Yes, as I have said, size is only one of the reasons of incompatibility with oxide ions. As you say, gold has a much higher electronegativity than cesium and r

Yes, as I have said, size is only one of the reasons of incompatibility with oxide ions. As you say, gold has a much higher electronegativity than cesium and rubidium, i.e. not much lower than that of silicon, which makes it a "soft" ion, and that reduces the stability of any compound with oxide or hydroxide or fluoride ions. On the other hand, the incompatibility with the "softer" sulfide is mostly caused by the size ratio.