Isomers in the ‘ Merry - go - round ‘ Crystal Structure * Process . M o

The relationship between crystal and molecular structure of the pairs of isomers in the ‘merry-go-round’ process [Ir4(CO),(p,-$CH,SCH2SkH2)] 1 and [Ir,(CO),(p-CO),(p,-$CH,SCH2SkH2)] 2, and of the ionic species [NMe,(CH,Ph),] [Ir,(CO),,(SCN)] 3 and [N(PPh,),] [Ir,(CO),(p-CO),(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 0 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 SCNgroups by the NMe,(CH,Ph),+ 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.