Early Lanthanides (Porphyrinato)(Crownphthalocyaninates): Efficient Synthesis and NIR Absorption Characteristics

Abstract

Series of early lanthanides heteroleptic complexes of doubleand triple-decker sandwich-type structure with tetra(15-crown-5)phthalocyanine [(15C5)4 PcH2] and tetrakis-meso-(4-methoxyphenyl)porphyrin [An4PH2] ([An4P] Ln[(15C5)4Pc] and [An4P]Ln[(15C5)4Pc]Ln[An4P]) are synthesized. It is found that the whole series of La-Eu acetylacetonates can be applied for a one-step formation of heteroleptic sandwich-type complexes. Triple-decker heteroleptic complexes [An4P]Ln[(15C5)4Pc]Ln[An4P] are formed regioselectively as a single isomer with internal position of crownphthalocyanine deck. Heteroleptic doubleand triple-decker complexes are found to be the only products of the reaction. Ligand scrambling is not observed and no homoleptic complexes are detected as side products. All the synthesized complexes are characterized with a set of physical-chemical methods. It was shown that the lanthanide-sensitive bands are present in NIR region of the spectra of all synthesized complexes. The position of NIR absorption is found to be linearly dependent on lanthanide ionic radius. Analysis of electronic absorption spectra of all synthesized complexes allowed to determine the influence of ligand environment on the oxidation state of cerium metal center. The comparison of the mentioned linear correlation and spectral data for cerium complexes allowed determination of the oxidation state in each particular case. It is found that cerium atom may utilize both +3 and +4 oxidation states in double-decker complex [An4P]Ce[(15C5)4Pc]. In contrast, coordination environment of tripledecker complex [An4P]Ce[(15C5)4Pc]Ce[An4P] effectively stabilizes CeIII state and prevents its oxidation to CeIV. The comparison of behaviour of Eu and Ce doubleand triple-decker complexes upon chemical oxidation is performed, that allowed to determine a set of redox forms and their stability.