Local structure of [Cu^I(CO)₂]⁺adducts hosted inside ZSM-5 zeolite probed by EXAFS, XANES and IR spectroscopies

Abstract

EXAFS spectroscopy, analysed in the frame of the multiple scattering theory, has been able to determine the local structure of [Cu(CO)2]+ complexes hosted inside ZSM-5 channels upon contacting the activated zeolite with CO from the gas phase at room temperature. We found that the number of coordinated CO molecules (1.8 +/- 0.3) is in good agreement with the [Cu(CO)2]+ stoichiometry suggested by IR. The Cu-C distance obtained for the [Cu(CO)2]+ complex is 1.88 +/- 0.02 A, with a C-O distance (1.12 +/- 0.03 A). This work complements a previous one [C. Lamberti, G. Turnes Palomino, S. Bordiga, G. Berlier, F. D'Acapito and A. Zecchina, Angew. Chem. Int. Ed., 2000, 39, 2138], performed at liquid nitrogen temperature, where the structure of [Cu(CO)3]+ complexes was identified by combined EXAFS/XANES/IR spectroscopies. An increase of the Cu-C distance of 0.05 A by moving from [Cu(CO)2]+ to [Cu(CO)3]+ complexes has been observed, which is the local rearrangement needed to accommodate a third CO ligand in the first coordination shell of copper. EXAFS determined that the Cu-C-O bond angle is linear within the error bars (170 +/- 10 degrees), while IR and XANES indicate that intrazeolitic [Cu(CO)2]+ complexes have C2v symmetry. The experimentally obtained moieties are in good agreement with the values obtained with advanced quantum mechanical methods.

Characterization of Cu-exchanged SSZ-13: a comparative FTIR, UV-Vis, and EPR study with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios

“…Note that this was not the case for the Cu-ZSM-5 8,98 and Cu-β 85 materials prepared in a stoichiometric gas phase reaction with CuCl. Note that this was not the case for the Cu-ZSM-5 8,98 and Cu-β 85 materials prepared in a stoichiometric gas phase reaction with CuCl.…”

Probing zeolites by vibrational spectroscopies

“…Full symbols refer to M + Á Á ÁCO adducts (blue-shifted main IR band); open symbols refer to M + Á Á ÁOC adducts (red-shifted minor IR band). The occurrence of a Cu + Á Á Á(CO)-Cu + Á Á Á(CO) 2 transformation has been proved using Cu K-edge EXAFS spectroscopy, 407 and two-dimensional correlation spectroscopy (2D-COS). Right axis: determination of the local electric field strength probed by CO from Dñ(CO) according to the Stark effect quantified by Pacchioni et al 282 The dotted and dashed curves indicate the best linear fits of the two datasets; the corresponding intercepts with the ordinate axis (R M -+ N limit) provides the magnitude of the negative electric field E z generated by the negatively charged zeolite cavities, see eqn (6).…”

“…228, 229, 283-287. resulting Dñ(CO) is located at a spectral position that is a compromise between blue and red shifting interactions. 161,378,379,384,404,407 The fact that both bands are IR-active indicates that the intrazeolitic Cu + Á Á Á(CO) 2 adducts have C 2v symmetry (or lower), whereas their homogeneous counterparts are linear (D Nh ). 393 Since the late 1980s they have been widely investigated because of their catalytic activity in the direct decomposition of NO.…”

“…The occurrence of a Cu + Á Á Á(CO)-Cu + Á Á Á(CO) 2 transformation has been proved using Cu K-edge EXAFS spectroscopy, 407 and two-dimensional correlation spectroscopy (2D-COS). A similar solvation effect promoted by the adsorption of CO has been observed for Cu + -ZSM-5, 404,407 Ni 2+ /SiO 2 , 419,420 and Cr 2+ /SiO 2 . It is used to assess statistical relationships between different spectroscopic features that change during a dynamic variation for extracting valuable information, which can otherwise be difficult to obtain.…”

Local Structure of CPO-27-Ni Metallorganic Framework upon Dehydration and Coordination of NO

“…Usually EXAFS is able to discriminate between linear or bent adsorption of a diatomic molecule on a metal center, because of the focusing effect that enhances the MS contributions in case of linear alignment of scattering atoms. 60,77,78 Unfortunately, in this case, EXAFS is not able to unambiguously discriminate between the two molecular orientations. This is due to the fact that the contribution of the O atom of the NO molecule falls around 3 Å, i.e., in the region dominated by the strong Ni-Ni contribution at 2.9 Å, see Figure 9b.…”