[BNW] Buying AI cities

I've tried to look up whether AIs are ever willing to sell their cities but to no avail.

So i thought i would ask here.

I tried buying cities from allies with 8-10 cities and even trying to buy new cities with 2 pop.

But noone ever was willing to sell, i had 10k gold 120 gpt and was willing to put in all my strategic resources and luxury resources.

Is it possible? DO i need more gold?