Synthesis, structure, spectroscopic properties, and electrochemistry of rare earth sandwich compounds with mixed 2,3-naphthalocyaninato and octaethylporphyrinato ligands

A series of 14 heteroleptic rare earth sandwich complexes [M-III-(nc)(oep)] (M = Y, La-Lu except Ce and Pm nc = 2,3-naphthalocyaninate; oep = octaethy lporphyrin ate) have been prepared by a one-pot procedure from the correspo nding [M(acac)(3)] . nH(2)O (acac = acetylacetonate), metal-free porphyrin H-2(oep), and naphthalonitrile in the presence of 1,8-diazabicyclo[5.4.0]un dec-7-ene (DBU) in n-octanol. The molecular structures of four of these com plexes (M = Sm, Gd, Y, Lu) are isostructural, exhibiting a slightly distort ed square antiprismatic geometry with two domed ligands. The interplanar di stance decreases from 2.823 to 2.646 A along the series as a result of lant hanide contraction. The whole series of complexes have also been characteri zed spectroscopically. All the electronic absorptions, except the two B-ban ds due to nc and the oep rings, are metal-dependent, indicating that there are substantial, pi-pi interactions. The hole or the unpaired electron in t hese double-deckers is delocalized over both macrocyclic ligands, as eviden ced by the co-appearance of the IR marker bands for the nc(.-)(1315-1325 cm (-1)) and oep(.-) (1510-1531 cm(-1)) pi radical ions. Three one electron ox idation couples and up to three one-electron reduction couples have been re vealed by electrochemical methods. All the potentials are linearly dependen t on the size of the metal center. The changes in absorption spectra during the first electro-oxidation and reduction of the La-III, Eu-III, and Y-III double-deckers have also been studied spectroelectrochemically. The spectr al data recorded for [M = Y(nc)(oep)](,M=Y, La-Lu except Ce and Pm) reduced chemically with hydrazine hydrate are in accord with those obtained by spe ctroelectrochemical methods. The first heteroleptic naphthalocyaninate-cont aining triple-deckers [M-2(III)(nc)-(oeP)(2)] (M = Nd, Eu) have also been p repared by a raise-by-one-story method by using [M-III(nc)(oep)] (M = Nd, E u), [M(acac)(3)1]. nH(2)O (M = Nd, Eu), and H2(oep) as starting materials. The compounds adopt a symmetrical tripledecker structure with two outer oep rings and one inner nc ring, which has been confirmed by H-1 NMR spectrosc opy and X-ray structural determination of the Nd complex. Both compounds gi ve a near-IR absorption at 1021 nm (for M = Nd) or 1101 nm (for M = Eu), wh ich has rarely been observed for neutral (or hole-free) tripledecker comple xes and can be ascribed to the lowest-energy Q'(0, 0) transition. Similarly to the double-decker analogues, these triple-decker complexes underao a se ries of one-electron transfer processes with a relatively small potential g ap (1.1-1.2 V) between the first oxidation and the first reduction.