Diffusion in weakly coordinating solvents

Abstract

Weakly coordinating solvents are of interest for the electrodeposition of p-block semiconductors for application in electronic devices. p-block complexes typically have weakly coordinated ligands that are easily displaced, making them incompatible with strongly Lewis basic solvents. In this work we use electrochemical measurements at microelectrodes to study diffusion in weakly coordinating solvents. Diffusion coefficients of the metallocenes decamethylferrocene, decamethylferrocenium hexafluorophosphate, cobaltocenium hexafluorophosphate, and the electrodeposition precursors tetrachloroantimonate(III) and tetrachlorobismuthate(III) were measured. The values are analyzed using the modified Stokes-Einstein equation and compared with the theoretical upper, Dmax, and lower, Dmin, bounds of the diffusion coefficients. This approach allows the interpretation of D values, whilst avoiding dealing with some of the uncertainties associated with molecular size in the Stokes-Einstein equation. The neutral decamethylferrocene was found to obey the Stokes-Einstein equation whereas the charged metallocene species had values which were less than the theoretical minimum, which was attributed to a larger than expected particle size caused by ion pairing. The importance of considering the modifications of the Stokes-Einstein equation is also highlighted.