Evidence of Ligand Elasticity Occurring in Temperature-, Light-, and Pressure-Induced Spin Crossover in 1D Coordination Polymers [Fe(3ditz)3]X2 (X = ClO4-, BF4-).

The complexes [M(3ditz)₃]X₂ [X = ClO₄^-, M = Fe^II (1), Zn^II (2); X = BF₄^-, 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, T1/2↑ = 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. [ABSTRACT FROM AUTHOR]