▁car b ony l , ▁where ▁carbon ▁mon ox ide ▁is ▁the ▁only ▁lig and ▁complex ed ▁with ▁a ▁metal . ▁ ▁Other ▁examples ▁include ▁oct ah ed ral ▁Cr ( CO ) 6 ▁and ▁t etra hed ral ▁Ni ( CO ) 4 . ▁Most ▁metal ▁car b ony ls ▁have ▁ 1 8 ▁val ence ▁electrons , ▁and ▁Fe ( CO ) 5 ▁fits ▁this ▁pattern ▁with ▁ 8 ▁val ence ▁electrons ▁on ▁Fe ▁and ▁five ▁pairs ▁of ▁electrons ▁provided ▁by ▁the ▁CO ▁lig ands . ▁ ▁Ref lect ing ▁its ▁symmet rical ▁structure ▁and ▁charge ▁neutral ity , ▁Fe ( CO ) 5 ▁is ▁vol atile ; ▁it ▁is ▁one ▁of ▁the ▁most ▁frequently ▁encountered ▁liquid ▁metal ▁complex es . ▁ ▁Fe ( CO ) 5 ▁adopt s ▁a ▁trig onal ▁b ip y ram idal ▁structure ▁with ▁the ▁Fe ▁atom ▁surrounded ▁by ▁five ▁CO ▁lig ands : ▁three ▁in ▁equ atorial ▁positions ▁and ▁two ▁ax ial ly ▁bound . ▁ ▁The ▁Fe – C – O ▁link ages ▁are ▁each ▁linear . ▁ ▁Fe ( CO ) 5 ▁exhib its ▁a ▁relatively ▁low ▁rate ▁of ▁inter change ▁between ▁the ▁ax ial ▁and ▁equ atorial ▁CO ▁groups ▁via ▁the ▁Ber ry ▁mechanism . ▁It ▁is ▁character ized ▁by ▁two ▁inten se ▁ ν CO ▁bands ▁in ▁the ▁IR ▁spectrum ▁at ▁ 2 0 3 4 ▁and ▁ 2 0 1 4   cm − 1 ▁( gas ▁phase ). ▁ ▁Syn thesis ▁and ▁other ▁iron ▁car b ony ls ▁Fe