Considerations on Gated CO Adsorption Behavior in One-Dimensional Porous Coordination Polymers Based on Paddlewheel-Type Dimetal Complexes: What Determines Gate-Opening Temperatures?

Low-dimensional coordination polymers such as one-dimensional chains often exhibit gated guest sorption accompanying structural transition at a temperature (), which is associated with an external pressure of the guest () characteristic to the material and guest used. This phenomenon can be evaluated using the Clausius-Clapeyron relationship with the equation d( )/d(1/) = /, where Δ and are the transition enthalpy and gas constant, respectively. In this study, gated CO adsorption behavior was investigated in a one-dimensional chain based on a benzoate-bridged paddlewheel diruthenium(II,II) complex with a phenazine (phz) linker, [Ru(-MeOPhCO)(phz)] (; -MeOPhCO = -anisate). Surprisingly, underwent gate opening (GO)/closing (GC) at a much higher , e.g., 385 K for GC, under = 100 kPa than those previously reported for such chain compounds, which usually appeared in the temperature range of 200-270 K. The transition entropy Δ in each system plays a key role in shifting ; results in a much smaller |Δ| in the series. Only produced a CO-accessible two-dimensional topological pore in its CO-adsorbed phase , whereas the others reported previously produced one-dimensional or discrete topological pores for CO accommodation, strongly reflecting the degree of freedom of CO molecules in pores, which is related to Δ.