Novel complexes of zinc(II) with different proton transfer ion pairs obtained from dipicolinic acid: Synthesis, characterization and X-ray crystal structure

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, (HNMR)-H-1 and C-13 NMR spectroscopy and single crystal X-ray diffraction. The chemical formulae and space groups of the complexes are (pipzH(2))[Zn(pydc)(2)] center dot 4H(2)O, P2(1/n) (1), (EDGnH(2))[Zn(pydc)(2)] center dot 3H(2)O, P2(1)/c (2) and (pdaH(2))[Zn (pydc)(2)]center dot 4H(2)O, P (1) over bar (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) angstrom, b = 13.4386(7) angstrom, c = 21.0557(11) angstrom, beta = 90.415(5)degrees for 1; a = 9.785(3) angstrom, b = 25.671(4) angstrom, c = 9.3402(16) angstrom, beta = 90.790(17)degrees for 2 and a = 8.411(5)angstrom, b = 11.650(7)angstrom, c = 12.793(8) angstrom, a = 115.534(9)degrees, beta = 92.791(10)degrees, c = 97.778(10)degrees 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 center dot center dot center dot O, N-H center dot center dot center dot Oand C-H center dot center dot center dot O hydrogen bonds are observed. These interactions as well as other noncovalent interactions such as ion - pairing and pi-pi stacking play an important role in the formation and stabilization of supramolecular systems in the crystal lattices.