The {Fe-III[Fe-III(L-1)(2)](3)} star-type single-molecule magnet

Star-shaped complex {Fe-III[Fe-III(L-1)(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 Mossbauer 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 . 4CHCl(3) contains the enantiomers (Delta)-[(S, S)(R, R)(R, R)] and (Lambda)-[(R, R)(S, S)(S, S)], whereas in case of 3 . 3CH(2)Cl(2) four independent molecules, forming pairs of the enantiomers [Lambda-(R, R)(R, R)(R, R)]-3 and [Delta-(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.