Raman spectroscopic characteristics of phthalocyanine and naphthalocyanine in sandwich-type phthalocyaninato and porphyrinato rare earth complexes: Part 4. Raman spectroscopic characteristics of naphthalocyanine in mixed (octaethylporphyrinato)(naphthalocyaninato) rare earth double-deckers

Abstract

Raman spectroscopic data in the range of 400–1800 cm −1 for a series of 15 mixed (octaethylporphyrinato)(naphthalocyaninato) double-decker complexes with tervalent rare earths M III(OEP)(2,3-Nc) (M=Y, La, …, Lu except Ce and Pm) and intermediate valent cerium Ce(OEP)(2,3-Nc) have been collected using laser excitation sources emitting at 632.8 and 785 nm. Comparison with the Raman spectra of the corresponding bis(naphthalocyaninato) rare earths reveals that the Raman characteristics of mixed ring double-deckers M(OEP)(2,3-Nc) are dominated by the metallonaphthalocyanine M(2,3-Nc) fragment. Under excitation at 632.8 nm, which is far away from the main Q absorption band of the naphthalocyanine ligand, the most intense Raman band appears at 1598 cm −1 for M III(OEP)(2,3-Nc) (M≠Ce), and is assigned to the naphthalene stretching. On the other hand, for Ce(OEP)(2,3-Nc), this vibration appears as a strongly enhanced peak at 1550 cm −1 together with a medium intense band at 1613 cm −1. Typical Raman marker bands of the monoanion radical Nc − were observed at 1499–1512 cm −1 as a medium band and at 1521−1538 cm −1 as a band whose intensity increases along with the rare earth contraction, resulting from the coupling of pyrrole CC and aza CN stretchings and aza CN-only stretchings, respectively. For Ce(OEP)(2,3-Nc), a weak and broad band centered at 1507 cm −1 with contribution from both pyrrole CC and aza CN stretches together with isoindole stretches was the marker Raman band of Nc 2−. When excited with laser radiation of 785 nm which is in close resonance with the main Q absorption band of naphthalocyanine ligand, the ring radial vibrations of the isoindole moieties at ca. 680 and 732 cm −1 in the Raman spectra of both M III(OEP)(2,3-Nc) and Ce(OEP)(2,3-Nc) are selectively intensified and appear as the most intense vibrations. The marker Raman bands of Nc − in M III(OEP)(2,3-Nc) and Nc 2− in Ce(OEP)(2,3-Nc) are observed in similar regions to those found for excitation at 632.8 nm. The scatterings with contribution from the Nc breathings, ring radial vibration, naphthalene stretchings, benzoisoindole stretchings, aza group stretchings, and the coupling of pyrrole CC and aza CN stretchings in M III(OEP)(2,3-Nc) all show dependence on the rare earth radius, shifting to higher energy along with the rare earth contraction and showing the rare earth ionic size effect on the Raman characteristics of naphthalocyanine in the mixed ring double-decker compounds.