(395af) QM and QM/MM Study On the Interaction of CO2 with CPL2

Metal-organic coordination networks (MOCNs) have high internal surface area, and the flexibility in their synthesis allows modifying the adsorptive properties of the pore very easily [1–6]. CPL2 (Cu2(pyrazine-2,3-dicarboxylate)2(4,4′-bipyridine)) is a MOCN that has a higher adsorption capacity for CO₂ than for other light molecules, such as O₂ and N₂ [7]. The objective of this project is to study CO₂ - CPL2 interactions using quantum mechanical (QM) calculations and ONIOM-EE, which is an integrated quantum mechanical molecular mechanical (QM/MM) method linked via electronic embedding. We have used two representative models for the CPL2 pore to reproduce binding sites in order to quantify energies of adsorption and to map possible adsorption mechanisms. For the QM calculations, we have compared two exchange/correlation functionals B3LYP and wB97XD, which has a specific treatment for Van der Waals forces. We have used a mix of 6-311G+ and LANL2DZ for the basis sets. The latter basis set was used solely on the transition metal atom.  For the ONIOM-EE calculations, we have used UFF to describe the low level part of the system. Our results demonstrate that there is an unpaired electron in the Cu atom. Electronic energies of reaction to form a CPL2 - CO₂ complex range from -2 kJ/mol to -28 kJ/mol, and the distance between the CO₂ and the closest atom of the framework is around of 2.7 Å, indicating  that there is a weak interaction on the CO₂-CPL2 complex.

Reference

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[6]       C. Janiak, “Engineering coordination polymers towards applications,” Dalton Transactions, no. 14, p. 2781, 2003.

[7]       O. J. García-Ricard and A. J. Hernández-Maldonado, “Cu2(pyrazine-2,3-dicarboxylate)2(4,4′-bipyridine) Porous Coordination Sorbents: Activation Temperature, Textural Properties, and CO2 Adsorption at Low Pressure Range,” The Journal of Physical Chemistry C, vol. 114, pp. 1827-1834, 2010.