Two new Fe(II) spin crossover complexes with tetrazol-1-yl-cycloalkane ligands

Two new 1-(tetrazol-1-yl)cycloalkanes [Cntz] with n = 5 and 6 were synthesised as ligands for iron(II) spin crossover complexes. Just recently, the [Fe(C3tz)6](BF4)2 showed that the rigid cyclopropyl-substituent of the tetrazole yielded a rather abrupt and complete spin transition at T½ ≈ 190 K [1]. Aiming for a deeper insight into the factors governing the spin transition behavior such as abruptness and spin transition temperature we synthesized the two new homologous complexes [Fe(C5tz)6](BF4)2 and [Fe(C6tz)6](BF4)2 which were characterized by XRPD, magnetic susceptibility measurements, DSC, 57Fe-Mössbauer, UV–Vis–NIR and MIR spectroscopy. The magnetic and structural properties of both [Fe(Cntz)6](BF4)2 with n = 5 and 6 are also compared with the [Fe(C3tz)6](BF4)2 and its structural peculiarities are discussed.