Determination of zinc incorporation in the Zn-substituted gallophosphate ZnULM-5 by multiple wavelength anomalous dispersion techniques.

The location of isomorphously substituted zinc over eight crystallographically different gallium sites has been determined in a single-crystal study of the gallophosphate ZnULM-5, Ga((16-x))Zn(x)(PO(4))(14)(HPO(4))(2)(OH)(2)F(7), [H(3)N{CH(2)}(6)NH(3)](4), 6H(2)O, in an 11 wavelength experiment, using data from Station 9.8, SRS Daresbury. The measurement of datasets around the K edges of both Ga and Zn, as well as two reference datasets away from each absorption edge, was utilized to selectively exploit dispersive differences of each metal atom type in turn, which allowed the major sites of Zn incorporation to be identified as the metal 1 and 3 sites, M1 and M3. The preferential substitution of Zn at these sites probably arises because they are located in double four-ring (D4R) building units which can relax to accommodate the incorporation of hetero atoms. As the crystal is non-centrosymmetric, with space group P2(1)2(1)2, it was also possible to use anomalous differences to corroborate the results obtained from the dispersive differences. These results were obtained firstly from difference Fourier maps, calculated using a phase set from the refined structure from data measured at the Zr K edge. Also, refined dispersive and anomalous occupancies, on an absolute scale, could be obtained using the program MLPHARE, allowing estimates for the Zn incorporation of approximately 22 and 18 at. % at the M1 and M3 sites to be obtained. In addition, f' and f'' values for Ga and Zn at each wavelength could be estimated both from MLPHARE results, and by refinement in JANA2006. The fully quantitative determinations of the dispersive and anomalous coefficients for Ga and Zn at each wavelength, as well as metal atom occupancies over the eight metal atom sites made use of the CCP4's MLPHARE program as well as SHELXL and JANA2006. The results by these methods agree closely, and JANA2006 allowed the ready determination of standard uncertainties on the occupancy parameters, which were for M1 and M3, 20.6 (3) and 17.2 (3) at %, respectively.

Science experiments via telepresence at a synchrotron radiation source facility.

Station 9.8 is one of the most oversubscribed and high-throughput stations at the Synchrotron Radiation Source, Daresbury, whereby awarded experimental time is limited, data collections last normally no longer than an hour, user changeover is normally every 24 h, and familiarity with the station systems can be low. Therefore time lost owing to technical failures on the station has a dramatic impact on productivity. To provide 24 h support, the application of a turnkey communication system has been implemented, and is described along with additional applications including its use for inter-continental classroom instruction, user training and remote participation.

The use of softer X-rays in the structure elucidation of microporous materials.

Microporous materials, such as zeolites and aluminophosphates, have many applications as molecular sieves and shape-selective catalysts. This is due to their three-dimensional frameworks, which contain regular pores and channels, to their high acidity, arising from Brønsted and Lewis acid active sites, and to the incorporation of transition metal atoms into framework sites. This review firstly provides an introduction into the nature and properties of these materials, and their important applications; the difficulties in their full characterization and possible methods of elucidating their structures are then outlined; finally, methods of characterization, utilizing 'softer X-rays' are introduced. The first method is the determination of low concentrations of transition metals, incorporated into the frameworks using single crystal anomalous dispersion crystallography; synchrotron radiation is used to tune to the absorption edge of the metal atom in question, in order to change its signal relative to that of the rest of the structure, thereby allowing the pinpointing of its positions and the determination of its concentration at each site in the framework. Secondly, the use of longer wavelengths in powder diffraction studies is described, which, by stretching out the powder pattern, thereby reduces the overlapping of the diffraction peaks, thus allowing the structure to be solved by conventional direct methods. Finally, the use of X-ray absorption spectroscopy to determine the metal incorporation and the nature of coordination at the metal atom sites, in Mn silicalite-1 and FAPO-36, are described.

Synthesis and characterization of uranyl compounds with iminodiacetate and oxydiacetate displaying variable denticity.

Eight uranyl compounds containing the dicarboxylate ligands iminodiacetate (IDA) or oxydiacetate (ODA) have been characterized in the solid state. The published polymeric structures for [UO(2)(C(4)H(6)NO(4))(2)] and [UO(2)(C(4)H(4)O(5))](n) have been confirmed, while Ba[UO(2)(C(4)H(5)NO(4))(2)] x 3H(2)O, [(CH(3))(2)NH(CH(2))(2)NH(CH(3))(2)][UO(2)(C(4)H(4)O(5))(2)] [orthorhombic space group Pnma, a = 10.996(5) A, b = 21.42(1) A, c = 8.700(3) A, Z = 4], and [C(2)H(5)NH(2)(CH(2))(2)NH(2)C(2)H(5)][UO(2)(C(4)H(4)O(5))(2)] [monoclinic space group P2(1)/n, a = 6.857(3) A, b = 9.209(5) A, c = 16.410(7) A, beta = 91.69(3), Z = 2] contain monomeric anions. The distance from the uranium atom to the central heteroatom (O or N) in the ligand varies. Crystallographic study shows that U-heteroatom (O/N) distances fall into two groups, one 2.6-2.7 A in length and one 3.1-3.2 A, the latter implying no bonding interaction. By contrast, EXAFS analysis of bulk samples suggests that either a long U-heteroatom (O/N) distance (2.9 A) or a range of distances may be present. Three possible structural types, two symmetric and one asymmetric, are identified on the basis of these results and on solid-state (13)C NMR spectroscopy. The two ligands in the complex can be 1,4,7-tridentate, giving five-membered rings, or 1,7-bidentate, to form an eight-membered ring. (C(4)H(12)N(2))[(UO(2))(2)(C(4)H(5)NO(4))(2)(OH)(2)] x 8H(2)O [monoclinic space group P2(1)/a, a = 7.955(9) A, b = 24.050(8) A, c = 8.223(6) A, beta = 112.24(6), Z = 2], (C(2)H(10)N(2))[(UO(2))(2)(C(4)H(5)NO(4))(2)(OH)(2)] x 4H(2)O, and (C(6)H(13)N(4))(2)[(UO(2))(2)(C(4)H(4)O(5))(2)(OH)(2)] x 2H(2)O [monoclinic space group C2/m, a = 19.024(9) A, b = 7.462(4) A, c = 2.467(6) A, beta = 107.75(4), Z = 4] have a dimeric structure with two capping tridentate ligands and two mu(2)-hydroxo bridges, giving edge-sharing pentagonal bipyramids.

Stereospecificity and stereoselectivity in electrophilic substitution reactions of non-alpha-heterosubstituted organolithiums and stannanes: a rotationally restricted amide as an internal stereochemical marker.

The complete stereochemical course of a tin-lithium exchange/electrophilic quench sequence has been unambiguously determined by stereochemical characterization (using X-ray crystallography or NOE studies) at every step. Pairs of diastereoisomeric stannanes of known stereochemistry bearing atropisomeric amide substituents undergo tin-lithium exchange with alkyllithiums to give diastereoisomeric benzylic organolithiums whose stereochemistry can be assigned by NMR. For one atropisomer of the stannanes, the tin-lithium exchange is fully stereospecific and proceeds with retention of stereochemistry. The other atropisomer undergoes nonstereospecific tin-lithium exchange: the first reported example of a lack of stereospecificity in electrophilic substitution of tin for lithium. One of the diastereoisomeric atropisomeric organolithiums produced by the tin-lithium exchange is deuterated and alkylated with retention but stannylated with inversion of stereochemistry. The other is alkylated nonstereospecifically but stannylated with retention.

Incorporation of Mn, Co and Zn cations into large-pore aluminophosphate molecular sieves MeAPO-50.

Large-pore metal modified aluminophosphate molecular sieves MeAPO-50 (Me=Co,Zn,Mn) were synthesised by hydrothermal crystallisation using di-n-propylamine as structure directing agent. EXAFS and XRD analysis show that cobalt(II), manganese(II) and zinc(II) are incorporated into the non-phosphorus tetrahedral framework sites of MeAPO-50 on the threefold-axis site, and on a site in a general position in the unit cell. Results of both methods on distribution of the metal over the two sites are compared.

(Z)-7-Chloro-3-[(3-chlorophenyl)-methylidene]-4-p-tosyl-3,4-dihydro-2H-1,4-benzoxazine.

In the title compound, C22H17Cl2NO3S, the molecule is a substituted 3,4-dihydro-2H-1,4-benzoxazine compound which has three phenyl rings which are essentially planar. The 3,4-dihydro-2H-oxazine part of the molecule is fused to the benzo ring and has a half-boat conformation; the dihedral angle between the planar part of the oxazine ring and the benzo ring is 10.2 (2) degrees. The (3-chlorophenyl)methylidene substituent has a Z configuration in relation to the ring N atom of the oxazine moiety. Interestingly, the p-toluenesulfonyl (p-tosyl) substituent on the ring N atom protrudes away from the 3-chlorophenyl substituent thus avoiding any steric interaction.

Partial reduction of annulated heterocycles as a general route to medium rings containing oxygen and nitrogen.

The preparation of annulated furans and pyrroles is described as part of a general strategy for the synthesis of medium ring heterocycles. After Birch reduction, the corresponding dihydro compounds were oxidatively cleaved to produce medium ring ethers and amines in an efficient manner. This methodology was successfully applied to the formation of eight- and nine-membered cyclic ethers and nine-membered cyclic amines. Attaching a chiral auxiliary (bismethoxymethylpyrrolidine) to the furan allowed the formation of nine-membered ethers in 95% ee.

The regioselective aminohydroxylation of allylic carbamates.

The synthesis and aminohydroxylation of a series of acyclic allylic carbamates is described: the formation of a putative O=Os=NR linkage between the transition metal and substrate is proposed to account for the high levels of regioselectivity that were observed; proof of the structure of one of the aminohydroxylation products was obtained through X-ray crystallography.

4-Methyl-N-

The title compound, C(20)H(19)NO(2)S(2), is formed by a palladium-copper-catalyzed reaction between 4-methyl-N-[2-(prop-2-ynylsulfanyl)phenyl]benzenesulfonamide and p-iodotoluene. The molecules contain three essentially planar parts, namely an aminothiophenol moiety (A), a toluenesulfone moiety excluding the oxo ligands (B) and a tolyl group (C), approximately orthogonal to each other; the dihedral angles A/B, A/C and B/C are 111.6 (1), 89.3 (1) and 101.4 (1) degrees, respectively. Intermolecular N-H.O hydrogen bonds link the molecules into infinite one-dimensional chains.

Atropisomeric amides as chiral ligands: using (-)-sparteine-directed enantioselective silylation to control the conformation of a stereogenic axis

An enantiomerically pure (1-trimethylsilyl)ethyl group, constructed by a (-)-sparteine-directed enantioselective quench of a laterally lithiated tertiary aromatic amide, exerts powerful thermodynamic control over the conformation of the adjacent tertiary amide substituent. Ortholithiation and functionalization of the amide in the 6-position allows the single amide conformer to be trapped as an enantiomerically and diastereoisomerically pure amide atropisomer. Protodesilylation of the amide gives functionalized atropisomeric amides with a stereogenic axis of single absolute configuration, whose barriers to racemization have been determined by polarimetry. Enantiomerically pure amides bearing phosphine substituents are effective ligands in a Pd-catalyzed allylic substitution reaction-the first use of a nonbiaryl atropisomer as a chiral ligand-and give products with 90% ee. The rate of racemization of the phosphine-substituted amide is powerfully influenced by the presence of palladium.

Bis

In the title compound, [Zn(C(8)H(10)N(3)O(2))(2)], the Zn atom displays a highly distorted octahedral coordination involving O and N atoms of two bidentate planar ligands approximately orthogonal to each other; the dihedral angle between the ligand planes is 84.95 (4) degrees. The ligand molecules show great asymmetry in their bonding to the Zn(2+) ion, with Zn-O bond distances ranging between 2.056 (2) and 2.534 (2) A. The planar phenyl ring and the trigonal-planar geometry about the triazene N atom bonded to the phenyl ring suggest a resonance interaction extending over adjacent atoms.

(E)-2-[2-(1-Naphthyl)vinyl]-3-tosyl-2,3-dihydro-1,3-benzothiazole.

The title compound, C(26)H(21)NO(2)S(2), which consists of a benzothiazole skeleton with alpha-naphthylvinyl and tosyl groups at positions 2 and 3, respectively, was prepared by palladium-copper-catalyzed heteroannulation. The E configuration of the molecule about the vinyl C=C bond is established by the benzothiazole-naphthyl C-C-C-C torsion angle of 177.5 (4) degrees. The five-membered heterocyclic ring adopts an envelope conformation with the Csp(3) atom 0.380 (6) A from the C(2)NS plane. The two S-C [1.751 (4) and 1.838 (4) A] and two N-C [1.426 (5) and 1.482 (5) A] bond lengths in the thiazole ring differ significantly.

Investigations of Amavadin.

The development of the understanding of the co-ordination chemistry and the properties of Amavadin, the chemical form in which vanadium is accumulated by the Amanita genus of mushrooms, is reviewed.

The synthesis and glass-forming properties of phthalocyanine-containing poly(aryl ether) dendrimers.

The synthesis, structural characterisation and properties of a number of phthalocyanine-containing dendrimers are described. Peripheral substitution of phthalocyanine (Pc) with four poly(aryl ether) dendritic wedges (1st, 2nd or 3rd generation) produces materials whose properties are dominated both by the columnar self-association of the Pc core and by the glass-forming character of the dendritic substituents. Asymmetric Pcs containing a single poly(aryl ether) dendron display a columnar mesophase, the structure of which can be frozen into an anisotropic glass at room temperature. Placing the dendritic wedges at the axial sites of silicon phthalocyanine prohibits self-association and gives materials from which can be fabricated robust, isotropic solid solutions of Pc with high glass transition temperatures. A single crystal X-ray diffraction analysis of one of these compounds illustrates the ability of the axial dendrons to prevent cofacial aggregation in the solid state.

Anomalous scattering for small-molecule crystallography.

Anomalous dispersion techniques in small-molecule crystallography have been used in recent years with the advent of intense tunable X-radiation from synchrotron X-ray sources. By tuning the wavelength of the radiation close to the absorption edges of specific elements, it is possible to identify and distinguish between atoms which are close together in atomic number, even when two or more such atoms occupy a single site. Anomalous dispersion techniques can also be used to distinguish between valence states of different sites of an element by the valence contrast method or to determine the coordination geometry of an atom. In some cases, when the coordination of an atom is asymmetric, the absorption-edge position may depend on the orientation of the crystal. Finally, anomalous dispersion techniques can be used for ab initio structure solution from powder diffraction data. The properties of microporous materials often depend on the incorporation of metal atoms into the framework. Two or more metal atoms close together in atomic number may be incorporated, sometimes occupying a single site. In one study the site of an Ni atom in the aluminophosphate NiAPO was determined by anomalous dispersion techniques and data from the NSLS. Also, the location of the isomorphously substituted cobalt over two crystallographically different zinc sites was determined in the zincophosphate CoZnPO-CZP, in a five-wavelength study using data from ELETTRA.

Determination of the site of incorporation of cobalt in CoZnPO-CZP by multiple-wavelength anomalous-dispersion crystallography.

Data were collected from a crystal of CoZnPO-CZP {sodium cobalt-zinc phosphate hydrate, Na(6)[Co(0.2)Zn(0.8)PO(4)](6).6H(2)O} using synchrotron radiation at ELETTRA at the inflection point and 'white line' for both the cobalt and zinc K edges, and at 1.45 Å, a wavelength remote from the K edges of both metals. The data were processed using the programs DENZO and SCALEPACK. The CCP4 program suite was used for the scaling of data sets and the subsequent calculation of dispersive difference Fourier maps. Optimal scaling was achieved by using a subset of reflections with little or no contribution from the metal atoms (i.e. which were essentially wavelength independent in their intensities) and using weights based on the sigma's to obtain an overall scale factor in each case. Phases were calculated with SHELXL97 based on the refined structure using a much higher resolution and complete Cu Kalpha data set. An occupancy of 100% by zinc at the two metal-atom sites was assumed. The dispersive difference Fourier map calculated for zinc gave two peaks above the background of similar heights at the expected metal-atom sites. The peak height at the Zn1 site was a little higher than at the Zn2 site. The dispersive difference Fourier map calculated for cobalt gave just one peak above the background, at the Zn1 site, and only a small peak at the Zn2 site, thus indicating that incorporation of cobalt takes place mainly at one site. Refinement of the zinc occupancies using MLPHARE reinforces this conclusion. The chemical environment of each site is discussed.

Surface coordination chemistry: corrosion inhibition by tetranuclear cluster formation of iron with salicylaldoxime.

A tetranuclear iron cluster is the principal component of the purple coatings produced by treating a mild steel surface with a salicylaldoxime corrosion inhibitor. This was shown by comparison of the spectroscopic data with those of the cluster [{Fe(salH)(HsalH)}4 ], which was obtained from FeCl3 and salicylaldoxime (H2 salH) and has a distorted tetrahedral arrangement of Fe(III) atoms coordinated by terminal (1-) and bridging (2-) salicylaldoximate ligands (the central core of the cluster is depicted).