Metal-to-Ligand Ratio Controlled Assembly of Two Ni(II) Complexes: Structures, Luminescent and Electrochemical Properties

Treatment of Ni(OAc) 2 ·4 H 2 O with 3,4-pyrazoledicarboxylic acid (H 3 pdc) and imidazole (ImH) in different metal-to-ligand ratios afforded two dinuclear nickel(II) complexes, [Ni(Hpdc)(ImH)(H 2 O) 2 ] 2 ·4 H 2 O ( 1 ) and [Ni(Hpdc)(ImH) 2 (H 2 O)] 2 ·2.5 H 2 O ( 2 ), which were characterized by elemental analysis (EA), IR spectra and X-ray diffraction analysis and thermogravimetric analysis (TGA). Both in 1 and 2 , the dinickle unit [Ni 2 ( µ 2 -Hdpc) 2 ] with six-numbered Ni 2 N 4 ring was formed by a pair of µ 2 -Hpdc 2− ligands linked two Ni(II) ions in N,O-chelating and N‒N-bridging fashions. The dinuclear units in 1 and 2 were expanded to 2D layer structures though hydrogen-bonding interactions between coordination water molecules, ImH molecules and carboxylate oxygen atoms, whereas the lattice water molecules in 1 and 2 just embedded in the 2D layer through intermolecular hydrogen bonding interactions. Finally, the 2D sheets in 1 were further assembled to a 3D supramolecular architecture via intermolecular C–H⋯O hydrogen bond. Besides, the luminescent and electrochemical properties of two complexes have been reported. Graphic Abstract Two dinuclear nickel(II) complexes, [Ni(Hpdc)(ImH)(H 2 O) 2 ] 2 ·4 H 2 O ( 1 ) and [Ni(Hpdc)(ImH) 2 (H 2 O)] 2 ·2.5 H 2 O ( 2 ), were obtained by assembling of a Ni(II) ion, 3,4-pyrazoledicarboxylic acid (H 3 pdc) and imidazole (ImH) in different metal-to-ligand ratios. In 1 and 2 , the O(C, N)−H⋯O hydrogen bonds expanded the dinuclear complexes to 3D/2D supramolecular structures, respectively.