Hans Miessner, Holger Landmesser, Nils Jaeger and Klaus Richter
Well defined surface carbonyls of CuI with unusually narrow (ν1/2<5 cm-1) IR carbonyl bands are formed during the interaction of CO with copper supported on highly dealuminated Y zeolite. A CuI monocarbonyl with an IR band at 2159 cm-1 forms, with additional CO, a dicarbonyl with well resolved IR bands at 2179 and 2153 cm-1. Isotopic exchange experiments combined with corresponding force field calculations reveal the C2v structure of the dicarbonyl and a correlation of the integrated carbonyl intensities shows the mutual conversion of mono- and di-carbonyl at the same CuI site. The reversible equilibrium between the two species is dependent on both the temperature and the CO pressure, with a formation energy of the CuI(CO)2 of 37 kJ mol-1. The bond angle between the carbonyl groups in the dicarbonyl is estimated to be 113°. Using a controlled hydration, several aquacarbonyls could be observed dependent on the water content. An aquacarbonyl species with a carbonyl band at 2141 cm-1 is observed when the first doses of water are added. It is transformed, with more water, into species with IR bands at 2136, 2129 and, finally, 2123 cm-1, which contain probably more than one water and/or hydroxy ligand coordinated to the CuI.