Abstract
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.
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