Synthesis and monolayer behavior of organogermanium clusters

Several organogermanium clusters (Or–GeCs) with different organic capping reagents have been synthesized, and their monolayer behaviors on a water surface studied. GeCl4 and organic bromides were reacted in a one-pot process using magnesium to synthesize the corresponding Or–GeCs. The structures of the Or–GeCs were characterized by UV–vis, NMR, and FT-IR spectroscopy. GPC measurements were also collected, and the results revealed that the cores of the clusters were composed of a 3-D Ge–Ge network capped with organic reagents. Surface pressure (π)–area (A) isotherms and Brewster angle microscopy (BAM) measurements indicated that the Or–GeCs with alkyl capping regents formed an oil, whereas those with aromatic capping regents formed a solid-like monolayer at the air–water interface. It was concluded that the occurrence of a π–π interaction between the aromatic capping reagents was necessary for the formation of a solid-like film. Phenyl-GeCs, which contained a phenyl group capping reagent, were transferred onto a solid substrate using the Langmuir–Schaeffer method, and atomic force microscopy (AFM) images revealed a uniform film (root mean square roughness of 0.6 nm) of 3–4 nm in thickness. Furthermore, a multilayer phenyl-GeC film was prepared by repeating the deposition process.

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► Organogermanium clusters were synthesized by simple one-pot reaction.
► Two-dimensional assemblies of clusters were prepared on air–water interfaces.
► Nanometer thick cluster films were prepared using the Langmuir–Schaefer method.