Complexation of 5-fluorosalicylic acid with copper(II): a pH-potentiometric, UV-vis spectroscopic, and electron spin resonance study by the two-dimensional simulation of spectra

The copper(II)–5-fluorosalicylic acid system was investigated in water and 50 v/v% water–methanol mixture by pH potentiometry combined with UV–vis spectrophotometry, and by the two-dimensional ESR simulation method, respectively. The data revealed that the stable paramagnetic mono- and bis(salicylato) copper(II) complexes [CuLH −1 ] and [CuL 2 H −2 ] 2− are formed, and at low excess of ligand, the ESR-silent mixed hydroxo complex [Cu 2 L 2 H −3 ] − is also a major species. By the two-dimensional ESR simulation method, the species [CuL] + in the acidic region, and the minor dimer [Cu 2 L 2 H −2 ] were also identified, and the cis and trans isomers of [CuL 2 H −2 ] 2− were characterized. In frozen solutions, the ESR analysis revealed a slight rhombic distortion of coordination polyhedra for the latter three species.