Synergistic Interaction Between Attractived10Bonding and Localized Excess Electrons, the Cases of Subvalent Ag5SiO4and Ag5GeO4

The compositions of Ag5SiO4 and Ag5GeO4 contravene classical rules of chemical valence, while the stoichiometric coefficients are integer. In order to disentangle the underlying bonding scheme, comparative studies at the two virtually isostructural candidates were conducted in real space and in momentum space. Analyses of the atomic structures have revealed that the orthoanions in both cases fully comply with reference data for such entities. The silver substructure, however, shows anomalous contractions that indicate accumulation of excess electrons in octahedral [Ag-6](4+) subunits, suggesting an electron count as [Ag-6](4+)(Ag+)(4)[(MO4)(4-)](2). The electronic structure of Ag5SiO4 and Ag5GeO4 was examined in reciprocal and position space in the framework of density functional theory. Both compounds are semiconducting with a band gap of about 1.6 eV. The analysis of the charge distribution as well as of the electron localization function suggest that the excess electrons in the silver partial structure are located in octahedral cluster like [Ag-6](4+) aggregates. The importance of d(10) dispersion interactions for the stability of subvalent silver oxides is discussed.