title: Accurate ab initio description of adsorption on coordinatively unsaturated Cu(2+) and Fe(3+) sites in MOFs.
abstract: The performance of different exchange-correlation functionals was evaluated for the description of the interaction of small molecules with (i) cluster models containing Cu(2+) and Fe(3+) coordinatively unsaturated metal sites and (ii) HKUST-1 metal organic framework (MOF). Adsorbates forming dispersion-bound complexes (CH4), complexes with important dispersion and electrostatic contributions (H2, N2, CO2), and complexes stabilized also by a partial dative bond (CO, H2O, and NH3) were considered. The interaction with coordinatively unsaturated sites was evaluated with respect to the coupled-cluster calculations for Cu(2+) and Fe(3+) centers represented by cluster models. The adsorption on dispersion-stabilized sites was examined for the cage-window and the cage-center sites in HKUST-1 with respect to the experimental and DFT/CC results. None of the functionals considered can accurately describe the interaction of all seven adsorbates with Cu(2+) and Fe(3+) sites and with dispersion-dominated adsorption sites. The interaction with coordinatively unsaturated sites was frequently underestimated, for adsorbates forming a partial dative bond in particular, while the adsorption at dispersion-stabilized sites was overestimated. Consequently, interaction energies calculated for different adsorption sites were often in qualitatively incorrect order. The optimal exchange-correlation functional for a particular adsorbate/MOF can thus be found by comparing the performance of various functionals with respect to highly accurate calculations on smaller cluster models as a good representative of MOF structural building blocks.
authors.affiliation: Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University in Prague , Hlavova 2030, CZ-128 40, Prague 2, Czech Republic.
authors.forename: Lukáš
authors.initials: L
authors.lastname: Grajciar
authors.affiliation: Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University in Prague , Hlavova 2030, CZ-128 40, Prague 2, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Nachtigall
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, Prague 6, 162 10, Czech Republic.
authors.forename: Ota
authors.initials: O
authors.lastname: Bludský
authors.affiliation: Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University in Prague , Hlavova 2030, CZ-128 40, Prague 2, Czech Republic.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Rubeš