Synthesis and Characterization of Symmetrically versus Unsymmetrically Proton-Bridged Hexa-Iron Clusters

Abstract

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF 4 ) 2 ·6H 2 O with each ligand (H 2 L1 and H 4 L2 ) in a methanolic-pyridine solution resulted in hexa-iron compounds ( C1 and C2 , respectively), which each contain two near-parallel metal triangles of [Fe 3 –μ 3 -O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the μ 3 -O groups. Within each metal triangle of C2 , Fe(III) ions are connected via the amine “straps” of (H 4 L2 -2H). Variable-temperature magnetic susceptibility and Mössbauer data of C1 and C2 indicate the presence of dominant antiferromagnetic interactions between the high-spin ( S = 5/2) Fe(III) centers. For C1 , two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe 3 –μ 3 -O] and [Fe 3 –μ 3 -OH] species were inferred. For C2 , a single sharp quadrupole doublet with splitting intermediate between those determined for C1 was observed, consistent with the symmetric [Fe 3 –μ 3 -O···H···μ 3 -O–Fe 3 ] species inferred crystallographically from the very short μ 3 -O···μ 3 -O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands.

Metallocyclic CuII–LnIII Single-Molecule Magnets from the Self-Assembly of 1,4-Diformylnaphthalene-2,3-diol

“…A combination of three transition metals and one lanthanide ion have, in the past, been used to template the macrocyclization of 2,3-dihydroxybenzene-1,4-dicarbaldehyde with various diamine linkers. − The Plieger group have previous experience in preparing multinuclear metal complexes with potentially interesting magnetic properties, − and the Ishida group have expertise in the magnetic characterization of 3d–4f complexes, particularly those involving copper­(II). − Inspired by the Zn 3 La system first reported by Nabeshima et al and later extended to other metal combinations by Brooker et al, ,,− we investigated the self-assembly and successful crystallization of L 3 Cu 3 Ln complexes using the acyclic ligand system 1,4-diformylnaphthalene-2,3-diol (H 2 L ). While there are numerous examples of magnetically coupled Cu–Ln systems, , throughout the literature, there are very few Cu 3 Ln complexes featuring four in-plane metal ions; − and a CCDC search indicated that, outside of the previously mentioned complexes of Nabeshima and Brooker, there are no other structurally characterized examples which exclusively contain Cu–O–Ln bridges.…”

A mono-oxo-bridged binuclear iron(iii) complex with a Fe–O–Fe angle of 180.0° and its catalytic activity for hydrogen evolution

“…Researchers still pay considerable attention to binuclear oxo-bridged non-haem iron complexes (containing the Fe–O–Fe unit) due to their potential uses in biological processes, catalysts, magnetic materials, etc. 1–8 We can design an appropriate ligand to chelate metal centers in a special frame and control the electron withdrawal from the metal ion core, thereby modifying the intramolecular exchange interaction. 9,10 Binuclear oxo-bridged complexes mainly contain tribridged-, 11 dibridged- 12,13 and monobridged- 14 species.…”