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 heter ogeneous [Cu-I(CO)(n)](+)A(-) (n = 1-3; A(-) = [AsF6](-) 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)](+)[AsF6](-) solid compounds, they are bent in the zeolite channels. The [AsF6](-) anio n has a base strength lower than that of the zeolite anion; consequently, t he [Cu-I(CO)(n)](+) moieties have a more positive character in the solid co mpounds than in the intrazeolitic ones. The Cu-I-framework distance is infl uenced by the formation of the [Cu-I(CO)(n)](+) complexes: this is demonstr ated 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, re spectively. The role of basic ligands in increasing the;pi-character of the Cu-CO bond (with simultaneous decrease of the electrostatic and a contribu tions) has been studied on [Cu-I(CO)(n)(NH3)](+)Z(-) (n = 1, 2) and [Cu-I(C O)(H2O)(n)](+)Z(-) (n = 1, 2) complexes synthesized in situ in the zeolite channels.