Crystal structure determination of molecular compounds from conventional powder diffraction data: Trimeric silver(I) 3,5-dimethylpyrazolate

In 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) \uc5, \u3b1 =68.293(6), \u3b2=78.350(7), and \u3b3=81.243(6)\ub0. 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<2\u3b8<103\ub0 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 efAg edges. \ua9 1998 International Centre for Diffraction Data

Crystal structure determination of molecular compounds from conventional powder diffraction data: Trimeric silver(I) 3,5-dimethylpyrazolate

In 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&lt;2θ&lt;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

AB-INITIO XRPD STRUCTURE DETERMINATION OF METAL-CARBONYL CLUSTERS - THE CASE OF [HGRU(CO)4]4

The crystal and molecular structure of the new [HgRu(CO)4]4 cluster has been determined exclusively from X-ray powder diffraction data from standard laboratory equipment and refined with a (modified) Rietveld procedure. The title compound crystallizes in the monoclinic space group P2(1)/n, with a = 13.032(1) angstrom, b = 18.293(2) angstrom, c = 6.501 (1) angstrom, beta = 111.81(2)-degrees, V = 1438.9(4) angstrom3, and Z = 2; the final refinement converged to R(p) and R(wp) values of 0.097 and 0. 126, respectively, for 3351 data collected (Cu Kalpha) at room temperature in the 18-85-degrees (20) range. [HgRu(CO)4]4 consists of a planar, centrosymmetric, eight-membered ring of alternating Hg and cis-Ru(CO)4 units of idealized D4h symmetry. XRPD is shown to be a powerful tool to obtain useful structural information on moderately complex organometallic systems, when single crystals cannot be grown, if all the available chemical knowledge is included in the refinement through constraints

SOLVING SIMPLE ORGANOMETALLIC STRUCTURES SOLELY FROM X-RAY-POWDER DIFFRACTION DATA - THE CASE OF POLYMERIC [(RU(CO)4)N]

The 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

White lumps in fifth- to seventeenth-century AD mortars from northern Italy

Ancient mortars from northern Italy, dating from the fifth to the seventeenth century AD, were examined in order to formulate an hypothesis regarding the origin of the white lumps often observed in these mortars and in other samples of the same geographical provenance. Various characterization techniques were employed, including scanning electron microscopy, X-ray powder diffraction and Fourier transform infrared (FTIR) and micro-FTIR spectroscopy

STRUCTURAL CHARACTERIZATION OF PYRIDAZINE (PYDZ) ADDUCTS OF MX(2) (M=MN, FE, CO, NI, CU OR ZN X=CL OR BR) - AB-INITIO X-RAY-POWDER DIFFRACTION DETERMINATION OF POLYMERIC [NIX(2)(PYDZ)] COMPLEXES

The pyridazine (pydz) complexes of metal halides MX(2) (M = Mn, Fe, Co, Ni, Cu or Zn; X = Cl or Br) have been prepared, using a reagent molar ratio of 1:1, and investigated by X-ray powder diffraction methods. The crystal structures (orthorhombic, space group lmma, Z = 4) of [NiCl2(pydz)] and [NiBr2(pydz)] have been determined, ab initio. from laboratory X-ray powder diffraction data only: [NiCl2(pydz)], a = 7.3758(4), b = 6.6069(3) and c = 12.7292(7) Angstrom. [NiBr2(pydz)], a = 7.5598(9), b = 6.8029(8) and c = 12.905(2) Angstrom. The structures have been solved by direct methods, and refined by the Rietveld technique down to R(profile) values of 0.062 and 0.078, respectively. for 4400 data points collected at room temperature in the-range 17 < 2 theta < 105 degrees. Both compounds consist of infinite polymeric chains of nickel atoms, bridged by X (CI or Br) and pyridazine ligands, showing an octahedral arrangement and trans- DDh NiX,N-2, chromophores. The Ni-Cl and Ni-Br distances are 2.422(1) and 2.560(2) Angstrom, respectively. Analyses of the other species have shown-that the analogues of Mn, Fe and Co are isomorphous with the nickel compounds. while those of Cu and Zn display different diffraction patterns

Ab-initio X-ray powder diffraction structural characterization of co-ordination compounds: Polymeric [{MX2(bipy)}n] complexes (M = Ni or Cu; X = Cl or Br; bipy = 4,4\u2032-bipyridyl)

In the absence of crystals of suitable quality, the crystal structures of five [MX(2)(bipy)] (M = Ni or Cu; X = Cl or Br; bipy = 4,4'-bipyridyl) phases were determined, nb initio, from powder diffraction data. The nickel compounds contain symmetrically bridging halides and trans-D-4h octahedrally co-ordinated metal atoms; on the contrary, the co-ordination about the copper atoms in [CuBr2(bipy)] is square planar, with long Cu ... Br contacts in the axial direction, due to Jahn-Teller distortion. Interestingly, [CuCl2(bipy)] is dimorphic; both in the orthorhombic and in the monoclinic phases, the copper co-ordination is substantially square planar as in the bromide analogue, but none of the two phases is isomorphous to it

P-RISCON - A REAL-SPACE SCAVENGER FOR CRYSTAL-STRUCTURE DETERMINATION FROM POWDER DIFFRACTION DATA

A computer program, P-RISCON, has been designed with the aim of finding the location and orientation of one or more independent fragments of known geometry in the unit cell from low-angle X-ray powder diffraction data only, provided that lattice parameters, space group and a set of integrated intensities are known. A 3D translational search is performed and, if required, rotations of each model about three orthogonal axes are applied, seeking the best match between observed and calculated data. No arbitrary partitioning of the intensity of severely overlapping reflections is required as the integrated intensity of a multiplet can be used as a single observation, thereby introducing very little error in its estimated value. A number of (known) test structures have been solved by this method