Electrosynthesis Cell for X-Ray Absorption Fine Structure Measurement: Reduction of Air-Sensitive Iron-Sulfur Compounds

Abstract

The design of a small-volume continuous-flow electrosynthesis cell, and its associated X-ray absorption fine structure (XAFS) cell, are reported. The extent of electrosynthesis of the solution used for collection of the XAFS data may be monitored, in line, by infrared (IR) or ultraviolet–visible (UV–vis) spectroscopy. The operation of the cell is demonstrated by the reduction of Fe₂S₂(CO)₆ to the related dimer dianion, [Fe₄S₄(CO)₁₂]^2-. While the immediate coordination environment about the iron is similar for the two compounds, dimer formation results in an additional Fe–S interaction at 3.62 Å, which contributes to significant changes in the XAFS data in the region 10–12 Å^-1. Analysis of the XAFS for the reduced species gave a full structural model which yielded a calculated multiple scattering (MS) XAFS pattern in good agreement with the data. Inclusion of the longer range Fe–Fe interactions (> 5 Å) did not give convergent fits within this formalism. These experiments demonstrate that ex situ electrosynthetic approaches provide an effective means of generating reactive species in a form suitable for XAFS examination.