A Proton Transfer Self-Associated Compound from Benzene-1,2,4,5-Tetracarboxylic Acid and Piperazine and Its Cobalt(II) Complex: Syntheses, Crystal Structures and Solution Studies

作者：Aghabozorg H^*; Mahfoozi F; Sharif M A; Shokrollahi A; Derki S; Shamsipur M; Khavasi H R

来源：Journal of the Iranian Chemical Society, 2010, 7(3): 727-739.

• Cobalt(II) complex
• Benzene-1,2,4,5-tetracarboxylic acid
• Piperazine
• Crystal structure
• Solution study
• Hydrogen bond

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)]center dot 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) over bar 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 center dot center dot center dot O, N-H center dot center dot center dot O and C-H center dot center dot center dot O) and ion pairing interactions connecting the various components into a supramolecular structure. There are also C-H center dot center dot center dot O and C-H it 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.

• 出版日期2010-9