46 research outputs found
On the nature of spin- and orbital-resolved charge transfer in the gas phase and at Cu(I) sites in zeolites
Electronic factors essential for NO activation by Cu(I) sites
in zeolites are investigated within spin-resolved analysis of
electron transfer channels (natural orbitals for chemical
valence). NOCV analysis is performed for three DFT-opti-
mized models of Cu(I)–NO site in ZSM-5: [CuNO]
?
,
(T1)CuNO, and (M7)CuNO. NO as a non-innocent, open-
shell ligand reveals significant differences between inde-
pendent deformation density components for
a
and
b
spins.
Four distinct components are identified: (i) unpaired electron
donation from NO
p
k
* antibonding orbital to Cu
s,d
; (ii)
backdonation from copper d
yz
to
p
\
* antibonding orbital;
(iii) donation from occupied
p
k
and Cu d
xz
to bonding region,
and (iv) donation from nitrogen lone-pair to Cu
s,d
. Channel
(i), corresponding to one-electron bond, shows-up solely for
spin majority and is effective only in the interaction of NO
with naked Cu
?
. Channel (ii) dominates for models b and c: it
strongly activates NO bond by populating antibonding
p
*
orbital and weakens the N–O bond in contrast to channel (i),
depopulating the antibonding orbital and strengthening N–O
bond. This picture perfectly agrees with IR experiment:
interaction with naked Cu
?
imposes small blue-shift of N stretching frequency while it becomes strongly red-shifted
for Cu(I) site in ZSM-5 due to enhanced backdonation