An attempt has been made to analyze the spin quenching
properties of Mn, as a representative of transition metals, in
MnMgO, MnCaO, OCMnMgO, and OCMnCaO complexes
formed at the regular (001) surfaces of MgO and CaO, as well as
the adsorption of CO on Mn deposited on MgO and CaO by
means of hybrid density functional theory calculations and
embedded cluster model. Clusters of moderate sizes were
embedded in the simulated Coulomb fields that closely
approximate the Madelung fields of the host surfaces. A test has
been made to examine the effect of artificial flow of charge.
While the spin states of Mn in MnMgO and MnCaO complexes
are preserved, the combined effects of adsorbate and substrate
in OCMnMgO and OCMnCaO complexes are strong enough
to favor the low spin states and to quench the spin. The
deposited Mn atoms enhance the adsorption of CO on MgO and
CaO surfaces. The significant weakening of bond strength
between OC and Mn in complexes supports the concept of
bond order conservation. The relation between the strength of
CO adsorption and the basicity of the support is verified. The
natural bond orbital analysis reveals that the electronic structure
of the adsorbed metal represents a qualitative change with
respect to that of the free metal. The effects of spin
contamination on the geometry, Mulliken charges, and
adsorption energy are examined. The binding of CO precursor is
dominated by the E(i)MnCO pairwise additive components in
MgO and CaO complexs, and the role of the support is not
restricted to supporting the metal. The adsorbed CO molecules
exhibit no remarkable deviation from linearity. Finally, relations
are established between the process of spin quenching and the
energy gaps between frontier orbitals. The results show that the
spin state of adsorbed metal atoms on oxide supports and the
role of precursor molecules on the magnetic and binding
properties of complexes need to be explicitly taken into
account. VC 2012 Wiley Periodicals, Inc. |
