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Issue 23, 2006
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The {FeIII[FeIII(L1)2]3} star-type single-molecule magnet

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Star-shaped complex {FeIII[FeIII(L1)2]3} (3) was synthesized starting from N-methyldiethanolamine H2L1 (1) and ferric chloride in the presence of sodium hydride. For 3, two different high-spin iron(III) ion sites were confirmed by Mössbauer spectroscopy at 77 K. Single-crystal X-ray structure determination revealed that 3 crystallizes with four molecules of chloroform, but, with only three molecules of dichloromethane. The unit cell of 3·4CHCl3 contains the enantiomers (Δ)-[(S,S)(R,R)(R,R)] and (Λ)-[(R,R)(S,S)(S,S)], whereas in case of 3·3CH2Cl2 four independent molecules, forming pairs of the enantiomers [Λ-(R,R)(R,R)(R,R)]-3 and [Δ-(S,S)(S,S)(S,S)]-3, were observed in the unit cell. According to SQUID measurements, the antiferromagnetic intramolecular coupling of the iron(III) ions in 3 results in a S = 10/2 ground state multiplet. The anisotropy is of the easy-axis type. EPR measurements enabled an accurate determination of the ligand-field splitting parameters. The ferric star 3 is a single-molecule magnet (SMM) and shows hysteretic magnetization characteristics below a blocking temperature of about 1.2 K. However, weak intermolecular couplings, mediated in a chainlike fashion via solvent molecules, have a strong influence on the magnetic properties. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were used to determine the structural and electronic properties of star-type tetranuclear iron(III) complex 3. The molecules were deposited onto highly ordered pyrolytic graphite (HOPG). Small, regular molecule clusters, two-dimensional monolayers as well as separated single molecules were observed. In our STS measurements we found a rather large contrast at the expected locations of the metal centers of the molecules. This direct addressing of the metal centers was confirmed by DFT calculations.

Graphical abstract: The {FeIII[FeIII(L1)2]3} star-type single-molecule magnet

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Publication details

The article was received on 10 Nov 2005, accepted on 21 Feb 2006 and first published on 02 May 2006

Article type: Paper
DOI: 10.1039/B515980F
Citation: Dalton Trans., 2006,0, 2865-2874
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    The {FeIII[FeIII(L1)2]3} star-type single-molecule magnet

    R. W. Saalfrank, A. Scheurer, I. Bernt, F. W. Heinemann, A. V. Postnikov, V. Schünemann, A. X. Trautwein, M. S. Alam, H. Rupp and P. Müller, Dalton Trans., 2006, 0, 2865
    DOI: 10.1039/B515980F

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