Rhodium Nanoparticles from Dirhodium(II) Ethylene Glycol Tetracarboxylates

A straightforward synthesis methodology for the preparation of rhodium(II) carboxylates [Rh2{O2CCH2(OCH2CH2)2OCH3}4]n (1) and [Rh{mu-O2CCH2(OCH2CH2)2OCH3}2(PPh3)]2 (2) is reported. The ethanol-mediated reduction of RhCl3.3H2O with [K{O2CCH2(OCH2CH2)2OCH3}] produced 1, which on further addition of PPh3 afforded 2. Single-crystal X-ray diffraction studies of 2 were carried out showing a paddlewheel arrangement of the dirhodium(II) tetracarboxylate unit with a RhRh distance of 2.4599(5) angstrom. Compounds 1 and 2 were applied in the formation of rhodium nanoparticles (NPs) using 1,2-ethanediol as reducing reagent and poly(vinylpyrrolidone) (PVP) as capping component. Rhodium NPs with a narrow size distribution (<4 nm) were obtained from 1. The dependency of the concentration and temperature on the NP size and size distribution is discussed. Characterization of the Rh colloids was performed by TEM, X-ray powder diffraction (XRPD), and electron-diffraction studies, which revealed that Rh NPs with diameters between (3.0 +/- 0.4) and (3.9 +/- 0.4) nm were formed. Additionally, the decomposition of 1 and 2 was studied by thermogravimetry (TG)MS coupling experiments, which showed their differing thermal behavior. Complex 1 follows a two-step decomposition, whereas degradation of 2 occurs in three steps. The main difference in degradation is that decarboxylation of 1 starts at 230 degrees C, whereas for 2 the main CO2 formation is observed above 600 degrees C.