The [Fe CN 5 NO ]4- complex, also known as pentacyanonitrosylferrate II , is a transition metal complex that exhibits interesting photochemical properties. The complex consists of an iron II ion coordinated to five cyanide CN- ligands and one nitrosyl NO ligand. The photochemical properties of this complex are mainly due to the presence of the nitrosyl ligand, which can undergo photoinduced electron transfer and ligand exchange reactions.Under different light conditions, the photochemical properties of the [Fe CN 5 NO ]4- complex can change significantly. Here are some key aspects:1. Absorption spectrum: The complex absorbs light in the visible region, with an absorption maximum around 400-450 nm. This absorption is attributed to the metal-to-ligand charge transfer MLCT transition, where an electron is promoted from the iron II ion to the nitrosyl ligand. The absorption spectrum can be influenced by the nature of the solvent and the presence of other coordinating ligands.2. Photoinduced electron transfer: Upon absorption of light, the [Fe CN 5 NO ]4- complex can undergo photoinduced electron transfer, leading to the formation of a metastable [Fe CN 5 NO ]3- species. This species is characterized by a reduced iron III center and a nitroxyl NO- ligand. The back electron transfer to regenerate the initial complex is also possible, depending on the surrounding environment and the presence of other redox-active species.3. Ligand exchange reactions: The photoexcited [Fe CN 5 NO ]4- complex can also undergo ligand exchange reactions, where the nitrosyl ligand is replaced by other ligands, such as water or other anions. This process can be facilitated by the presence of light, which can increase the rate of ligand exchange.4. Photocatalytic activity: Due to its photochemical properties, the [Fe CN 5 NO ]4- complex has been studied as a photocatalyst for various reactions, such as the reduction of nitrite to nitric oxide and the oxidation of organic substrates. The photocatalytic activity of the complex can be influenced by factors such as the light intensity, wavelength, and the presence of other catalysts or additives.In summary, the photochemical properties of the [Fe CN 5 NO ]4- complex are mainly governed by the MLCT transition and the photoinduced electron transfer and ligand exchange reactions involving the nitrosyl ligand. These properties can change significantly under different light conditions, making this complex an interesting candidate for various photochemical and photocatalytic applications.