Enhancement of IR and VCD intensities due to charge transfer

Signatures of counter-ion association and hydrogen bonding in vibrational circular dichroism spectra

“…15, in order to achieve good agreement between the experimental VCD spectrum reported by Nafie et al in ref. 13 and our calculations performed for the L-dddÁ Á Á2Cl À complex, we have scaled with different factors the frequencies of the N-H stretching modes and C-H stretching modes according to the suggestion in ref.…”

“…15 We will show here that the VCD sign changes observed in the N-H bending modes and the giant enhancement of the IR/VCD intensities observed in the N-H stretching modes are manifestations of the same phenomenon.…”

“…As a result only the x and y components of the MDTM (which are zero by symmetry) are expected to be affected by charge transfer. As we have analyzed in detail before, 15 in such a case the movements of electronic charge in the z direction do show up in larger x and y components of MDTM contributions of individual atoms, but they continue to sum to zero by symmetry. We can therefore conclude that indeed the mechanism described in Section 6.1 in case (B1) is responsible for the VCD sign change observed for mode 60 of FM upon association of two Cl À ions.…”

“…15. As the situation is similar also in the case of the L-dddÁ Á Á3Cl À and L-dddÁ Á Á5Cl À complexes we will not perform such an analysis here.…”

“…15 As a result charge will be transferred between the Cl À ions and the N-H bonds in all three molecular complexes considered here, i.e. L-dddÁ Á Á2Cl À , L-dddÁ Á Á3Cl À and L-dddÁ Á Á5Cl À .…”