Molecular Structure, Spin Density Distribution, and Hyperfine Coupling Constants of the η{CuNO}¹¹ Adduct in the ZSM-5 Zeolite:  DFT Calculations and Comparison with EPR Data

Abstract

DFT calculations of the molecular structure of the intrazeolite η 1 {CuNO} 11 adduct and the 14 N and 17 O hyperfine and 63 Cu superhyperfine coupling constants were performed and compared with previous EPR results. The calculations confirmed the choice of signs adopted in the previous analysis of the experimental data and the character of the SOMO. The influence of the basis set and the exchange-correlation functional on the HFCC and the spin-density distribution was investigated and briefly discussed. The global repartition of the spin density over Cu (F ) 0.11), N(F ) 0.58), and O (F ) 0.34) atoms determined from the Mulliken population analysis compared well with the experiment. The 14 N hyperfine tensor was successfully reproduced with the LanL2DZ basis and BPW91 functional, whereas in the case of the 63 Cu superhyperfine dipolar tensor T the agreement, except for that of the T zz component, was less satisfactory because of an overestimated polarization of the 3d yz orbital, regardless of the computation level. For the calculation of a iso (Cu), because LanL2DZ treats inner electrons with the effective core potential, a 6-311G(df) basis set appeared to be the most appropriate, leading to excellent agreement between the experimental and calculated values.

Electron spin resonance studies of Cu(I)NO complexes formed over copper-exchanged three- and unidimensional zeolites

“…By using DFT methods, Pietrzyk et al 18 obtained isotropic Cu hf couplings of 158.7 ð 10 4 cm 1 and 168.7 ð 10 4 cm 1 for Cu(I)-NO complexes formed at the M5(7) and I2 sites, respectively, which are in close agreement with the experimentally determined A Cu iso values of Cu-ZSM-5 (Table 1). Therefore, it seems natural to assign species A and species B to a Cu(I)-NO complexes formed at either Cu(I) cation site M5(7) or I2, respectively.…”

“…The formation of two different Cu(I)-NO adsorption complexes with probably three (species A) or two (species B) framework oxygen co-ligands observed for Cu-ZSM-5, Cu-MCM-58, and Cu-ZSM-12 can be interpreted in terms of recent quantum chemical studies 18,20 of NO complex formation with Cu(I) cations at the M5(7) and I2 sites of zeolite Cu-ZSM-5. By using DFT methods, Pietrzyk et al 18 obtained isotropic Cu hf couplings of 158.7 ð 10 4 cm 1 and 168.7 ð 10 4 cm 1 for Cu(I)-NO complexes formed at the M5(7) and I2 sites, respectively, which are in close agreement with the experimentally determined A Cu iso values of Cu-ZSM-5 (Table 1).…”

“…The M5 (7) site is located at the wall of the straight main channel and the I2 site is at the intersection of the main and sinusoidal channels. channels and at their intersections with the sinusoidal channels, respectively, 18 which results in two different ESR-active Cu(I)-NO species A (formed at M5 (7) 19 The study firmly established that A Cu iso rapidly decreases with increase in the number of oxygen co-ligands. This effect has been explained by an enhanced charge transfer from the oxygen atoms to the Cu(I)-NO unit owing to the increasing number of oxygen donor co-ligands, which in turn hinders the spin transfer from the NO radical to the cuprous ion.…”

“…The DFT calculations performed for Cu-ZSM-5 18,20 predict the presence of Cu(I) cation sites in the five-or six-membered ring systems (M5(7) site) of the zeolite framework as a prerequisite for the formation of species A, whereas Cu(I) cations located near the framework AlO 4 tetrahedra in the channel intersections (I2 site) are believed to be responsible for the formation of species B. In order to validate these predictions, we compare the formation of Cu(I)-NO complex in the well-studied Cu-ZSM-5 reference system with three other zeolites, Cu-MCM-58(n Si /n Al D 22), Cu-ZSM-12 (n Si /n Al D 9), and Cu-L (n Si /n Al D 3), having different framework topologies.…”

EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [LnRuII‐NO·]k

“…[34,35] The presence of states lying close to the radical ground state is also responsible for the rapid relaxation as evident from the EPR silence at room temperature. The relatively large A 2 hyperfine value of 3.8 mT for 14 [36,37] we found no evidence for conversion into a five-coordinate complex in the paramagnetic ruthenium species studied here.…”