= P b ▁double ▁bond ▁in ▁di pl um ben es ▁being ▁less ▁ener get ically ▁fav ou rable ▁compared ▁to ▁the ▁overlap ▁of ▁sp n ▁orbit als ▁( with ▁a ▁higher ▁degree ▁of ▁hy brid ization ▁than ▁in ▁di pl um ben es ) ▁in ▁the ▁P b – P b ▁single ▁bond ▁in ▁di pl um ban es . ▁ ▁In ▁mon oh al ogen ated ▁pl um by len es , ▁the ▁hal ogen ▁atom ▁on ▁one ▁pl um by l ene ▁is ▁able ▁to ▁don ate ▁a ▁l one ▁pair ▁into ▁the ▁vac ant ▁ 6 p ▁orb ital ▁of ▁the ▁lead ▁atom ▁on ▁a ▁separate ▁pl um by l ene ▁in ▁a ▁brid ging ▁mode . ▁Mon oh al ogen ated ▁pl um by len es ▁have ▁been ▁found ▁to ▁generally ▁exist ▁as ▁mon om ers ▁in ▁solution ▁and ▁dim ers ▁in ▁the ▁solid ▁state , ▁but , ▁again , ▁sufficiently ▁bul ky ▁subst itu ents ▁on ▁lead ▁can ▁ster ically ▁block ▁this ▁dim er ization ▁mode . ▁ ▁Due ▁to ▁decre asing ▁dim er ization ▁energy ▁down ▁Group ▁ 1 4 , ▁while ▁mon oh al ogen ated ▁st anny len es ▁and ▁pl um by len es ▁dim er ize ▁via ▁the ▁hal ogen - brid ging ▁mode , ▁mon oh al ogen ated ▁s ily len es ▁and ▁germ y len es ▁tend ▁to ▁dim er ize ▁via ▁the ▁ab ov ement ioned ▁multiply - b ond ed ▁mode ▁instead . ▁ ▁In ▁a ▁recent