Self-assembled hybrid bilayers of palladium alkanethiolates

Abstract

Octane (C₈), dodecane (C₁₂), and hexadecane (C₁₆) thiolates of palladium, as well as their binary mixtures covering the entire range of compositions, have been prepared from organic media and characterized using powder X-ray diffraction (XRD), infrared spectroscopy (FTIR), and scanning tunneling microscopy (STM). All thiolatesmono as well as mixedadopt bilayered lamellar structures as evidenced by XRD and STM. In monothiolates, the thickness of the bilayer as measured by the d₀₀₁ spacing is governed by the length of the alkyl chain, while in hybrid bilayers, the thickness depends on the binary composition as well. In C₈−C₁₂ and C₁₂−C₁₆ bilayers, in which the difference in the chain lengths of the constituent thiols is four methylene units, the thickness varies nearly proportionally to the weighted average of the chain lengths. In contrast, the C₈−C₁₆ system shows a steplike behavior with only a few compositions (C₈, 60−80%) exhibiting intermediate d values. The alkyl chains are in all-trans conformation in monothiolates, while in hybrid bilayers, especially in C₁₂−C₁₆, gauche defects are observed, their concentration being the highest around 50:50 composition. Interestingly, these hybrid thiolates seem to provide adequate free volume to entrap small molecular species.