title: Synthesis, magnetism and Mössbauer studies of tetranuclear heterometallic {Fe(III)2Ln2}(Ln = Gd, Dy, Tb) complexes: evidence of slow relaxation of magnetization in the terbium analogue.
abstract: A new family of tetranuclear heterometallic assemblies, [Fe(III)2Gd2(H2L)4(η(2)-NO3)2]·2ClO4·2CH3OH·2H2O (1), [Fe(III)2Dy2(H2L)4(η(2)-NO3)2]·2ClO4·2CH3OH·2H2O (2), [Fe(III)2Tb2(H2L)4(η(2)-NO3)2]·2ClO4·2CH3OH·2H2O (3), have been synthesized employing a multi-dentate Schiff-base ligand, (E)-2,2'-(2-hydroxy-3-((2-hydroxyphenylimino)methyl)-5-methylbenzylazanediyl)-diethanol (H4L), Fe(ClO4)2·6H2O, and Ln(III) nitrate salts. These compounds have been structurally characterized by various analytical and spectroscopic techniques. The molecular structures of 1-3 have been confirmed by single crystal X-ray crystallography. All the three complexes contain two Fe(III) ions at the periphery and two Ln(III) ions in the centre. The entire assembly is held together by four doubly deprotonated [LH2](2-) ligands. All the three complexes (1-3) are dicationic in nature and possess an overall Z-type topology. Magnetic measurements reveal the presence of predominant ferromagnetic coupling for all the three compounds at low temperature. The presence of a frequency-dependent out-of-phase signal in the imaginary part of the ac susceptibility plot suggests a slow relaxation of magnetization for 3 (Fe(III)2Tb2). Furthermore, the magnetization dynamics of all the three complexes have been corroborated by Mössbauer spectroscopy.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India.
authors.forename: Prasenjit
authors.initials: P
authors.lastname: Bag
authors.forename: Joydeb
authors.initials: J
authors.lastname: Goura
authors.forename: Valeriu
authors.initials: V
authors.lastname: Mereacre
authors.forename: Ghenadie
authors.initials: G
authors.lastname: Novitchi
authors.forename: Annie K
authors.initials: AK
authors.lastname: Powell
authors.forename: Vadapalli
authors.initials: V
authors.lastname: Chandrasekhar