AVS 53rd International Symposium
    Surface Science Thursday Sessions
       Session SS2+EM-ThM

Paper SS2+EM-ThM1
Odd-Even Effects in Self-Assembled Monolayers of Biphenyl-Substituted Alkaneselenolates on Noble Metal Substrates

Thursday, November 16, 2006, 8:00 am, Room 2004

Session: Self-Assembled Monolayers
Presenter: M. Zharnikov, Universität Heidelberg, Germany
Authors: M. Zharnikov, Universität Heidelberg, Germany
A. Shaporenko, Universität Heidelberg, Germany
J. Müller, Universität Hamburg, Germany
A. Terfort, Universität Hamburg, Germany
Correspondent: Click to Email
Self-assembled monolayers (SAMs) of selenolates can be considered as an alternative to thiolates for the functionalization of noble metal surfaces. In view of this option, we studied SAMs formed from biphenyl-substituted dialkanediselenides (CH@sub 3@(C@sub 6@H@sub 4@)@sub 2@(CH@sub 2@)@sub n@Se-)@sub 2@ (BPnSe,  n = 1 - 6, 10, 11) on polycrystalline (111) gold and silver substrates. The SAMs were characterized by several complementary experimental techniques. Similar to the analogous systems with the thiolate headgroup, the packing density of the SAM constituents and the orientation of the biphenyl moieties in the BPnSe films exhibited a pronounced odd-even variation with the number of methylene groups in the aliphatic linker, which was opposite on silver as compared to gold. A higher packing density and a corresponding smaller inclination of the biphenyl moieties was observed for odd numbers of the methylene units in BPnSe on Au, and for even numbers of these units in BPnSe on Ag. The observed odd-even effects are explained by the strong dependence of the bending potentials in the metal-Se-C bond on the deviation of the respective angle from an optimal value of about 104° for Au and about 180° for Ag. The optimal metal-Se-C angles are presumably determined by the hybridization of the selenium in the metal-selenolate bond, which seems to have sp@super 3@ hybridization on Au and an sp hybridization on Ag, respectively.