Organic Phase Cyclopentadienylnickelthiolate Sensor System for Electrochemical Determination of Sulfur Dioxide

A series of cyclopentadienylnickelthiolate complexes, [Ni(PBu 3 )(η 5 ‐C 5 H 5 )(SC 6 H 4 X‐4)] (X=F, Cl, Br, NH 2 ), were shown to express stable reversible electrochemical properties even after formation of SO 2 adducts in organic phase consisting of argon purged CH 2 Cl 2 /0.1 M [ n ‐Bu 4 N][BF 4 ]. The formal potentials ( E °′) values of the compounds ranged from 265 to 431 mV/Ag‐AgCl depending on the para substituent of the benzene thiolate ligand. Electrochemical, UV‐vis and 1 H NMR spectroscopic analyses show that the formation of SO 2 adducts causes the perturbation of the electronic density of the nickel metal center, indicated by shifts in the E °′ values of the Ni II/III redox couple that is dependent on SO 2 concentration. The detection limits of the resulting organic phase electrochemical gas sensor system was as low as 0.56 ppm SO 2 for the fluoro complex, while the linear range was as high as 700–2000 ppm SO 2 for the amino complex.