Isomers in the ‘merry-go-round’ process. Molecular versus crystal structure

Abstract

The relationship between crystal and molecular structure of the pairs of isomers in the ‘merry-go-round’ process [Ir₄(CO)₉(µ₃-[graphic omitted]H₂)]1 and [Ir₄(CO)₆(µ-CO)₃(µ₃-[graphic omitted]H₂)]2, and of the ionic species [NMe₂(CH₂Ph)₂][Ir₄(CO)₁₁(SCN)]3 and [N(PPh₃)₂][Ir₄(CO)₈(µ-CO)₃(SCN)]4 has been investigated by means of atom–atom potential-energy calculations and packing analysis. It has been shown that in both 1 and 2 a network of weak C–H ⋯ O hydrogen-bonding interactions is established. In 2 these interactions involve only the bridging CO ligands. In 4 the cluster anions show a clear tendency to form anion piles surrounded by cation belts, while segregation of the SCN^– groups by the NMe₂(CH₂Ph)₂⁺ cations has been observed in 3. Tighter crystal packings are associated with the bridged isomers which also possess smaller molecular volumes than the all-terminal species.