COO-ZNO SOLID-SOLUTION AS A MODEL TO INVESTIGATE THE CO-CATION INTERACTION - AN FTIR AND HRTEM STUDY

The IR spectra of CO adsorbed at 77 K on ZnO ex-carbonate (and for com parison on ZnO kadox), on CoO and on CoO-ZnO solid solution (containin g 0.05 mole fraction of CoO) are reported. By diluting the cobalt ions within a ZnO matrix, we have designed a model solid where the Co2+ io ns (having a d(7) configuration and frontier orbitals with d character ) emerging on the surface experience the same ionicity and coordinativ e situation as Zn2+ (d(10) configuration and frontier orbitals without d character). Consequently, the observed difference in the CO stretch ing vibrations of the Zn2+... CO and Co2+... CO surface complexes has been ascribed to differences in the d-pi overlap contributions. The in creased d-pi overlap effects are also responsible for the strong incre ase in the permanent (mu(00), mu(11)) and transition (mu(01)) dipole m oments of CO adsorbed on Co2+ in ZnO, compared with those on Co2+ in t he MgO matrix and also those of CO adsorbed on ZnO and MgO.