The other planets of Gliese 581 are: b, 15 Jovian masses at 5.366 days, eccentricity near 0, and semimajor axis 0.040596754 Astronomical Units; and d, 7.7 Earth masses at 83.6 days, eccentricity 0.2, semimajor axis 0.253094533. (Planets b & c seem to be in an orbital resonance of 12:5. Planets c & d at 13:2 also.) I call these Avatar and Usk.

Usk has a blackbody temperature of 187.0063531 K average, 209.0793925 at periastron and 170.7126091 at apastron. The tidal effect of the primary on this planet is 4.839451763, which means its solar day should be on the order of 38 days.

Using an albedo of 0.5 and a greenhouse of 61, its greybody temperature works out to be -55 °C (-36 °C summer & -68 °C winter), with a daily variation of ±40 °C. Liquid anhydrous ammonia fits this temperature range well (though it freezes at -78 °C i.e. most nights). Its pressure would have to be at least 4.5 atmospheres to keep from boiling at summer periastron, which isn’t unlikely.