Solid state coordination chemistry of mononuclear mixed-ligand complexes of Ni(II), Cu(II) and Zn(II) with α-hydroxycarboxylic acids and imidazole

Abstract

Nine mononuclear metal complexes of monoanionic α-hydroxycarboxylates (HL ′) with imidazole as a co-ligand have been synthesised and structurally characterized by X-ray diffraction. The nickel(II) complexes can be described by two formulae: [Ni(HL ′) 2(Im) 2], HL ′=2-methyllactate (HmL) ( 1) or mandelate (HM) ( 2), and [Ni(HB) 2(Im) 3], HB=benzylate ( 3). In these compounds the nickel atom is in a distorted octahedral environment. The copper(II) complexes of the general formula [Cu(HL ′) 2(Im)], HL ′=glycolate (HG) ( 4), lactate (HL) ( 5) or 2-methyllactate (HmL) ( 6) presents a square pyramidal coordination geometry with a distortion evaluated in terms of the τ parameter. The zinc(II) complexes have the general formula [Zn(HL ′) 2(Im) 2] · xH 2O, HL ′=lactate (HL) and x=1/2 ( 7), 2-methyllactate (HmL) and x=0 ( 8) and display a distorted octahedral geometry. However, the reaction with H 2B afforded the imidazole complex [Zn(Im) 6](HB) 2, HB=benzylate ( 9), which has two uncoordinated benzylate units. In most of the complexes the α-hydroxycarboxylato ligands behave as bidentate monoanionic systems, apart from in 3, where one ligand is monodentate. All of the complexes are extended into 2D or 3D frameworks through hydrogen bonding. The complexes were also characterized by elemental analysis, FT-IR and UV/Vis spectroscopy. The nickel and copper compounds were also studied by room temperature magnetic susceptibility and room temperature ESR spectra were obtained for the copper compounds. Finally, the thermal behaviour of all the compounds was investigated.