Heteroleptic Bis(Phthalocyaninato) Europium(III) Complexes Fused with Different Numbers of 15-Crown-5 Moieties. Synthesis, Spectroscopy, Electrochemistry, and Supramolecular Structure

Abstract

A series of heteroleptic bis(phthalocyaninato) europium(III) complexes, namely, Eu(Pc)[Pc(15C5)] (2), Eu(Pc)[Pc(opp-15C5)2] (3), Eu(Pc)[Pc(adj-15C5)2] (4), Eu(Pc)[Pc(15C5)3] (5), and Eu(Pc)[Pc(15C5)4] (6) [Pc = unsubstituted phthalocyaninate; Pc(15C5) = 2,3-(15-crown-5)phthalocyaninate; Pc(opp-15C5)2 = 2,3,16,17-bis(15-crown-5)phthalocyaninate; Pc(adj-15C5)2 = 2,3,9,10-bis(15-crown-5)phthalocyaninate; Pc(15C5)3 = 2,3,9,10,16,17-tris(15-crown-5)phthalocyaninate, Pc(15C5)4 = 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninate], with one, two, three, and four 15-crown-5 voids attached at different positions of one of the two phthalocyaninato ligands in the double-decker molecules, have been devised and prepared by Eu(Pc)(acac)-induced (Hacac = acetylacetone) mixed cyclization of the two corresponding phthalonitriles in the presence of organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in n-pentanol. For the purpose of comparative studies, homoleptic counterparts Eu(Pc)2 (1) and Eu[Pc(15C5)4]2 (7) have also been prepared. These sandwich double-decker complexes have been characterized by a wide range of spectroscopic methods in addition to elemental analysis. Their electrochemistry has also been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The molecular structure of Eu(Pc)[Pc(15C5)4] (6) has been determined by X-ray diffraction analysis. Their supramolecular structure-formation properties, in particular for compounds 5 and 6 in the presence of potassium ions, have also been comparatively studied for the purpose of future functional investigation.

Behaviour of Low-Symmetry Crown-Phthalocyanine in Solution: Concentration Aggregation vs. Cation-Induced Assembly

“…[43] Studies of aggregation of symmetrical tetra-crownsubstituted phthalocyanines M[(15C5) 4 ) [45][46][47][48] evidence that their interaction with potassium ions can be described as a process with nonlinear cooperativity -binding of first cation by two receptor molecules results in formation of dimeric species, which are preorganized for stronger subsequent binding of next three cations with the formation of highly stable eclipsed dimers -{2M[(15C5) 4 Pc]·4K + }. [22,40] The investigation, performed herein, supports this mechanism -indeed, the dimer, where phthalocyanine molecules are linked just with one potassium ion, already has conformation close to eclipsed. This is due to synergetic effect of ion binding and intramolecular stacking interaction, which results in formation of supramolecular dimer with high stability constant.…”

“…This mixture could be separated by column chromatography, the yields of individual complexes, characterized by UV-Vis, MCD and NMR spectra, were 5-13 %. [22] Inter- [23,24] Aggregation of these complexes, induced by interaction with potassium ions, was studied by spectrophotometric titration. [23] Phthalocyanines, containing two and more crownsubstituted fragments, exhibit good solubility in common organic solvents, while mono-crown-substituted complexes have only limited solubility.…”

Supramolecular Approach for Enhancing Single‐Molecule Magnet Properties of Terbium(III)‐Phthalocyaninato Double‐Decker Complexes with Crown Moieties

“…Crown ethers, first reported by Pedersen, are excellent units for accommodating various positively charged cations including alkali metal ions . Combining crown ether units with planar phthalocyanine ligands has led to functional materials, the color changes of which are vivid in the presence of alkali metal ions because the guest (alkali metal ions) induces aggregation . Ishikawa et al.…”

A series of homoleptic bis(phthalocyaninato) rare earth sandwich complexes with large two-photon absorption cross-section

“…phthalocyaninato)lanthanide( Ⅲ ) complexes and could be assigned similarly[37][38][39]. All complexes exhibit Soret bands with maxima around 350-375 nm, intense Q-band at 648-688 nm and the π-radical related band at 450-513 nm.…”