Iron(II) Complexes Supported by a Tetradentate Ligand Providing a Strained Equatorial Coordination Environment: Geometric and Electronic‐Structural Implications

Abstract Searching for SCO compounds with tetradentate equatorial ligands suitable to surface attachment we decided to synthesize iron(II) complexes with the ligand o ‐bpy [ o ‐bpy = 1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane]. For coordination in axial position three different ligands with increasing ligand field strength were considered: isothiocyanate, pyridine, and imidazole. The new iron(II) complexes [Fe( o ‐bpy)(NCS) 2 ], [Fe( o ‐bpy)(py) 2 ](BPh 4 ) 2 , and [Fe( o ‐bpy)(im) 2 ](BPh 4 ) 2 were characterized with the help of Mössbauer spectroscopy, magnetic measurements, and X‐ray crystallography. The Mössbauer data and magnetic susceptibility measurements show that all three synthesized compounds are in the high‐spin state between 300 and 2 K. To explain these findings DFT calculations are employed. The experimental and theoretical results indicate the presence of distortions from octahedral symmetry due to steric restrictions imposed by the o ‐bpy ligand, which reduce its ligand‐field strength, leading to the observed S = 2 ground states.