UV-Vis Studies
The absorption spectra of isatin and its complexes were measured in ethanol. Isatin displayed three bands at 249, 296, and 420 nm due to π-π* and n-π* transitions, Table 3. The solvent effect on the position of the longer wavelength absorption band of isatin indicates that the nπ* transition has some charge transfer (CT) character; the nitrogen atom being the electron donor and the β-carbonyl group the acceptor. Absorption spectra of the complexes obtained from the reaction of M(CO)6; M=Cr or Mo with isatin only as a ligand showed a shift or disappearance of the CT band due to complexation through carbonyl group in isatin [3]. The electronic spectra of the complexes showed new bands in the range 360– 387 nm due to complexation and a weak band in the range of 445–490 nm. The longer wavelength band could be attributed to metal-to-ligand charge transfer transitions. The charge transfer bands for the [Mo(CO)3(isatH)(PPh3)] were appeared at longer wavelength than the [W(CO)3(isatH)(PPh3)] Figure 1. This trend was observed for the complexes [Mo(CO)3(pbiH)(PPh3)] and [W(CO)3(pbiH) (PPh3)]; pbiH=2-(2′-pyridyl)benzimidazole [14].