Bis[1,4,8,11,15,18,22,25-octa(butyloxyl)phthalocyaninato] rare earth double-decker complexes: synthesis, spectroscopy, and molecular structure

Abstract

Homoleptic octa-α-substituted bis(phthalocyaninato) rare earth double-deckers HM^III[Pc(α-OC₄H₉)₈]₂ [M = Eu (1), Y (2); Pc(α-OC₄H₉)₈ = 1,4,8,11,15,18,22,25-octa(butyloxyl)phthalocyanine] have been prepared by treating the metal-free phthalocyanine H₂Pc(α-OC₄H₉)₈ with the corresponding M(acac)₃·nH₂O (acac = acetylacetonate) in the presence of organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and benzo-18-crown-6/benzo-15-crown-5 in refluxing n-octanol. To the best of our knowledge, it is the first example of homoleptic non-peripherally octa(alkoxyl)-substituted bis(phthalocyaninato) rare earth complexes. Comparative studies on a series of reactions reveal the key role of DBU as catalyst and crown ether as template in the formation of homoleptic rare earth double-decker complexes with structurally highly deformed non-peripherally octa(butyloxy)-substituted phthalocyanine ligand. The molecular structure of complex 1 has been determined by single-crystal X-ray diffraction analysis. The metal center is octa-coordinated by the isoindole nitrogen atoms of the two phthalocyaninato ligands, forming a distorted square antiprism. Despite the extremely non-planar saddle conformation employed by metal free H₂Pc(α-OC₄H₉)₈ molecule, both the phthalocyanine rings in HEu^III[Pc(α-OC₄H₉)₈]₂ (1) adopt a conformation that is domed toward the europium center, similar to corresponding unsubstituted or β-substituted bis(phthalocyaninato) analogues. These two bis(phthalocyaninato) rare earth double-deckers have also been characterized by a wide range of spectroscopic methods including MS, ¹H NMR, UV-vis, IR, and EPR. Structural and spectroscopic studies reveal that the π–π interaction between the two Pc(α-OC₄H₉)₈ rings is weaker than that for the corresponding unsubstituted or β-substituted bis(phthalocyaninato) analogues.