Quintuple-Decker Heteroleptic Phthalocyanine Heterometallic Samarium-Cadmium Complexes. Synthesis, Crystal Structure, Electrochemical Behavior, and Spectroscopic Investigation.

A one-pot synthesis methodology was employed for obtaining diverse quintuple-decker phthalocyanine heterometallic lanthanide-cadmium complexes. By using the reaction of a double-decker homoleptic/heteroleptic phthalocyanine samarium compound with metal-free phthalocyanine and cadmium acetate in 1,2,4-trichlorobenzene at 200 °C, two novel quintuple-decker heteroleptic phthalocyanine heterometallic samarium-cadmium compounds, {(Pc)Sm(Pc)Cd(Pc*)Cd(Pc)Sm(Pc)} (1) and {(Pc)Sm(Pc*)Cd(Pc*)Cd(Pc*)Sm(Pc)} (2), together with one homoleptic phthalocyanine species, {(Pc*)Sm(Pc*)Cd(Pc*)Cd(Pc*)Sm(Pc*)} (3), were successfully fabricated, where H2Pc and H2Pc* represent unsubstituted phthalocyanine and 2,3,9,10,16,17,23,24-octakis(n-pentyloxy)phthalocyanine, respectively. Their quintuple-decker structures have been disclosed by various spectroscopic techniques and single-crystal X-ray diffraction. In addition, valence tautomerization of these three quintuple-decker complexes has been achieved by the addition of phenoxathiin hexachloroantimonate, giving three oxidized forms including one-, two-, and three-electron oxidation products. From 1 to 3 with the same oxidation state, the increased number of n-pentyloxy substituents of phthalocyanine ligands induces the blue shift of electronic absorption in the IR region due to the increased gap associated with the introduction of electron-donating substituents. In particular, the electronic absorption spectra of one- and two-electron oxidation products for 1 exhibit a rare band in the middle-IR region around 3000 nm, being one of the farthest electronic transitions captured by UV-vis spectroscopy. The three-electron oxidation product of 1 displays two bands at 2231 and 2740 nm, respectively. These data are well confirmed by IR spectroscopic data and theoretical calculation results.