Structural Diversity of Iron Complexes Based on Chelating 5,5′‐dimethyl‐2,2′‐bipyridine Ligand

Using different synthetic procedures, four complexes [Fe 2 Cl 4 ( 5dmbpy ) 2 ] ( 1 ), [Fe( acac )Cl 2 ( 5dmbpy )] ( 2 ), [Fe( 5dmbpy ) 3 ][Fe 2 Cl 6 O] ( 3 ), and [Fe( 5dmbpy ) 3 ][Fe 2 Cl 6 O]·CH 3 CN ( 4 ) ( 5dmbpy is 5,5′‐dimethyl‐2,2′‐bipyridine; acac is acetylacetonate) are prepared and characterized. Complex 1 is built up of dinuclear molecules in which two pentacoordinate Fe(II) atoms are linked by a pair of chloride ligands and coordination is completed by chelating 5dmbpy and terminal chloride ligand. Complex 2 exhibits a molecular structure in which the hexacoordination of the Fe(III) is achieved by chelating 5dmbpy and acac ligands and two chloride ligands. Complexes 3 and 4 exhibit ionic structures and they are built up of [Fe( 5dmbpy ) 3 ] 2+ complex cation and dinuclear complex anion [Cl 3 FeOFeCl 3 ] 2− in which Fe(III) atoms are bridged by a μ‐oxido ligand. Complex 4 contains an additional acetonitrile solvate molecule. The crystal structures are stabilized by weak hydrogen interactions 2 – 4 and π–π stacking interactions 1 . Complex 1 is stable up to a temperature of 180 °C and complex 4 up to 160 °C, while complexes 2 and 3 display higher thermal stabilities up to 240 °C. The solid residues of the thermal decompositions of 1 – 3 at 800 °C are formed by α ‐Fe 2 O 3 as corroborated by a combination of X‐ray powder diffraction, scanning electron microscope, and energy‐dispersive X‐ray spectroscopy.