N-H···S Hydrogen Bonds in a Ferredoxin Model

The Fe4S4 complex {(CH3)3NCH2CONH2}2[Fe4S4( t 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 (Sγ) of one tert-butylthiolate 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 [Fe4S4]2+ cluster core. Additionally, this is the first synthetic Fd model in which N−H···S hydrogen bonding to a cluster has been achieved.