| 1. |
- Lyxell, D G, et al.
(författare)
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Multicomponent polyanions. 53. Structure of tetrakis(trimethylammonium) tetra-mu-oxo-bis(triaquahexadecaoxo(trioxophenylphosphato)hexamolybdate) dihydrate, [NH(CH3)(3)](4)[{(C6H5P)Mo6O21(H2O)(3)}(2)].2H(2)O
- 1998
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Ingår i: Acta Crystallographica Section B. - 0108-7681 .- 1600-5740. ; 54, s. 424-430
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Tidskriftsartikel (refereegranskat)abstract
- The title compound crystallized in the monoclinic space group P2(1)/n (No. 14) [a = 11.211 (5), b = 12.862 (3), c = 23.05 (1) Angstrom, beta = 94.37 (3)degrees, V = 3314 (2) Angstrom(3), Z = 2]. The polyanion can be regarded as a dimer of a phenylphosphonatohexamolybdate, (C6H5P)Mo6O23(H2O)(3), Linked by four O atoms. In this monomeric unit the six molybdenum octahedra are grouped into two parts consisting of four and two edge-sharing octahedra, respectively. These two parts are connected by two corner-sharing O atoms to form a bent Mo-6 ring. The phenylphosphonate group coordinates to the Mo-6 ring from the narrow side as a tripodal Ligand. The {(C6H5P)Mo6O21 (H2O)(3)}(2) units form layers parallel to (001) and the structure is stabilized by hydrogen bonds between water and neighboring anions. The monomeric unit has been shown to be a key structure in the process of deducing the aqueous solution structures of the (C6H5P)Mo-6(2-) and (C6H5P)Mo-7(4-) species found in a previous equilibrium study of the H+-MoO42-(C6H5P)O-3(2-) system.
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| 2. |
- Ptasiewicz-Bak, H., et al.
(författare)
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Charge density in NiCl2.4H2O at 295 and 30 K
- 1999
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Ingår i: Acta Crystallographica Section B. - : International Union of Crystallography (IUCr). - 0108-7681 .- 1600-5740. ; 55:6, s. 830-840
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Tidskriftsartikel (refereegranskat)abstract
- The charge distribution has been determined by multipole refinements against single-crystal X-ray diffraction data. In the refinements a comparison was made between the densities based on H-atom parameters from X-ray and neutron data, respectively. X-ray study: (Mo K ) = 0.71073 Å, F(000) = 408; at 30 K: R(F) = 0.015 for 6686 reflections; at 295 K: R(F) = 0.022 for 4630 reflections. The nickel ion is octahedrally surrounded by four water molecules and two chloride ions, forming a locally neutral Ni(H2O)4Cl2 complex. Two of the water molecules are coordinated to nickel approximately in one of the tetrahedral (`lone-pair') directions; the other two are trigonally coordinated. At 30 K one H atom in one of the trigonally coordinated water molecules is disordered, with equal occupation of two different positions. Owing to the polarizing influence of the nickel ion there are two peaks in the lone-pair plane of the water molecules when these are tetrahedrally coordinated; for those trigonally coordinated there is just one peak. The individual (`partial') charge densities, calculated from the deformation functions of only nickel or the separate water molecules, have also been calculated to study the effects of superposition of the individual densities. In the individual density of nickel an excess is observed in the diagonal directions and a deficiency in the ligand directions. However, owing to the influence of the whole crystalline environment, the maxima around nickel are not found in the planes defined by nickel and the six ligands.
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| 3. |
- Ptasiewicz-Bak, H., et al.
(författare)
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Charge Density in Orthorhombic NiSO4.7H2O at Room Temperature and 25 K
- 1997
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Ingår i: Acta Crystallographica Section B. - : International Union of Crystallography (IUCr). - 0108-7681 .- 1600-5740. ; 53:3, s. 325-336
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Tidskriftsartikel (refereegranskat)abstract
- The charge-density distribution in the title compound nickel sulfate heptahydrate has been determined by multipole refinement against single-crystal X-ray intensity data. For the refinement at 25 K hydrogen positions and displacement parameters were fixed to values determined from neutron data. The charge density based on the deformation functions of all atoms in the structure is compared with the individual densities calculated from the deformation functions of only nickel or the separate water molecules. In this way the effects of simple superposition of the individual densities have been studied. The individual deformation density around nickel is in good qualitative agreement with that expected for an approximately octahedral Ni(H2O)62+ complex in a weak ligand field. However, the maximum densities are not found precisely in the planes defined by nickel and the six water ligands, which illustrates that it is necessary to consider the crystal field due to the whole crystalline environment. The individual densities of the water molecules show clear polarization of the lone-pair densities according to the coordination of the water molecules: tetrahedral coordination leads to two resolved lone-pair peaks, whereas planar trigonal coordination leads to just one single peak. Crystal data: NiSO4.7H2O, Mr = 280.87, P212121, Z = 4. At T = 25 K: a = 6.706 (3), b = 11.796 (6), c = 11.949 (6) Å, V = 945 (1) Å3, Dx = 1.977 Mg m-3. At 295 K: a = 6.751 (4), b = 11.746 (7), c = 12.003 (8) Å, V = 952 (1) Å3, Dx = 1.959 Mg m-3. X-ray study: F(000) = 584, (Mo K ) = 0.71069 Å, = 2.255 mm-1. At 25 K: R(F) = 0.014 for 10 185 reflections. At 295 K: R(F) = 0.015 for 5723 reflections. Neutron study at 25 K: = 1.215 Å, = 0.261 mm-1, R(F) = 0.034 for 1381 reflections.
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| 4. |
- Ptasiewicz-Bak, H., et al.
(författare)
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Structure, Charge and Spin Density in Na2Ni(CN)4.3H2O at 295 and 30 K
- 1998
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Ingår i: Acta Crystallographica Section B. - : International Union of Crystallography (IUCr). - 0108-7681 .- 1600-5740. ; 54:5, s. 600-612
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Tidskriftsartikel (refereegranskat)abstract
- The earlier reported structure of the title compound,disodium tetracyanonickelate(II) trihydrate,Na 2 Ni(CN) 4.3H 2O, has been found to be incorrect andhas now been redetermined. The charge distribution hasbeen determined by multipole reÆnements againstsingle-crystal X-ray diffraction data. In the reÆnementbased on 30 K data a comparison was made between theresults obtained using hydrogen positions and displace-ment parameters from X-ray diffraction with those usingthe values determined by neutron diffraction. The spindensity was investigated by polarized neutron diffrac-tion at 1.6 K. Crystal data: at T = 30 K: a = 7.278 (4), b =8.856 (5), c = 15.131 (8) A, = 89.32 (5), = 87.39 (4),= 83.61 (4); at 295 K: a = 7.392 (4), b = 8.895 (4), c =15.115 (8) A, = 89.12 (2), = 87.46 (2), = 84.54 (2).The structure contains practically square planarNi(CN) 2ˇ4 ions, which are stacked on top of each otherin almost linear chains along the a direction. Theseparation between the Ni(CN) 2ˇ4 planes is rather large,with Ni–Ni distances around 3.7 A. The six crystal-lographically independent water molecules are eachcoordinated to two sodium ions, approximately in thetetrahedral (lone-pair) directions, and the polarizinginØuence of these sodium ions also appears to bereØected in the deformation density in the lone-pairplane. The charge density based on the deformationfunctions of all atoms in the structure is compared withthe individual densities calculated from the deformationfunctions of only nickel or the separate water molecules.In this way the effects of simple superposition of theindividual densities have been studied. In the planarNi(CN) 2ˇ4 ion the individual deformation density ofnickel is in qualitative agreement with that expectedfrom crystal-Æeld theory. As the repulsion from theelectrons is much weaker perpendicular to the Ni(CN) 2ˇ4plane than within this plane, the deformation density isconsiderably larger in the perpendicular direction.However, the largest maxima in the individual deforma-tion density around nickel are not found precisely in theplanes deÆned by nickel and the four cyanide ligands orin the perpendicular direction just mentioned, whichillustrates that it is necessary to consider the crystal Æelddue to the whole crystalline environment.
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