Bridging ligand LUMO

Mixed-valence complexes with multidentate polypyridine bridging ligands are expected to follow the same general patterns, but the details are complicated by the variations in the basic properties of the systems, such as the bridging-ligand LUMOs the energy... 

Interestingly, metal-metal interaction appears to be dependent on the oxidation state of the system. This is clearly evidenced by the results obtained for Os2 in liquid SO2 at —70°C, in that in these experimental conditions both the first and the second oxidation of each metal center can be seen (Fig. 5.4 Table 5.1).15 Potential splitting for the first oxidation process is 370 mV, whereas potential splitting for the second oxidation process is 150 mV. This result confirms the electron transfer pathway for the superexchange interaction once mono-oxidized, the Os(III)-based orbitals are stabilized and their interaction with the bridge-based LUMO orbitals decreases. A similar result has been recently obtained in molecular grids based on similar polypyridine ligands.25... 

If Ru orbitals closely match the energy of the HOMO or LUMO of the bridging ligand, covalency is approached and the distinction between formal oxidation states becomes blurred, resulting in the extreme case of a radical bridging ligand. The situation is illustrated below ... 

For the complex [ (bpy)2Ru 2(p.-adc)]3+ (38), researchers invoked a contribution of resonance form II to the ground state in order to explain ESR and electronic absorption spectroscopy results. Alternatively, if Ru orbitals closely match the energy of the LUMO of the bridging ligand, the following resonance forms may result ... 

Most of the studies of linked transition metal D/A complexes have employed bridging ligands that have relatively low-energy rr-type LUMOs and metals in which the electron-transfer process involves cirr-orbitals. There are fewer studies of purely a analogs, partly for reasons of complex instability. Some general features are characteristic of any type of bridging ligand. 

Although the cyclic voltammetry for this complex seems fairly similar to the trinuclear ruthenium cluster dimers, the lower-lying LUMO (as evidenced by the lower reduction potential) of the triazine bridging ligand plays an important role in explaining the details of the spectroelectrochemistry observed for this LCD. The CO stretching frequency of the neutral complex appears at 1940 cm Upon application of— 1.050 V (vi. Ag pseudoreference, roughly 0 to... 

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