This work comprises the synthesis and characterization of novel pyrazolate-bridged bimetallic iron complexes with bis(pentadentate) ligand scaffolds and the activation of dioxygen and nitric oxide at their diferrous sites. It describes the development of two new bridging ligand systems providing two compartments with a fivefold coordination environment for each metal ion. Furthermore, properties of the obtained diferrous complexes were studied by a series of analytical techniques including x-ray diffraction, Mössbauer spectroscopy and temperature dependent UV/Vis spectroscopy. In particular a temperature dependent spin crossover was observed, both in solid state and solution. Small molecule activation was monitored by optical spectroscopy. Especially two diiron dinitrosyl congeners ([{Fe(NO)}7]2 ) are presented and studied in detail as low molecular weight analogues for Flavodiiron proteins with different reaction pathways, one including the formation of nitrous oxide upon reduction.
