Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 15, Issue 42, Pages 11390-11400Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200900629
Keywords
magnetic properties; quinodimethanes; radicals; rare earths; single-molecule magnets
Categories
Funding
- DOE [DE-FG02-02ER45999]
- NSF [CHE-0610019, NSF-9974899]
- Welch Foundation [A-1449]
- CCD diffractometer [NSF-9807975]
- ANR-PNANO MolNanoSpin [ANR-08-NANO-002]
- ERC Advanced Grant MolNanoSpin [226558]
- STEP MolSpin QIP
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A series of isostructural compounds with formula [M(TCNQF(4))(2)-(H2O)(6)]TCNQF(4)center dot 3H(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.
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