Quantifying cooperative intermolecular interactions for improved carbon dioxide capture materials

We have optimized the geometry and calculated interaction energies for over 100 different complexes of CO2 with various combinations of electron accepting (Lewis acid) and electron donating (Lewis base) molecules. We have used the recently developed explicitly correlated coupled cluster singles doubles and perturbative triples [CCSD(T)-F12] methods and the associated VXZ-F12 (where X = D, T, Q) basis sets. We observe only modest changes in the geometric parameters of CO2 upon complexation, which suggests that the geometry of CO2 adsorbed in a nanoporous material should be similar to that of CO2 in gas phase. When CO2 forms a complex with two Lewis acids via the two electron rich terminal oxygen atoms, the interaction energy is less than twice what would be expected for the same complex involving a single Lewis acid. We consider a series of complexes that exhibit simultaneous CO2-Lewis acid and CO2-Lewis base intermolecular interactions, with total interaction energies spanning 14.1-105.9 kJ mol(-1). For these cooperative complexes, we find that the total interaction energy is greater than the sum of the interaction energies of the constituent complexes. Furthermore, the intermolecular distances of the cooperative complexes are contracted as compared to the constituent complexes. We suggest that metal-organic-framework or similar nanoporous materials could be designed with adsorption sites specifically tailored for CO2 to allow cooperative intermolecular interactions, facilitating enhanced CO2 adsorption. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3624363]