Utilizing the adaptive polyoxometalate [As2W19O 67(H2O)]14- to support a polynuclear lanthanoid-based single-molecule magnet

Chris Ritchie, Manfred Speldrich, Robert W. Gable, Lorenzo Sorace, Paul Kögerler, Colette Boskovic

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102 Citations (Scopus)

Abstract

Five members of a new family of polyoxometalate (POM)-ligated tetranuclear rare earth metal complexes have been synthesized and characterized. These compounds have the general formula (HDABCO)8H5Li 8[Ln4As5W40O144(H 2O)10(gly)2]•25H2O [Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Y = (5), HDABCO = monoprotonated 1,4-diazabicyclooctane, gly = glycine] and were synthesized from the preformed POM precursor [As2W19O67(H2O)] 14-. The structure is comprised of two {As2W 19O68} building blocks linked by a unit containing four rare earth ions and two additional tungsten centers, with the two glycine ligands playing a key bridging role. Two crystallographically distinct rare earth ions are present in each complex, both of which possess axially compressed, approximate square antiprismatic coordination geometry. The variable-temperature magnetic susceptibility profiles for 2-4 are dominated by population/depopulation of the MJ sublevels of the relevant ground terms, and fitting of the data has afforded the ligand field parameters in each case, from which the energies of the MJ sublevels can be calculated. Alternating current magnetic susceptibility data have revealed the onset of slow magnetic relaxation for 3, with the energy barrier to magnetization reversal determined to be 3.9(1) K. As for other lanthanoid complexes that display slow magnetic relaxation, this energy barrier is due to the splitting of the M J sublevels of the Dy3+ ions such that the ground sublevel has a relatively large |MJ| value, thereby affording Ising-type magnetic anisotropy. This complex is thus the first POM-supported polynuclear lanthanoid-based SMM. Simulation of the W-band EPR spectrum of 1 has afforded the spin Hamiltonian parameters for this species, while the X-band EPR spectrum of 3 indicates the presence of a non-negligible fourth-order transverse component of the anisotropy, which is responsible for the small effective energy barrier observed for 3 and the absence of slow magnetic relaxation for 4.

Original languageEnglish
Pages (from-to)7004-7014
Number of pages11
JournalInorganic Chemistry
Volume50
Issue number15
DOIs
Publication statusPublished - 1 Aug 2011
Externally publishedYes

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