1 gave, with ca. 85% net retention, the K⁺ salt of (S)- 4a . Reaction of the [K⁺ ? 18-c-6] alkoxide of geraniol ( 2 ) with CO at 50 bar and 40° for 65–70 h gave myrcene ( 10 ) and geranyl formate ( 11 ) in a ca. 40–50% yield each based on ca. 85% converted alkoxide. Reaction of the [K⁺ ? 18-c-6] alkoxide of 3-pentyl-1,4-pentadien-3-ol ( 14 ) at 50 bar and r.t. for 70 h gave a mixture of the [K⁺ ? 18-c-6] salts of 2-pentyl-2-vinyl-3-butenoic acid ( 15a ) (67%) and the 4-pentyl-2,4-hexadienoic acids 18a and 19a (together 23% of the mixture) in a ca. 90% combined yield based on ca. 65% converted alkoxide.     

Syntheses and Structures of 5-Membered Heterocycles Featuring 1,2-Diphospha-1,3-Butadiene and Its Radical Anion

LGa(P₂OC)cAAC 2 features a 1,2-diphospha-1,3-butadiene unit with a delocalized π-type HOMO and a π*-type LUMO according to DFT calculations. [LGa(P₂OC)cAAC][K(DB-18-c-6)] 3 [K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene radical anion 3 ⋅ ⁻ was isolated from the reaction of 2 with KC₈ and dibenzo-18-crown-6. 3 reacted with [Fc][B(C₆F₅)₄] (Fc=ferrocenium) to 2 and with TEMPO to [L^−HGa(P₂OC)cAAC][K(DB-18-c-6)] 4 [K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene anion 4⁻ . The solid state structures of 2 , 3 K(DB-18-c-6], and 4 [K(DB-18-c-6] were determined by single crystal X-ray diffraction (sc-XRD).     

A Diruthenium Complex of an N-Pyridyl-o-aminophenol Derivative: A Route to Mixed Valency

An N-pyridyl-o-aminophenol derivative that stabilises mixed-valence states of ruthenium ions is disclosed. A diruthenium complex, [(L_IQ⁰)Ru₂Cl₅] ⋅ MeOH ( 1⋅ MeOH) is successfully isolated, in which L_IQ⁰ is the o-iminobenzoquinone form of 2-[(3-nitropyridin-2-yl)amino]phenol (L_APH₂). In 1 , L_IQ⁰ oriented towards one ruthenium centre is a non-innocent NO-donor redox ligand, whereas another oriented towards another ruthenium centre is an innocent pyridine-donor redox ligand. Complex 1 is a diruthenium(II,III) mixed-valence complex, [Ru^II(L_IQ⁰)(μ-Cl)₂Ru^III], with a minor contribution from the diruthenium(III,III) state. [Ru^III(L_ISQ^.−)(μ-Cl)₂Ru^III] contains L_ISQ^.−, which is the o-iminobenzosemiquinonate anion radical form of the ligand. Complexes 1 ⁻ and 1 ⁺ are diruthenium(II,II), [Ru^II(L_IQ⁰)(μ-Cl)₂Ru^II], and diruthenium(III,III), [Ru^III(L_IQ⁰)(μ-Cl)₂Ru^III], complexes, respectively, of L_IQ⁰. Complex 1 ²⁻ is a diruthenium(II,II) complex of the o-iminobenzosemiquinonate anion radical (L_ISQ^.−), [Ru^II(L_ISQ^.−)(μ-Cl)₂Ru^II], with a minor contribution from the diruthenium(III,II) form, [Ru^III(L_AP²⁻)(μ-Cl)₂Ru^II]. Complex 1 ²⁺ is a diruthenium(III,IV) mixed-valence complex of L_IQ⁰, [Ru^III(L_IQ⁰)(μ-Cl)₂Ru^IV]. Complexes 1 and 1 ²⁺ exhibit inter-valence charge-transfer transitions at λ=1300 and 1370 nm, respectively.     

Molecular Structure and Magnetic and Optical Properties of Endometallonitridofullerene Sc3N@Ih-C80 in Neutral,Radical Anion,and Dimeric Anionic Forms

A series of compounds with Sc₃N@I_h-C₈₀ in the neutral, monomeric, and dimeric anion states have been prepared in the crystalline form and their molecular structures and optical and magnetic properties have been studied. The neutral Sc₃N@I_h-C₈₀ ⋅ 3 C₆H₄Cl₂ ( 1 ) and (Sc₃N@I_h-C₈₀)₃(TPC)₂ ⋅ 5 C₆H₄Cl₂ ( 2 , TPC=triptycene) compounds both crystallized in a high-symmetry trigonal structure. The reduction of Sc₃N@I_h-C₈₀ to the radical anion resulted in dimerization to form diamagnetic singly bonded (Sc₃N@I_h-C₈₀⁻)₂ dimers. In contrast to {[2.2.2]cryptand(Na⁺)}₂(Sc₃N@I_h-C₈₀⁻)₂ ⋅ 2.5 C₆H₄Cl₂ ( 3 ) with strongly disordered components, we synthesized new dimeric phases {[2.2.2]cryptand- (K⁺)}₂(Sc₃N@I_h-C₈₀⁻)₂ ⋅ 2 C₆H₄Cl₂ ( 4 ) and {[2.2.2]cryptand- (Cs⁺)}₂(Sc₃N@I_h-C₈₀⁻)₂ ⋅ 2 C₆H₄Cl₂ ( 5 ) in which only one major dimer orientation was found. The thermal stability of the (Sc₃N@I_h-C₈₀⁻)₂ dimers was studied by EPR analysis of 3 to show their dissociation in the 400–460 K range producing monomeric Sc₃N@I_h-C₈₀^.− radical anions. This species shows an EPR signal with a hyperfine splitting of 5.8 mT. The energy of the intercage C−C bond was estimated to be 234±7 kJ mol⁻¹, the highest value among negatively charged fullerene dimers. The EPR spectra of crystalline (Bu₃MeP⁺)₃(Sc₃N@I_h-C₈₀^.−)₃ ⋅ C₆H₄Cl₂ ( 6 ) are presented for the first time. The salt shows an asymmetric EPR signal, which could be fitted by three lines. Two lines were attributed to Sc₃N@I_h-C₈₀^.−. Hyperfine splitting is manifested above 180 K due to the hyperfine interaction of the electron spin with the three scandium atoms (a total of 22 lines with an average splitting of 5.32 mT are observed at 220 K). Furthermore, each of the 22 lines is additionally split into six lines with an average separation of 0.82 mT. The large splitting indicates intrinsic charge and spin density transfer from the fullerene cage to the Sc₃N cluster. Both the monomeric and dimeric Sc₃N@I_h-C₈₀⁻ anions show an intrinsic shift of the IR bands attributed to the Sc₃N cluster and new bands corresponding to these species appear in the NIR range of their UV/Vis/NIR spectra, which allows these anions to be distinguished from neutral species.     

A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium–Nitrogen Radical Anion

Interaction of the tetradentate redox-active 6,6′-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H₄L) with TeCl₄ leads to neutral diamagnetic compound TeL ( 1 ) in high yield. The molecule of 1 has a nearly planar TeN₂O₂ fragment, which suggests the formulation of 1 as Te^IIL²⁻, in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp₂] leads to quantitative formation of the paramagnetic salt [CoCp₂]⁺[ 1 ]^.−, which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp₂]⁺[ 1 ]^.− at room temperature features a quintet due to splitting on two equivalent ¹⁴N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the ¹²⁵Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(¹⁴N) HFI constants and A_∥(¹²⁵Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1 ^.− is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1 ^.− can be regarded as the first example of a structurally characterised monomeric tellurium–nitrogen radical anion.     

Solution Synthesis,Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−

The first crystallographically characterizable complex of Sc²⁺, [Sc(NR₂)₃]⁻ (R=SiMe₃), has been obtained by LnA₃/M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR₂)₃ with K in the presence of 2.2.2‐cryptand (crypt) and 18‐crown‐6 (18‐c‐6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]⁺, [K(18‐c‐6)]⁺, and [Cs(crypt)]⁺ salts of the [Sc(NR₂)₃]⁻ anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight‐line EPR spectra arising from the I =7/2 ⁴⁵Sc nucleus. The Sc(NR₂)₃ reduction differs from Ln(NR₂)₃ reactions (Ln=Y and lanthanides) in that it occurs under N₂ without formation of isolable reduced dinitrogen species. [K(18‐c‐6)][Sc(NR₂)₃] reacts with CO₂ to produce an oxalate complex, {K₂(18‐c‐6)₃}{[(R₂N)₃Sc]₂(μ‐C₂O₄‐κ ¹O:κ ¹O′′)}, and a CO₂⁻ radical anion complex, [(R₂N)₃Sc(μ‐OCO‐κ ¹O:κ ¹O′)K(18‐c‐6)]_n .     

Solution Synthesis,Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−

The first crystallographically characterizable complex of Sc²⁺, [Sc(NR₂)₃]⁻ (R=SiMe₃), has been obtained by LnA₃/M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR₂)₃ with K in the presence of 2.2.2‐cryptand (crypt) and 18‐crown‐6 (18‐c‐6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]⁺, [K(18‐c‐6)]⁺, and [Cs(crypt)]⁺ salts of the [Sc(NR₂)₃]⁻ anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight‐line EPR spectra arising from the I =7/2 ⁴⁵Sc nucleus. The Sc(NR₂)₃ reduction differs from Ln(NR₂)₃ reactions (Ln=Y and lanthanides) in that it occurs under N₂ without formation of isolable reduced dinitrogen species. [K(18‐c‐6)][Sc(NR₂)₃] reacts with CO₂ to produce an oxalate complex, {K₂(18‐c‐6)₃}{[(R₂N)₃Sc]₂(μ‐C₂O₄‐κ ¹O:κ ¹O′′)}, and a CO₂⁻ radical anion complex, [(R₂N)₃Sc(μ‐OCO‐κ ¹O:κ ¹O′)K(18‐c‐6)]_n .     

Formation of cation–radical anion pairs derived from carboxybenzophenone–tetrabutylammonium salts. Pulse radiolysis studies

Pulse radiolysis of acetonitrile solutions of tetra-n-butyl ammonium salts of 2- and 4-carboxybenzophenones [BP-COO⁻···N⁺(C₄H₉)₄] were performed in order to generate directly the reduced forms of the benzophenone moieties within pre-formed ion pairs. In earlier studies on photochemical electron transfer reactions, ion pairs containing a tetraalkyl ammonium cation and a benzophenone radical anion were formed in an electron transfer to the triplet BP from a quencher consisting of a tetraalkyl ammonium salt of (phenylthio)acetic acid. In the current work, the [BP^•−COO⁻···N⁺(C₄H₉)₄] ion pairs were formed by direct reduction of the salts without the complication of a third moiety, i.e., the (phenylthio)acetic anion. The spectra and kinetic parameters of the radiolytically-reduced salts were compared to the behavior of reduced forms of the 2- and 4-COOH substituted benzophenones. The results from the pulse radiolysis and photochemistry were compared and explained in terms of the different structures of the ion pairs.     

Structure of (BEDT-TTF)-Based Organic Metals with Photochromic Nitroprusside Anion (BEDT-TTF)4M[FeNO(CN)5]2, where M = Na+, K+, NH+4, Tl+, Rb+, and Cs+

The crystal and molecular structures of a family of three-component radical cation salts bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), (BEDT-TTF)₄M[NP]₂, where M = Na⁺, K⁺, NH⁺ ₄, Tl⁺, Rb⁺, and Cs⁺and NP is the nitroprusside anion [FeNO(CN)₅]^2–, are studied by X-ray structure analysis. These salts are isostructural and behave as stable metals down to helium temperatures. Their structures are characterized by radical cation layers of the "-type alternating with layers of complex anions [M⁺(NP^2–)₂]^3–. The conducting radical cation system and photochromic nitroprusside anion in the crystals were shown to affect each other. On the one hand, this changes the geometric parameters of the nitroprusside anion as compared to those of the Na₂[NP] · 2H₂O crystals in the ground state and, on the other hand, makes the geometries of the two crystallographically independent BEDT-TTF molecules with a different number of shortened contacts with the anion different. Based on the data of crystallochemical analysis of the (BEDT-TTF)₄M[FeNO(CN)₅]₂structures, we suggest their possible routes of chemical modification with the purpose of changing their physical properties.     

Mono-reduced Corannulene: To Couple and Not to Couple in One Crystal

One-electron reduction of corannulene, C₂₀H₁₀, with Li metal in diglyme resulted in crystallization of [{Li⁺(diglyme)₂}₄(C₂₀H₁₀^.−)₂(C₂₀H₁₀-C₂₀H₁₀)²⁻] ( 1 ), as revealed by single-crystal X-ray diffraction. This hybrid product contains two corannulene monoanion-radicals along with a dianionic dimer, crystallized with four Li⁺ ions wrapped by diglyme molecules. The dimeric (C₂₀H₁₀-C₂₀H₁₀)²⁻ anion provides the first crystallographically confirmed example of spontaneous radical dimerization for C₂₀H₁₀^.−. The C−C bond length between the two C₂₀H₁₀^.− bowls of 1.588(5) Å is consistent with the single σ-bond character of the linker. The trans-disposition of two bowls in the centrosymmetric (C₂₀H₁₀-C₂₀H₁₀)²⁻ dimer is observed with the torsion angle around the central C−C bond of 180°. Comprehensive theoretical analysis of formation/decomposition processes of the dimeric dianion has been carried out in order to evaluate the nature of bonding and energetics of the C₂₀H₁₀^.− coupling. It is found that such σ-bonded dimers are thermodynamically unstable due to large preparation energy and repulsive Pauli component of the bonding, but kinetically persistent due to a high energy barrier provided by the existing spin-crossing point.     

Infrared Spectroscopy of Size-Selected Hydrated Carbon Dioxide Radical Anions CO2.−(H2O)n (n=2–61) in the C−O Stretch Region

Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO₂^.−(H₂O)_n is relevant for electrochemical carbon dioxide functionalization. CO₂^.−(H₂O)_n (n=2–61) is investigated by using infrared action spectroscopy in the 1150–2220 cm⁻¹ region in an ICR (ion cyclotron resonance) cell cooled to T=80 K. The spectra show an absorption band around 1280 cm⁻¹, which is assigned to the symmetric C−O stretching vibration ν_s. It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n=20. The antisymmetric C−O vibration ν_as is strongly coupled with the water bending mode ν₂, causing a broad feature at approximately 1650 cm⁻¹. For larger clusters, an additional broad and weak band appears above 1900 cm⁻¹ similar to bulk water, which is assigned to a combination band of water bending and libration modes. Quantum chemical calculations provide insight into the interaction of CO₂^.− with the hydrogen-bonding network.     

The iso­thio­cyanate complex of tri­phenyl­borane forms an unusual coordination polymer with [K(18‐crown‐6)]+, both in the solid state and in solution

The title salt, (1,4,7,10,13,16‐hexa­oxa­cyclo­octa­decane‐κ⁶O)[(iso­thio­cyanato)­tri­phenyl­borato‐κS]­potassium(I), [K(C₁₉H₁₅BNS)(C₁₂H₂₄O₆)] or [K(SCNBPh₃)(18‐crown‐6)], where 18‐crown‐6 is 1,4,7,10,13,16‐hexaoxa­cyclo­octa­decane and [SCNBPh₃]⁻ is the (iso­thio­cyanato)­tri­phenyl­borate anion, exhibits a supramol­ecular structure that is best described as a helical coordination polymer or molecular screw. This unusual supramolecular structure is based on a framework in which the SCN⁻ ion bridges the chelated K⁺ ion and the B atom of BPh₃ in a μ₂ fashion. The X‐ray crystal structure of the title salt has been determined at 100 (1) and 293 (2) K. The K⁺ ion exhibits axial ligation by the S atom of the [SCNBPh₃]⁻ anion, with a K—S distance of 3.2617 (17) Å (100 K). The trans‐axial ligand is an unexpected η²‐bound C=C bond of a phenyl group (meta‐ and para‐C atoms) that belongs to the BPh₃ moiety of a neighboring mol­ecule. The K—C bond distances span the range 3.099 (3)–3.310 (3) Å (100 K) and are apparently retained in CDCl₃ solution (as evidenced by ¹³C NMR spectroscopy). By virtue of the latter interaction, the supramolecular structure is a helical coordination polymer, with the helix axis parallel to the b axis of the unit cell. IR spectroscopy and semi‐empirical molecular orbital (AM1) calculations have been used to investigate further the electronic structure of the [SCNBPh₃]⁻ ion.     

catena‐Poly[bis(μ‐2,2′‐bipyridin‐6‐olato)‐κ3N,N′:O;O:N,N′‐dicopper(I,II) [[tetrafluoridoniobium(V)]‐μ‐oxido]]

A novel copper–niobium oxyfluoride, {[Cu₂(C₁₀H₇N₂O)₂][NbOF₄]}_n, has been synthesized by a hydrothermal method and characterized by elemental analysis, EDS, IR, XPS and single‐crystal X‐ray diffraction. The structural unit consists of one C₂‐symmetric [NbOF₄]⁻ anion and one centrosymmetric coordinated [Cu₂(obpy)₂]⁺ cation (obpy is 2,2′‐bipyridin‐6‐olate). In the [NbOF₄]⁻ anion, each Nb^V metal centre is five‐coordinated by four F atoms and one O atom in the first coordination shell, forming a square‐pyramidal coordination geometry. These square pyramids are then further connected to each other via trans O atoms [Nb—O = 2.187 (3) Å], forming an infinite linear {[NbOF₄]⁻}_n polyanion. In the coordinated [Cu₂(obpy)₂]⁺ cation, the oxidation state of each Cu site is disordered, which is confirmed by the XPS results. The disordered Cu sites are coordinated by two N atoms and one O atom from two different obpy ligands. The [NbOF₄]⁻ and [Cu₂(obpy)₂]⁺ units are assembled via weak C—H...F hydrogen bonds, resulting in the formation of a three‐dimensional supramolecular structure. π–π stacking interactions between the pyridine rings [centroid–centroid distance = 3.610 (2) Å] may further stabilize the crystal structure.     

Potassium carbamoyldi­cyano­methanide

The crystal structure of the title compound, K[(CN)₂CC(O)NH₂)] or K⁺·C₄H₂N₃O⁻, conventionally abbreviated as Kcdm, where cdm is carbamoyldi­cyano­methanide, is described. The bond lengths and angles of the cdm cation are comparable to those reported previously for [M(cdm)₂(H₂O)₄]·2H₂O (M = Ni, Mn and Co). The K atoms are coordinated to four nitrile N atoms and two carbonyl O atoms in a distorted trigonal prismatic fashion, with two further N atoms semicoordinated through the centers of two prism side faces. This coordination leads to the formation of mixed anion–cation sheets parallel to the ab plane, which are joined together via hydrogen‐bonding interactions. The cdm anion is potentially useful for the formation of transition metal coordination polymers, in which magnetic superexchange could occur through a bidentate cdm bridge. Kcdm provides a model compound by which the molecular geometry of the cdm anion can be analyzed.     

New coordination modes in potassium edta salts: K2[H2edta]·2H2O,K3[Hedta]·2H2O and K4[edta]·3.92H2O

Three potassium edta (edta is ethylenediaminetetraacetic acid, H₄Y) salts which have different degrees of ionization of the edta anion, namely dipotassium 2‐({2‐[bis(carboxylatomethyl)azaniumyl]ethyl}(carboxylatomethyl)azaniumyl)acetate dihydrate, 2K⁺·C₁₀H₁₄N₂O₈²⁻·2H₂O, (I), tripotassium 2,2′‐({2‐[bis(carboxylatomethyl)amino]ethyl}ammonio)diacetate dihydrate, 3K⁺·C₁₀H₁₃N₂O₈³⁻·2H₂O, (II), and tetrapotassium 2,2′,2′′,2′′′‐(ethane‐1,2‐diyldinitrilo)tetraacetate 3.92‐hydrate, 4K⁺·C₁₀H₁₂N₂O₈⁴⁻·3.92H₂O, (III), were obtained in crystalline form from water solutions after mixing edta with potassium hydroxide in different molar ratios. In (II), a new mode of coordination of the edta anion to the metal is observed. The HY³⁻ anion contains one deprotonated N atom coordinated to K⁺ and the second N atom is involved in intramolecular bifurcated N—H...O and N—H...N hydrogen bonds. The overall conformation of the HY³⁻ anions is very similar to that of the Y⁴⁻ anions in (III), although a slightly different spatial arrangement of the –CH₂COO⁻ groups in relation to (III) is observed, whereas the H₂Y²⁻ anions in (I) adopt a distinctly different geometry. The preferred synclinal conformation of the –NCH₂CH₂N– moiety was found for all edta anions. In all three crystals, the anions and water molecules are arranged in three‐dimensional networks linked via O—H...O and C—H...O [and N—H...O in (I) and (II)] hydrogen bonds. K...O interactions also contribute to the three‐dimensional polymeric architecture of the salts.     

Structures and magnetic properties of two series of Schiff base binuclear lanthanide complexes

Until now, although there are many examples of studying the magnetic properties of Schiff base binuclear lanthanide complexes, the relationship between the structure and magnetic properties of the complexes still is worth further investigation in order to improve the magnetic properties of Schiff base lanthanide complexes. In this work, we successfully obtained two series of binuclear Ln complexes by in situ reaction of 4-diethylaminosalicylaldehyde, benzoic hydrazide and different lanthanide salts at 80°C under solvothermal conditions, namely, [Ln₂(L)₃(NO₃)₃]·CH₃CN·CH₃OH·H₂O [Ln = Dy ( 1 ), Ho ( 2 ), Gd ( 3 ) L = deprotonated 4-diethylamino salicylaldehyde benzoylhydrazine], [Ln₂(L)₄(CH₃COO)]CH₃COO·CH₃CN [Ln = Dy ( 4 ), Ho ( 5 ), Gd ( 6 )]. The complex 1 contains three Schiff base ligands L, two Dy (III) ions, and three NO₃⁻. The ligand H₁L is formed by in situ Schiff base reaction with 4-diethylaminosalicylaldehyde and benzoic hydrazide with the participation of Ln (NO₃)₃. When replacing Ln (NO₃)₃ with Ln (OAc)₃, obtained three μ₂-OAc bridged binuclear Ln (III) complexes. The magnetic study showed that complex 4 exhibits field-induced single-molecule magnet (SMM) behavior while complex 1 does not show any SMMs behavior. In addition, we have studied the magnetocaloric effect of complexes 3 and 6 , their maximum −ΔS_m values are 21.37 J kg⁻¹ K⁻¹ and 15.32 J kg⁻¹ K⁻¹, respectively, under ΔH = 7 T and T = 2 K.