N-H⋯S hydrogen bonds in a ferredoxin model

The Fe ₄S ₄ complex {(CH ₃) ₃NCH ₂CONH ₂} ₂[Fe ₄S ₄(BuS) ₄] (1) was synthesized to replicate the ferredoxin active site with a subset of its N-H⋯S hydrogen bonds. The two cationic counterions mimic the polypeptide backbone of ferredoxin (Fd) as amide hydrogen-bond donors to sulfur atoms of the iron-sulfur cluster. X-ray crystallographic data show that the organic sulfur (S _y) of one tertbutylthiolate ligand and one inorganic sulfur of the cluster core serve as N-H⋯S hydrogen-bond acceptors. The cluster core of complex 1 is tetragonally elongated in contrast to that of Fd, which is tetragonally compressed. This is the first observation of an elongated [Fe ₄S ₄] ²⁺ cluster core. Additionally, this is the first synthetic Fd model in which N-H⋯S hydrogen bonding to a cluster has been achieved.