( VI ) ▁ion ▁( X e F 8 2 − ) ▁in ▁the ▁salt ▁nit ro son ium ▁oct a flu or ox en ate ( VI ); ▁however , ▁the ▁mole c ule ▁is ▁dist orted ▁away ▁from ▁the ▁ideal ized ▁square ▁anti pr ism . ▁Very ▁few ▁ ions ▁are ▁cub ical ▁because ▁such ▁a ▁shape ▁would ▁cause ▁large ▁rep ulsion ▁between ▁lig ands ; ▁ ▁is ▁one ▁of ▁the ▁few ▁examples . ▁ ▁In ▁addition , ▁the ▁element ▁sul fur ▁forms ▁oct atomic ▁S 8 ▁mole cules ▁as ▁its ▁most ▁stable ▁all ot ro pe . ▁The ▁S 8 ▁mole c ule ▁has ▁a ▁structure ▁based ▁on ▁the ▁square ▁anti pr ism , ▁in ▁which ▁the ▁eight ▁atoms ▁occup y ▁the ▁eight ▁vertices ▁of ▁the ▁anti pr ism , ▁and ▁the ▁eight ▁triangle - triangle ▁edges ▁of ▁the ▁anti pr ism ▁correspond ▁to ▁single ▁c oval ent ▁b onds ▁between ▁sul fur ▁atoms . ▁ ▁In ▁architecture ▁ ▁The ▁main ▁building ▁block ▁of ▁the ▁One ▁World ▁Trade ▁Center ▁( at ▁the ▁site ▁of ▁the ▁old ▁World ▁Trade ▁Center ▁destroyed ▁on ▁September ▁ 1 1 , ▁ 2 0 0 1 ) ▁has ▁the ▁shape ▁of ▁an ▁extremely ▁tall ▁tap ering ▁square ▁anti pr ism . ▁It ▁is ▁not ▁a ▁true ▁anti pr ism ▁because ▁of ▁its ▁t aper : ▁the ▁top ▁square ▁has ▁half ▁the ▁area ▁of ▁the ▁bottom ▁one . ▁ ▁Top olog ically ▁identical ▁poly hed ra ▁ ▁Tw isted ▁pr ism ▁A ▁tw isted ▁pr ism