Evidence of Ligand Elasticity Occurring in Temperature‐, Light‐, and Pressure‐Induced Spin Crossover in 1D Coordination Polymers [Fe(3ditz) 3 ]X 2 (X = ClO 4 – , BF 4 – )

The complexes [M( 3ditz ) 3 ]X 2 [X = ClO 4 – , M = Fe II ( 1 ), Zn II ( 2 ); X = BF 4 – , M = Fe II ( 3 ), Zn II ( 4 ); 3ditz = 1,3‐di(tetrazol‐1‐yl)propane] were prepared. Disordering of the propylene chain in 3ditz is not affected by thermally induced spin crossover in 1 ( T 1/2 ↓ = 149 K, T 1/2 ↑ = 150 K) and 3 ( T 1/2 ↓ = 158, T 1/2 ↑ = 161 K). Low‐spin to high‐spin (LS→HS) switching triggered by laser‐light irradiation (520 nm) also does not influence the disordering of the ligand, leading to restoration of the initial HS phase. Pressurization of crystals results in a reduction of the Fe–N distances by about 0.19 Å, which indicates practically complete spin crossover (SCO). Also, in this case, the disordering of the ligand remains unchanged, although thermally and pressure‐induced SCO is accompanied by different changes of 3ditz molecules. Upon thermally induced SCO, perturbation resulting from the reduction of the Fe–N distances is accompanied by a slight elongation of the bridging ligand. In contrast, in the range 0.25–0.55 GPa, the pressure‐induced SCO is associated with shrinkage of the 3ditz molecule. Further elevation of pressure results in the inversion of structural changes and – similar to temperature‐induced spin crossover – a slight elongation of the ligand molecule takes place.