Charge density investigations on [2,2]-paracyclophane – in data we trust

Abstract

Four datasets on [2,2]-paracyclophane were collected in-house and at the Advanced Photon Source at two different temperatures for charge density investigation. Global data quality indicators such as high resolution, high I/σ(I) values, low merging R values and high multiplicity were matched for all four datasets. The structural parameters did not show significant differences, but the synchrotron data depicted deficiencies in the topological analysis. In retrospect these deficiencies could be assigned to the low quality of the innermost data, which could have been identified by e.g. merging R values for only these reflections. In the multipole refinement these deficiencies could be monitored using DRK-plot and residual density analysis. In this particular example the differences in the topological parameters were relatively small but significant.

Quantum Crystallography: Current Developments and Future Perspectives

“…Thus, first principles of quantum mechanics are not imposed during this process, as they are in the case of quantum mechanicalc omputations. [99] With the ever-rising quality of experimental data, more and finer details of the electron density are observed with the help of the multipole model:c hemical bonds, lone pairs, crystal field effects on electron density of transition metals, [100] core region contraction upon chemical bond formation, [89] intermolecular charget ransfer [101] and electron density polarization upon interaction with neighboring molecules. Nevertheless, the multipole modelc an provide ac harged ensity model as good as ad ouble-zeta basis-set representation, is mature and its application is fast.…”

“…Moreover,u nlike in X-ray wavefunction refinement, [76,98] the extracted experimental information can be easily identified and the danger to "get what you put in" is smaller ("in data we trust"). [99] With the ever-rising quality of experimental data, more and finer details of the electron density are observed with the help of the multipole model:c hemical bonds, lone pairs, crystal field effects on electron density of transition metals, [100] core region contraction upon chemical bond formation, [89] intermolecular charget ransfer [101] and electron density polarization upon interaction with neighboring molecules. [92] In addition, the model providest he meanst oo bserve ah igh degree of transferability of atoms in similar chemical environments and to build pseudoatom databanks.…”

Analysis of oscillatory rocking curve by dynamical diffraction in protein crystals

“…Such analysis performed with a high-energy beam can be based on the kinematical theory of diffraction (30). However, the analysis of the diffraction intensities of low-order reflections is often poor even when the high-order reflection intensities are well resolved (31). The accurate analysis of the diffraction intensities of lower-order reflections is a prerequisite, especially for the evaluation of the valence electron distribution.…”

Homochiral [2.2]Paracyclophane Self‐Assembly Promoted by Transannular Hydrogen Bonding

“…a) Top, structure of [2.2]paracyclophane (pCp) and its standard carbon numbering. Bottom, X‐ray crystal structure (data at 15 K) of pCp with transannular distances and benzene ring deformation indicated . b) Familiar names of two pCp substitution patterns; planar chirality is indicated (±).…”