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 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.