Anion exchange in trimethyl- and triphenyltin complexes with chromogenic ligands: solution equilibria and colorimetric anion sensing

Abstract

A series of organotin(IV) compounds R3Sn(A) where R = Me or Ph and A is a chromogenic nitrophenolate ligand were prepared and studied as possible colorimetric sensors for anions (F−, Cl−, Br−, AcO−, H2PO4−). Equilibrium constants for a complete set of reactions between R3Sn(A) with A = 2-amino-4-nitrophenolate (ANP) or 4-nitrophenolate and anions (X−) involving formation of complexes R3Sn(A)(X)− and substitution products R3Sn(X) and R3Sn(X)2− were determined by UV-vis and 1H NMR titrations in MeCN and DMSO. The binding selectivity was AcO− > F− > H2PO4− > Cl− ≫ Br− in both solvents and both for R = Me and Ph with higher affinity for R = Ph. Compounds with A = ANP were found to have the optimum properties as anion sensors allowing optical detection of F−, AcO− and H2PO4− anions in the 5–100 µM range by appearance of an intense absorption band of free ANP resulting from its substitution with the analyte. Selectivity and affinity of anion interactions with R3Sn(ANP) are similar to those for thiourea receptors, but the organotin receptor produces a much larger naked eye detected optical signal, operates equally well in nonpolar and polar solvents and tolerates the presence of up to 20% vol. of water in DMSO. Copyright © 2011 John Wiley & Sons, Ltd.