3.3 IR spectra and mode of bonding

In order to ascertain the mode of bonding, the IR spectrum of the free ligands was compared with those of their La complexes. By careful comparison of the spectra of the complexes with those of the free ligands, it was found that the band at 3430 cm<sup>1</sup> is found to be disappeared by complexation suggesting the involvement of OH groups of the phenolic groups in complex formation with their deprotonation. The bands due to NH and SH are shifted to higher or lower frequencies indicating the participation of –N and –S donors in the coordination, while the bands due to C=O are unchanged. The strong bands at 1622 and 1298 cm<sup>1</sup> due to υC=<sup>N</sup> and υC▬<sup>O</sup> (azomethine and phenolic groups) are shifted to lower wave number 1609–1565 and 1280–1242 cm<sup>1</sup> , respectively, in metal complexes indicating the participation of nitrogen of azomethine and oxygen of phenolic group in complexation. The complexes showing also three bands at the range 1480–1400, 1380–1350, and 1170–1020 cm<sup>1</sup> indicate the unidentate coordination mode of the nitrate group. The curves also, showed that shift in the peaks of O▬H, C▬O, C▬S groups (complex 3) due to their sharing in the complexation and that recorded by the M▬O, and M▬S peaks. All these results are in good agreement with the conductance data. Another evidence for the coordination is the observance of new bands in the far IR region at 570–505, 520–440, and 432–524 cm<sup>1</sup> which may be due to υM▬<sup>O</sup> υM▬<sup>N</sup> and υM▬S, respectively, that are not observed in the spectrum of the free ligands [26, 27].
