X-ray crystal structures of [NHR3]2[Fe4S4X4] (X = PhS, R = Et or nBu; X = Cl, R = nBu): implications for sites of protonation in Fe–S clusters

The X-ray crystal structures of [NHR3]2[Fe4S4X4] (X = PhS, R = Et or nBu; X = Cl, R = nBu), reported in this paper, show NH…X interactions between the cation and the cubanoid cluster. Comparison of the cluster dimensions in [NHR3]2[Fe4S4X4] with those reported earlier for [NR′4]2[Fe4S4X4] (R′ = Me, X = PhS; R′ = Et, X = Cl) indicates that N–H…X interactions have a negligible effect on the dimensions of the cluster. The relevance of these structures to understanding where on [Fe4S4X4]2− protonation labilises the cluster to substitution is discussed.