Ruthenium charge distributions

The synthesis of this cluster provided the addition of the two acetyl IR chromophores to aid in characterisation of the reduced state. In the neutral state, this monomer contains three ruthenium atoms, one formally in the (+2) (bonded to CO) and two in the (+3) (bonded to acpy ligands) redox states. However, this formal description of the charge may not accurately represent the actual charge distribution over the cluster. Infrared spectroelectrochemistry was carried out on this monomer to determine whether the charge was in fact localised in this manner. 

Analysis of the spectral lineshapes of 5 and 6 gave an uphill rate for charge transfer of 6.5 x lO" s (Table 5.2), and an equilibrium constant of 2.2 for the charge distribution, which compares well with previously reported rate constants for similar mixed-valence dimers of trinuclear ruthenium clusters. 

Comparisons of the spectroscopic and electrochemical properties of [(NH3)5RuNCFcCNRu(HN3)s] and [(NH3)5RuNCFcCNf where Fc is ferrocene, leads to the conclusions that the two ruthenium chromophores in the trimetallic ion do not interact strongly. This allows differences in the IT transition energies of the mixed-valence complexes to be ascribed to differences in charge distribution, in good agreement with theory. 

Tris(2,2 -bipyridine)ruthenium(II) (Ru(bpy)3" ) is dispersed in a Nafion membrane coated on an ITO electrode. By cycKc voltammetry oxidation and re-reduetion of Ru(bpy)3 /Ru(bpy)3 was studied. A eritieal distanee of the Ru-eomplexes for efficient charge hopping between redox centers of approximately 1.3 mn is found and ealeulated. The maximum of a Poisson distribution of distanees is >0.1 M of Ru(bpy)i+ [394,395]. 

The administration of robust complexes such as those of Pt or Au will be of use when their reactivity with the target is pharmacokinetically appropriate — the window of reactivity must be recognised and will depend on chemical factors such as hydrolysis and ligand exchange as well as uptake and distribution. Uptake of metal complexes may be best for neutral species, since no transport process need be activated but it is well to remember that this is not an absolute requirement. The charged amine complexes, close analogues of cisplatin, enter cells (Chapter 3.1) and indeed lipophilicity may enhance this uptake an example is the ruthenium (II) chelate of (3,4,7,8-)tetramethyl-l,10-phenanthroline (Chapter 6.1.3). 

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