Tables for
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

International Tables for Crystallography (2006). Vol. G. ch. 3.5, pp. 141-142

Section Specification of local axes at each atom

P. R. Mallinsona* and I. D. Brownb

aDepartment of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, and bBrockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L8S 4M1
Correspondence e-mail: Specification of local axes at each atom

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Data items in this category are as follows:

ATOM_LOCAL_AXES [Scheme scheme1] The bullet (•) indicates a category key. The arrow [(\rightarrow)] 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 [\theta] is measured, [\varphi] is measured from the x axis in the xy plane with the y axis having a value of [\varphi = +90 ^\circ].

Example[link] 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[link]).

Example Definition of the local Cartesian axis system for the atoms in a proton sponge complex.

[Scheme scheme2]


First citationMallinson, 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

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