A ternary Fe(II)-terpyridyl complex-based single platform for reversible multiple-ion recognition

Multiple ion-recognition activity by a ternary Fe(ii)-terpyridyl complex, [Fe(PhT)(PT)12 (1) (PhT = 4'-pheny12,2`:6',2-terpyricline; PT = 4'-pyridyl-2,2:6`,2-terpyridine), is demonstrated for cyanide (CN-1, fluoride (F-1 and hydroxide (OH-) ions in an aqueous medium with sufficient sensitivity, fast response, reproducibility and selectivity with a dual optical read-out. The sensing event was reversible with the by-eye visualization of back and forth colour changes. Three cyanide ions replaced PT from 1, as observed from the crystal structure of the 1 I CN-couple. Fluoride and hydroxide ions appeared to show multivariate interactions with 1. Observed structural and spectral changes correlated well with theoretical calculations. A string of cations at quantitative levels (Ag2+/Hg2+/Fe2+/Fe3+) was used to decouple the 1 + anion complex to yield 1 which enabled the recognition of these cations while permitting the reuse of 1 for at least five set-reset cycles.