Soft-landing isolation of vanadium-benzene sandwich clusters on a room-temperature substrate using n-alkanethiolate self-assembled monolayer matrixes

Gas-phase synthesized vanadium-benzene 1:2 (VBz₂) sandwich clusters were size-selectively deposited onto bare gold and long-chain n-alkanethiolate [-S-(CH₂)_n-1-CH₃; n = 16, 18, and 22] self-assembled monolayer (SAM)-coated gold substrates under ultrahigh vacuum (UHV) conditions. Investigation of the resulting deposited clusters was performed by infrared reflection absorption spectroscopy (IRAS) and thermal desorption spectroscopy (TDS). The IR frequencies of the soft-landed VBz ₂ clusters show excellent agreement with the fundamentals reported in IR data of VBz₂ in an argon matrix. The analysis of IRAS spectra reveals that while there was no orientational preference of the VBz₂ clusters on a bare gold substrate, the VBz₂ clusters deposited onto the SAM substrates were highly oriented with the molecular axis 70-80° tilted off the surface normal. In addition, analysis of TDS spectra revealed unusually large adsorption heats of the physisorbed VBz₂ clusters. The present results are explained by cluster penetration into the long-chain alkanethiolate SAM and for the first time demonstrate the matrix isolation of gas-phase organometallic clusters around room temperature.