Mono-, Di-, and Tricarbonylic Species in Copper(I)-Exchanged Zeolite ZSM-5:  Comparison with Homogeneous Copper(I) Carbonylic Structures

The structural and spectroscopic similarities between homogeneous and heterogeneous [Cu I (CO) n ] + A - ( n = 1−3; A - = [AsF 6 ] - or zeolite anion Z - ) carbonyls are evidenced and discussed. While [Cu I (CO) 2 ] + and [Cu I (CO) 3 ] + have linear and planar structures in [Cu I (CO) n ] + [AsF 6 ] - solid compounds, they are bent in the zeolite channels. The [AsF 6 ] - anion has a base strength lower than that of the zeolite anion; consequently, the [Cu I (CO) n ] + moieties have a more positive character in the solid compounds than in the intrazeolitic ones. The Cu I −framework distance is influenced by the formation of the [Cu I (CO) n ] + complexes: this is demonstrated by both EXAFS and IR results concerning the effect of CO complexation on the Cu I −framework distance and on the Cu I -sensitive skeletal modes, respectively. The role of basic ligands in increasing the π-character of the Cu−CO bond (with simultaneous decrease of the electrostatic and σ contributions) has been studied on [Cu I (CO) n (NH 3 )] + Z - ( n = 1, 2) and [Cu I (CO)(H 2 O) n ] + Z - ( n = 1, 2) complexes synthesized in situ in the zeolite channels.