The isoelectronic species are...

methane, ammonium ion and borohydride ion...these all look the same but they surely do have different chemical properties

 

carbon monoxide, cyanide ion and nitrogen gas...whew, nitrogen gas has a couple of bad guys that look like it...It is interesting that both cyanide and carbon monoxide are very toxic and we inhale nitrogen gas all the time with no ill effects...good thing that N₂ doesn't have any charges or dipoles to tie up with hemoglobin!

sulfate anion, phosphate anion and perchlorate anion...The formal charge on the central atom explains the relative acidities of the parent acids!

carbonate anion and nitrate anion