title: The [Fe(III)[Fe(III)(L1)2]3] star-type single-molecule magnet.
abstract: Star-shaped complex [Fe(III)[Fe(III)(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 (delta)-[(S,S)(R,R)(R,R)] and (lambda)-[(R,R)(S,S)(S,S)], whereas in case of 3.3CH2Cl2 four independent molecules, forming pairs of the enantiomers [lambda-(R,R)(R,R)(R,R)]-3 and [lambda-(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.
authors.affiliation: Institut für Organische Chemie, Universität Erlangen-Nürnberg, Henkestr. 42, 91054, Erlangen, Germany. saalfrank@chemie.uni-erlangen.de
authors.forename: Rolf W
authors.initials: RW
authors.lastname: Saalfrank
authors.forename: Andreas
authors.initials: A
authors.lastname: Scheurer
authors.forename: Ingo
authors.initials: I
authors.lastname: Bernt
authors.forename: Frank W
authors.initials: FW
authors.lastname: Heinemann
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Postnikov
authors.forename: Volker
authors.initials: V
authors.lastname: Schünemann
authors.forename: Alfred X
authors.initials: AX
authors.lastname: Trautwein
authors.forename: Mohammad S
authors.initials: MS
authors.lastname: Alam
authors.forename: Holger
authors.initials: H
authors.lastname: Rupp
authors.forename: Paul
authors.initials: P
authors.lastname: Müller