Effect of One- and Two-Electron Reduction of Terbium(III) Double-Decker Phthalocyanine on Single-Ion Magnet Behavior and NIR Absorption.

Reduction of terbium(III) double-decker phthalocyanine, TbPc (1), by sodium fluorenone ketyl in the presence of bis(triphenylphosphoranylidene)ammonium cations yields one-electron-reduced (PPN){Tb(Pc)}·2.5CHCl (2) containing the dianionic Pc macrocycles, whereas a stronger NaCpCo(CO) reductant in the presence of an excess of cryptand yields two-electron-reduced {Cryptand(Na)}{(Pc)Tb(Pc)} (3) containing the Pc radical trianionic macrocycle. Isolated pairs of the {Tb(Pc)} anions are formed in 2, whereas compound 3 has unique 3D packing of the macrocycles with weak π-orbitals overlapping in all three directions. This is the first example of the two-electron-reduced lanthanide double-decker containing Pc radical trianion studied in solid state. Compound 2 manifests single-ion magnet (SIM) behavior with a large effective spin-reversal energy barrier of U = 538 cm in comparison with previously studied (BuN){Tb(Pc)} ( U = 230 cm). Thus, changes in cation size and shape affect the molecular packing of {Tb(Pc)} and increase the spin-reversal energy barrier. At the same time, two-electron-reduced species 3 containing Tb and Pc show no signs of SIM such as hysteresis loop at 1.9 K, and no peaks are observed on the temperature dependencies of in-phase (χ') and out-of-phase (χ″) signals. In contrast to EPR silent 2, both compounds 1 and 3 manifest broad signals from paramagnetic Tb ions. Narrower signals attributed to Pc are of high intensity only in 3. In addition to the absorption bands of Pc in the UV and visible spectral range, compound 3 manifests the lowest energy absorption band in solid-state spectra even in the near IR range at 4700 cm (2130 nm), whereas such bands are not observed in the spectrum of 2. These data show that the reduction of the Pc macrocycles in the lanthanide double-deckers leads to the appearance of new very low-energy new transitions associated with Pc whose energy is the lowest among known reduced metal phthalocyanines.