Infrared Spectra of Phthalocyanine and Naphthalocyanine in Sandwich-Type (Na)phthalocyaninato and Porphyrinato Rare-Earth Complexes. II. The Effects of Rare-Earth Ionic Size on the IR Characteristics of Naphthalocyaninein Bis(naphthalocyaninato) Rare-Earth Complexes

Abstract

The infra-red (IR) spectroscopic data for a series of 28 homoleptic substituted bis(naphthalocyaninato) rare-earth complexes M(2,3-Nc*)₂ [M = Y, La–Lu except Pm; H₂Nc* = 3(4),12(13),21(22),30(31)-tetra(tert-butyl)-2,3- naphthalocyanine (H₂TBNc) and 3,4,12,13,21,22,30,31-octa(dodecylthio)-2,3-naphthalocyanine (H₂ODTNc)] have been collected with a resolution of 2 cm^–1. These neutral sandwich complexes are radicals due to their composition (Nc*)^2–M^III(Nc*)^–, wherein the unpaired electron is delocalized over both macrocycles on the vibrational time scale. Compared to spectra obtained with low resolution, such as 4 cm^–1, a larger number of vibrational modes could be distinguished. The IR spectra for M(ODTNc)₂ are much simpler than those of M(TBNc)₂, revealing the relatively higher symmetry of the former molecules. By analogy with bis(phthalocyaninato) rare-earth counterparts, the pyrrole stretching absorptions at 1314–1317 and 1323–1330 cm^–1 for M(TBNc)₂ and at 1316–1327 cm^–1 for M(ODTNc)₂ are assigned to the IR marker bands of the respective naphthalocyanine mono-anion radicals. These marker bands, together with those at 746–753 cm^–1 assigned to C–H wagging, 1350–1355 cm^–1 attributed to pyrrole stretchings, and 1389–1394 cm^–1 due to naphthalene stretchings, have been found to shift slightly to higher energy along with the rare-earth contraction, clearly demonstrating the effect of rare-earth ionic radius.