[3:1] Site-Differentiated [4Fe–4S] Clusters Having One Carboxylate and Three Thiolates

[4Fe–4S]
clusters modeled after those in organisms having three cysteine thiolates
and one carboxylate were synthesized by using the tridentate thiolato
chelate. X-ray structural analysis reveals that the carboxylates coordinate
to the unique irons in an η1 manner rather than η2. Redox potentials show a positive shift from that of the
cluster having ethanethiolate and the tridentate thiolato chelate.
These properties conform to the arrangement of the [4Fe–4S]
clusters in the electron transfer systems included in Rc dark operative protochlorophyllide oxidoreductase (DPOR) and formaldehyde
oxidoreductase (FOR) with Pf ferredoxin.