N , N′ ‐Bis(2,2′‐bipyridine‐6‐ylmethyl)‐2,2′‐biphenylenediamines: A Tuneable Ligand Scaffold for Room Temperature Fe 2+ SCO Complexes

Condensation and subsequent reduction of 2,2′‐diaminobiphenyls 5 with 6′‐ and 5′‐substituted 6‐carbaldehyde‐2,2′‐bipyridines 4 yielded N , N′ ‐bis(2,2′‐bipyridine‐6‐ylmethyl)‐2,2′‐biphenyl‐enediamines 7 , which were employed as hexadendate ligands with N6 donor sets in the synthesis of dicationic [Fe 2+ ( 7 ‐κ 6 N )] complexes 8 . Dependent on the substitution pattern the respective complexes are found in the HS state ( 8b and 8c ) or show SCO behaviour. By means of temperature‐dependent susceptibility measurements, usingEvans' method, the thermodynamic parameters Δ H , Δ S and T 1/2 for the SCO have been determined. T 1/2 as well as Δ H are remarkably susceptible to substitution next to the central C–C bond of the biphenyl bridge.