Hochauflösende Röntgen‐Strukturanalyse – eine experimentelle Methode zur Beschreibung chemischer Bindungen

X-Ray diffraction studies on electron density in organic crystals

“…The specific C-H...N interactions in the 1,2,3-triazine crystal were in fact discovered on the basis of this feature 10 (a priori the appearance of such hydrogen bond was regarded as unlikely).…”

“…Thus, in the Mn 2 (CO)i 0 dimer examined below, the population of the d orbitals forming the Mn-Mn bond diminishes under the influence of the ligand field, which is in fact the main reason for the absence of the δρ peak on this bond. 51 However, despite the above stipulations and effects due to the formation of bonds, the height of the δρ,^ peak usually varies in parallel with the quantity n p -n p according to Angermund et al;10 this indicates the predominance of the orientation effect.…”

“…9 Allowance for thermal diffuse scattering is extremely important. 10 Without it, the thermal parameters of atoms proved to be too low (for example, by 12% in oxalic acid), but this is not reflected in the qualitative features of the distributions of δρ in the region of chemical bonds and lone pairs. 11 The greatest difficulty arises in allowing for the extinction contribution.…”

“…The distribution of the total electron density contains in principle exhaustive information about the nature of intramolecular and intermolecular interactions 10 (and also about all the one-electron properties of the system 7 ), but its direct interpretation is difficult. 8 To facilitate the use of such information, additional procedures and concepts are introduced.…”

“…87 However, the differences between the values of 8p max in a single molecule can indicate the non-equivalence of isotypical bonds, which has been confirmed both theoretically and experimentally. For example, in the case of 9-t-butylanthracene QsHig, the values of δρπωχ are approximately proportional to the overlap populations 10 calculated with the aid of the extended Hiickel method. The extremely small value of δρ,^χ on the elongated C-C bridge bond in the compound Ci3HgN 2 45 indicates that this is the weakest bond in the molecule.…”