ZN4O(ACETATE)6, A WELL-TAILORED MOLECULAR-MODEL OF ZNO - AN EXPERIMENTAL AND THEORETICAL INVESTIGATION OF THE ELECTRONIC-STRUCTURE OF ZN4O(ACETATE)6 AND ZNO BY MEANS OF UV AND X-RAY PHOTOELECTRON SPECTROSCOPIES AND 1ST PRINCIPLE LOCAL DENSITY MOLECULAR CLUSTER CALCULATIONS

A thorough investigation of the electronic structure of Zn4O(acetate)6 and ZnO has been used to test the hypothesis that the former compound is a well-tailored molecular model of the latter solid. First principle local density molecular cluster calculations relative to Zn4O(acetate)6 and ZnO indicate that the tetrahedral arrangement of four Zn atoms around the central oxygen present in the title compound is a very good model of the oxygen chemical environment in ZnO. Furthermore, the obtained theoretical results allowed us to describe the rather complex nature of the lowest energy electronic absorption transition of Zn4O(acetate)6, pointing out once more the leading role played by the tetrahedral arrangement of the central oxygen to explain the observed optical properties. Moreover, the computed different electronic charges found in the nearest volume surrounding unlike oxygen atoms in Zn4O(acetate)6 and transition state ionization energies were found to agree very well with X-ray and UV photoelectron measurements, respectively. Quite surprisingly, a satisfactory description of the electronic structure of the solid ZnO by means of the OZn4O12(18-) cluster, embedded in the ZnO crystalline potential, was obtained only by using an extended basis set for the oxygen atoms, including their 3s and 3p virtual levels. In such a case, the agreement between the computed Zn and O partial density of states, the HOMO-LUMO DELTA-E, and literature experimental data was excellent and allowed to gain new insights into the Zn-O covalent interaction.