Local structure of [CuI(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 Å, with a C–O distance (1.12 ± 0.03 Å). 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 Å 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°), while IR and XANES indicate that intrazeolitic [Cu(CO)₂]⁺ complexes have C_2v symmetry. The experimentally obtained moieties are in good agreement with the values obtained with advanced quantum mechanical methods.