There are "saddle" or "over the sill" window units that might fit nicely in this window. NOTE make sure the unit you buy will fit through the fully open window during installation.
They're good for rentals as they don't require mounting brackets or screws. There will be a narrow gap on the sides of the unit that you'll have to fill. There are foam strip kits you can buy to do that, and/or use strips of wood or plastic. With these units it's easy to open the window when not in use and for that reason you should not fill the gaps by taping/gluing anything to the window. Make sure the wall is not thicker than the saddle width of the machine.
