Abstract:
Ethylenediamine has been used as the backbone to synthesize the novel Pt-N^N complexes. The
outstanding binding ability of ethylenediamine allows it to be used in the synthesis of hydrophilic
ligand systems, by substituting the terminal amine group with bulky aromatic sulphonamide
fragments which would also incorporate lipophilicity as well as enhanced fluorescence. Employing
such amphipathic ligand systems would be an optimal approach of synthesizing platinum coordination
complexes for biological applications with improved uptake by targeted cells. In this study, two
ligands (L1=N(SO2biphenyl)ethylenediamine, L2=N(SO2azobenzene)ethylenediamine) (Figure 1)
and their corresponding novel platinum complexes(C1=PtCl2(N(SO2biphenyl)ethylenediamine),
C2=PtCl2(N(SO2azobenzene)ethylenediamine)) were synthesized. UV-Visible spectra of the ligands
indicate clear changes from starting material along with the presence of intra-ligand π→π* and n→π*
transitions, giving rise to absorption peaks around 200-400 nm. Shifts of these peaks can be observed
in the UV-Visible spectra of the complexes related to MLCT transitions. The strong S-N band
detected in the FTIR spectra of the ligands is found at 820 cm-1 in L1 and 842 cm-1 in L2 and shifts
to lower wavenumbers in ethylenediamine complexes (801 in C1 and 836 cm-1 in C2) due to direct
donation of nitrogen lone pair to platinum. Disappearance of the -NH and -NH2 stretching vibration
frequency in the FTIR spectra of the complexes, found around 3300 cm-1 in the ligands, indicates the
deprotonation of the amine groups on coordination in the complex. Methylene protons of the amine
moiety of the ligands can be seen to be magnetically inequivalent in L1 and L2, appearing as triplets
within the 2.00 - 3.00 ppm range in 1H NMR spectra. Complexes display slightly higher fluorescence
intensity compared to the ligands, possibly due to rigidification of the ligand systems on developing
the coordination complex. Structural data was obtained from single crystal X-ray diffraction of L2
and C1 which validated the formation of the ligand and complex.
