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TOPOLOGICAL ANALYSIS OF THE CHARGE DENSITY IN CRYSTALS: WHAT CAN WE LEARN ABOUT THE NATURE OF CHEMICAL BONDS
Konstantine A. Lyssenko, Mikhail Yu. Antipin
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Science, 117813, Vavilova st. 28, B-334, Moscow, Russia, e-mail: kostya@xray.ineos.ac.ru
Keywords: AIM theory, charge density, high-resolution x-ray analysis
The topological analysis of the charge density
function based on R. Bader's theory of "Atoms in
molecules" (AIM) [1] has been performed for a series of
crystals of organic and organoelement compounds using
low-temperature high-resolution X-ray diffraction data. Multipole
refinement of the X-ray data has been done with XD programme
package. The main goal of the work was to find particular
relations between the nature of the chemical bonds of the
different types and their topological characteristics. The next
list of organic and organoelement compounds we have studied:
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Taking into account the well known depletion of deformation electron density (DED) in the region of the O-O bond in the peroxides we have carried out the topological analysis of the electron density (r(r)) in the crystals of organic hydroperoxides (I) and (II). It has been found, that in contrast to theoretical data, the d2r(r) is positive in the (3,-1) bond critical point (b.c.p.) in the O-O bonds what corresponds to the local depletion of r(r) (closed shell interaction). Thus homopolar O-O bond in peroxides differs significantly from the other known bonds formed by the elements of the second period,except the F-F bond in F2.
In the structural study of the low-coordinated phosphorus compounds we have studied charge density distribution in molecules (III) and (IV) representatives of the mono- and two-coordinated phosphorus. Analysis of the DED maps and the ellipticity of the P=C and P=C (3,-1) b.c.p. have demonstrated that the "banana bonds" model is more preferable for the description of the multiple phosphorus-carbon bonds, than the standard (s+2p) scheme.
Analysis of the r(r) values in the (3,-1) b.c.p. in the molecule of the hypervalent 5-coordinated silicon (V) revealed that the 4c-3e description of the O-Si-Cl bond is the most preferable.
In zwitterionic 1,4-ylide pyridinium (VI) unusual contact (Pyd+...CNd-) between the cyano group and nitrogen atom of the pyridinium gas been found. The role of this contact in the stabilisation of this compound and its influence on the electron density distribution in the dicyano group has been established on the basis of the topological analysis, DED and electrostatic pontential mapping.
1. R.W. Bader, Atoms in Molecules. A Quantum
Theory, Clarrendon Press., Oxford,. 1990
