Interaction of Small Gases with the Unsaturated Metal Centers of the HKUST‑1 Metal Organic Framework

The
interactions of CO, CO2, OCS, SO2, NO,
NO2, N2O, NH3, PH3, and
other small molecules with the undercoordinated metal centers of the
HKUST-1 metal organic framework are studied by means of density functional
theory. These molecules are potentially harmful for humans and the
environment and are widely studied because of their spectroscopic
properties. In this work, the energetic and vibrational characteristics
of the adsorbed species are calculated. Adsorption energies on the
Cu2+ sites of the paddlewheel have been calculated, and
the order is: NH3 > H2O > PH3 > H2S > SO2 > CO ∼ OCS ∼
CO2 ∼ NyOx > N2 > O2. The results
show that the interactions
can be classified into three categories: (1) weak physisorption, (2)
polarization and electrostatics, and (3) strong acid–base.
Moreover, interesting vibrational properties are calculated especially
for carbonyl sulfide and dinitrogen monoxide, which can be bound via
two different configurations on the metal atoms. The vibrational modes
are shifting in different directions depending on the binding way
of the molecule; e.g., the symmetric stretching of OCS is shifted
by +17 or −16 cm–1 when bound via the oxygen
or the sulfur atom, respectively.