International
Tables for Crystallography Volume G Definition and exchange of crystallographic data Edited by S. R. Hall and B. McMahon © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. G. ch. 3.5, pp. 141-142
Section 3.5.3.1. Specification of local axes at each atom^{a}Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, and ^{b}Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L8S 4M1 |
Data items in this category are as follows:
ATOM_LOCAL_AXES The bullet (•) indicates a category key. The arrow is a reference to a parent data item.
The ATOM_LOCAL_AXES category is used to define a local Cartesian axis system for each atom. Data items in this category are looped, with the category key ( _atom_local_axes_atom_label) being a pointer to the _atom_site_label defined in the ATOM_SITE category of the core CIF dictionary. The orientation of the Cartesian basis is defined in terms of vectors between atoms, and any arbitrary orientation can be described by including dummy atoms if necessary. The spherical coordinate system used in the description of the multipoles is defined in terms of the local Cartesian basis: z is the polar axis from which the angle is measured, is measured from the x axis in the xy plane with the y axis having a value of .
Example 3.5.3.1 shows how the category is used in part of an electron density CIF relating to a charge density study of the complex of 1,8-bis(dimethylamino)naphthalene with 1,2-dichloromaleic acid (a `proton sponge') (Mallinson et al., 1997).
Example 3.5.3.1. Definition of the local Cartesian axis system for the atoms in a proton sponge complex.
References
Mallinson, P. R., Wozniak, K., Smith, G. T. & McCormack, K. L. (1997). A charge density analysis of cationic and anionic hydrogen bonds in a `proton sponge' complex. J. Am. Chem. Soc. 119, 11502–11509.Google Scholar