Comparative Spectroscopic and Electrochemical Properties of Bis(octakis(dodecylthio)naphthalocyaninato)europium(III) and Bis(tetra-tert-butylnaphthalocyaninato)europium(III) Complexes

Bis(substituted-2,3-naphthalocyaninato)europium(III) complexes:  bis(octakis(dodecylthio)-2,3-naphthalocyaninato)europium(III) {Eu[2,3-Nc(SC₁₂H₂₅)₈]₂, 1} and bis(tetra-tert-butyl-2,3-naphthalocyaninato)europium(III) {Eu[2,3-Nc(t-Bu)₄]₂, 2} have been synthesized by cyclic tetramerization of naphthalonitriles with Eu(acac)₃·H₂O in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in refluxing n-octanol. These compounds were characterized by UV−visible, magnetic circular dichroism (MCD), near-IR, IR, EPR, and mass spectroscopies. The absorption and MCD spectra of 1 showed splitting of the Q band, with peaks at 700 and 784 nm, red shifted from the Q band of 2 at 763 nm. The absorption and MCD spectral band deconvolution calculations of complex 1 gave two A terms in the Q-band region. The A terms are assigned to ²A₂ → ²E₁ transitions. Cyclic voltammograms of 1 and 2 showed reversible oxidation couples at E_1/2 = −0.28 V (for 2) and −0.25 V (for 1) vs ferrocenium/ferrocene (Fc⁺/Fc). The second oxidation exhibited a complicated behavior for both complexes. The reduction couples for 2 were observed at E_1/2 = −0.61, −1.64, −1.97, and −2.42 V, and for 1 they were observed at E_1/2 = −0.62, −1.60, −1.86, and −2.27 V vs Fc⁺/Fc. Spectral changes observed on chemical oxidation and reduction of the complexes are presented, and the behaviors of 1 and 2 are compared.