1,721,147 research outputs found
The contribution of powder diffraction methods to structural co-ordination chemistry
No full textAb-initio X-ray powder diffraction (see cover for typical spectra) is shown to be a powerful structural tool for (i) insoluble, thermally unstable, compounds which cannot be (re)crystallised from solution or from the melt; (ii) metastable phases destroyed or modified upon manipulation; (iii) twins; (iv) very small crystals and/or crystal aggregates; (v) gas/solid, liquid/solid and solid-state reactions fragmenting and misorienting the coherent domains of the starting crystals but conserving the (poly)crystalline nature of the sample
Solving protein crystal structures
No full textIn this contribution we present the basics of the structure solution methods typically used in macromolecular crystallography. Tailored methods, different from conventional small molecule crystallography, are indeed necessary, and are here reviewed
Synthesis, characterization and XRPD studies of metal-organic frameworks containing 1,4 bis(4-pyrazolyl) and 1,4 bis(5-tetrazolyl)benzene ligands
No full textIn the last decade we have been deeply exploring the coordination chemistry of polydentate ligands possessing multiple donor sites. Nowadays we decided to increased the complexity of the polytopic N-ligands aiming at the formation of oligomeric and polymeric species with different functional properties.
Inspires to the 1,4-benzene-dicarboxylate (BDC) the ligand of the highly porous and capable of H2 sorption MOF-5 proposed by Yaghi et al., and planning to employ polytopic longer spacers possessing nitrogen coordination sites (with the possibility of an exobidentate coordination), we turned our attention to the 1,4-bis(5-tetrazolyl)benzene species (C8H6N8, H2btb).
After having tailored high-yield, cheap and atoxic syntheses for H2btb [1], we started coupling this ligand with a transition metal ions aiming at the formation of microcrystalline materials of well defined stoichiometry, structure and functional properties: nanoporosity, cooperative magnetism and catalytic activity.
The isolated materials shows a variety of stoichiometries, each one with its own peculiar structure: homoleptic species [Ag2(btb), Cu(btb) and Co(btb)], hydrated (or solvated) compounds [Co(btb)•2H2O and Zn(btb)•nDMF], and even hydroxo complexes [Cu2(μ3-OH)2(btb)]. These compounds are either dense or moderately porous and, therefore, they are not prone to gas sorption or storage, as originally targeted [2].
In this context, we decided to develop a new strategy to synthesized the analogous 1,4-bis(4-pyrazolyl)benzene (C12H10N4, H2bpb) [1] with the hope to obtain microporous and non-dense species with the coordination of the metal transition elements. Specifically, in our research, we have coupled these ligands with Ni, Cu, Zn, Hg to afford the species Ni(bpb), Zn(bpb), Cu2(bpb) and Hg(bpb). These species are isolated by solvothermal reaction and fully characterized by elemental and thermogravimetric analysis, IR spectroscopy and we attained their full structural characterization resorting to state-of-the-art powder diffraction methods, occasionally coupled to thermodiffractometry analysis.
Adsorption capacities are also studied with preliminary gas sorption analysis, towards N2, and showing attractive adsorption capacities of the compound Ni(bpb) and Zn(bpb) in agreement with their structural characterization that shows a very low density and regulars networks.
[1] A. Maspero, S. Galli, N. Masciocchi, G. Palmisano, Chem. Lett., 2008, in press.
[2] A.Maspero, S. Galli, V.Colombo, G.Peli, N.Masciocchi, S.Stagni, E.Barea, J.A.R. Navarro, Inorg. Chim. ACTA, 2008, in press
Structural characterization of the three complexes [HRe(CO)4]n (n = 2, 3, 4), including a rare example of a square arrangement of metal atoms
No full textComments on the elusive crystal structure of 4-iodo-4'-nitrobiphenyl
No full textThe recently proposed crystal structure of 4-iodo-4'-nitrobiphenyl (Sarma et al. 1997) is here confirmed from exptl. diffraction data on single crystals and powders of high crystallinity; a reinterpretation of the nature of the (faulted) material studied in the original paper is also presented. Crystallog. data are given. [on SciFinder (R)
Synthesis and X-ray powder diffraction characterization of tetra- and hexa-imidazole complexes of magnesium(II)
No full textX-ray powder diffraction data for two ionic salts contg. imidazole (Him) complexes of the magnesium(II) ion, [Mg(Him)4(H2O)2]Cl2 and [Mg(Him)6](NO3)2, are reported. Their crystal and mol. structures were detd. by simulated annealing and full-profile Rietveld refinement methods. [Mg(Him)4(H2O)2]Cl2 was found to crystallize in the monoclinic system with space group C2/c, a=12.3980(3) A, b=11.0234(2) A, c=14.4691(3) A, and =107.024(1). [Mg(Him)6](NO3)2 crystallizes in the trigonal R-3 space group with a=b=12.4631(4) A and c=14.9449(6) A. Both species contain centrosym. complexes, and Mg is octahedrally coordinated by six imidazoles, as in [Mg(Him)6](NO3)2, or by four imidazoles and two water mols., as in [Mg(Him)4(H2O)2]Cl2. Addnl. analytic, thermogravimetric, calorimetric, and spectroscopic characterizations were also performed
Crystal structure determination of molecular compounds from conventional powder diffraction data: Trimeric silver(I) 3,5-dimethylpyrazolate
No full textIn the absence of single crystals, silver(I) 3,5-dimethylpyrazolate, [Ag(dmpz)]3, has been structurally characterized by ab initio X-ray powder diffraction, using conventional laboratory data. Its crystals are triclinic, P1, with a=8.0876(10), b=11.1204(13), c=11.6136(16) Å, α =68.293(6), β=78.350(7), and γ=81.243(6)°. The structure has been solved by Patterson, difference Fourier, and geometrical modeling, and ultimately refined by the Rietveld method down to Rp=0.068, Rwp=0.085, and RF=0.055, for 4300 observations in the 17<2θ<103° range. Each molecule consists of a cyclic, trimeric assembly of Ag(dmpz) fragments, with the dmpz ligand bridging, in the exo-bidentate mode, nonbonded Ag⋯Ag edges. © 1998 International Centre for Diffraction Data
Structural powder diffraction characterization of organometallic species : the role of complementary information
Full text linkX-ray powder diffraction (XRPD) has been employed in the last years as an active structural tool, well beyond its classical usage in qualitative, quantitative and microstructural analyses. The complexity of the materials studied by this method has steadily grown, allowing the full structural characterization of molecular systems, of organic and organometallic nature. Here we emphasize that, when dealing with such moderately complex molecular materials, the power of XRPD can be enhanced not only by increasing the radiation flux or the instrumental resolution, but also (and cheaply) by using additional (experimental or computational) information
SOLVING SIMPLE ORGANOMETALLIC STRUCTURES SOLELY FROM X-RAY-POWDER DIFFRACTION DATA - THE CASE OF POLYMERIC [(RU(CO)4)N]
No full textThe crystal and molecular structure of [Ru(CO)4n] has been determined solely from X-ray powder diffraction data using standard laboratory equipment and refined with a (modified) Rietveld procedure. The compound crystallizes in the orthorhombic space group Ibam, with a = 14.147(4), b = 7.060(2) and c = 5.720(1) angstrom, Z = 4; the final refinement (19 variables) converged to R(p') R(wp) and R(Bragg) of 0.077, 0.102 and 0.025, respectively, for 4001 data collected at room temperature in the 5-85-degrees (2theta) range. The structure, which consists of a polymeric stack of staggered trans-D4h Ru(CO)4 fragments separated by a Ru-Ru contact of 2.860(1) angstrom, is the first polymeric binary metal carbonyl compound so far characterized. Strain and particle-size broadening effects have been observed, and the microstructural properties of the compound are discussed
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