Synthesis, structure, spectra and magnetic properties of the unsymmetrical oxo-bridged complex [Fe 2 O(OAsPh 3 ) 4 Cl 3 ] 2 [Fe 2 OCl 6 ].2CH 3 CN

Tris(1,10-phenanthroline)iron(II) μ-oxido-bis-[trichloridoferrate(III)]

In the title salt, [Fe(C₁₂H₈N₂)₃][Fe₂Cl₆O], the ionic components are linked into a two-dimensional supra­molecular layer by two pairs of C—H⋯Cl hydrogen bonds and π–π stacking inter­actions [centroid–centroid distances = 3.655 (4) and 3.498 (3) Å]. The salt is characterized as a mixed-valent Fe^II–Fe^III compound, in which an Fe^II atom is coordinated by three phen ligands, forming a six-coordinated cationic entity and the anionic part is formed by two Fe^III atoms in tetra­hedral coordination environments constructed by three chloride ions and one bridging oxide ligand. Intra­molecular C—H⋯N hydrogen bonds are observed.

Effect of N-Methylation of Macrocyclic Amine Ligands on the Spin State of Iron(III): A Tale of Two Fluoro Complexes

Syntheses and characterization of [(cyclamacetate)FeF]PF6 (1) and the corresponding N-methylated complex [(trimethylcyclamacetate)FeF]PF6 (3) are presented. Compound 1 is prepared in good yields from the analogous chloro complex, whereas 3 is prepared by hydrolysis of the oxo-bridged diiron compound (Me3cyclam-acetate)Fe-O-FeCl3 (2) in the presence of PF(6) anions. Magnetic susceptibility and spectroscopic data including electron paramagnetic resonance and Mössbauer spectra indicate that 1 contains low-spin Fe(III) (S = 1/2), while 3 is high spin (S = 5/2). Both octahedral fluoro complexes were investigated theoretically by density functional theory in order to determine why the spin states of the two molecules are different. Energies calculated using the B3LYP functional correctly predict 1 to have a low-spin S = 1/2 ground state and 3 to be high spin, regardless of whether a solvation model is included. The difference between 1 and 3 is most likely a combination of steric effects caused by the N-methyl groups, which compel the Fe-N bond distances to be longer in 3 than they ordinarily would be, and also electronic effects, which cause the N-methylated ligand to be a weaker sigma donor than its nonmethylated counterpart.