Iron(II) Spin Crossover (SCO) Materials Based on Dipyridyl-N-Alkylamine

We present here a new series of spin crossover (SCO) Fe(II) complexes based on dipyridyl-N-alkylamine and thiocyanate ligands, with the chemical formulae [Fe(dpea)(2)(NCS)(2)] (1) (dpea = 2,2'-dipyridyl-N-ethylamine), I-[Fe(dppa)(2)(NCS)(2)], (2) INFe(dppa)(2)(NCS)(2)], and (2') (dppa = 2,2'-dipyridyl-N-propylamine). The three complexes displayed nearly identical discrete molecular structures, where two chelating ligands (dpea (1) and dppa (2 and 2')) stand in the cis-positions, and two thiocyanato-kappa N ligands complete the coordination sphere in the two remaining cis-positions. Magnetic studies as a function of temperature revealed the presence of a complete high-spin (HS) to low-spin (LS) transition at T-1/2 = 229 K for 1, while the two polymorphs I-[Fe(dppa)(2)(NCS)(2)] (2) and INFe(dppa)(2)(NCS)(2)] (2') displayed similar magnetic behaviors with lower transition temperatures (T-1/2 = 211 K for 2; 212 K for 2'). Intermolecular contacts in the three complexes indicated the absence of any significant interaction, in agreement with the gradual SCO behaviors revealed by the magnetic data. The higher transition temperature observed for complex 1 agrees well with the more pronounced linearity of the Fe-N-C angles recently evidenced by experimental and theoretical magnetostructural studies.