The use of n.m.r. spectroscopy in the structure determination of natural products: two-dimensional methods

1989 ◽  
Vol 6 (2) ◽  
pp. 111 ◽  
Author(s):  
A. E. Derome
Keyword(s):  
Natural Products ◽  
Structure Determination ◽  
Two Dimensional

scholarly journals Limitations of LEED-Structure Determination of Reconstructed Crystal Surfaces

1982 ◽  
Vol 37 (10) ◽  
pp. 1103-1118 ◽  
Author(s):  
H. Jagodzinski
Keyword(s):  
Structure Determination ◽  
Crystal Surface ◽  
Dimensional Space ◽  
Point Group ◽  
Two Dimensional ◽  
Crystal Surfaces ◽  
Difficult Situation ◽  
3 Dimensional ◽  
Lattice Constants

Although a strictly ordered reconstructed crystal surface may have the two-dimensional symmetry prescribed by the bulk (two-dimensional subsymmetry of the 3-dimensional space group), it belongs more frequently to a subgroup. In the LEED-pattern a lower symmetry of the translation group can easily be detected on account of the superstructure reflections observed. In this case anti-phase domains can hardly be avoided. An even more difficult situation arises if the symmetry of the point group is violated, although the symmetry of the diffraction pattern is not altered at the end of the reconstruction. Twin domains without changes of lattice constants have to be taken into account.Dynamical scattering of anti-phase domains is calculated by applying the "Cluster embedded chain"-method for various distributions of domains. It is shown that the incoherent superposition of scattering amplitudes, normally applied in LEED-calculations may lead to serious errors in structure determination. This effect is even more pronounced for twin domains. As an example we discuss the reconstruction of the (001)-surface of Si and Ge, and show that the wellknown (2 X 1)-structure is an averaged structure only, consisting of anti-phase domains with the (4 x 2)-structure. It may be concluded therefrom that none of the present model structures of this reconstruction agrees with this experimental observation.

scholarly journals Crystal structure of bis(azido-κN)bis(quinolin-8-amine-κ2N,N′)iron(II)

2016 ◽  
Vol 72 (10) ◽  
pp. 1488-1491
Author(s):  
Fatima Setifi ◽  
Dohyun Moon ◽  
Robeyns Koen ◽  
Zouaoui Setifi ◽  
Morad Lamsayah ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Magnetic Properties ◽  
Structure Determination ◽  
Crystal Packing ◽  
Octahedral Geometry ◽  
Title Complex ◽  
Two Dimensional ◽  
Azide Ion ◽  
Amine Ligands

The search for new molecular materials with interesting magnetic properties using the pseudohalide azide ion and quinolin-8-amine (aqin, C9H8N2) as a chelating ligand, led to the synthesis and structure determination of the title complex, [Fe(N3)2(C9H8N2)2]. The complex shows an octahedral geometry, with the FeIIatom surrounded by six N atoms; the two N3−anions coordinate in acisconfiguration, while the remaining N atoms originate from the two quinolin-8-amine ligands with the quinoline N atoms lying on opposite sides of the Fe atom. The crystal packing is dominated by layers of hydrophilic and aromatic regions parallel to theacplane, stabilized by a two-dimensional hydrogen-bonded network and π–π stacking.

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