ESR and pH-potentiometric study of the mixed–ligand complex formation in the copper(II)–4-fluorosalicylic acid– N, N-diethylnicotinamide system: Structure and spectral properties of [Cu(4-fluorosalicylate) 2( N, N-diethylnicotinamide) 2(H 2O) 2] complex

Abstract

EPR simulation method together with pH-potentiometry combined with UV–Vis spectrophotometry were used for the study of the ternary system 4-fuorosalicylic acid (H A)– N, N-diethylnicotinamide ( B)–copper(II) in aqueous solution. The N, N-diethylnicotinamide ligand is a weak donor, its mixed–ligand complexes with 4-fluorosalicylate anions are more favoured. The number of coordinated N, N-diethylnicotinamide molecules increases with decreasing temperature: up to four ones were detected in the coordination sphere of copper(II) in frozen solutions. The formation of [CuH −1 AB 2] and [CuH −1 A] was detected by all methods at neutral pH. At lower pH values, [Cu A 2 B 2] and [Cu B] become dominant, and this fact is in good agreement with [Cu A 2 B 2(H 2O) 2] crystals obtained from similar solutions. The structural unit of the [Cu A 2 B 2(H 2O) 2] complex consists of a copper(II) ion, which is monodentately coordinated by a pair of 4-fluorosalicylate anions and by a pair of N, N-diethylnicotinamide in trans positions in the basal plane, and by two water molecules in the axial positions of a tetragonal bipyramid.