▁linear . ▁ ▁There ▁are ▁also ▁claims ▁of ▁arg on ▁forming ▁coord ination ▁mole cules ▁in ▁N b O 2 Ar 2 , ▁N b O 4 Ar , ▁Ta O 4 Ar , ▁V O 2 Ar 2 , ▁V O 4 Ar , ▁Rh ( η 2 - O 2 ) Ar 2 , ▁Rh ( η 2 - O 2 ) 2 Ar 2 , ▁Rh ( η 2 - O 2 ) 2 ( η 1 - O O ) Ar . ▁ ▁T ung sten ▁tri ox ide , ▁W O 3 , ▁and ▁t ung sten ▁dio x ide ▁mon o - super ox ide ▁( η 2 - O 2 ) W O 2 ▁can ▁both ▁coordinate ▁arg on ▁in ▁an ▁arg on ▁matrix . ▁The ▁arg on ▁can ▁be ▁replaced ▁by ▁x en on ▁or ▁mole cular ▁o xygen ▁to ▁make ▁x en on ▁coordin ated ▁comp ounds ▁or ▁super ox ides . ▁For ▁W O 3 Ar ▁the ▁binding ▁energy ▁is ▁ 9 . 4 ▁k cal / m ol ▁and ▁for ▁( η 2 - O 2 ) W O 2 ▁it ▁is ▁ 8 . 1 ▁k cal / m ol . ▁ ▁Other ▁transition ▁metal ▁comp ounds ▁Ar N i N 2 ▁bind s ▁arg on ▁with ▁ 1 1 . 5 2   k cal / m ol . ▁The ▁b ending ▁frequency ▁of ▁Ar N 2 ▁is ▁changed ▁from ▁ 3 1 0 . 7 ▁to ▁ 3 5