Is Cl in middle, singly bonded with 4 O's, with full octets? I thought this would be the answer, but the central atom formal charge is 3. But when I add all the FC's up, I get -1, so I think I am right but am not 100% sure.

Similar to sulfate. 7 electrons from chlorine donated to oxygen. 4 oxygen get 8 electrons. One is from the negative charge.

https://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/Perchlorate-2D-dimensions.png/170px-Perchlorate-2D-dimensions.png