CO2-Induced Spin-State Switching at Room Temperature in a Monomeric Cobalt(II) Complex with the Porous Nature

CO2-responsive spin-state conversion between high-spin (HS) and low-spin (LS) states at room temperature was achieved in a monomeric cobalt(II) complex. A neutral cobalt(II) complex, [Co-II(COO-terpy)(2)]center dot 4 H2O (1 center dot 4 H2O), stably formed cavities generated via pi-pi stacking motifs and hydrogen bond networks, resulting in the accommodation of four water molecules. Crystalline 1 center dot 4 H2O transformed to solvent-free1without loss of porosity by heating to 420 K. Compound 1 exhibited a selective CO(2)adsorption via a gate-open type of the structural modification. Furthermore, the HS/LS transition temperature (T-1/2) was able to be tuned by the CO2 pressure over a wide temperature range. Unlike 1 exhibits the HS state at 290 K, the CO2 accomodated form 1 superset of CO2(P-CO2=110 kPa) was stabilized in the LS state at 290 K, probably caused by a chemical pressure effect by CO(2)accommodation, which provides reversible spin-state conversion by introducing/evacuating CO(2)gas into/from1.