J. Phys. Chem. C 2010, 114, 5305–5311
5305
Soft-Landing of CoIII(salen)+ and MnIII(salen)+ on Self-Assembled Monolayer Surfaces† Julia Laskin,* Peng Wang, and Omar Hadjar Chemical and Materials Science DiVision, Pacific Northwest National Laboratory, Richland, Washington 99352 ReceiVed: May 11, 2009; ReVised Manuscript ReceiVed: July 29, 2009
Soft-landing of mass-selected CoIII(salen)+ and MnIII(salen)+ complexes [salen ) N,N′-ethylenebis(salicylideneaminato)] was performed using self-assembled monolayer surfaces of alkanethiol (HSAM) and fluorinated alkanethiol (FSAM) on gold as targets. Physical processes associated with ion deposition were studied using time-resolved in situ secondary ion mass spectrometry (SIMS) in a specially designed Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). We demonstrate charge retention by a significant fraction of precursor ions on the FSAM and complete neutralization on the HSAM surface. Our results indicate efficient electron transfer from gold to the deposited species for the HSAM surface and inefficient, if any, electron transfer on the FSAM surface. Formation of abundant cluster ions observed in SIMS spectra is attributed to gas-phase reactions in the SIMS plume. Detailed analysis allowed us to extract the kinetics of both ionic and neutral complexes trapped on the FSAM surface. The results indicate that neutralization on this surface most likely takes place on the defect sites. Introduciton Metal-salen complexes [salen ) N,N′-ethylenebis(salicylideneaminato)] have attracted significant attention in research areas ranging from catalysis1-3 to development of electrochemical sensors4 and single-molecule magnets.5 Chiral metal-salen complexes are used as asymmetric catalysts in a variety of oxidation reactions.1,6 Catalytic efficiency of the complex to a particular transformation strongly depends on the transition metal. For example, manganese-salen complexes are commonly used for epoxidation of alkenes, oxidation of sulfides, aziridination, and hydroxylation reactions,1,7 while cobalt-salen complexes catalyze epoxide ring-opening, cyclopropanation, and some hydroxylation reactions.1 Because preparation of environmentally benign, reusable catalysts for organic synthesis is commonly achieved through immobilization of transition metal complexes on substrates, preparation of substrate-supported metal-salen complexes has recently attracted considerable attention.8-10 Deposition of mass-selected hyperthermal (
