The resonance Raman spectra are reported for the Mn(II), Cu(II), Ni(II), and Co(II) complexes of the dianonic N4 macrocyclic ligand 5,7,12,14-tetramethyldibenzo[b,i] [1,4,8,11]tetraazacyclotetradecahexenate (L2-). Raman intensity patterns as a function of excitation frequency covering the argon ion laser emission lines (and the Rhodamine 6G dye laser emission region for NiIIL) have been constructed. MnIIL and CuIIL show a simple one-term frequency dependence with the ligand π → π* transition near 380 nm. NiIIL shows selective Raman intensity enhancement of low-frequency modes in resonance with a charge transfer band at 585 nm. Incontrast, the resonance behavior near the π → π* transition shows characteristic enhancement of high-frequency ligand modes. In each region a one-term theoretical curve fits the data well. CoIIL shows a strong antiresonance interference effect near 460 nm within a weak charge transfer band on the shoulder of the π → π* transition. This is the first observation of Raman antiresonance involving only allowed electronic transitions. The data are fit with a two-term theoretical expression which demonstrates the origin of the antiresonance behavior. The interpretation of the Raman intensity patterns leads us to assign the 460 nm band in CoIIL and the 585 nm band in NiIIL to charge transfer transitions and indicates that the 460 nm band is coupled to the ligand π → π* transition while the 585 nm band is not.
ASJC Scopus subject areas
- Colloid and Surface Chemistry