4. Computational details
All calculations for the studied compounds were carried out using
Gaussian 03 software [40]. Without any symmetry restrictions and
starting with the X-ray structures as input files, geometry optimization
followed by frequency calculationswas performed by DFT/B3LYP method
using 6-311G(d,p) basis set. No negative vibrational modeswere obtained.
GaussView4.1 has been used to draw the structures of the
optimized geometries [41]. Optimized structural parameters were
used in the electronic properties and isotropic chemical shift calculations.