Synthesis and characterization of Zwitterionic Zn(II) and Cu(II) coordination compounds with ring-substituted 2,2′-biimidazole derivatives

Abstract

Zwitterionic coordination compounds with strongly asymmetrical charge distribution were synthesized and characterized. Ring-substituted biimidazoles were used as the primary ligands for Zn and Cu compounds. Formation of Zwitterionic coordination compound was found to be strongly dependent on the pH of the reaction medium as well as on the ring and nitrogen substituents of the ligand. Reaction of the Df-R 2 biim (Df-R 2 biim = 2,2´-bi-1R-imidazole-5,5´-dicarboxaldehyde, R= Me, Et or Pr) with ZnCl 2 in neutral conditions led to binuclear compounds [Zn 2 Cl 4 (Df-R 2 biim) 2 ] with two bridging ligands (1a-c). Reaction with CuCl 2 ⋅2H 2 O gave neutral mononuclear compound [CuCl 2 (Df-Me2biim)] (1d) with chelating biimidazole ligand. In acidic conditions (pH = 3−4) the imidazole nitrogens were either fully or partially protonated, which prevented the bidentate coordination of the ligands. Furthermore, aldehyde substituents of Df-R 2 biim ligands were involved in acetal formation with methanol solvent. Under acidic conditions the primary products were either ion pairs [MCl 4 ][C 14 H 24 N 4 O 4 ] (M=Zn 3a, M=Cu 3b) with fully protonated H 2 L 2+ counter cation or desired Zwitterionic coordination compounds [ZnCl 3 (C 16 H 27 N 4 O 4)] (2a), [ZnCl 3 (C 18 H 31 N 4 O 4)] (2b), [CuCl 3 (C 16 H 27 N 4 O 4)] (2c), or [CuCl 3 (C 18 H 31 N 4 O 4)] (2d) with partially protonated monodentate HL + ligand. Zwitterions were obtained only with ligands having both aldehyde groups as ring-substituents and longer alkyl chains (ethyl or propyl) as N-substituents. In other cases ion pairs were formed as final products. Zwitterions were found to decompose in alcoholic solutions. In methanol solution, Zwitterionic compounds released neutral ligand and HZnCl 3. All main products were characterized by NMR, elemental analysis and single-crystal X-ray diffraction.

Construction of a PbII coordination polymer from a semi-rigid ditopic 2,2-biimidazole derivative: synthesis, crystal structure and characterization

“…In the past few decades, 2,2 0 -biimidazole (biim) and its derivatives have attracted much attention due to their versatile chemical properties (Tatikonda et al, 2016;Das et al, 2015;Mardanya et al, 2016;Rommel et al, 2017). However, the construction of novel Pb II CPs utilizing biim derivatives has been less studied (Sang et al, 2008).…”

Construction of Coordination Polymers from Semirigid Ditopic 2,2′-Biimidazole Derivatives: Synthesis, Crystal Structures, and Characterization

“…[34][35][36][37] Typical coordination geometries of copper(I or II) complexes include tetrahedral, square planar and square pyramidal structures. [38][39][40] In this study, we report the synthesis, crystal structures, and characterization of several transition metal (Cu + , Cu 2+ , Zn 2+ , and Ag + ) coordination polymers with two biim based semi-rigid ligands (L1 and L2), where they act as bi-, tri-or tetradentate ligands.…”

“…Copper and silver were selected to provide more flexible coordination geometries. The common geometries of silver­(I) complexes are linear, trigonal, and tetrahedral. − Typical coordination geometries of copper­(I or II) complexes include tetrahedral, square planar, and square pyramidal structures. − …”