2,6-Bis(pyrazol-3-yl)pyridine as Meridional Capping Ligand: Synthesis, Characterization, and Crystal Structure of the First Corresponding Hexanuclear Iron(III) Complex

Based on the 2,6-bis(pyrazol-3-yl)pyridine ligand (H(2)bPP) the hexanuclear iron(III) complex [Fe-6(bPP)(4)(eta(3)-O)(2)(mu-OMe)(3)(mu-OH)Cl-2] (1) was synthesized. The reaction with iron(II) chloride and additional pyridine leads to the exclusive formation of the complex through self-assembly process. Six octahedrally coordinated iron atoms arc linked through the pyrazolido groups of four H(2)bpp ligands. These arc further linked through bridging hydroxido, methoxido, and oxido groups. The complex has been characterized by IR spectroscopy, ESI mass spectrometry, elemental analysis and X-ray crystallography. Temperature-dependent magnetic measurements indicate strong antiferromagnetic exchange interaction between the high-spin iron(111) ions within the complex, which leads to an S = 0 spin ground state. As a result of the two Fe-3(mu(3)-O) fragments two frustrated exchange pathways are present. In addition the properties of H(2)bpp as a potential capping ligand for the synthesis of heteroleptic trinuclear complexes based on the triaminoguanidine core is investigated.