Ligand bands

The low-energy d-d bands of planar Co(II) complexes have rather low intensities, but the visible spectra are often dominated by high-intensity charge-transfer and ligand bands 14). 

Three types of electronic transition can be distinguished among compounds of the d block transition elements d-d bands, charge transfer (or electron-transfer) bands and intra-ligand bands. Configuration interaction may make the distinctions rather hazy, however. 

Strong erbium luminescence with a full-width at half-maximum of 100 nm is also generated by the ternary complex [Er(pos)3phen] upon excitation in the ancillary ligand band at 333 nm. With respect to direct Er111 excitation into the 2Hn/2 level at 520 nm, the photoluminescence signal increases by a factor 20 (Van Deun et al., 2004b). 

Assignment was uncertain owing to the presence of a ligand band in this region. 

The complex is obtained as deep olive-green platelike crystals, m.p. 142° (decomposes). The solid compound decomposes slowly on exposure to the atmosphere the process is greatly accelerated if the material is finely divided. The preparation of samples for physical measurements must be carried out in a nitrogen atmosphere. The complex forms very air-sensitive solutions in 1-butanol or nitromethane. The infrared spectrum exhibits characteristic ionic perchlorate absorptions at 1100 and 625 cm, and there are strong ligand bands at 1625, 1400, 575, 500, and 380 cm-i. 

The bis(base) (where base = tV-methylimidazole, 1,5-dicyclohexylimidazole, pyridine) complexes of FeII(TpivPP), where TpivPP = tetrakis(o-pivalamidophe-nyl)porphyrin, give characteristic porphyrinate ligand bands.218 Resonance Raman spectra were used to obtain excitation profiles for two a2g ligand modes for a range of iron(II) porphyrins.219 Ligand modes in the resonance Raman spectra of trarax-cross-linked basket-handle iron(II) porphyrins were used to characterise the ruffled, six-coordinated low-spin iron(II) porphyrin complexes.220... 

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