Mixed (phthalocyanine)(Schiff-base) terbium(iii)–alkali metal(i)/zinc(ii) complexes: synthesis, structures, and spectroscopic properties

Abstract

A series of five mixed (phthalocyanine)(Schiff-base) terbium(III)–alkali metal(I) complexes, Li(Pc)Tb(L)(CH₃OH)₂·(THF) (1) and M(Pc)Tb(L)(CH₃OH) (M = Na, K, Rb, Cs) (2–5), have been synthesized and isolated from the reaction between a metal free Schiff-base ligand of N,N′-bis(3-methyloxysalicylidene)benzene-1,2-diamine (H₂L) and a half-sandwich phthalocyaninato terbium compound M(Pc)(acac) (H₂Pc = metal free phthalocyanine, Hacac = acetylacetone) with the help of a corresponding alkali ion. The sandwich nature, with a mixed phthalocyanine and Schiff-base ligand, of the whole series of five compounds has been unambiguously revealed on the basis of single crystal X-ray diffraction analysis. Electronic absorption and luminescence spectroscopic studies, in particular the titration of 1–5 in mixed methanol/tetrahydrofuran with an equivalent amount of Zn(II) ions, leads to almost the same electronic absorption and luminescence spectra, suggesting the replacement of the alkali metal(I) ion locating at the O₄ cavity of the Schiff-base ligand by a Zn(II) ion. This is confirmed by the X-ray diffraction analysis result for single crystals of the novel mixed (phthalocyanine)(Schiff-base) terbium(III)–zinc(II) complex Zn(Pc)Tb(L)(Py)₂(NO₃)·(CH₃OH)₂·(THF) (6) obtained from the reaction of K(Pc)Tb(L)(CH₃OH) (3) with an excess amount of zinc nitrate in the presence of pyridine (Py). The present results will certainly attract interest for the design, synthesis, and further functional exploration of novel sandwich-type rare earth complexes involving tetrapyrrole and other macrocyclic ligands.