Piperazinium Bis(hydrogen-3,5-pyrazoledicarboxylate) Proton Transfer Compound and Its Zinc(II) Complex: Synthesis, Characterization and Crystal Structure

Abstract

Two compounds including a proton transfer ion pair, (pipzH2)(pdcH)2·2H2O (1) (where pipz: piperazine and pdcH2: pyrazole-3,5-dicarboxylic acid) and its Zn(II) complex (2), (pipzH2)[Zn(pdc)2(H2O)2]·6H2O, were synthesized and characterized using elemental analysis, IR spectroscopy and single crystal X-ray diffraction methods. The compound 1 crystallizes in the triclinic space group P $$\bar {1}$$ with Z = 2. The unit cell dimensions are: a = 6.886(3) A, b = 8.132(3) A, c = 8.902(3) A, α = 94.707(9)°, β = 99.632(9)°, γ = 111.508(8)°. The crystal system of 2 is monoclinic with space group P21/c and has two molecules per unit cell. The unit cell dimensions are: a = 12.050(2) A, b = 13.163(2) A, c = 7.610(1) A, β = 97.610(4)°. The zinc(II) atom has a distorted octahedral coordination geometry. The two pdc2− units are almost coplanar to each other. In both crystal structures, a wide range of noncovalent interactions including hydrogen bonding (types of O–H⋯O, N–H⋯O and C–H⋯O), π–π stacking and ion pairing connect the various components into supramolecular structures. X-ray crystal structure of the novel 1:2 proton transfer compound, (pipzH2)(pdcH)2·2H2O (where pipz: piperazine and pdcH2: pyrazole-3,5-dicarboxylic acid) and its Zn(II) complex, (pipzH2)[Zn(pdc)2(H2O)2]·6H2O, show intermolecular N–H⋯O, O–H⋯O and C–H⋯O hydrogen bonds and π–π stacking, together with ion pairing, are responsible for extending the structure in three dimensions, resulting in a supramolecular network.