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A PVC-based membrane of dibenzodiazathia-18-crown-6-dione reveals a Nernstian potentiometric response for Hg 2 over a wide concentration range (8.0610À6 to 1.0610). It has a response time of about 10 s and can be used for at least 3 months without any divergence. The proposed electrode revealed very good selectivities for Hg 2 over a wide variety of alkali, alkaline earth, transition and heavy metal ions and could be used in a pH range of 0.5±2.5. It was successfully used as an indicator electrode in potentiometric titration of mercury ions.

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Two compounds containing a proton transfer ion pair (pipzH 2 )(btcH 2 ), 1, and its Co(II) complex, were synthesized and characterized using IR spectroscopy and single crystal X-ray diffraction method. The chemical formula is {(pipzH 2 )[Co(btc)(H 2 O) 4 ].4H 2 O} n for Co(II) complex, 2, (pipz:piperazine, btcH 4 :benzene-1,2,4,5-tetracarboxylic acid). The space group and crystal system of both compounds are P 1 and triclinic. The proton transfer ion pair 1 was prepared by the reaction between piperazine and benzene-1,2,4,5-tetracarboxylic acid, and its Co(II) complex, 2, was synthesized by the reaction of 1 with cobalt(II) sulphate. The complex 2 is a polymeric substance with Co(II) atoms linked by two O atoms from one benzene-1,2,4,5-tetracarboxylate. In both crystal structures, a wide range of noncovalent interactions consisting of hydrogen bonding (types of O-H···O, N-H···O and C-H···O) and ion pairing interactions connecting the various components into a supramolecular structure. There are also C-H···O and C-H···ʌ intermolecular interactions in compound 2 which take part in the stabilization of molecular packing. The protonation constants of pipz and btcH 4 , the equilibrium constants for the btcH 4 -pipz proton transfer system and the stoichiometry and stability of this system with Co 2+ ion in aqueous solution were investigated by potentiometric pH titrations. The stoicheiometry of one of the most abundant complexed species in solution was found to be the same as that of the crystalline cobalt(II) complex.