Crystal structures of salts of transition-metal halide clusters

The ion organization in crystalline salts formed by transition-metal carbonyl cluster anions containing halide ligands has been investigated. It has been shown that the presence of the heteroligand(s) drives either towards the 'trapping' of two halogen atoms within a cage of counter ions or towards the formation of anion rows insulated by cation rows. The formation of either type of pattern appears to be due to the size and mode of bonding of the halogen atoms, the first type being preferred with small terminal halogens or with large halogens in bridging bonding mode, while the second is observed with large halogens in terminal bonding mode.