L. Rodriguezsantiago et al., COORDINATION OF CU- AN AB-INITIO DENSITY-FUNCTIONAL STUDY( IONS TO ZEOLITE FRAMEWORKS STRONGLY ENHANCES THEIR ABILITY TO BIND NO2 ), Journal of the American Chemical Society, 120(7), 1998, pp. 1545-1551
Comparison is made of the interaction of NO2 with Cu+ ions in the gas
phase and inside zeolites using density functional theory (B3LYP funct
ional). The zeolite is represented by a tritetrahedra model embedded i
n the periodic structure of zeolite ZSM-5 and by a free space cluster
model. Both models yield virtually the same results. Cu+ is coordinate
d to two oxygen atoms of the zeolite framework only. For the complexes
with NO2, several minima and transition structures on the potential e
nergy surfaces are localized. The naked Cu+ ion preferentially binds N
O2 in the eta(1)-O trans mode, while in zeolites the Cu+ site binds NO
2 in a (2) eta-O,O coordination. For the 2 eta-O,O structure the bindi
ng is three to four times stronger in the zeolite (43 kcal/mol) than i
n the gas phase which is due to a three-body zeolite framework-Cu+ ion
-NO2 interaction. d(10)-s(1)d(9) promotion leads to a more favorable o
rbital interaction between Cu+ and NO2 in the (2)A '' state and, due t
o reduced repulsion, to a stronger electrostatic interaction between C
u+ and the zeolite framework.