Reversible Chemisorption of Sulfur Dioxide in a Spin Crossover Porous Coordination Polymer

The chemisorption
of sulfur dioxide (SO2) on the Hofmann-like spin crossover
porous coordination polymer (SCO-PCP) {Fe­(pz)­[Pt­(CN)4]}
has been investigated at room temperature. Thermal analysis and adsorption–desorption
isotherms showed that ca. 1 mol of SO2 per mol of {Fe­(pz)­[Pt­(CN)4]} was retained in the pores. Nevertheless, the SO2 was loosely attached to the walls of the host network and completely
released in 24 h at 298 K. Single crystals of {Fe­(pz)­[Pt­(CN)4]}·nSO2 (n ≈
0.25) were grown in water solutions saturated with SO2,
and its crystal structure was analyzed at 120 K. The SO2 molecule is coordinated to the PtII ion through the sulfur
atom ion, Pt–S = 2.585(4) Å. This coordination slightly
stabilizes the low-spin state of the FeII ions shifting
the critical temperatures of the spin transition by 8–12 K.
DFT calculations have been performed to rationalize these observations.