Structural investigation of cellulose Iα and Iβ by 2D RFDR NMR spectroscopy: determination of sequence of magnetically inequivalent d-glucose units along cellulose chain

In our previous studies of the crystal structure of native cellulose (cellulose I) by solid-state two-dimensional (2D) ¹³C–¹³C INADEQUATE, it was revealed that cellulose I_α contains two kinds of β-d-glucose residues (A and A′) in the unit cell and that cellulose I_β contains another two kinds of residues (B and B′). In the present study, the sequence of residues A and A′ along the same chains in cellulose I_α and that of residues B and B′ in I_β were investigated by 2D ¹³C–¹³C rotor-synchronized radiofrequency-driven recoupling (RFDR) experiments using, respectively, uniformly ¹³C₆-labeled (U−¹³C₆) bacterial cellulose and the same [U−¹³C₆] cellulose sample after thermal treatment at 260 °C. The RFDR spectra recorded with a short mixing time (1.0 ms) showed dipolar-coupled ¹³C spin pairs of only the neighboring carbon of the both phases, while those recorded with a longer mixing time (3.0–15 ms) provided correlations between weakly coupled ¹³C spin pairs as well as strongly coupled ¹³C spin pairs such as neighboring carbon nuclei. In the RFDR spectrum of the [U−¹³C₆] cellulose recorded with a mixing time of 15 ms, the inter-residue ¹³C–¹³C correlation between C4 of residue A and C2 of residue A′ and that between C3 of residue A and C4 of residue A′ were clearly observed. In the case of cellulose I_β, however, inter-residue ¹³C–¹³C correlations between residues B and B′ could not be detected in the series of RFDR spectra recorded with different mixing times of annealed [U−¹³C₆] cellulose. From these findings, that cellulose I_α was revealed to have the –A–A′– repeating units along the cellulose chain. For cellulose I_β, it was revealed that the respective residues B and B′ are composed of independent chains (–B–B– and –B′–B′– repeating units) and that there are no –B–B′– repeating units in the chain.     

Mathematische und experimentelle Studien an wiederholten Auszügen aus Adsorptionssystemen,die sich im Gleichgewicht befinden,II

Zusammenfassung Die an den in einer vorangehenden Abhandlung aufgestellten Gleichungen der wiederholten Auszüge x^p=(x₀ ^p- K) (1−r)^pq+K (A) oder x^p=A_x(1−r)^pq+K (a)θ ^p=θ ₀ ^p −K _θ )(1−r)^pq+K _θ (B) oderθ ^p=A _θ (1−r)^pq+K _θ (b) angestellten überlegungen betrafen unter anderem die Bestimmung der Parameter A_x, A _θ , K und K _θ durch graphische Darstellung. Es wurde auch der auf die Werte von K und K _θ ausgeübte Einflu?, der durch ?nderung von m, der Menge des Adsorbenten, und von V, des Volumens der L?sung, infolge einer ?nderung in der quantitativen Zusammensetzung des Systems entstand, er?rtert. Es wurde auf die Verkleinerung von K und K _θ , die nach einer gewissen Zahl von Auszügen infolge einer zu starken Verdünnung der L?sung des Systems eintreten mu?, aufmerksam gemacht. Diese Verkleinerung erkl?rt sich aus der Anwesenheit des Koeffizienten a und des Exponenten n der Adsorptionsisotherme in den Gleichungen ; denn die beiden Werte von α und n sind nur für einen beschr?nkten Konzentrationsbereich praktisch konstant. Es wurde auch gefunden, da? die Werte vonθ, der Substanzmenge in L?sung, oder von x, der Konzentration in 1 ccm, die nach einem Auszug einer beliebigen Ordnung bestimmt wurden, den Gleichungen (b) und (a) für die Werte p′ von p, die andere sind als der zum untersuchten System geh?rende Wert, genügen unter der Bedingung, für K, K _θ , A_x und A _θ angemessene Werte zu finden. Die oben erw?hnte Schlu?folgerung gilt auch für p=1. Man erh?lt die beiden Gleichungen x=A′(1−r)^q+ K′ (E)θ=A (1−r)^q+K′θ, (F) die x undθ, die einer Auszugsordnung q entsprechen, direkt ergeben. Die Parameter A′, A, K′ und K′θ k?nnen graphisch ermittelt werden. Multipliziert man die Gleichung (F) mit r, dem bei dem Auszug entnommenen Volumteil, so erh?lt man die dem System durch einen Auszug entzogene Substanzmenge a_q: a_q=rA(1−r)^q−1+ c, (G) wo c=rK′θ. Am Schlu? der Abhandlung wird auf bestimmte Vorteile der Gleichungen (F) und (G) aufmerksam gemacht. I. Teil: Kolloid-Z.66, 322 (1934). übersetzt von E. Lottermoser (Leipzig).     

Quenching of Li (2P) by H2: potential energy surfaces, conical intersection seam, and diabatic bases

The quenching of Li (1s ²2p; ²P) to Li (1s ²2s; ²S) by H₂ is considered using coupled-cluster and multireference configuration-interaction techniques. C _{2 v} (²A₁, ²B₂) and C _{∞ v} (²Π,²Σ⁺) sections of the 1²A^′ and 2²A^′ potential energy surfaces are determined. The C _{2 v} portion of the 1²A^′−2²A^′ seam of conical intersection is studied. Perhaps the most significant finding is a surprising trifurcation of this seam into a portion with only C _s symmetry and the aforementioned C _{2 v} portion. The adiabatic-to-diabatic state transformation is considered in the vicinity of the seam of conical intersection using both perturbation theory and the dipole moment operator. The ²B₂ section of the 2²A^′ potential energy surface exhibits an exciplex in the general vicinity of the seam of conical intersection. The ²Π section of the 2²A^′ potential energy surface possesses a global minimum lying 1.86kcal/mol below the Li (²P)+H₂ asymptote. A van der Waals-like minimum with C _{∞ v} symmetry was found on the 1²A^′ potential energy surface. Received: 14 August 1998 / Accepted: 20 August 1998 / Published online: 11 November 1998     

Syntheses of the eight-coordinate NH4[ErIII(Cydta)(H2O)2] · 4.5H2O and (NH4)2[Er 2III (Pdta)2(H2O)2] · 2H2O complexes and their structural investigation

In this work, the title complexes, NH₄[Er^III(Cydta)(H₂O)₂] · 4.5H₂O (I) (H₄Cydta = trans-1,2-cyclo-hexanediamine-N,N,N′,N′-tetraacetic acid) and (NH₄)₂[Er₂^III(Pdta)₂(H₂O)₂] · 2H₂O (II) (H₄Pdta= propylene-diamine-N,N,N′,N′-tetraacetic acid), were prepared, respectively, and their composition and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques. Complex I selects a mononu-clear structure with pseudosquare antiprismatic geometry crystallized in the triclinic crystal system with space group $ P\bar 1 $ P\bar 1 and the central Er³⁺ ion is eight-coordinated by the hexadentate Cydta ligand and two water molecules. The crystal data are as follows: a = 8.568(3), b = 10.024(3), c = 14.377(4) ?, α = 88.404(4)°, β = 75.411(4)°, γ = 88.332(4)°, V = 1194.2(6) ?³, Z = 1, ρ _c = 1.793 g/cm³, μ = 3.586 mm⁻¹, F(000) = 648, R = 0.0257, and wR = 0.0667 for 4169 observed reflections with I ≥ 2σ(I). Complex II is eight-coordinated as well, which selects a binuclear structure with two pseudosquare antiprismatic geometry and crystallizes in the monoclinic crystal system with space group P2₁/n. The central Er³⁺ ion is coordinated by two nitrogens and four oxygens from one hexadentate Pdta ligand. Besides, two oxygens come from one carboxylic group of the neighboring Pdta ligand and one water molecule, respectively. The crystal data are as follows: a = 12.7576(8), b = 9.3151(6), c = 14.3278(9) ?, β = 96.1380(10)°, V = 1692.93(19) ?³, Z = 4, ρ _c = 2.054 g/cm³, μ = 5.015 mm⁻¹, F(000) = 1028, R= 0.0228, and wR = 0.0534 for 2984 observed reflections with I ≥ 2σ(I).     

Electrochemical Studies on <Emphasis Type="Italic">cis</Emphasis>-[Cr<Superscript>III</Superscript>(bipy)<Subscript>2</Subscript>(SCN)<Subscript>2</Subscript>]I<Subscript>3</Subscript> (Where bipy Denotes 2,2′-Bipyridine) in Acetonitrile

The molar conductivities (Λ) of solutions of bis(2,2′-bipyridine)bis(thiocyanate)chromium(III) triiodide [Cr^III(bipy)₂(SCN)₂]I₃ (where bipy denotes 2,2′-bipyridine, C₁₀H₈N₂), [ _3^-\mathrm{A}^{+}\mathrm{I}_{3}^{-} ], were measured in acetonitrile (ACN) at the temperatures 294.15, 299.15, and 305.15 K. In addition, cyclic voltammograms (CVs) of [ A⁺I₃^-\mathrm{A}^{+}\mathrm{I}_{3}^{-} ] were recorded on platinum, gold, and glassy carbon working electrodes in ACN, using n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as the supporting electrolyte, at scan rates (v) ranging from 0.05 to 0.12 V⋅s⁻¹. Furthermore, electrochemical impedance spectroscopic (EIS) measurements were carried out in the frequency range 50 Hz<f<50 kHz using these three working electrodes. The measured molar conductivities (Λ) demonstrate that [ A⁺I₃^-\mathrm{A}^{+}\mathrm{I}_{3}^{-} ] behaves as uni-univalent electrolyte in ACN over the investigated temperature range. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ _o), as well as the thermodynamic association constants (K _A), at each experimental temperature for formation of [A⁺ I₃^-\mathrm{I}_{3}^{-} ] ion-pairs. The limiting ionic conductivities ( l_±^o\lambda_{\pm}^{\mathrm{o}} ), the diffusion coefficients at infinite dilution (D _±), as well as the Stokes’ radii (r _St) were determined for both A⁺ and I₃^-\mathrm{I}_{3}^{-} ions. The thermodynamic parameters for the ionic association process, i.e. the Gibbs energy ( DG_A^o\Delta G_{\mathrm{A}}^{\mathrm{o}} ), enthalpy ( DH_A^o\Delta H_{\mathrm{A}}^{\mathrm{o}} ), and entropy ( DS_A^o\Delta S_{\mathrm{A}}^{\mathrm{o}} ), were also determined. The mobility and diffusivity of the A⁺ ion increase linearly with increasing temperature because the solvent medium becomes less viscous as the temperature increases. The K _A values indicate that significant ion association occurs that is not influenced by temperature changes. The ion-pair formation process is exothermic ( DH_A^o < 0\Delta H_{\mathrm{A}}^{\mathrm{o}}<0 ), leading to the generation of additional entropy ( $\Delta S_{\mathrm{A}}^{\mathrm{o}}>0$\Delta S_{\mathrm{A}}^{\mathrm{o}}>0 ). As a result, the Gibbs energy DG_A^o\Delta G_{\mathrm{A}}^{\mathrm{o}} is negative ( DG_A^o < 0\Delta G_{\mathrm{A}}^{\mathrm{o}}<0 ) and the formation of [A⁺I₃^-][\mathrm{A}^{+}\mathrm{I}_{3}^{-}] becomes favorable. CV studies on [A⁺I₃^-][\mathrm{A}^{+}\mathrm{I}_{3}^{-}] solutions indicated that the redox pair Cr^3+/2+ appears to be quasi-reversible on a glassy carbon electrode but is completely irreversible on platinum and gold electrodes. EIS experiments confirm that, among these three electrodes, the glassy carbon working electrode has the smallest resistance to electron transfer.     

(18-Crown-6)potassium tetrachloroferrate(III), dibromodichloroferrate(III), and tetrabromoferrate(III): Synthesis and crystal structures

Three new crystalline complexes are synthesized: [K(18-crown-6)]⁺ · An, where An = [FeCl₄]^?(I), [FeBr₂Cl₂]^? (II), and [FeBr₄]^? (III). The crystals of compounds I–III are cubic and isomorphic, space group Fd $ \bar 3 Three new crystalline complexes are synthesized: [K(18-crown-6)]⁺ · An, where An = [FeCl₄]⁻(I), [FeBr₂Cl₂]⁻ (II), and [FeBr₄]⁻ (III). The crystals of compounds I–III are cubic and isomorphic, space group Fd (Z = 16): a = 20.770(2) ? for I, 20.844(3) ? for II, and 20.878(4) ? for III. Structures I–III are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.047 (I), 0.059 (II), and 0.098 (III) for all 680 (I), 684 (II), and 686 (III) independent reflections. In two tetrahedral anions [Fe(1)X₄]⁻ and [Fe(2)X₄]⁻ in structures I–III, all halogen atoms (X = Cl and Br) are randomly disordered over three close positions relative to the crystallographic axes 3. Structures I–III contain the [K(18-crown-6)]⁺ host-quest complex cation. The K⁺ cation (CN = 8) resides in the cavity of the 18-crown-6 ligand and coordinated by its six O atoms and two disordered halogen X atoms. The coordination polyhedron of the K⁺ cation in complexes I–III is a distorted hexagonal bipyramid. Original Russian Text ? A.N. Chekhlov, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 9, pp. 1566–1570.     

Synthesis and structures of nine-coordinate K[SmIII (Edta)(H2O)3] · 2H2O and Ten-Coordinate K2[SmIII(Pdta)(H2O)2]2 · 4.5H2O complexes

The title complexes, K[Sm^III(Edta)(H₂O)₃] · 2H₂O(I)(H₄Edta = ethylenediamine-N,N,N′,N′-tetraacetic acid) and K₂[Sm^III(Pdta)(H₂O)₂]₂ · 4.5H₂O (II) (H₄Pdta = propylenediamine-N,N,N′,N′-tetraacetic acid), were prepared and their compositions and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques, respectively. Complex I has a mononuclear structure, and the Sm³⁺ ion is nine-coordinated by an Edta ligand and three water molecules, yielding a pseudo-monocapped square antiprismatic conformation, and the complex crystallizes in the orthorhombic crystal system with space group Fdd2. The crystal data are as follows: a = 19.84(5), b = 35.58(9), c = 12.15(3) ?, V = 8580(38) ?³, Z = 16, ρ _c = 1.925 g/cm³, μ = 3.010 mm⁻¹, F(000) = 4976, R = 0.0252, and wR = 0.0560 for 3510 observed reflections with I ≥ 2σ(I). Complex II has a binuclear structure and the Sm³⁺ ion is ten-coordinated by a Pdta ligand, two oxygen atoms from a carboxylic group of adjacent Pdta ligand and two water molecules, yielding a distorted bicapped square antiprismatic prism. The complex crystallizes in the triclinic crystal system with space group P $ \bar 1 $ \bar 1 . The crystal data are as follows: a = 8.9523(15), b = 10.7106(15), c = 11.6900(19) ?, α = 80.613(5)°, β = 80.397(5)°, γ = 76.530(4)°, V = 1065.7(3) ?³, Z = 1, ρc = 1.970 g/cm³, μ = 2.532 mm⁻¹, F(000) = 1620, R = 0.0332 and wR = 0.0924 for 5390 observed reflections with I ≥ 2σ(I).     

Mechanisms for the formation of layered A<Subscript>4</Subscript>B<Subscript>3</Subscript>O<Subscript>12</Subscript> compounds from coprecipitated hydroxocarbonate and hydroxide systems

We have established and analyzed the sequences of phase transitions in synthesis of layered compounds in the A_nB_n–1O_3n family ( \textA₃^\textII\textLnB₃^\textV\textO₁₂ {\text{A}}_3^{\text{II}}{\text{LnB}}_3^{\text{V}}{{\text{O}}_{{12}}} (A^II = Ba, Sr, Ln = La, Nd, B^V = Nb, Ta) and La₄Ti₃O₁₂ with n = 4) from coprecipitated hydroxocarbonate and hydroxide systems, including steps involving the formation, solid-phase reaction, or structural rearrangement of intermediates.     

Theoretical studies on N-loss predissociation mechanisms of N2O+ (A?2Σ+) in Cs symmetry

The N-loss predissociation mechanisms of the A ²Σ⁺ (2 ² A′) state of N₂O⁺ to the first and second dissociation limits were studied in the C _s symmetry. The potential energy curves (PECs) and minimum energy crossing points (MECPs) for the C _s states of N₂O⁺ were calculated at the CAS levels. On the basis of our CAS calculation results (CASPT2 energetic results and CASSCF spin orbit couplings), we suggest two processes for N-loss predissociation mechanisms of A ²Σ⁺ (2 ² A′) to the first and second limits. The first two steps in the two processes are the same: A ²Σ⁺ passes through the 2 ² A′/1 ⁴ A″ MECP and then reaches the 1 ⁴ A″ (1 ⁴Σ⁻) PEC. The 2 ² A′/1 ⁴ A″ MECP has a bent geometry and is slightly higher in energy than the transition state along the 1 ⁴ A″ PEC. Our mechanisms are different from the previously suggested mechanisms (via 1 ⁴Π).     

Spectroscopic study of protonation of oligonucleotides containing adenine and cytosine

Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pK _HL = 9.65 ± 0.04, pK _H2L = 4.18 ± 0.04), adenosine (pK _H2L = 3.59 ± 0.05), cytosine (pK _H2L = 4.56 ± 0.01), cytidine (pK _H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH ⁰ = (−17 ± 4) kJ mol⁻¹, ΔS ⁰ = (23 ± 13) J K⁻¹ mol⁻¹), cytosine (ΔH ⁰ = (−22 ± 1) kJ mol⁻¹, ΔS ⁰ = (13 ± 5) J K⁻¹ mol⁻¹) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)₃, 5′AAA-CCC-CCC3′ = A₃C₆, 5′CCC-AAA-CCC3′ = C₃A₃C₃) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning (C⁺-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature.     

Recurrence and Differential Relations for Spherical Spinors

We present a comprehensive table of recurrence and differential relations obeyed by spin one-half spherical spinors (spinor spherical harmonics) Ω_{κ μ}(n) used in relativistic atomic, molecular, and solid state physics, as well as in relativistic quantum chemistry. First, we list finite expansions in the spherical spinor basis of the expressions A·B Ω_κμ(n) and A·(B×C) Ω_κμ(n), where A, B, and C are either of the following vectors or vector operators: n=r/r (the radial unit vector), e ₀, e _±1 (the spherical, or cyclic, versors), (the 2×2 Pauli matrix vector), (the dimensionless orbital angular momentum operator; I is the 2×2 unit matrix), (the dimensionless total angular momentum operator). Then, we list finite expansions in the spherical spinor basis of the expressions A·B F(r)Ω_κμ(n) and A·(B×C) F(r)Ω_κμ(n), where at least one of the objects A, B, C is the nabla operator , while the remaining ones are chosen from the set .     

New π ligand N,N,N,N′,N′,N′-hexaallylethylenediaminium (L2+): Synthesis and crystal structures of LBr2 · 2H2O and its cuprocomplexes L[CuII(Br0.45Cl3.55)], L[Cu 4I (Br4.55Cl1.45)], and L[Cu 4I Br6]

The alkylation of ethylenediamine with allyl bromide in the presence of a fourfold (with respect to ethylenediamine) molar amount of NaHCO₃ in acetone with an ethanol admixture (15: 1) affords LBr₂ · 2H₂O (I), where L²⁺ is the N,N,N,N′,N′,N′-hexaallylethylenediaminium cation. Single crystals of complexes L[Cu^II(Br_0.45Cl_3.55)] (II), L[Cu₄^I(Br_4.55Cl_1.45)] (III), and L[Cu₄^IBr₆] (IV) are prepared by ac electrochemical synthesis from an ethanolic solution of LBr₂ · 2H₂O, CuCl₂ · 2H₂O (or CuBr₂) at copper wire electrodes. The crystal structures of compounds I–IV are determined by X-ray diffraction analysis. The crystals of complex I are monoclinic: space group P2₁/n, a = 8.544(3), b = 10.404(3), c = 13.350(4) ?, β = 97.29(3)°, V = 1177.2(6) ?³, Z = 2. The bromine anions in compound I are bonded to the L²⁺ cations and water molecules through hydrogen contacts (E)H…Br (E = O, C) of 2.57(3)–2.86(3) ?. The crystals of compounds II–IV are triclinic: space group P . For II: a = 8.762(4), b = 9.163(4), c = 16.500(6) ?, α = 95.62(4)°, β = 96.39(4)°, γ = 111.46(4)°, V = 1211.4(9) ?³, Z = 2; for III: a = 9.074(4), b = 9.435(4), c = 9.829(5) ?, α = 116.12(4)°, β = 104.14(4)°, γ = 100.22(4)°, V = 692.3(6) ?³, Z = 1; for IV isostructural III: a = 9.084(4), b = 9.404(4), c = 9.869(4) ?, α = 116.31(3)°, β = 104.00(3)°, γ = 100.37(3)°, V = 692.1(5) ?³, Z = 1. Unlike the isolated tetrahedral CuX₄²⁻ anion in structure II, an original chain anion (Cu₄X₆²⁻) _n is observed in the structures of π complexes III and IV. Original Russian Text ? M.M. Monchak, A.V. Pavlyuk, V.V. Kinzhibalo, M.G. Mys’kiv, 2009, published in Koordinatsionnaya Khimiya, 2009, Vol. 35, No. 6, pp. 414–419.     

Syntheses and crystal structures of nine-coordinate K2[EuIII(dtpa)(H2O)]·5H2O and Na2[TbIII(Httha)]·6H2O complexes

The title complexes, K₂[Eu^III(dtpa)(H₂O)]·5H₂O (H₅dtpa = diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid), Na₂[Tb^III(Httha)]·6H₂O (H₆ttha = triethylenetetramine-N,N,N′,N′,N″,N″-hexaacetic acid), were prepared, and their compositions and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques. The crystal of K₂[Eu^III(dtpa)(H₂O)]·5H₂O belongs to triclinic crystal system and $ P\bar 1 $ P\bar 1 space group. The crystal data are as follows: a = 8.3540(17), b = 10.147(2), c = 15.059(3) α = 84.63(3)?, β = 82.02(3)°, γ = 83.96(3)°, V = 1253.1(4)?³, Z = 2, R = 0.0325 and wR = 0.1013 for 4407 observed reflections with I ≥ 2σ(I). The [Eu^III(dtpa)(H₂O)]²⁻ has a nine-coordinate pseudo-monocapped square antiprismatic structure, in which the nine coordinate atoms, three N and six O are from one dtpa ligand and one water molecule. The crystal of the Na2[Tb^III(Httha)]·6H₂O belongs to monoclinic system and P2₁/c space group. The crystal data are as follows: a = 10.3976(10), b = 12.7908(13), c = 23.199(2) ? = 90.914(2)°, V = 3084.9(5)?³, Z = 4, R = 0.0309 and wR = 0.0704 for 5429 observed reflections with I ≥ 2σ(I). In the [Tb^III(Httha)]²⁻, the Tb³⁺ ion is nine-coordinated yielding a pseudo-monocapped square antiprismatic conformation, in which the ttha ligand coordinates to the central Tb³⁺ ion with four N atoms and five O atoms. There is a free non-coordinate carboxyl group (−CH₂COOH) that can be modified by some biological molecules having target function.     

Structural determination of new eight-coordinate NH4[EuIII(Cydta)(H2O)2]·4.5H2O and K2[Eu 2III (pdta)2(H2O)2]·6H2O complexes

The NH₄[Eu^III(Cydta)(H₂O)₂]·4.5H₂O (I) (H₄Cydta = trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid) and K₂[Eu₂^III(pdta)₂(H₂O)₂]·6H₂O (II) (H₄pdta = propylenediamine-N,N,N′,N′-tetraacetic acid) complexes are prepared by heat-refluxing and acidity-adjusting methods respectively, and their composition and structures are determined by elemental analyses and single crystal X-ray diffraction techniques. The complex I has a mononuclear structure, crystallizes in the triclinic crystal system with the P[`1]P\bar 1 space group; the central Eu^III ion is eight-coordinated by a hexadentate Cydta ligand and two water molecules. The crystal data are as follows: a = 8.653(4) ?, b = 10.041(4) ?, c = 14.405(6) ?, α = 88.469(6)°, β = 74.892(6)°, γ = 88.256(7)°, V = 1207.5(9) ?³, Z = 1, D _c = 1.731 g/cm³, μ = 2.669 mm⁻¹, F(000) = 638, R = 0.0257, and wR = 0.0667 for 3807 observed reflections with I ≥ 2σ(I). The EuN₂O₆ part in the [Eu^III(Cydta)(H₂O)₂]⁻ complex anion forms a pseudo-square antiprismatic polyhedron. The complex II is eight-coordinate as well; it is a binuclear structure that crystallizes in the monoclinic crystal system with the C ₂/c space group; half of the central Eu^III ion is coordinated by two nitrogen atoms from one hexadentate pdta ligand and six oxygen atoms from the same pdta ligand, one water molecule and carboxylic group from the neighboring pdta ligand respectively. The crystal data are as follows: a = 19.866(3) ?, b = 9.1017(12) ?, c = 21.010(3) ?, β = 104.972(2)°, V = 3670.1(9) ?³, Z = 8, D _c = 2.046 g/cm³, μ = 3.710 mm⁻¹, F(000) = 2240, R = 0.0213 and wR = 0.0460 for 4183 observed reflections with I ≥ 2σ(I). Otherwise, the two EuN₂O₆ parts in the [Eu₂^III(pdta)₂(H₂O)₂]²⁻ complex anion form a pseudo-square antiprismatic polyhedron.     

New nine-coordinate (NH4)3[YbIII(ttha)]·5H2O and eight-coordinate (NH4)[YbIII(pdta)(H2O)2]·5H2O complexes: Structural determination

The (NH₄)₃[Yb^III(ttha)]·5H₂O (I) (H₆ttha = triethylenetetramine-N,N,N′,N″,N‴,N‴-hexaacetic acid) and (NH₄)[Yb^III(pdta)(H₂O)₂]·5H₂O (II) (H₄pdta = propylenediamine-N,N,N′,N′-tetraacetic acid) complexes are synthesized by heat-refluxing and acidity-adjusting methods, and their structures are determined by single crystal X-ray diffraction techniques. These two complexes are all mononuclear structures. The complex I crystallizes in ttha monoclinic crystal system with the P2₁/c space group. The central Yb^III ion is nine-coordinated only by one the ligand, and one non-coordinate carboxyl group is left. The crystal data are as follows: a = 10.321(4) ?, b = 12.744(5) ?, c = 23.203(9) ?, β = 91.082(6)°, V = 3051(2) ?³, Z = 4, D _c = 1.754 g/cm³, μ = 3.150 mm⁻¹, F(000) = 1636, R = 0.0357, and wR = 0.0672 for 6203 observed reflections with I ≥ 2σ(I). The YbN₄O₅ part in the [Yb^III(ttha)]³⁻ complex anion forms a pseudo-monocapped square antiprismatic polyhedron. The complex II is coordinated with one pdta ligand and two water molecules, which form an eight-coordinate structure, and crystallizes in the triclinic crystal system with the P[`1]P\bar 1 space group. The YbN₂O₆ part in the [Yb^III(pdta)(H₂O)₂]⁻ complex anion makes a pseudo-square antiprismatic polyhedron. The crystal data are as follows: a = 9.8923(9)?, b = 10.9627(10) ?, c = 12.2618(11) ?, α = 67.284(5)°, β = 70.956(6)°, γ = 68.741(5)°, V = 1115.97(18) ?³, Z = 2, D _c = 1.843 g/cm³, μ = 4.264 mm⁻¹, F(000) = 618, R = 0.0177, and wR = 0.0409 for 4036 observed reflections with I ≥ 2σ(I).     

A new square niobium cluster {Nb4(μ4-O)I8}2+. Crystal structure of a [Nb4OI8][Mo6I14]2∞ polymer

A crystal structure of a new layered [Nb₄OI₈][Mo₆I1₄]_2∞ polymer containing a previously unknown niobium cluster {Nb₄(μ₄-O)I₈}²⁺ with a μ₄ oxygen atom is determined. The compound crystallizes in the P$\bar 1$\bar 1 triclinic space group with unit cell parameters a = 10.1842(6) ?, b = 10.1880(6) ?, c = 11.5700(6) ?, α = 78.058(2)°, β = 77.944(2)°, γ = 80.738(2)°, V = 1139.85(11) ?³, Z = 1, R _f = 0.0414. The electronic structure of the [{Nb₄(μ₄-O)I₈}I₄]²⁻ cluster complex is calculated.     

Synthesis and Structure of Vitamin B<Subscript>12</Subscript>-Derivatives with a Modified Ribose-Unit

Summary. The acylation at the 5′-OH group of the ribose-unit of vitamin B₁₂ (cyanocobalamin) or of aquocobalamin with two conventional reagents gave mono-acylated B₁₂-derivatives with good to very high selectivity. The site of the modification was deduced from spectral data of the products and was further supported by the crystal structure data of three such modified B₁₂-derivatives. These three B₁₂-derivatives were found to crystallize in the space group P2₁2₁2₁, irrespective of the nature of the appendage. Acylation at 5′-OH has been used to protect (or block) this group in the context of functionalization of 2′-OH or elsewhere in the B₁₂-molecule. Attachment of the bifunctional succinyl-unit has allowed the preparation of further modified derivatives of vitamin B₁₂ and binding of B₁₂-derivatives to biological carriers and other macromolecules. In aqueous solution, 5′-acylcobalamins turned out to be rather susceptible to hydrolytic loss of the acyl-functionality. Bernhard Kr?utler: In memoriam Prof. Karl Schl?gl     

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

The reactions between Fe(Phen)₃²⁺[phen = tris-(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm⁻³ (NaCl/HCl). Plots of k₂ versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (Z_AZ_B) for the reactions of Fe(Phen)₃²⁺ with the chloro-, bromo- and iodo- complexes respectively. Z_AZ_B of ≈ −2 suggests that the charge on these Co^III complexes cannot be −3 but is −1. This suggests the possibility of protonation of these Co^III complexes. Protonation was investigated over the range [H⁺] = 0.0001 −0.06 mol dm⁻³ and the protonation constants K_a obtained are 1.22 × 10³, 7.31 × 10³ and 9.90 × 10² dm⁶ mol⁻³ for X = Cl, Br and I, respectively.     

Synthesis and structures of nine-coordinate K[Dy(Edta)(H2O)3] · 3.5H2O, (NH4)3 [Dy(Ttha)] · 5H2O, and eight-coordinate NH4[Dy(Cydta)(H2O)2] · 4.5H2O complexes

The title complexes, K[Dy(Edta)(H₂O)₃] · 3.5 H₂O (I) (H₄Edta = ethylenediamine-N,N,N′,N′-tetraacetic acid), (NH₄)₃[Dy(Ttha)] · 5H₂O (II) (H₆Ttha = triethylenetetramine-N, N,N′,N″,N‴,N‴-hexaacetic acid), and NH₄[Dy(Cydta)(H₂O)₂] · 4.5H₂O (III) (H₄Cydta = trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid), were prepared, and their compositions and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques, respectively. In complex I, the Dy³⁺ ion is nine-coordinated by an Edta ligand and three water molecules, yielding a pseudo-monocapped square antiprismatic conformation, and the complex crystallizes in the orthorhombic crystal system with space group Fdd2. The crystal data are as follows: a = 19.751(7), b = 35.573(12), c = 12.227(4) ?, V = 8591(5) ?³, Z = 16, space group Fdd2 ρ_c = 1.877 g/cm³, μ = 3.742 mm⁻¹, F(000) = 4800, R = 0.0259, and wR = 0.0616 for 3218 observed reflections with I ≥ 2σ(I). For complex II, the Dy³⁺ ion is nine-coordinated by a Ttha ligand, yielding a pseudo-monocapped square antiprismatic conformation, and the complex crystallizes in the monoclinic crystal system with space group P2₁/c. In addition, there is a free non-coordinate carboxyl group (-CH₂COO⁻) in the [Dy(Ttha)]³⁻ complex anion. The crystal data are as follows: a = 10.353(3), b = 12.746(4), c = 23.141(7) ?, β = 91.005(5)°, V = 3053.2(15) ?³, Z = 4, space group P2₁/c ρ_c = 1.730 g/cm³, μ = 2.532 mm⁻¹, F(000) = 1620, R = 0.0332 and wR = 0.0924 for 5390 observed reflections with I ≥ 2σ(I). For complex III, the Dy³⁺ ion is eight-coordinated by a ligand Cydta and two water molecules, yielding a distorted square antiprismatic conformation, and the complex crystallizes in the triclinic system with space group P . The crystal data are as follows: a = 8.604(3), b = 10.012(4), c = 14.369(6) ?, α = 88.330(6)°, β = 75.363(6)°, γ = 88.285(6)°, space group P V = 1196.9(8) ?³, Z = 2, ρ_c = 1.776 g/cm³, μ = 3.194 mm⁻¹, F(000) = 644, R = 0.0445 and wR = 0.1041 for 3931 observed reflections with I ≥ 2σ(I). The article is published in the original.     

Estimation of the critical temperature of thermal explosion for azido-acetic-acid-2-(2-azido-acetoxy)-ethylester using non-isothermal DSC

A method for estimating the critical temperatures (T _b) of thermal explosion for energetic materials is derived from Semenov’s thermal explosion theory and the non-isothermal kinetic equation dα/dt=A ₀ T ^B f(α)e^−E/RT using reasonable hypotheses. The final formula of calculating the value of T _b is $ \left( {\frac{B} {{T_b }} + \frac{E} {{RT_b^2 }}} \right) $ \left( {\frac{B} {{T_b }} + \frac{E} {{RT_b^2 }}} \right) (T _b−T _e0=1. The data needed for the method, E and T _e0, can be obtained from analyses of the non-isothermal DSC curves. When B=0.5 the critical temperature (T _b) of thermal explosion of azido-acetic-acid-2-(2-azido-acetoxy)-ethylester (EGBAA) is determined as 475.65 K.