You're biggest trouble with that is the total pressure on a single pane of glass. Just looking at it from an engineering perspective. The farther apart the "corners" the greater the amount of pressure against the pane of glass. Your trouble won't primarily be the necessary thickness so much as bracing. You really can't have a tank that long without multiple braces in my opinion.
There are a few threads on here about DIY tanks, and the primary thing I've taken from skimming them is that you need very high quality silicone, not something you would get at Home Depot/Lowes most likely.
If you could be liable for thousands of dollars of damage in your apartment, it seems worth it to work with a custom tank building company if there are any local ones. That way if something fails, you can blame their own workmanship. Not that I like to point the finger, but when you're talking about 50+ gallons of water suddenly coming loose in an apartment... better safe than sorry.
Christian, husband, brother, friend, hobbyist.