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

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 angstrom, with a C - O distance ( 1.12 +/- 0.03 angstrom). 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 angstrom 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 C-2v symmetry. The experimentally obtained moieties are in good agreement with the values obtained with advanced quantum mechanical methods.