Preferred exocyclic-amino coordination of W(CO)5 on 2-aminopyrimidine and 4-aminopyrimidine vs. heterocyclic N-1 coordination for 2-aminopyridine

2-Aminopyrimidine (2-ampym) and 4-aminopyrimidine (4-ampym) coordinate to W(CO)₅ predominantly via the exocyclic amino group (>91% in 10 min photolysis) rather than to the endocyclic N-1 position as found for 2-aminopyridine (2-ampy). Photolysis of W(CO)₆ in acetone in the presence of these ligands forms amino-bound [W(CO)₅(2-ampym)] and [W(CO)₅(4-ampym)] complexes. Secondary photolysis generates 18% (1.0 h photolysis) [W(CO)₄(2-ampym)] or [W(CO)₄(4-ampym)], chelated via the exocyclic amine and the adjacent endocyclic position (N-1 and N-3, respectively). Only ca. 10% of the more unhindered N-1-bound W(CO)₅(4-ampym) was detected compared to virtually complete coordination via the exocyclic amino group for [W(CO)₅(2-ampym)]. M 94 calculations show that the W(CO)₅ coordination to the exocyclic donor is favored by 98.8 and 95.6 kcal/mol over the adjacent endocyclic position in the 2-ampym and 4-ampym complexes, respectively. Calculated W–N bond lengths by the M 94 methods gave exo-amine W–N bond distances of 2.24 and 2.26 Å and theoretical adjacent endocyclic W–N bond distances of 2.37 and 2.35 Å (isomers not observed from photolysis) for the 2-ampym and 4-ampym complexes, respectively. A W–(N-1) bond of 2.28 Å for this isomer of [W(CO)₅(4-ampym)] was calculated. All W–N bonds are near the 2.18–2.33 Å range (mean of 2.27±0.06) for [W(CO)₅L] (L=pyridine, piperidine, glycine, 1-(2-py)-1,2,4-triazole, [W(CO)₅CN]⁻, 5-MeU⁻).     

Structure refinement of the as-synthesized and the calcined form of zeolite RUB-3 (RTE)

The structure analysis based on single crystal and powder data revealed that the framework structure of RUB-3 (structure type code RTE) consists of small [4⁴5⁴6²] building units and medium–large [4⁶5⁴6⁶8²] cages with a free volume of ca. 300 ų. Interconnected cages form a one-dimensional channel system with narrow, slightly elliptical pore openings (free diameter 3.6×4.3 Ų). ¹H–¹³C CP MAS NMR spectroscopy proved that the cages are occupied by disordered (±)-exo-2-aminobicyclo[2.2.1]heptane molecules which were used as templates during the synthesis. The unit cell composition of as-synthesized RUB-3 is (C₇H₁₃N)₂·[Si₂₄O₄₈]. The lattice parameters, bond lengths, bond angles and unit cell volumes are nearly identical for the as-synthesized [a=14.039(2) Å, b=13.602(2) Å, c=7.428(1) Å, β=102.22(3)°] and calcined form [a=14.018(1) Å, b=13.612(1) Å, c=7.418(1) Å, β=102.12(1)°] of RUB-3. The RTE structure even keeps its symmetry (C2/m) during the calcination process, indicating that the RTE framework topology is very rigid. All crystals are four-fold twins with twin planes {110}.     

A hemidirected 1-D coordination polymer [Pb2(H2O)2(HBTC)2] · 3H2O extended in holodirected 3-D by weak Pb–O interactions

A new complex, [Pb₂(H₂O)₂(HBTC)₂] · 3H₂O (H₃BTC = 1,3,5-Benzenetricarboxylic acid) (1), has been synthesized under hydrothermal condition. The single-crystal analysis shows that 1 consists of 1-D double-chains with Pb(II) six-coordinated by three H₃BTC and one H₂O molecule with the Pb–O bond distances in the range of 2.56–2.76 Å. When the Pb–O bonding limit extends from 2.76 to 2.90 Å, the potential weak bonds of Pb–O can be found and the coordination number of Pb will increase from six to nine. As a result, the coordination geometry of Pb(II) transforms from hemidirected to holodirected and an infinite 3-D framework is obtained by the connection of the double-chains. The IR spectrum and the TGA–DTA curve of 1 are also reported in this paper.     

Effect of metal additives on the physico-chemical characteristics of activated carbon exemplified by benzene and acetic acid adsorption

The effects of treatment with inorganic salts exemplified by Mg (NO₃)₂ or Ba (NO₃)₂ on the physical-chemical characteristics of activated carbon were studied. Results indicate that the pore volume remains relatively unchanged upon salt treatment when the pore diameter ranges between 7 Å and 20 Å. Significant variation in pore volume was observed when pore diameter is less than 7 Å; generally, the pore volume of AC is greater than AC–Ba and AC–Mg. Major oxygen functional groups such as hydroxyl group for AC, carboxyl group for AC–Ba, and hydroxyl and carbonyl groups for AC–Mg were created. Regenerated at a temperature of 400°C, creates more pore volume especially when treated with Mg(NO₃)₂ with an increase of 13.0%. The regenerated AC–Mg exhibits the greatest acetic acid adsorption capacity among all activated carbons studies.     

Diplatinum(III) [Cl2(μ2-amidinate)4] compound derived from air oxidation of mononuclear cis-[Pt(NH3)2(amidine-κ)2] complex

The dinuclear platinum(III) complex [Pt₂Cl₂{μ₂-N(H)C(Et)N(H)}₄] (2) has been prepared by heating cis-[Pt(NH₃)₂{NHC(NH₂)Et}₂](Cl)₂ (cis-1) under aeration conditions in an EtOH/H₂O mixture at 70 °C for 2 d and it was characterized by elemental analyses (C, H, N), ESI⁺-MS, IR, ¹H and ¹³C NMR spectroscopies and also by X-ray diffraction. Complex 2 represents the second Pt^III dimer stabilized by the amidinate ligand ever known and it has a lantern-type structure with four amidinate ligands bridging two Pt^III centers with Pt–Pt distance of 2.4809(2) Å.     

Structure of a methylamine sorption complex of fully dehydrated Cd-exchanged zeolite X, Cd46(CH3NH2)16[Si100Al92O384]-FAU

The structure of a methylamine sorption complex of fully dehydrated, fully Cd²⁺-exchanged zeolite X, Cd₄₆(CH₃NH₂)₁₆[Si₁₀₀Al₉₂O₃₈₄]-FAU (a = 24.863(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group at 21(1) °C. An aqueous exchange solution 0.05 M in Cd²⁺ was allowed to flow past the crystal for 5 days. The crystal was then dehydrated at 480 °C and 2 × 10⁻⁶ Torr for 2 days (colorless), and exposed to 160 Torr of methylamine gas at 21(1) °C for 2 h (yellow). Diffraction data were then gathered in this atmosphere and were refined using all data to the final error indices (based upon the 524 reflections for which F_o > 4σ(F_o)) of R₁ = 0.069 and wR₂ = 0.200. In this structure, Cd²⁺ ions occupy three crystallographic sites. The octahedral sites I at the centers of the hexagonal prisms are filled with 16 Cd²⁺ ions per unit cell (Cd–O = 2.369(8) Å). The remaining 30 Cd²⁺ ions are located at two non-equivalent sites II with occupancies of 14 and 16. The 16 methylamine molecules per unit cell lie in the supercage where each interacts with one of the latter 16 site-II Cd²⁺ ions: N–Cd = 2.11(8) Å. The imprecisely determined N–C bond length, 1.49(22) Å, agrees with that in gaseous methylamine, 1.474 Å. The positions of the hydrogen atoms were calculated. It appears that one of the amino hydrogen atoms hydrogen bonds to a 6-ring oxygen, and that the other forms a bifurcated hydrogen bond to this and another 6-ring oxygen. The methyl group is not involved in hydrogen bonding.     

Hydrogen generation by catalytic gasification of motor oils in an integrated fuel processor

Catalytic gasification of waste motor oil (MO) for the generation of high purity of hydrogen and then integrated to a proton exchange membrane fuel cell (PEMFC) is economically and environmentally attractive. Thus, the objective of the present work was to investigate a MO catalytic gasification for generating high-purity hydrogen with 15 wt.% NiO/Al₂O₃ catalysts. In a lab-scale fixed-bed downdraft experimental approach, catalytic gasification of MO was accompanied by a substantial production of syngas at 760–900 K. From the XANES spectra, most of the Ni(II) reduced to Ni(0) was found in the MO catalytic gasification process. The EXAFS data also showed that the central Ni atoms have a Ni–O and a Ni–Ni with bond distances of 2.04 ± 0.05 Å and 2.48 ± 0.05 Å, respectively. In addition to over 85% of syngas generation, approximately 8.35 × 10⁵ kcal h⁻¹ of thermal energy was recovered and cold gas efficiency (CGE) was 77–84% when the catalytic gasifier was operated at O/C atomic ratios between 1.1 and 1.3. The proposed syngas production unit can be integrated in a fuel processor (e.g. PEMFC), in order to separate and purify the syngas to yield a 99.99% hydrogen stream. Moreover, cost or benefit analyses of MO catalytic gasifiers of 10- and 20-TPD (tons per day) were also performed.     

A novel polyoxometalate chain constructed from sandwich lanthanide-containing polyanion [Ce(PW11O39)2] and sodium ion linker

A novel sandwich-type lanthanide polyoxometalate (NH₄)₂[N(CH₃)₄]₆Na₂[Ce(PW₁₁O₃₉)₂] · 14H₂O (1) has been synthesized and characterized by cyclic voltammetry, IR spectroscopy and single crystal X-ray diffraction. X-ray diffraction result reveals that the sandwich-type polyanions are linked by sodium ions to form a structure of zigzag chains, and the chains are further connected into an extensive two-dimensional (2D) framework depending on hydrogen bond.     

[Zn(BDC)(H2O)2]n: a novel blue luminescent coordination polymer constructed from BDC-bridged 1-D chains via interchain hydrogen bonds (BDC = 1,4-benzenedicarboxylate)

A novel coordination polymer [Zn(BDC)(H₂O)₂]_n 1 (where BDC = 1,4-benzenedicarboxylate), has been synthesized and characterized by X-ray diffraction. 1 crystallizes in the monoclinic space group C2/c, a=15.09(2) Å, b=5.058(7) Å, c=12.196(16) Å, β=103.62(2)°, , Z=4. The most striking feature of 1 is that it consists of a high-dimensional network structure constructed from BDC-bridged 1-D chains via interchain hydrogen bonds. The coordination sphere of the zinc(II) ion is a distorted tetrahedron completed by four oxygen atoms from two water molecules and two BDC ligands. BDC adopts the bis-monodentated (syn–anti) coordination mode linking two adjacent zinc(II) ions. 1 shows strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state.     

Investigation of Co–B–S system as anode material for secondary alkaline battery

A series of novel Co–S–B systems were prepared by simple chemical reduction method as the anode material for secondary alkaline batteries. The prepared samples were investigated by inductivity coupled plasma optical emission spectrum (ICP), Brunauer–Emmetr–Teller (BET) method, scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray energy dispersive spectroscopy (EDS) and charge–discharge method. It was found that the BET surface area of Co–S–B system increases and its particle size decreases with increasing the sulfur content. Sulfur incorporation suppresses initial capacity fading of Co–B compound due to irreversible dissolution of boron, and Co–S–B electrodes show enhanced electrochemical capacity and excellent cycle performance. The discharge capacity of Co_75.4B₁₇S_7.6 reaches 513.6 mAh/g at a moderate current density of 100 mA/g and 470 mAh/g after 60 cycles, which is about 1.5 times that of conventional AB₅-type alloy. A proper mechanism was proposed to explain the electrochemical reaction process of Co–S–B electrode.     

Time-of-flight Rietveld neutron structure refinement and quantum chemistry study of Y-α-sialon

A Y-α-sialon was prepared using a specially designed temperature regime supporting formation of α-sialon and the amount of non-crystalline phase was remarkably reduced by a chemical treatment. Chemical composition of the sample was determined by EDX analysis. Crystal structure of Y-α-sialon was refined using high quality time-of-flight neutron powder diffraction data taken with the General Purpose Powder Diffractometer (GPPD) at the IPNS, Argonne National Laboratory. Unrestrained structure refinement was done in the P31c space group. The list of simultaneously refined parameters included profile parameters, atomic coordinates, individual isotropic temperature parameters and the occupancy parameter of Y. The contents of Y in the cell refined to 0.38(1) and calculated Si–N distances in tetrahedra varied from 1.716(3) to 1.773(3) Å, but their distributions in the respective tetrahedra differ as in the parent structure of α-Si₃N₄. Anisotropic temperature parameters refinement, as well as constrained refinements of the occupancy parameters of Si–Al and N–O pairs, were also attempted, but they all ended with unphysical values. Variation of the background was analyzed using RDF formalism. Three peaks centered around 1.7 Å (with a shoulder at 2.2 Å), 2.8 Å and 3.5 Å proved that the composition of amorphous phase was close to that of crystalline. Ab initio cluster calculations performed at the B3LYP/6-31G** level of theory excluded configuration with O atoms bonded to three Si atoms and proved that the most probable is the configuration where an O atom is shared by three Al atoms.     

Preparation of poly(2-pyridone-3,5-diyl)s with –(CH2)4–SO3M (M = H or Na) side chains

Poly(2-pyridone-3,5-diyl)s with –(CH₂)₄–SO₃M (M = H or Na) side chains have been prepared by nickel-complex promoted dehalogenative polycondensation. A composite film of the polymer with –(CH₂)₄–SO₃H side chains and poly(vinyl alcohol) showed a proton conductivity of 1.5 × 10^?1 S cm^?1 at 80 °C and 95% humidity. A copolymer with pyridine showed a high stability against oxidation by a Fenton reagent.     

The hydrothermal synthesis and structure of a one-dimensional Fe(II)molybdophosphate

A new one-dimensional Fe(II)molybdophosphate of the formula, [(C₁₀H₈N₂)H₂]₂[Fe₄^(II)Mo₁₂^(V)(HPO₄)₆(PO₄)₂(H₂O)₈(OH)₆O₂₄]·8H₂O, (1), has been synthesized by employing hydrothermal methods and characterized by single crystal X-ray diffraction. The structure consists of a network of MO₆ (M = Fe, Mo) octahedra and (H)PO₄ tetrahedra linked through their vertices. The connectivity between the polyhedral units gives rise to one-dimensional chains with eight-membered apertures. The hydrogen bonded interactions between the chains form pseudo two-dimensional layers. Extensive hydrogen bonding also exists between the amine molecule, 4,4^′-bipyridine, water molecule and framework oxygen atoms. Crystal data for 1: monoclinic, space group = P2₁ (no. 4), a=12.549(3) (Å), b=23.496(5) (Å), c=14.551(3) (Å), β=114.87(3)°, , and Z=2.     

Preparation, structure, and electrical conductivity of vanadium fluoridegraphite intercalation compound

Graphite intercalation compounds (GIC) of vanadium fluoride have been prepared in a fluorine atmosphere. The GICs prepared from highly oriented pyrolytic graphite (HOPG) were stage 1–8 compounds with composition, C_8.4–79.5VF_5.8–6.0. The apparent size of intercalated VF₆⁻(d_i) decreased from 5.33 Å to 4.15 Å along the c axis with increasing x in C_xVF₆. Various intercalated structures of VF₆⁻ between the carbon layers have been proposed for this change in d_i values. The compounds with small d_i around 4.2 Å show high stability in the air, which is due to the nestling of the VF₆⁻ anion between the carbon layers. Electron diffraction measurements have indicated that a well-nestled stage 2 GIC has high regularity in orientation of intercalated VF₆⁻ anions, which make two large unit cells of the hexagonal system ( ) with the different vectors by ±14° from that of graphite lattice. The ¹⁹F-NMR spectra and X-ray diffraction data in the low temperature region suggest a reversible phase transition. The highest electrical conductivity was 1.97 × 10⁵Scm⁻¹, which is 12 times that of pristine HOPG.     

Synthesis and structure of Mu-33, a new layered aluminophosphate

Mu-33, a new layered aluminophosphate with an Al/P ratio of 0.66, was obtained from a quasi non-aqueous synthesis in which tert-butylformamide (tBF) was the main solvent and only limited amounts of water were present. During the synthesis, tBF decomposed and the resulting protonated tert-butylamine is occluded in the as-synthesized material. The approximate structure was determined from data collected on a microcrystal (200 × 25 × 5 μm³) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, but the quality of these data did not allow satisfactory refinement. Therefore the structure was refined using high-resolution powder diffraction data, also collected at the ESRF. The structure (P2₁/c, a = 9.8922(6) Å, b = 26.180(2) Å, c = 16.729(1) Å and β = 90.4(1)°) consists of anionic aluminophosphate layers that can be described as a six-ring honeycomb of alternating corner-sharing AlO₄ and PO₄ tetrahedra with additional P-atoms above and below the honeycomb layer bridging between Al-atoms. The tert-butylammonium ions and water molecules located in the interlayer spacing interact via hydrogen-bonds with the terminal oxygens of the P-atoms. The characterization of this new aluminophosphate by ¹³C, ³¹P, ¹H–³¹P heteronuclear correlation (HETCOR) and ²⁷Al 3QMAS solid state NMR spectroscopy is also reported.     

IR-spectroscopic investigations of cycloalkanes

Summary A homologous series of cycloalkanes from (CH₂)₁₄ up to (CH₂)₉₆ as model systems for tight folding in CH₂-chain molecules was investigated by infrared spectroscopy. In comparison with the corresponding spectra of the nalkanes we found two additional new absorption bands at 700 cm^–1 and 1442 cm^–1 which can be assigned to a characteristic fold vibration. The already known fold band in the wagging region at about 1344 cm^–1 could also be found in all cycloalkane spectra. A numerical decomposition of the bands enables the calibration of the fold concentration. The Davydov splitting of the (CH₂)-rocking and (CH₂)-bending vibration in the melt crystallized form of the molecules (CH₂)₇₂ and (CH₂)₉₆ show the occurence of a orthorhombic subcell of the larger rings whereas the smaller rings and the larger ones in the solution crystallized form only crystallize in a monoclinic form.presented at the Frühjahrstagung der DPG und ÖPG, march 24, 1980 in Leoben, Österreich     

A novel lamella 2D Ag(I) coordination polymer of graphite-like structure featuring short interlayer distance

The reaction of Ag₂O with a mixture of benzene-1,3,5-tricarboxylic acid (H₃BTC) and 2-aminopyrazine (APYZ) under the ammoniacal conditions gives rise to a novel metal–organic coordination polymer Ag₆(BTC)₂(APYZ)₆·9H₂O (1). The structure of 1 possesses a high ordered lamella 2D structure with an interesting graphite-like 6³ net which is comprised of Ag₄ and Ag₆ fused hexagonal rings respectively. 1 exhibits photoluminescence maximized at 416 nm upon 330 nm excitation at room temperature, which may be mainly ascribed to ligand-to-ligand charge transfer (LLCT). Semiconducting behavior was also measured at ambient temperature with σ values of 5.56 × 10⁻⁷ S cm⁻¹ based on the π–π stacking and Ag(I)–π interactions.     

A manganese(III) complex that exhibits spin crossover behavior

A novel Mn^III(d⁴) complex, which exhibit spin crossover (SCO) phenomenon arising from the spin transition of LS ↔ HS state, was characterized structurally as well as magnetically. Single crystal X-ray diffraction methods structurally determined the compound as [Mn^III(OL1)₂]Cl · 3H₂O. Two facially coordinating tridentate ligands are bound to the manganese(III) ion, resulting in an MnN₄O₂ chromophore with an axially-compressed octahedral geometry. The nitrogen donors are all in the equatorial plane with Mn–N distances ranging from 2.14 to 2.19 Å, the two oxygen donors occupy the axial positions at 1.86 Å. Magnetic susceptibilities were measured between 77 and 300 K. At 77 K, the magnetic moment converges close to the expected low spin (LS) value of 2.8 μB, whereas at 300 K the high spin (HS) limit is entropically inaccessible, as this is a one-electron SCO.     

A CdSO4-like 3-D framework constructed from monosodium substituted Keggin arsenotungstates and copper(II)-ethylenediamine complexes

A 6⁵·8 CdSO₄-like 3-D framework [Cu(en)₂]₃[α-AsW₁₁NaO₃₉]·2H₂O (1) constructed by monosodium-substituted Keggin arsenotungstates and copper(II)-ethylenediamine complexes (en = ethylenediamine) has been synthesized by reaction of Na₈[α-HAsW₉O₃₄]·11H₂O, CuCl₂·2H₂O and ethylenediamine under hydrothermal conditions and structurally characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. Crystal data for 1: C₁₂H₅₂AsCu₃N₁₂NaO₄₁W₁₁, monoclinic, Cc, a = 20.409(9) Å, b = 16.737(8) Å, c = 16.561(7) Å, β = 104.607(7)°, V = 5474(4) Å³, T = 296(2) K; Z = 4, μ = 24.860 mm⁻¹, GOOF = 1.086, R₁ = 0.0284, wR₂ = 0.0759. To the best of our knowledge, 1 represents the first 6⁵·8 CdSO₄-like 3-D monovacant Keggin arsenotungstate derivative in polyoxometalate chemistry.     

Modification of electrodes with nanostructured functionalized thiadiazole polymer film and its application to the determination of ascorbic acid

We report the electropolymerization of 2-amino-1,3,4-thiadiazole (ATD) on glassy carbon (GC) and indium tin oxide (ITO) electrodes in 0.10 M H₂SO₄. The electropolymerized ATD (p-ATD) film was characterized by cyclic voltammetry, attenuated total reflectance (ATR)-FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The AFM image showed that the p-ATD formed a spherical-like structure with a thickness of 25 nm. XPS of the p-ATD film showed binding energies at 398.7, 400.3 and 401.3 eV in the N 1s region corresponding to –N, –NH– and –N⁺H–, respectively, and at 285.5 and 287.0 eV in the C 1s region corresponding to C–N and CN, respectively. The appearance of binding energies at 285.5 and 287.0 eV confirmed that the p-ATD film proceeded via C–N and CN linkages and not via C–C or CC linkages. The p-ATD film deposited on the GC electrode was successfully used for the determination of ascorbic acid (AA) at physiological pH. The amperometric current was increased linearly from 7.5 × 10⁻⁸ to 2.0 × 10⁻⁵, and the detection limit was found to be 0.28 nM (S/N = 3).