| 1. |
- Davies, K., et al.
(författare)
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Topological studies of three related metal-organic frameworks of GdIII and 5-nitroisophthalate
- 2012
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Ingår i: Acta Crystallographica Section B: Structural Science. - : International Union of Crystallography (IUCr). - 0108-7681 .- 1600-5740. ; 68:5, s. 528-535
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Tidskriftsartikel (refereegranskat)abstract
- The reaction of 5-nitroisophthalic acid (H(2)NIA) with Gd(NO3)(3)center dot 6H(2)O in DMF afforded three new metal-organic frameworks: [Gd(NIA)(1.5)(DMF)(2)]center dot DMF (I), [Gd-2(NIA)(3)(DMF)(4)]center dot xH(2)O (II) and [Gd-4(NIA)(6)(DMF)(5.5)(H2O)(3)]center dot 4DMF center dot H2O (III). These compounds can be prepared through a variety of methods. Compounds (I) and (II) are more reproducibly formed than compound (III). Network analysis revealed (I) to have a (4(12).6(3))-pcu topology, while (II) displays a (4(2).8(4))(4(2).8(4))-pts topology. Compound (III) was found to present the uncommon 4,5,6T11 topological net, which combines aspects of both the pcu and pts topologies. The short symbol of this net is (4(4).6(2))(4(6).6(4))(2)(4(8).6(6).8).
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| 2. |
- Dopieralski, Przemyslaw D., et al.
(författare)
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Proton-transfer dynamics in the (HCO3-)(2) dimer of KHCO3 from Car-Parrinello and path-integrals molecular dynamics calculations
- 2010
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Ingår i: Acta Crystallographica Section B. - 0108-7681 .- 1600-5740. ; 66, s. 222-228
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Tidskriftsartikel (refereegranskat)abstract
- The proton motion in the (HCO3-)(2) dimer of KHCO3 at 298 K has been studied with Car-Parrinello molecular dynamics (CPMD) and path-integrals molecular dynamics (PIMD) simulations. According to earlier neutron diffraction studies at 298 K hydrogen is disordered and occupies two positions with an occupancy ratio of 0.804/0.196. A simulation with only one unit cell is not sufficient to reproduce the disorder of the protons found in the experiments. The CPMD results with four cells, 0.783/0.217, are in close agreement with experiment. The motion of the two protons along the O center dot center dot center dot O bridge is highly correlated inside one dimer, but strongly uncoupled between different dimers. The present results support a mechanism for the disorder which involves proton transfer from donor to acceptor and not orientational disordering of the entire dimer. The question of simultaneous or successive proton transfer in the two hydrogen bonds in the dimer remains unanswered. During the simulation situations with almost simultaneous proton transfer with a time gap of around 1 fs were observed, as well as successive processes where first one proton is transferred and then the second one with a time gap of around 20 fs. The calculated vibrational spectrum is in good agreement with the experimental IR spectrum, but a slightly different assignment of the bands is indicated by the present simulations.
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| 3. |
- Li, Mingrun, et al.
(författare)
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A complicated quasicrystal approximant ε16 predicted by the strong-reflections approach
- 2010
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Ingår i: Acta Crystallographica Section B. - 0108-7681 .- 1600-5740. ; 66:part 1, s. 17-26
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Tidskriftsartikel (refereegranskat)abstract
- The structure of a complicated quasicrystal approximant ϵ16 was predicted from a known and related quasicrystal approximant ϵ6 by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of ϵ16 were deduced from those of the known ϵ6 structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of ϵ16. An electron-density map of ϵ16 was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of ϵ6, the predicted structure of ϵ16 contains eight layers in each unit cell, stacked along the b axis. Along the b axis, ϵ16 is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. ϵ16 with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted.
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| 4. |
- Zheng, Ran, et al.
(författare)
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Two novel Zn-MOFs : structures and characterization
- 2012
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Ingår i: Acta Crystallographica Section B. - 0108-7681 .- 1600-5740. ; 68, s. 158-163
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Tidskriftsartikel (refereegranskat)abstract
- Two novel three-dimensional Zn-MOFs (zinc metal-organic frameworks), Zn5(mu 3-OH)(BTC)3(Phen)4 center dot 5H2O (denoted as HUT-11) and Zn4(mu 4-O)(BTC)2(Phen)2 center dot 4H2O (denoted as HUT-12), have been synthesized by metalligand-directed assembly under hydrothermal conditions. Here, BTC and Phen are denoted as 1,3,5-benzenetricarboxylate and phenanthroline. HUT-11 contains two kinds of secondary building units (SBUs), Zn3(mu 3-OH)(COO)5 clusters and Zn2(COO)4 clusters. This material exhibits a new three-dimensional (3,4,5)-connected topology with the Schlafli symbol (4.6.8)2(4.82)(4.64.85)(42.62.82). Two perpendicular planes cross at five coordinated Zn1-Zn3-Zn5 nodes, giving a new three-dimensional network. HUT-12 is composed of Zn4(mu 4-O)(COO)6 clusters as the secondary building units and displays a two-dimensional (3,6)-connected TiS2 related net topology with the Schlafli symbol (42.6)(44.62.88.10). Both MOFs show blue light emission and a high thermal stability above 673 K.
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