Novel Complexes of Zinc(II) with Different Proton Transfer Ion Pairs Obtained from Dipicolinic Acid: Synthesis, Characterization and X-ray Crystal Structure

Abstract

Three new complexes of zinc(II) with three different proton transfer compounds, obtained from pyridine-2,6-dicarboxylic acid (dipicolinic acid) and different Lewis bases, were synthesized and characterized using IR, 1H NMR and 13C NMR spectroscopy and single crystal X-ray diffraction. The chemical formulae and space groups of the complexes are (pipzH2)[Zn(pydc)2] · 4H2O, P21/n (1), (EDGnH2)[Zn(pydc)2] · 3H2O, P21/c (2) and (pdaH2)[Zn(pydc)2] · 4H2O, $$ P\ifmmode\expandafter\bar\else\expandafter\=\fi{1} $$ (3) where pydc, pipz, EDGn and pda are standing for dipicolinic acid, piperazine, ethylenediguanidine and 1,3-propanediamine respectively. Cell parameters of the complexes are a = 7.9493(4) A, b = 13.4386(7) A, c = 21.0557(11) A, β = 90.415(5)° for 1; a = 9.785(3) A, b = 25.671(4) A, c = 9.3402(16) A, β = 90.790(17)° for 2 and a = 8.411(5) A, b = 11.650(7) A, c = 12.793(8) A, α = 115.534(9)°, β = 92.791(10)°, γ = 97.778(10)° for 3. The three crystal structures illustrate that the metal ion is six-coordinated by two pydc’s. In all three compounds a large number of O–H⋯O, N–H⋯O and C–H⋯O hydrogen bonds are observed. These interactions as well as other noncovalent interactions such as ion–pairing and π–π stacking play an important role in the formation and stabilization of supramolecular systems in the crystal lattices. The main purpose of this paper is to report and discuss about the synthesis, characterization, crystal structure and non-covalent interactions of three supramolecular frameworks of six-coordinated Zn(II) complexes, obtained by the reaction of different proton transfer compounds, i.e. (pipzH2)(pydc), (EDGnH2) (pydc) · 3H2O and (pdaH2)(pydc) · (pydcH2) · 2.5H2O with corresponding metallic salts.