Redox-state effects on small molecule bin multimetallic iron complexes

Abstract

The biochem. processing of a variety of small mols. including H_2, N_2, CO_2, CO and NO_x requires complex machinery. Metalloenzymes are highly specialized in such transformations, and often employ multi-metal cooperativity. Controlling, rationally, the assembly of multiple metals into a single synthetic framework remains a challenge. Furthermore, understanding multi-metal cooperativity and esp. the role that different redox-states play in small mol. activation is of fundamental importance. As such, we have shown previously how redoxinactive metals influence the redn. potential in different hetero-metallic clusters. Here we present a new class of tetra-iron complexes that are site differentiated, with three iron centers that are six-coordinate and one unique four-coordinate iron center. We show that nitric oxide (NO) is able to bind at the unique iron center and, subsequently, the NO binding was investigated as a function of the redox-state of the metal cluster. Structural and spectroscopic characterization indicates that the change in redox-states occurs at a distal site of the metal cluster, and the obsd. distal redox-modulation is responsible for the different degree of NO activation.