Kiralj R., Ferreira M. M. C., “Use of the Cambridge Structural Database in Study of Single and Partial Double C-X (X=C,N,O) Bonds in Organic Molecules in Crystalline State”. São Carlos, SP, 16-19/03/2003: XVI Reunião da Sociedade Brasileira de Cristalografia [16th Meeting of Brazilian Crystallographic Society], Livro de Resumos [Book of Abstracts], (2003) 32. Oral, poster OPQM02.

OPQM02. Use of the Cambridge Structural Database in Study of Single and
Partial Double  C-X  (X = C, N, O) Bonds in Organic Molecules in Crystalline
State

Kiralj R. and Ferreira M. M. C
Instituto deQuímica,UniversidadeEstadualde Campinas.E-mails:rudolf@iqm.unicamp.br,
marcia@iqm.unicamp.br
 

The  Cambridge  Structural  Database   (CSD)   [1]  is   an  organic/organometallic   crystal
structures database  with various possibilities  of  visualization and analysis of the hits.  The
current CSD version (November 2002)  contains  272066  crystal structures determined by
diffraction methods  (X-ray, neutron, synchrotron)  [2].  This is an encouragement to study
multiple C-X bonds, where X is usually C, N or O  in typical organic compounds.  Another
reason  to  study these bonds is their presence  in bioactive molecules as  drugs  and natural
biomolecules,   and   in   environmental   pollutants  as  polycyclic  aromatic  hydrocarbons
(PAHs)  and their derivatives. Moreover,  C-C bonds  were  among the first ones exhibiting
structure correlation as bond length-bond order relationships [3]. Today, when  the number
of  determined crystal structures with  high-level  precision is  increasing,  it  is  possible  to
update such relationships,  generalize to other bond  types  and  molecular classes,  and  by
careful analysis qualify and even quantify delocalization,  substitution  and  crystal  packing
effects  on bond lenghts.   Furthermore,  in  structural,   organic  and  theoretical chemistry,
simple equations for calculation of bond lengths  from some simple variables,  are welcome.
The  aim  of  this  work  is  to  present  new  proper  findings  on  bond  length-bond  order
relationships  taking  into  account  those  phenomena   affecting  the  bond length.  Current
findings  on  extremely long  C-C  bond length  around  3 Å [4]  put traditional teaching  on
chemical bonding  to  be  reexamined  and  more generalized,  what is  also the aim  of  this
work.   This  presentation discusses accurate  CSD  searches appropriate  for  chemometric
analysis,   and  generation of bond variables  as  bond  orders,   topological  indices,   crytal
packing effect  parameters.   Finally,   regression  equations  for  bond length prediction  are
established, validated and interpreted. The  compounds under study are PAHs, nucleobases,
aza-PAHs and carbon allotropic modifications and carbon clusters,  all  obtained from CSD.

[1] F. H. Allen, Acta Cryst., B58 (2002) 380.

[2] The Cambridge Structural Database. http://www.ccdc.cam.ac.uk/support/

[3] L. Pauling, L. O. Brockway, J. Y. Beach, J. Am. Chem. Soc., 57 (1935) 2705.

[4] J. J. Novoa et al., Angew. Chem. Int. Ed., 40 (2001) 2540.

The authors acknowledge FAPESP for the support.
 
 

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