ELECTRONIC-TRANSITIONS OF SALICYLALDEHYDEETHYLENEDIIMINE AND ITS CU(II) COMPLEXES

Electronic absorption spectra of salicylaldehydeethylenediimine (salen) and its Cu(II) complexes have been measured in various media at various temperatures. It is found that salen takes an enol-imine-type structure in cyclohexane and exists as an equilibrium mixture of enol-imine and keto-amine type species in alcoholic media. The polarization spectrum of salen-Cu(II) measured in the stretched PVA film shows that 282, approximately 290, approximately 250, and 230.4 nm bands are polarized along the longer-molecular-axis, and 354, 273.0, 242.4 and approximately 220 nm bands along the shorter-molecular-axis. The 242.4 and approximately 250 nm bands can be assigned to intramolecular charge transfer (CT) transitions between the metal ion and ligand and between the two pi-electronic systems of the ligand, respectively. The complex of salen-Cu(II) forms a dimer in EPA (ether: isopentane: ethanol = 5: 5: 2 in volume) at low temperatures. The first two bands of the monomer at 380 and 362 nm are blue-shifted by the dimer formation, and appear at 370 and 351 nm, respectively, and the 278 nm monomer band splits into two bands at 275 and 267 nm. These spectral changes on the dimer formation are well reproduced by an extended PPP calculation.