1. Water-Assisted Concerted Proton-Electron Transfer at Co(II)-Aquo Sites in Polyoxotungstates With Photogenerated Ru
- Author
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Francesco, Rigodanza, Nadia, Marino, Alessandro, Bonetto, Antonio, Marcomini, Marcella, Bonchio, Mirco, Natali, and Andrea, Sartorel
- Subjects
Light ,Polymers ,Water ,Electrons ,Cobalt ,Articles ,Tungsten Compounds ,Oxidants ,hydrogen bonding ,Ruthenium ,Article ,Kinetics ,flash photolysis ,Coordination Complexes ,Very Important Paper ,Organometallic Compounds ,proton coupled electron transfer ,Co-aquo moiety ,Protons ,Oxidation-Reduction ,cobalt polyoxometalate - Abstract
The cobalt substituted polyoxotungstate [Co6(H2O)2(α‐B‐PW9O34)2(PW6O26)]17− (Co6) displays fast electron transfer (ET) kinetics to photogenerated RuIII(bpy)3 3+, 4 to 5 orders of magnitude faster than the corresponding ET observed for cobalt oxide nanoparticles. Mechanistic evidence has been acquired indicating that: (i) the one‐electron oxidation of Co6 involves Co(II) aquo or Co(II) hydroxo groups (abbreviated as Co6(II)−OH2 and Co6(II)−OH, respectively, whose speciation in aqueous solution is associated to a pKa of 7.6), and generates a Co(III)−OH moiety (Co6(III)−OH), as proven by transient absorption spectroscopy; (ii) at pH>pKa, the Co6(II)−OH→RuIII(bpy)3 3+ ET occurs via bimolecular kinetics, with a rate constant k close to the diffusion limit and dependent on the ionic strength of the medium, consistent with reaction between charged species; (iii) at pH, Kinetic investigation by laser flash photolysis supports the occurrence of a concerted proton electron transfer (CPET) from a CoII−OH2 unit embedded in a polyoxotungstate to photogenerated RuIII(bpy)3 3+, with water acting as the base within a hydrogen bonding network.
- Published
- 2021