Spin Dynamics in the Negatively Charged Terbium (III) Bis-phthalocyaninato Complex

Abstract

The experimental and theoretical study of the electron spin dynamics in the anionic form of a single-ion molecule magnet (SIMM), the bis-phthalocyaninato terbium (III) molecule [Pc(2)Tb](-)[TBA](+), has been addressed by means of solid state (1)H NMR spectroscopy. The magnetic properties of the caged Tb(3+) metal center were investigated in a series of diamagnetically diluted preparations, where the excess of tetrabutylamonium bromide ([TBA]Br)(n) salt was used as diamagnetic matrix complement. We found that a high temperature activated spin dynamics characterizes the systems, which involved phonon-assisted transitions among the crystal field levels in qualitative agreements with literature results. However, the activation barriers in these processes range from 641 cm(-1) for the diamagnetically diluted samples to 584 cm(-1) for those undiluted; thus, they exhibit barriers 2-3 times larger than witnessed in earlier (230 cm(-1)) reports (e.g., Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.; Kaizu, Y. J. Am. Chem. Soc. 2003, 125, 8694-8695). At cryogenic temperatures, fluctuations are driven by tunneling processes between the m = +6 and -6 low-energy levels. We found that the barrier Delta and the tunneling rates change from sample to sample and especially the diamagnetically diluted [Pc(2)Tb](-) molecules appear affected by the sample's magneto/thermal history. These observations emphasize that matrix arrangements around [Pc(2)Tb](-) can appreciably alter the splitting of the crystal field levels, its symmetry, and hence, the spin dynamics. Therefore, understanding how small differences in molecular surroundings (as for instance occurring by depositing on surfaces) can trigger substantial modifications in the SIMM property is of utmost importance for the effective operation of such molecules for single-molecule data storage, for example.

Low-energy spin dynamics in the[YPc2]0

“…All reagents were purchased from Across or Aldrich and used without further purification. A mixture of 1,2-dicyanobenzene (42 mmol), Y(acac) 3 ·4H 2 O (5 mmol), and 1,8-diazabicyclo [5,4,0]undec-7-ene (DBU) (21 mmol) in 50 mL of 1-pentanol was refluxed for 1.5 days. The solution was allowed to cool to room temperature.…”

“…Pc-based compounds have attracted significant interest in the last decade after it has been suggested that high temperature superconductivity could be induced in these materials by alkali doping 3 and, more recently, when it has been recognized that neutral [LnPc 2 ] 0 molecules, with Ln a lanthanide ion, are molecular nanomagnets with extremely long coherence times at liquid nitrogen temperature. [4][5][6][7][8] Owing to the flat shape of Pc molecules, the structure of Pc-based materials is typically characterized by chains along which Pc molecules tend to stack. 9 Accordingly some of the Pc-based materials show many similarities to the Beechgaard salts.…”

Real-space observation of spin-split molecular orbitals of adsorbed single-molecule magnets

“…Further progress in the field requires a detailed understanding of structural properties and magnetic interactions of an individual SMM in contact with a ferromagnetic electrode in an atomically well-defined environment. We select bis(phthalo cyaninato)terbium(III) (TbPc 2 ) as a model-type system because of its high blocking temperature (T B~3 0-50 K) 11,12 , its comparably small size and its high stability that allows for thermal deposition in ultrahigh vacuum environments.…”

Molecular Design for Single-molecule Magnetism of Lanthanide Complexes

“…Doping a small amount of the paramagnetic ion into a diamagnetic host lattice (e.g., the Y III isostructure molecules) often results in reduced QTM. 35 The effects of intramolecular ff interaction on the rate of QTM are complicated. 36 In heteroleptic triple-decker [(Pc)Tb(Pc)-Tb(Pc (29) with an octabutoxyphthalocyanate and two unsubstituted phthalocyanates, the lanthanide ions exist along the fourfold symmetry axis with a separation of ca.…”