Redox Chemistry in Thin Layers of Organometallic Complexes Prepared Using Ion Soft Landing
Soft landing (SL) of mass-selected ions is used to introduce catalytically-active metal complexes complete with organic ligands into the gas phase and then to transfer them as ions onto an inert surface. This is part of an effort to prepare materials with defined active sites and thus achieve molecular design of surfaces in a highly controlled way. Solution-phase electrochemical studies have shown that VIVO(salen) reacts in the presence of acid to form VVO(salen)+ and the deoxygenated VIII(salen)+ complex -- a key intermediate in the four electron reduction of O2 by vanadium-salen. In this work, the VVO(salen)+ and [NiII(salen)+H]+ complexes were generated by electrospray ionization and mass-selected before being deposited into an inert fluorinated self-assembled monolayer (FSAM) surface on gold. A time dependence study after ion deposition showed loss of O from VVO(salen)+ forming VIII(salen)+ over a four-day period, indicating a slow interfacial reduction process. Similar results were obtained when other protonated molecules were co-deposited with VVO(salen)+ on the FSAM surface. In all these experiments oxidation of the VIII(salen)+ product occurred upon exposure to oxygen or to air. The cyclic regeneration of VVO(salen)+ upon exposure to molecular oxygen and its subsequent reduction to VIII(salen)+ in vacuum completes the catalytic cycle of O2 reduction by the immobilized vanadium-salen species. Moreover, our results represent the first evidence of formation of reactive organometallic complexes on substrates in the absence of solvent. Remarkably, deoxygenation of the oxo-vanadium complex, previously observed only in highly acidic non-aqueous solvents, occurs on the surface in the UHV environment using an acid which is deposited into the inert monolayer. This acid can be a protonated metal complex, e.g. [NiII(salen)+H]+ or an organic acid such as protonated diaminododecane.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1024532
- Report Number(s):
- PNNL-SA-75788; 34913; 30445; 19594; KC0302020; KC0302020; TRN: US201119%%444
- Journal Information:
- Physical Chemistry Chemical Physics. PCCP, 13(1):267-275, Vol. 13, Issue 1; ISSN 1463-9076
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AIR
CHEMISTRY
DEPOSITION
DESIGN
ELECTRONS
GOLD
IONIZATION
NONAQUEOUS SOLVENTS
ORGANIC ACIDS
OXIDATION
OXYGEN
REGENERATION
SUBSTRATES
TIME DEPENDENCE
ion soft landing
electrospray ionization
redox reactions
metal-salen complexes
self-assembled monolayer surfaces
mass spectrometry
catalysis
Environmental Molecular Sciences Laboratory