Slow Self‐Assembly Favors Hysteresis above Room Temperature for an Iron(II) 1D‐Chain Spin‐Crossover Complex

Abstract

AbstractThe X‐ray structures and magnetic properties of three new iron(II) coordination polymers with the general formula [FeL1(Lax)]n are presented. L1 is the tetradentate N2O22– Schiff‐base‐like ligand (E,E)‐{dimethyl‐2,2′‐[1,2‐phenylenebis(iminomethylidyne)]bis(3‐oxobutanato)(2–)‐N,N′,O3,O3′}. For the axial coordination, 4,4′‐bipyridine (bipy), 1,2‐bis(4‐pyridyl)ethane (bpea), and 1,2‐bis(4‐pyridyl)ethene (bpee) were used. Spin‐transition behavior was observed for the bpea and the bipy complexes. In both cases, two different polymorphs were isolated, showing different magnetic properties. In the case of the bipy complex 1, different preparation methods were tested to elucidate which conditions favor one polymorph over another. It appears that a slow precipitation of the coordination polymer favors a cooperative spin transition above room temperature, whereas a fast precipitation results in a gradual spin transition at lower temperatures. In the case of the bpea complex, an incomplete spin transition is observed, which can be explained by the crystal packing.