Figure 2. Molecular structures of crystal 1 in the low- and high-temperature phase.

(a) The cobalt ions are coordinated by one tripodal L ligand and two nitrate anions in both phases. The molecules stack in parallel along the c axis with different distances between molecules in the low- and high-temperature phases. The n-butyl group of the ligand rotates ca. 100° around the C13–C14 bond following phase transition. Green, Co; grey, C; blue, N; red, O. Hydrogen and disordered carbon atoms (C14′ and C15′) are omitted for clarity. (b) The crystal length changes from 1.78 to 1.90 mm along [001] from 228 to 253 K and switches back to the original state upon cooling, scale bar represents 500 μm.