Novel lanthanide-based polymeric chains and corresponding ultrafast dynamics in solution

Thielemann, Dominique T., Klinger, Melanie, Wolf, Thomas J. A., Lan, Yanhua, Wernsdorfer, Wolfgang, Busse, Madleen, Roesky, Peter W., Unterreiner, Andreas-N., Powell, Annie K., Junk, Peter C., and Deacon, Glen B. (2011) Novel lanthanide-based polymeric chains and corresponding ultrafast dynamics in solution. Inorganic Chemistry, 50 (23). pp. 11990-12000.

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Two types of structurally related one-dimensional coordination polymers were prepared by reacting lanthanide trichloride hydrates [LnCl3·(H2O)m] with dibenzoylmethane (Ph2acacH) and a base. Using cesium carbonate (Cs2CO3) and praseodymium, neodymium, samarium, or dysprosium salts yielded [Cs{Ln(Ph2acac)4}]n (Ln = Pr (1), Nd (2), Sm (3), Dy (4)) in considerable yields. Reaction of potassium tert-butoxide (KOtBu) and the neodymium salt [NdCl3·(H2O)6] with Ph2acacH resulted in [K{Nd(Ph2acac)4}]n (5). All polymers exhibit a heterobimetallic backbone composed of alternating lanthanide and alkali metal atoms which are bridged by the Ph2acac ligands in a linear fashion. ESI-MS investigations on DMF solutions of 1−5 revealed a dissociation of all the five compounds upon dissolution, irrespective of the individual lanthanide and alkali metal present. Temporal profiles of changes in optical density were acquired performing pump/probe experiments with DMF solutions of 1−5 via femtosecond laser spectroscopy, highlighting a lanthanide-specific relaxation dynamic. The corresponding relaxation times ranging from seven picoseconds to a few hundred picoseconds are strongly dependent on the central lanthanide atom, indicating an intramolecular energy transfer from ligands to lanthanides. This interpretation also demands efficient intersystem crossing within one to two picoseconds from the S1 to T1 level of the ligands. Magnetic studies show that [Cs{Dy(Ph2acac)4}]n (4) has slow relaxation of the magnetization arising from the single Dy3+ ions and can be described as a single-ion single molecule magnet (SMM). Below 0.5 K, hysteresis loops of the magnetization are observed, which show weak single chain magnet (SCM) behavior.

Item ID: 29667
Item Type: Article (Research - C1)
ISSN: 1520-510X
Keywords: intramolecular energy-transfer; MRI contrast agents; magnetic-resonance; crystal-structure; structural-characterization; coordination polymers; donor ligands; ionic liquid; complexes; luminescence
Funders: Deutsche Forschungsgemeinschaft (DFG) , DFG-Center for Functional Nanostructures within Research Area Council, Australian Research Council (ARC), Fonds der Chemisthen Industrie , European Research Council (ERC), STEP MolSpinQIP
Projects and Grants: Australian Research Council (ARC) DP0984775, ERC Advanced Grant MolNanoSpin no. 226558
Date Deposited: 02 Oct 2013 10:34
FoR Codes: 03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030202 f-Block Chemistry @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 100%
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