[djtango]

Thanks for sharing this - excellent content. I've been out of the game for a long time now but isn't this just the case that Gold is too soft as an ion to mix well with stuff like oxides?

Cs(I) should be larger than Au(I) but it seems to form a comparatively stable oxide Cs2O. But yes Tellurium is also a nice soft element so AuTl have a good affinity for one another.

Was unaware of their chemistry, it doesn't even ring a bell tbh I wonder if I had ever encountered it before. I did enjoy studying the Post Transition Group Metals back in the day

[adrian_b]

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.