The association constant, Kass, between R1 and the anions F− & AcO− was determined from the ratio of intercept/slope and it was found to be 1.4 × 104 M−1 for fluoride and 1.3 × 104 M−1 for acetate anions respectively, from which it is inferred that R1 has almost equal affinity towards both the anions fluoride and acetate. Table 1 shows the association constant Kass (M−1) of the R1 with all the anions in DMSO at 298.2 ± 0.1 K.