1-Hydroxybenzotriazole (HOBt) acidity, formation constant with different metals and thermodynamic parameters: Synthesis and characterization of some HOBt metal complexes – Crystal structures of two polymers: [Cu 2(H 2O) 5(OBt) 2(μ-OBt) 2] · 2H 2O · EtOH ( 1A) and [Cu(μ-OBt)(HOBt)(OBt)(EtOH)] ( 1B)

Abstract

The dissociation constants of 1-hydroxybenzotriazole (HOBt) and the formation constants of its complexes with cobalt(II), copper(II), nickel(II), iron(III), zinc(II), lead(II), mercury(II), and cadmium(II) were evaluated at different temperatures (20–45 °C) by potentiometric measurements in the presence of different percentages of ethanol–water and dioxane–water media. The thermodynamic parameters were calculated and discussed. HOBt complexes of copper, nickel, cobalt, and zinc were synthesized and characterized by IR, magnetism, elemental analysis and mass spectra. Entropies of activation (Δ S ∗) were calculated from differential thermal analysis (DTA) curves of complexes. Electrical conductivity measurements indicated that all the complexes exhibit semiconductor behavior and the electrons in the available orbitals are not of high mobility. The crystal structure of coordination polymer [Cu 2(H 2O) 5(OBt) 2(μ-OBt) 2] · 2H 2O · EtOH ( 1A) is composed of helical chains of Cu(II) ions with alternating chromophores bridged by 1-hydroxybenzotriazolate ligand. Copper exhibits octahedral and square pyramidal coordination geometry. Both intra- and inter-molecular π−π interactions exist in the structure of 1A. While [Cu(μ-OBt)(HOBt)(OBt)(EtOH)] ( 1B) is composed of zigzag polymeric chains of Cu(II) atoms bridged by 1-hydroxybenzotriazolate ligand, the copper has a square pyramidal environment. Both H-bond and π−π interaction exist in the structure of ( 1B).