Spin-crossover behavior of isomorphous bi- and mononuclear iron(III) complexes

Isomorphous bi- and mononuclear iron(III) complexes, [(Fe2L2)-L-III(bimb)](BPh4)(2) (1) and [(FeL)-L-III(meim)]BPh4 (2), where H2L=bis(3-methoxysalicylideneaminopropyl)amine, bimb=1,4-bisimidazolylbutane, meim=N-methylimidazole, and BPh4-=tetraphenylborate, respectively, were synthsized. Binuclear complex 1 showed a two-step spin-crossover (SCO) behavior at T-1/2=60 and 90 K, whereas mononuclear complex 2 showed a one-step SCO behavior at T-1/2=215 K. The different SCO behavior can be ascribed to the quasi-one-dimensional structure constructed by pi - pi stacking and the binuclear structure.