Binding Studies of a Luminescent Pt(II) Organometallic Calix[4]pyrrole with Halide Salts

monitor the binding. The binding affinity of PtL2 for MTOA·Cl is 2-fold smaller than that of the C[4]P precursor. This difference is attributed to dissimilar anion−π interactions and binding geometries in the ion-paired complexes of the two receptors, (Cl⊂PtL2/C[4]P)@MTOA. Isothermal titration calorimetry (ITC) experiments revealed subtle differences in enthalpy and entropy. The entropic term, although negative, was very small, suggesting the relevance of the dissociation/association processes of the salt and the ion-paired complexes. We investigated the binding selectivity of PtL2 toward a series of halides in acetone solution favoring ion-pair dissociation. PtL2 binds chloride selectively and with a high affinity, producing mainly an anionic complex.