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Electron density dictionary (rhoCIF) version 1.0.1




   This category contains information about the multipole
   coefficients used to describe the electron density.
   High-resolution X-ray diffraction methods enable the
   determination of the electron density distribution in
   crystal lattices and molecules, which in turn allows for a
   characterization of chemical interactions (Coppens, 1997;
   Koritsanszky & Coppens, 2001). This is accomplished by
   the construction of a mathematical model of the charge
   density in a crystal and then by fitting the parameters of
   such a model to the experimental pattern of diffracted
   X-rays. The model on which this dictionary is based
   is the so-called multipole formalism proposed by Hansen
   & Coppens (1978). In this model, the electron density in
   a crystal is described by a sum of aspherical "pseudoatoms"
   where the pseudoatom density has the form defined in the
   _atom_rho_multipole_* items. Each pseudoatom density
   consists of terms representing the core density, the spherical
   part of the valence density and the deviation of the valence
   density from sphericity. The continuous electron density in the
   crystal is then modelled as a sum of atom-centred charge
   distributions. Once the experimental electron density has been
   established, the "atoms in molecules" theory of Bader (1990)
   provides tools for the interpretation of the density
   distribution in terms of its topological properties.

   Ref:  Bader, R. F. W. (1990). Atoms in molecules: a quantum
           theory. Oxford University Press.
         Coppens, P. (1997). X-ray charge densities and chemical
           bonding. Oxford University Press.
         Hansen, N. K. & Coppens, P.  (1978). Acta Cryst. A34,
         Koritsanszky, T. S. & Coppens, P. (2001). Chem. Rev. 101,


Example 1 - Multipole coefficients for the nickel ion in [Ni(H3L)][NO3][PF6], [H3L = N,N',N''-tris(2-hydroxy-3-methylbutyl)-1,4,7-triazacyclononane] [G.T. Smith et al. (1997). J. Am. Chem. Soc. 119, 5028-5034].
    Ni2+(1)  2.38(4)  0.32(4)  0.00  0.00 -0.02(1)
             0.00(2)  0.00     0.00  0.00  0.00
            -0.08(1)  0.00     0.00  0.00  0.00      0.06(1)  -0.04(1)
             0.05(1)  0.00     0.00  0.00  0.00     -0.20(1)   0.08(1)
             0.00     0.00
             1.04(1)  0.44(1)  0.44  1.15(4)   0.44  1.15

Type: null

Category: category_overview