Synthesis and crystal structure of Mn(II) and Hg(II) compounds and solution studies of Mn(II), Zn(II), Cd(II) and Hg(II) compounds based on piperazinediium pyridine-2,3-dicarboxylate

Abstract

Novel metal organic frameworks including {(pipzH₂)[Mn(py-2,3-dc)₂]·7.75H₂O}_n, 1, {(pipzH₂)[Zn(py-2,3-dc)₂]·4H₂O}_n, 2, [Cd(py-2,3-dc)(H₂O)₃]_n, 3 and {(pipzH₂)[Hg₄Cl₁₀]}_n, 4, in which pipz is piperazine and py-2,3-dcH₂ is pyridine-2,3-dicarboxylic acid were synthesized applying a proton transfer ion pair i.e. (pipzH₂)(py-2,3-dcH)₂ and corresponding metallic salts and studied by IR, ¹H NMR, ¹³C NMR spectroscopy and single crystal X-ray diffractometry. The space group of compounds 1 and 4 are P2₁/c and C2/c of monoclinic system, respectively. The crystal dimensions are a = 20.108(2) Å, b = 19.910(2) Å, c = 12.997(1) Å, β = 94.354(2)° for 1 and a = 15.940(1) Å, b = 11.2690(9) Å, c = 11.1307(9) Å, β = 90.685(2)° for 4. The crystal structures of 2 and 3 have been reported previously. However, their solution studies are discussed here. The compounds had all polymeric structures. Although Zn^II, Cd^II and Hg^II were elements of the same group, their behavior against the ion pair was essentially different. Various supramolecular interactions mainly hydrogen bonds of the type O-H⋯O, N-H⋯O, C-H⋯O, N-H…Cl and C-H⋯Cl were observed in the structures. There was an unusual and huge water cluster in the structure of compound 1. The solution states of compounds 1–4 were studied and reported. The protonation constants of pipz and py-2,3-dc, the py-2,3-dc/pipz proton transfer equilibrium constants and stoichiometry and stability of the system with Mn²⁺, Zn²⁺, Cd²⁺ and Hg²⁺ ions in aqueous solution were investigated by potentiometric pH titrations.