Heterospin Single‐Molecule Magnets Based on Terbium Ions and TCNQF₄ Radicals: Interplay between Single‐Molecule Magnet and Phonon Bottleneck Phenomena Investigated by Dilution Studies

Abstract

A series of isostructural compounds with formula [M(TCNQF(4))(2)(H(2)O)(6)]TCNQF(4)3 H(2)O (M=Tb (1), Y (2), Y:Tb (74:26) (3), and Y:Tb (97:3) (4); TCNQF(4)= tetrafluorotetracyanoquinodimethane) were prepared and their magnetic properties investigated. Compounds 1, 3, and 4 show the beginning of a frequency-dependent out-of-phase ac signal, and decreasing intensity of the signal with decreased concentration of Tb(III) ions in the diluted samples is observed. No out-of-phase signal was observed for 2, an indication that the behavior of 1, 3, and 4 is indicative of slow paramagnetic relaxation of Tb(III) ions in the samples. A more detailed micro-SQUID study at low temperature revealed an interplay between single-molecule magnetic (SMM) behavior and a phonon bottleneck (PB) effect, and that these properties depend on the concentration of diamagnetic yttrium ions. A combination of SMM and PB phenomena was found for 1, whereby the PB effect increases with increasing dilution until eventually a pure PB effect is observed for 2. The PB behavior is interpreted as being due to the presence of a "sea of organic S=1/2 radicals" from the TCNQF(4) radicals in these compounds. The present data underscore the fact that the presence of an out-of-phase ac signal may not, in fact, be caused by SMM behavior, particularly when magnetic metal ions are combined with organic radical ligands such as those found in the organocyanide family.

Application of the Hubbard Model to Cp*2Yb(bipy), a Model System for Strong Exchange Coupling in Lanthanide Systems

“…Previous investigations have observed that exchange coupling can enhance SMM behavior in Ln complexes. 12,[32][33][34][35][36] Exchange coupling in Cp* 2 Yb(bipy) (3)…”

Crystal field and exchange interactions in rare earth transition metal salen compounds containing bipyridine, pyrazole complexes

“…As there is no information regarding the electrical conductivity of the systems, it is difficult to explain the positive Pr-Cu exchange effect. Amongst the compounds prepared with such types of ligands with Gd 3+ , Dy 3+ and Tb 3+ as the lanthanide counterpart, both the ferromagnetic and antiferromagnetic types of 3d-4f magnetic exchange interaction have been observed [15][16][17][18]. The nature of interaction depends on the environment of the metal ions and on the structural parameters.…”

Magnetic and Luminescent Properties of Sm, Eu, Tb, and Dy Coordination Polymers with 2‐Hydroxynicotinic Acid

“…The ac susceptibility measurements were also performed under 1 kOe applied magnetic field, which led to a shift in the out-of-phase signal to higher temperature ( Figure S1 in the Supporting Information) due to fast quantum tunneling suppressed by applying the magnetic field. [25] Unfortunately, the peak of the out-of-phase signal was not detected due to the temperature limitations of the low-temperature apparatus. The origin of slow relaxation of the magnetization is still under question, but the large anisotropy provided by the Dy III ions might play an important role in the phenomenon.…”