An experimental and theoretical study of [RhCl(PF3)2]2 fragmentation

Abstract

Experimental and theoretical techniques have been applied to study the decomposition of the [RhCl(PF₃)₂]₂ molecule which is known as a precursor in electron beam induced deposition (EBID) of Rh. Mass spectrometry (MS) has been carried out to study the electron ionisation and fragmentation of isolated molecules. Auger electron spectroscopy has been used to characterize the EBID deposit. The MS data indicate the presence of free phosphorus and rhodium ions. This is in agreement with the analysis of the composition of the EBID deposit containing: 60% Rh, 12–25% P, 2–13% Cl, no F, 3–20% O and N. Theoretical calculations (density functional theory) has been used to characterize the precursor molecule and to derive the enthalpies of several simple decomposition reactions. The calculated geometries are in a good agreement with the available X-ray crystallographic data. The [RhCl(PF₃)₂]₂ appears not to be rigid: the PF₃ groups can rotate with a relatively low barrier (0.6 kcal mol⁻¹) whereas the barrier for the butterfly-like motion of (RhCl)₂ moiety is only 3.5 kcal mol⁻¹. According to the theoretical results, the lowest energy pathway of the decomposition corresponds to a consecutive loss of PF₃ ligands, resulting in a (RhCl)₂ moiety (without phosphorus). The same conclusion is also valid for the ionised precursor. Experimental data combined with the theoretical results concerning the energetics of the considered various simple decomposition processes indicate that the electron induced dissociation of the precursor cannot be seen as a simple one-step decomposition process.