Quantum chemistry as a tool to assess energetic and spectroscopic properties of C1 and C2 hydrocarbons in MOF-74-Mg

Abstract

Periodic boundary conditions as implemented within a linear combination of atomic orbital approach are applied to determine the infrared spectra of methane, acetylene, ethylene, and ethane in MOF-74-Mg. Intensities and frequency shifts with respect to the molecules in the gas phase are described and discussed with respect to geometrical arrangements and structural modifications of the molecules adsorbed in the framework. Given the predictive nature of the work and in the attempt of providing a better ground for comparison with experimental spectroscopic observations, different molecular loadings are considered where one (low loading), three (medium loading), and six (full loading) molecules are adsorbed at the primary adsorption binding site identified by the MgO5 inorganic brick of the MOF structure. In addition, enthalpies of adsorption are reported for methane and acetylene whose addition to previous works by the same authors, provides an overall assessment at electronic structure level of the energetic behavior of C1–C4 hydrocarbons in MOF-74-Mg. Calculations are conducted at B3LYP-D2* level of theory as implemented in the Crystal14 program.