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

Dmitri V Konarev; Salavat S Khasanov; Mikhail S Batov; Alexander G Martynov; Irina V Nefedova; Yulia G Gorbunova; Akihiro Otsuka; Hideki Yamochi; Hiroshi Kitagawa; Rimma N Lyubovskaya

doi:10.1021/acs.inorgchem.9b00131

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

Inorg Chem. 2019 Apr 15;58(8):5058-5068. doi: 10.1021/acs.inorgchem.9b00131. Epub 2019 Mar 25.

Authors

Dmitri V Konarev¹, Salavat S Khasanov², Mikhail S Batov^{1

3}, Alexander G Martynov⁴, Irina V Nefedova⁵, Yulia G Gorbunova^{4

5}, Akihiro Otsuka, Hideki Yamochi, Hiroshi Kitagawa, Rimma N Lyubovskaya¹

Affiliations

¹ Institute of Problems of Chemical Physics RAS , Chernogolovka , Moscow Region , 142432 Russia.
² Institute of Solid State Physics RAS , Chernogolovka , Moscow Region , 142432 Russia.
³ Lomonosov Moscow State University , Leninskie Gory, Moscow , 119991 Russia.
⁴ A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS , Leninskii pr., 31, Bldg. 4 , Moscow , 119071 Russia.
⁵ N. S. Kurnakov Institute of General and Inorganic Chemistry RAS , Leninskii pr., 31 , Moscow , 119991 Russia.

PMID: 30907600
DOI: 10.1021/acs.inorgchem.9b00131

Abstract

Reduction of terbium(III) double-decker phthalocyanine, Tb^IIIPc₂ (1), by sodium fluorenone ketyl in the presence of bis(triphenylphosphoranylidene)ammonium cations yields one-electron-reduced (PPN⁺){Tb^III(Pc^2-)₂}^-·2.5C₆H₄Cl₂ (2) containing the dianionic Pc^2- macrocycles, whereas a stronger NaCpCo(CO)₂ reductant in the presence of an excess of cryptand yields two-electron-reduced {Cryptand(Na⁺)}₂{(Pc^2-)Tb^III(Pc^•3-)}^2- (3) containing the Pc^•3- radical trianionic macrocycle. Isolated pairs of the {Tb^III(Pc^2-)₂}^- 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^•3- radical trianion studied in solid state. Compound 2 manifests single-ion magnet (SIM) behavior with a large effective spin-reversal energy barrier of U_eff = 538 cm^-1 in comparison with previously studied (Bu₄N⁺){Tb^III(Pc^2-)₂}^- ( U_eff = 230 cm^-1). Thus, changes in cation size and shape affect the molecular packing of {Tb^III(Pc^2-)₂}^- and increase the spin-reversal energy barrier. At the same time, two-electron-reduced species 3 containing Tb^III and Pc^•3- 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^III ions. Narrower signals attributed to Pc^•3- 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^-1 (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^•3- whose energy is the lowest among known reduced metal phthalocyanines.