Terminal Ligand Assignments Based on Trends in Metal−Ligand Bond Lengths of Cubane-Type [Fe4S4]2+,+ Clusters

Trends in Fe−L bond distances in [Fe4S4L4]2-,3- cubane-type clusters with L = Cl- and RS- are summarized. The compound (Et4N)3[Fe4S4(SH)4]·Et4NCl was prepared and structurally characterized. The Fe−SH bond lengths of this cluster and previously reported (Ph4P)2[Fe4S4(SH)4] fall in the ranges for clusters with alkyl- and arenethiolate terminal ligands. Upon slow crystallization from 1,2-dichloroethane/THF, the compound (Pr4N)2[Fe4S4(SH)4] undergoes chloride substitution to form (Pr4N)2[Fe4S4Cl4], which may be identified by its Fe−Cl distance. An X-ray structure recently attributed to (Pr4N)2[Fe4S4(SH)4] is that of (Pr4N)2[Fe4S4Cl4].