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. GeCl(4) 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.