Water wire clusters in isostructural Cu(II) and Ni(II) complexes: Synthesis, characterization, and thermal analyses

Abstract

Hydrogen bonding (HB) interactions are well known to impact the properties of bulk water and within hydrated materials. Most notably, 1D water wires are involved in proton and water transport. Therefore, the design and synthesis of efficient proton conductors in terms of cost and performance are of great interest. In this work, isostructural Cu(II) and Ni(II) complexes based on N,N'-(ethane-1,2-diyl)bis(1-methyl-1H-imidazole-2-carboxamide) (H2L) have been synthesized and fully characterized by single crystal X-ray diffraction, spectroscopic methods, and thermal analysis. Both complexes crystalize in the monoclinic space group P21/c. The asymmetric unit of 1 and 2 contain two equivalents of CuL or NiL and four molecules of water of hydration. In the solid state packing of both complexes, the extended hydrogen bonding (HB) networks form 1D coiled zig-zag chains of water along the crystallographic b-axis. For both complexes, the identical ligand framework, coordination geometries, and solid state packing result in formation of similar HB expansion motifs, which result in analogous thermal stabilities and phase transitions at elevated temperature.