that's a fascinating idea! frozen electrides! it's a lot freezier than methane (195 kelvin, a difference large enough to make a methane eutectic much less likely) to the point where you might even be able to freeze it with convenient and safe dry ice rather than liquid nitrogen. and, i don't know, maybe if dry ice by itself won't do the trick, maybe dry ice mixed with liquid ammonia will. trying to buy anhydrous ammonia around here gets you put on a list, though, so i'm gonna opt out of this one

there are a lot of solvated ionic eutectics with atmospheric-pressure water ice, despite the absence of metallic bonding