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

A series of organotin(IV) compounds R 3 Sn(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 − , H 2 PO 4 − ). Equilibrium constants for a complete set of reactions between R 3 Sn(A) with A = 2‐amino‐4‐nitrophenolate (ANP) or 4‐nitrophenolate and anions (X − ) involving formation of complexes R 3 Sn(A)(X) − and substitution products R 3 Sn(X) and R 3 Sn(X) 2 − were determined by UV‐vis and 1 H NMR titrations in MeCN and DMSO. The binding selectivity was AcO − > F − > H 2 PO 4 − > 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 H 2 PO 4 − anions in the 5–100 µ M 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 R 3 Sn(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.