Growth of the metal framework in linear ruthenium and osmium carbonyls

Formation of the linear chain ruthenium and osmium carbonyls by successive linkage of mononuclear M(CO)₄Cl₂] units and by opening trinuclear clusters M₃(CO)₁₂] and FeM₂(CO)₁₂] (M = Ru, Os) with chlorine gas have been studied by computational DFT methods. Energetically the formation of dinuclear M₂(CO)₈Cl₂] from M(CO)₄Cl₂] units is the most demanding step. The following chain growth by adding new mononuclear units proceeds more easily with nearly constant energy per step. Cluster opening by chlorine gas to obtain trinuclear M₃(CO)₁₂Cl₂] is a facile reaction for both ruthenium and osmium clusters as well as for mixed metal clusters. Mixed metal clusters FeOs₂(CO)₁₂] and FeRu₂(CO)₁₂] open preferably between iron-osmium or iron-ruthenium bonds producing linear trinuclear Fe-M-M-type of compound. In the case of mixed metal Os-Ru clusters, the cleavage of Os-Ru bond is not clearly preferred. Fragmentation of the cluster to shorter units cis(Cl)-M(CO)₄Cl₂] or M₂(CO)₈Cl₂] with equatorial chlorides is highly favorable and competes with the cluster opening. No preferences on the bond type (Os-Ru, Os-Os, or Ru-Ru) that are broken can be found in the case of mixed metal Os-Ru clusters.