Spin crossover complexes with ligands suitable for further functionalization could allow for an easy access to multifunctional switchable materials. Within this context, we recently characterized the Fe(II) SCO complexes of propargyl-1H-tetrazole. Although the design of the ligand seems similar to the one of the well-known propyl-1H-tetrazole, the spin transition behavior is notably different. Both compounds reported herein feature a gradual spin transition with a T_1/2 shifted to lower temperatures, compared to the more flexible propyl-ligand. Due to the potential instable structure of these compounds, especially of the perchlorate complex, we also investigated our compounds with regard to their sensitivity against thermal and mechanical stress. These experiments led to the conclusion that the proper handling includes no enhanced risk of explosive decomposition.

The two achiral ligands tris(1-methyl-1H-imidazol-2-yl)methanol ((mim)₃COH) and bis(1-methyl-1H-imidazol-2-yl)(3-methylpyridin-2-yl)methanol ((mim)₂(mpy)COH) form on reaction with Fe(BF₄)₂∙6H₂O, the octahedral low-spin complexes [Fe((mim)₃COH)₂](BF₄)₂∙MeCN (1) and [Fe((mim)₂(mpy)COH)₂](BF₄)₂∙0.5MeCN (2). Both octahedral complexes immediately rearrange to the chiral [Fe₄O₄]-cubane clusters [Fe₄(mim)₃CO)₄](BF₄)₄ (3) and [Fe₄(mim)₃CO)₄](BF₄)₄∙CHCl₃ (4), whereas the highly symmetrical 3 crystallizes as racemate, 4 resolves based on the asymmetry introduced by the 2-methylpyridine moiety and crystallizes as an enantiomerically pure sample. Both clusters feature redox active [Fe₄O₄]-cubane cores with up to four individual accessible states, which directs towards a potential application as electron-shuttle.